Interactions between soluble sugars and POPC (1-palmitoyl-2-oleoylphosphatidylcholine) during dehydration: vitrification of sugars alters the phase behavior of the phospholipid

Measurement of the rotational relaxation time of intracellular water in dried yeast and Jurkat cells by near infrared spectroscopy

Molecular mobility of intracellular water is a crucial parameter in the study of the mechanism of desiccation tolerance. As one of the parameters that reflecting molecular mobility, the viscosity of intracellular water has been found intimately related with the protection of the phospholipid membrane because it quantifies the diffusion ability of water and mass in the intracellular environment. In this work we measured the intracellular water relaxation time, which can be translated into water viscosity, by using a previously established NIR-dielectric method to monitor the drying process of baker's yeast and Jurkat cells with different desiccation tolerance. We found that intracellular saccharide can significