Membrane permeabilization of phosphatidylcholine liposomes induced by cryopreservation and vitrification solutions

Detecting changes of testicular interstitial cell membranes with a fluorescent probe after incubation and cryopreservation with cryoprotective agents

Membrane alterations are among central factors predetermining cell survival during cryopreservation. In the present research, we tested some serum-/xeno-free cryoprotective compositions including dimethyl sulfoxide (Me2SO) and polymers for their osmotic impact and toxicity towards testicular interstitial cells (ICs). IC survival was determined after their contact with Me2SO, dextran (D40), hydroxyethyl starch (HES), polyethylene glycols (PEG1500 and PEG400), or after cryopreservation and cryoprotective agent (CPA) removal. A ratiometric fluorescent membrane probe 2-(2'-hydroxyphenyl)-5-phenyl-1,3-oxazole (probe O1O) was applied to assess changes in the plasma membrane of ICs. The cell survival study has shown that Me2SO decreased IC survival in a time- and dosage-dependent manner. The CPA decreased the metabolic activity of ICs, thus implying its toxic effect on the living cell as a whole. Using probe O1O, we have demonstrated that the toxic effect also influenced the plasma membrane. IC membranes were not altered after incubation with 0.7 M Me2SO. The presence of D40, HES, or PEGs in such Me2SO containing media resulted in plasma membrane hydration and damage to the membranes of cells incubated with PEGs. Cryopreservation caused pronounced membrane dehydration of the survived ICs even after CPA removal in PEG-containing media and low indicators of IC survival. Interestingly, cryopreservation with the best cryoprotective media supplemented with 0.7 M Me2SO and 100 mg/ml D40 resulted in minimal membrane alterations, thus implying its higher ability to protect membranes during cryopreservation.

Ethosomal Gel for Topical Administration of Dimethyl Fumarate in the Treatment of HSV-1 Infections

The infections caused by the HSV-1 virus induce lesions on the lips, mouth, face, and eye. In this study, an ethosome gel loaded with dimethyl fumarate was investigated as a possible approach to treat HSV-1 infections. A formulative study was conducted, evaluating the effect of drug concentration on size distribution and dimensional stability of ethosomes by photon correlation spectroscopy. Ethosome morphology was investigated by cryogenic transmission electron microscopy, while the interaction between dimethyl fumarate and vesicles, and the drug entrapment capacity were respectively evaluated by FTIR and HPLC. To favor the topical application of ethosomes on mucosa and skin, different semisolid forms, based on xanthan gum or poloxamer 407, were designed and compared for spreadability and leakage. Dimethyl fumarate release and diffusion kinetics were evaluated in vitro by Franz cells. The antiviral activity against HSV-1 was tested by plaque reduction assay in Vero and HRPE monolayer cells, while skin irritation effect was evaluated by patch test on 20 healthy volunteers. The lower drug concentration was selected, resulting in smaller and longer stable vesicles, mainly characterized by a multilamellar organization. Dimethyl fumarate entrapment in ethosome was 91% w/w, suggesting an almost total recovery of the drug in the lipid phase. Xanthan gum 0.5%, selected to thicken the ethosome dispersion, allowed to control drug release and diffusion. The antiviral effect of dimethyl fumarate loaded in ethosome gel was demonstrated by a reduction in viral growth both 1 h and 4 h post-infection. Moreover, the patch test demonstrated the safety of the ethosomal gel applied on the skin.

Infrared spectroscopic analysis of hydrogen-bonding interactions in cryopreservation solutions

BACKGROUND

In this study we investigated hydrogen bonding interactions in hydrated and frozen solutions of different cryoprotective agents (CPAs) including dimethyl sulfoxide, glycerol, ethylene glycol, propylene glycol, and trehalose. We also investigated the effect of CPAs on ice crystal growth during storage and correlated this with storage stability of liposomes.

METHODS

FTIR spectroscopy was used to study hydrogen bonding interactions in CPA solutions in H₂O and D₂O, and their thermal response was analyzed using van 't Hoff analysis. The effect of CPAs on ice crystal growth during storage was investigated by microscopy and correlated with storage stability of liposomes encapsulated with a fluorescent dye.

RESULTS

Principal component analyses demonstrated that different CPAs can be recognized based on the shape of the OD band region only. Chemically similar molecules such as glycerol and ethylene glycol closely group together in a principal component score plot, whereas trehalose and DMSO appear as condensed separated clusters. The OH/OD band of CPA solutions exhibits an overall shift to higher wavenumbers with increasing temperature and changed fractions of weak and strong hydrogen interactions. CPAs diminish ice crystal formation in frozen samples during storage and minimize liposome leakage during freezing but cannot prevent leakage during frozen storage.

CONCLUSIONS

CPAs can be distinguished from one another based on the hydrogen bonding network that is formed in solution. DMSO-water mixtures behave anomalous compared to other CPAs that have OH groups. CPAs modulate ice crystal formation during frozen storage but cannot prevent liposome leakage during frozen storage.

The Role of Cryoprotective Agents in Liposome Stabilization and Preservation

To improve liposomes’ usage as drug delivery vehicles, cryoprotectants can be utilized to prevent constituent leakage and liposome instability. Cryoprotective agents (CPAs) or cryoprotectants can protect liposomes from the mechanical stress of ice by vitrifying at a specific temperature, which forms a glassy matrix. The majority of studies on cryoprotectants demonstrate that as the concentration of the cryoprotectant is increased, the liposomal stability improves, resulting in decreased aggregation. The effectiveness of CPAs in maintaining liposome stability in the aqueous state essentially depends on a complex interaction between protectants and bilayer composition. Furthermore, different types of CPAs have distinct effective mechanisms of action; therefore, the combination of several cryoprotectants may be beneficial and novel attributed to the synergistic actions of the CPAs. In this review, we discuss the use of liposomes as drug delivery vehicles, phospholipid–CPA interactions, their thermotropic behavior during freezing, types of CPA and their mechanism for preventing leakage of drugs from liposomes.

Cryopreservation and Cryobanking of Cells from 100 Coral Species

When coral species become extinct, their genetic resources cannot be recovered. Coral cryobanks can be employed to preserve coral samples and thereby maintain the availability of the samples and increase their potential to be restocked. In this study, we developed a procedure to determine coral species-specific requirements for cryobank freezing through determining suitable cryoprotective agents (CPAs), CPA concentrations, equilibration times, holding durations, viability rates, and cell amounts for banked coral cells, and we established the first ever coral cell cryobank. Coral cells, including supporting and gland cells, epidermal nematocysts, Symbiodiniaceae and symbiotic endoderm cells (SEC) were found from the extracted protocol. Approximately half of the corals from the experimental corals consisted of spindle and cluster cells. Gastrodermal nematocysts were the least common. The overall concentration of Symbiodiniaceae in the coral cells was 8.6%. Freezing using DMSO as a CPA was suitable for approximately half of the corals, and for the other half of species, successful cell cryopreservation was achieved using MeOH and EG. EG and DMSO had similar suitabilities for Acanthastrea, Euphyllia, Favites, Lobophyllia, Pavona, Seriatopora, and Turbinaria, as did EG and MeOH for Acropora, Echinopyllia, and Sinularia and MeOH and DMSO for Platygyra after freezing. At least 14 straws from each species of coral were cryobanked in this study, totaling more than 1884 straws (0.5 mL) with an average concentration of 6.4 × 10⁶ per mL. The results of this study may serve as a framework for cryobanks worldwide and contribute to the long-term conservation of coral reefs.

Enhancing the Stabilization Potential of Lyophilization for Extracellular Vesicles

Extracellular vesicles (EV) are an emerging technology as immune therapeutics and drug delivery vehicles. However, EVs are usually stored at -80 °C which limits potential clinical applicability. Freeze-drying of EVs striving for long-term stable formulations is therefore studied. The most appropriate formulation parameters are identified in freeze-thawing studies with two different EV types. After a freeze-drying feasibility study, four lyophilized EV formulations are tested for storage stability for up to 6 months. Freeze-thawing studies revealed improved colloidal EV stability in presence of sucrose or potassium phosphate buffer instead of sodium phosphate buffer or phosphate-buffered saline. Less aggregation and/or vesicle fusion occurred at neutral pH compared to slightly acidic or alkaline pH. EVs colloidal stability can be most effectively preserved by addition of low amounts of poloxamer 188. Polyvinyl pyrrolidone failed to preserve EVs upon freeze-drying. Particle size and concentration of EVs are retained over 6 months at 40 °C in lyophilizates containing 10 mm K- or Na-phosphate buffer, 0.02% poloxamer 188, and 5% sucrose. The biological activity of associated beta-glucuronidase is maintained for 1 month, but decreased after 6 months. Here optimized parameters for lyophilization of EVs that contribute to generate long-term stable EV formulations are presented.

Isolation of intact extracellular vesicles from cryopreserved samples

Extracellular vesicles (EVs) have emerged as promising candidates in biomarker discovery and diagnostics. Protected by the lipid bilayer, the molecular content of EVs in diverse biofluids are protected from RNases and proteases in the surrounding environment that may rapidly degrade targets of interests. Nonetheless, cryopreservation of EV-containing samples to -80°C may expose the lipid bilayer to physical and biological stressors which may result in cryoinjury and contribute to changes in EV yield, function, or molecular cargo. In the present work, we systematically evaluate the effect of cryopreservation at -80°C for a relatively short duration of storage (up to 12 days) on plasma- and media-derived EV particle count and/or RNA yield/quality, as compared to paired fresh controls. On average, we found that the plasma-derived EV concentration of stored samples decreased to 23% of fresh samples. Further, this significant decrease in EV particle count was matched with a corresponding significant decrease in RNA yield whereby plasma-derived stored samples contained only 47-52% of the total RNA from fresh samples, depending on the extraction method used. Similarly, media-derived EVs showed a statistically significant decrease in RNA yield whereby stored samples were 58% of the total RNA from fresh samples. In contrast, we did not obtain clear evidence of decreased RNA quality through analysis of RNA traces. These results suggest that samples stored for up to 12 days can indeed produce high-quality RNA; however, we note that when directly comparing fresh versus cryopreserved samples without cryoprotective agents there are significant losses in total RNA. Finally, we demonstrate that the addition of the commonly used cryoprotectant agent, DMSO, alongside greater control of the rate of cooling/warming, can rescue EVs from damaging ice formation and improve RNA yield.

Lipid Remodeling Confers Osmotic Stress Tolerance to Embryogenic Cells during Cryopreservation

Plant species conservation through cryopreservation using plant vitrification solutions (PVS) is based in empiricism and the mechanisms that confer cell integrity are not well understood. Using ESI-MS/MS analysis and quantification, we generated 12 comparative lipidomics datasets for membranes of embryogenic cells (ECs) of Magnolia officinalis during cryogenic treatments. Each step of the complex PVS-based cryoprotocol had a profoundly different impact on membrane lipid composition. Loading treatment (osmoprotection) remodeled the cell membrane by lipid turnover, between increased phosphatidic acid (PA) and phosphatidylglycerol (PG) and decreased phosphatidylcholine (PC) and phosphatidylethanolamine (PE). The PA increase likely serves as an intermediate for adjustments in lipid metabolism to desiccation stress. Following PVS treatment, lipid levels increased, including PC and PE, and this effectively counteracted the potential for massive loss of lipid species when cryopreservation was implemented in the absence of cryoprotection. The present detailed cryobiotechnology findings suggest that the remodeling of membrane lipids and attenuation of lipid degradation are critical for the successful use of PVS. As lipid metabolism and composition varies with species, these new insights provide a framework for technology development for the preservation of other species at increasing risk of extinction.

The combination treatment of cholesterol-loaded methyl-β-cyclodextrin and methyl-β-cyclodextrin significantly improves the fertilization capacity of vitrified bovine oocytes by protecting fertilization protein JUNO

Many experiments show that vitrification significantly reduces the fertilization capacity of mammalian oocytes, restricting the application of vitrified oocytes. It has been proven that the JUNO protein plays a vital role in mammalian oocytes fertilization. However, little information is available about the effects of vitrification on the JUNO protein and the procedure to protect it in bovine oocytes. Here, the present study was designed to investigate the effect of vitrification on the JUNO protein level in bovine oocytes. In this study, MII oocytes were treated with cholesterol-loaded methyl-β-cyclodextrin (CLC; 0, 10, 15, 20 mM) for 45 min before vitrification and methyl-β-cyclodextrin (MβCD; 0, 2.25, 4.25, 6.25 mM) for 45 min after thawing (38-39°C). Then, the expression level and function of JUNO protein, cholesterol level in the membrane, the externalization of phosphatidylserine, sperm binding capacity and the developmental ability of vitrified bovine oocytes were examined. Our results showed that vitrification significantly decreased the JUNO protein level, cholesterol level, sperm binding capacity, development ability, and increased the promoter methylation level of the JUNO gene and apoptosis level of bovine oocytes. Furthermore, 15 mM CLC + 4.25 mM MβCD treatment significantly improved the cholesterol level and increased sperm binding and development ability of vitrified bovine oocytes. In conclusion, the combination treatment of cholesterol-loaded methyl-β-cyclodextrin and methyl-β-cyclodextrin significantly improves the fertilization capacity of vitrified bovine oocytes by protecting fertilization protein JUNO.

Principles Underlying Cryopreservation and Freeze-Drying of Cells and Tissues

Cryopreservation and freeze-drying can be used to preserve cells or tissues for prolonged periods. Vitrification, or ice-free cryopreservation, is an alternative to cryopreservation that enables cooling cells to cryogenic temperatures in the absence of ice. The processing pathways involved in (ice-free) cryopreservation and freeze-drying of cells and tissues, however, can be very damaging. In this chapter, we describe the principles underlying preservation of cells for which freezing and drying are normally lethal processes as well as for cells that are able to survive in a reversible state of suspended animation. Freezing results in solution effects injury and/or intracellular ice formation, whereas drying results in removal of (non-freezable) water normally bound to biomolecules, which is generally more damaging. Cryopreservation and freeze-drying require different types of protective agents. Different mechanistic modes of action of cryoprotective and lyoprotective agents are described including minimizing ice formation, preferential exclusion, water replacement, and vitrification. Furthermore, it is discussed how protective agents can be introduced into cells avoiding damage due to too large cell volume excursions, and how knowledge of cell-specific membrane permeability properties in various temperature regimes can be used to rationally design (ice-free) cryopreservation and freeze-drying protocols.

Enhancing transient protein expression in HEK-293 cells by briefly exposing the culture to DMSO

BACKGROUND

Transient expression of proteins in mammalian cells is a key technique for many functional and structural studies of human and higher eukaryotic genes as well as for the production of recombinant protein therapeutics. Maximizing the expression efficiency to achieve a higher expression yield is desirable and may be even critical when, for instance, an expressed protein must be characterized at the single-cell level.

NEW METHODS

Our goal was to develop a simple method by which protein expression yield in human embryonic kidney (HEK)-293 cells could be enhanced with a brief treatment of dimethyl sulfoxide (DMSO) solution.

RESULTS

By expressing green fluorescent protein (GFP) as a reporter protein using the calcium phosphate transfection method and imaging a large population of cells, we found that a 5-min exposure of 10 % DMSO to HEK-293 cells, 4 h after transfection of the protein of interest, leads to ∼1.6-fold increase in the expression yield without causing any appreciable cytotoxicity. By expressing an α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) and separately a kainate receptor in HEK-293 cells and measuring glutamate-induced whole-cell current response, we also found that such a brief DMSO treatment did not affect channel activity.

CONCLUSION

This method is simple, efficient and inexpensive to use for enhancing transient transfection yield in HEK-293 cells.

Semen extender and seminal plasma alter the extent of neutrophil extracellular traps (NET) formation in cattle

During artificial insemination in bovine, the deposition of semen into the uterus results in an immune reaction which is based on polymorphonuclear neutrophils activity, including the formation of neutrophil extracellular traps. The formation of neutrophil extracellular traps as a reaction of neutrophils to spermatozoa was recently described. However, it is not completely clear which components of the semen are responsible for this reaction. The objective of this study was to quantify and compare the formation of neutrophil extracellular traps following in vitro incubation of bovine polymorphonuclear neutrophils with semen and extenders of different origins and conditions. We investigated the interactions between bovine polymorphonuclear neutrophils and different semen extenders, various seminal plasma concentrations from young and old bulls as well as sexed and non-sexed semen and their corresponding extenders. Three different semen extenders from two companies in fresh and frozen-thawed conditions were compared. Fresh semen extenders showed higher neutrophil extracellular traps induction than did frozen-thawed ones. The formation of neutrophil extracellular traps were also dependent on the presence of seminal plasma. We could show that seminal plasma alone, without any sperm cells, induced the reaction and that the addition of at least 1% seminal plasma already resulted in the formation of neutrophil extracellular traps. Furthermore, seminal plasma from young bulls led to significant higher neutrophil extracellular traps induction. No difference between non-sex-sorted and sex-sorted sperm and its extenders was observed. Taken together, different semen extenders as well as the amount and origin of seminal plasma influence neutrophil extracellular traps formation, whereas sex-sorted sperm did not affect the reaction.

Development of an Oil-in-Water Self-Emulsifying Microemulsion for Cutaneous Delivery of Rose Bengal: Investigation of Anti-Melanoma Properties

The topical delivery route is proposed as an alternative or adjunctive approach to melanoma treatment, since the target site for melanoma treatment-the epidermal basal layer-is potentially accessible by this route. Microemulsion systems are effective delivery vehicles for enhanced, targeted skin delivery. This work investigated the effect of Rose Bengal (RB) and RB-loaded self-emulsifying microemulsions (SEMEs) on growth inhibition of human melanoma and normal skin cell monolayers, the safety of the excipients incorporated in SEMEs on human cell lines, and the in-vitro human skin penetration of RB delivered in SEMEs and control solution. Cellular toxicity was assessed by the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay, and the growth inhibitory mechanism of RB was investigated by flow cytometry using PI staining. Unloaded SEMEs caused reduced cellular toxicity compared to the surfactant excipient, Labrasol^®. RB-loaded SEMEs increased cell growth inhibition compared to the RB aqueous solution. Flow cytometry revealed apoptotic cells after treatment with RB-loaded SEMEs, indicating that apoptosis may be one of the mechanisms of cell death. Preliminary results of multiphoton microscopy with fluorescence lifetime imaging (MPM-FLIM) analysis showed deeper penetration with greater skin concentrations of RB delivered from SEMEs compared to the RB aqueous solution. This study highlights the enhanced skin penetration and antimelanoma effects of RB loaded in a SEME system.

Multifunctional carriers for controlled drug delivery

In the review we describe a method for concentration of anionic liposomes with encapsulated water-soluble substances within a small volume via electrostatic liposome adsorption on the surface of polymer particles with grafted cationic chains (spherical polycationic brushes), or cationic microgel particles. Dozens of intact liposomes can be bound to each polymer particle, the resulting polymer/liposome complex does not dissociate into the original components in a physiological solution. This allows fabrication of multi-liposomal complexes (MLCs) with a required ratio of encapsulated substances. Two approaches are discussed for the synthesis of stimuli-sensitive MLCs. The first is to incorporate the conformation switch, morpholinocyclohexanol-based lipid, into the liposomal membrane thus forming pH-sensitive liposomes capable of releasing their cargo when acidifying the surrounding solution. These liposomes complexed with the brushes release encapsulated substances much faster than the uncomplexed liposomes. The second is to adsorb liposomes on cationic thermo-responsive microgels. The resulting MLCs contracts upon heating over a volume phase transition temperature from the swollen to the collapsed state of microgel, thus causing the adsorbed liposomes to change drastically their morphology and release an encapsulated substance. Complexation of anionic liposomes with chitosan microgels and polylactide micelles gives MLCs which degrade in the presence of enzymes down to small particles, 10–15 nm in diameter. A novel promising approach suggests that immobilized liposomes can act as a capacious depot for biologically active compounds and ensure their controllable leakage to surrounding solution.

Sublingual delivery of chondroitin sulfate conjugated tapentadol loaded nanovesicles for the treatment of osteoarthritis

Recent treatment approaches of osteoarthritis (OA) face a number of obstacles due to the progressive multitude of pain generators, nociceptive mechanisms, first pass mechanism, less efficacy and compromised safety. The present study was aimed to bring a novel approach for the effective management of OA, by developing sublingual targeted nanovesicles (NVs) bearing tapentadol HCl (TAP), surface modified with chondroitin sulfate (CS). Optimized nontargeted nanovesicle formulation (MB-NV) was developed by an ultrasound method, characterized as spherical in shape, nanometric in size (around 150 nm) with narrow size distribution (polydispersity index <0.5), and good entrapment efficiency (around 50%). MB-NV conjugated with CS which was confirmed by IR and ¹H NMR spectroscopy. C-MB-NV showed improved pharmacokinetics parameters i.e. increased t_1/2 (9.7 h), AUC (159.725 μg/mL*h), and MRT (14.99 h) of TAP than nontargeted formulation and plain drug soln. C-MB-NV in in vitro release studies proved sustained drug release pattern for more than 24 h following Higuchi model kinetics with Fickian diffusion (n ≤ 0.5).Targeted nanovesicles exhibited an improved bioavailability and enhanced analgesic activity in a disease-induced Wistar rat model which indicated the superior targeting potential of C-MB-NV exploiting CD44 receptors as mediators, overexpressed at the affected joints in the OA model. It could be a propitious approach to accustomed therapies for methodical and efficient management in advanced OA therapy.

Dimethyl sulfoxide: a central player since the dawn of cryobiology, is efficacy balanced by toxicity?

Dimethyl sulfoxide (DMSO) is the cryoprotectant of choice for most animal cell systems since the early history of cryopreservation. It has been used for decades in many thousands of cell transplants. These treatments would not have taken place without suitable sources of DMSO that enabled stable and safe storage of bone marrow and blood cells until needed for transfusion. Nevertheless, its effects on cell biology and apparent toxicity in patients have been an ongoing topic of debate, driving the search for less cytotoxic cryoprotectants. This review seeks to place the toxicity of DMSO in context of its effectiveness. It will also consider means of reducing its toxic effects, the alternatives to its use and their readiness for active use in clinical settings.

Human oocytes and zygotes are ready for ultra-fast vitrification after 2 minutes of exposure to standard CPA solutions

Vitrification of human oocytes and embryos in different stages of development is a key element of daily clinical practice of in vitro fertilization treatments. Despite the cooling and warming of the cells is ultra-fast, the procedure as a whole is time consuming. Most of the duration is employed in a long (8–15 minutes), gradual or direct exposure to a non-vitrifying cryoprotectant solution, which is followed by a short exposure to a more concentrated vitrifying solution. A reduction in the duration of the protocols is desirable to improve the workflow in the IVF setting and reduce the time of exposure to suboptimal temperature and osmolarity, as well as potentially toxic cryoprotectants. In this work it is shown that this reduction is feasible. In silico (MatLab program using two-parameter permeability model) and in vitro observations of the oocytes’ osmotic behaviour indicate that the dehydration upon exposure to standard cryoprotectant solutions occurs very fast: the point of minimum volume of the shrink-swell curve is reached within 60 seconds. At that point, intracellular water ejection is complete, which coupled with the permeation of low molecular weight cryoprotectants results in similar intracellular and extracellular solute concentrations. This shows that prolonging the exposure to the cryoprotectant solutions does not improve the cytosolic glass forming tendency and could be avoided. To test this finding, human oocytes and zygotes that were donated for research were subjected to a shortened, dehydration-based protocol, consisting of two consecutive exposures of one-minute to two standard cryoprotectant solutions, containing ethylene glycol, dimethyl sulfoxide and sucrose. At the end of this two-minute dehydration protocol, the critical intracellular solute concentration necessary for successful vitrification was attained, confirmed by the post-warming survival and ability to resume cytokinesis of the cells. Further studies of the developmental competency of oocytes and embryos would be necessary to determine the suitability of this specific dehydration protocol for clinical practice, but based on our results, short times of exposure to increasingly hypertonic solutions could be a more time-efficient strategy to prepare human oocytes and embryos for vitrification.

Solvation properties of raft-like model membranes

Dimethyl sulfoxide (DMSO) is a universal water-soluble solvent widely used in many biotechnological and medical applications, such as cells cryopreservation, and for the treatment of different human diseases (e.g. amyloidosis). Despite the great number of reported studies, the effects of DMSO on the physico-chemical properties of biological membranes are poorly understood. Often, these studies are limited to model membranes composed of phosphatidylcholines (PCs) and cholesterol (Chol). In this work, we explored the effect of DMSO on liposomes composed of the natural egg sphingomyelin (ESM) and Chol as raft-like model membranes. With a multi-technique approach we probe the structure and the thermal stability of ESM/Chol bilayer at different Chol mole fractions. In particular, we investigate the ESM-solvent interactions to clarify the role of DMSO in perturbing the solvating conditions of lipid vesicles and show that the addition of DMSO increases the thermal stability of vesicles. An increase of transition temperature, a decrease of both enthalpy and entropy as well as a decrease of the cooperativity of the gel to liquid phase transition are observed at 0.1 DMSO mole fraction. Fluorescence experiments with the probe Laurdan and FTIR spectra strongly indicate that DMSO exerts a dehydration effect on the membrane. Besides, FTIR measurements with tungsten hexacarbonyl, in combination with fluorescence data of the probe NBD-PE, indicate that DMSO promotes the formation of a highly packed membrane by reducing the thickness of the membrane.

Factors Affecting the Membrane Permeability Barrier Function of Cells during Preservation Technologies

Cellular membranes are exposed to extreme conditions during the processing steps involved in cryopreservation (and freeze-drying) of cells. The first processing step involves adding protective agents. Exposing cells to protective agents causes fluxes of both water and solutes (i.e., permeating cryoprotective agents) across the cellular membrane, resulting in cell volume changes and possibly osmotic stress. In addition, protective molecules may interact with lipids, which may lead to membrane structural changes and permeabilization. After loading with protective agents, subsequent freezing exposes cells to severe osmotic and mechanical stresses, caused by extra and/or intracellular ice formation and a drastically increased solute concentration in the unfrozen fraction. Furthermore, cellular membranes undergo thermotropic and lyotropic phase transitions during cooling and freezing, which drastically alter the membrane permeability and its barrier function. In this article, it is shown that membrane permeability to water and solutes is dependent on the temperature, medium osmolality, types of solutes present, cell hydration level, and absence or presence of ice. Freezing most drastically alters the membrane permeability barrier function, which is reflected as a change in the activation energy for water transport. In addition, membranes become temporarily leaky during freezing-induced fluid-to-gel membrane phase transitions, resulting in the uptake of impermeable solutes.

Storage stability of liposomes stored at elevated subzero temperatures in DMSO/sucrose mixtures

Cryopreservation of biological materials is predominantly done using liquid nitrogen, and its application involves high maintenance costs and the need for periodical refilling of liquid nitrogen. Stable storage in mechanical freezers at −80°C would eliminate these issues and allow for shipment of frozen specimens using dry ice. In this work, the possibility of increasing the storage temperature of cryopreserved samples to −80°C by using combinations of DMSO and sucrose has been studied. Preservation efficacy was studied by measuring stability of liposomes encapsulated with carboxyfluorescein during storage at −150, −80 and −25°C for up to three months. Thermal and molecular mobility properties of the different DMSO-sucrose formulations were measured using differential scanning calorimetry, whereas hydrogen bonding interactions of the formulations were probed by Fourier transform infrared spectroscopy. It was found that addition of sucrose to DMSO solutions increases the T_g, and decreases molecular mobility in the glassy state at a particular temperature. Although it was expected that storage above or close to T_g at −80°C would affect liposome stability, stability was found to be similar compared to that of samples stored at −150°C. Higher molecular mobility in the glassy state could not be associated with faster CF-leakage rates. Distinct differences in storage stability at −25°C, far above T_g, were found among the sucrose/DMSO formulations, which were explained by the differences in permeability of sucrose and DMSO resulting in different levels of osmotic stress in the formulations.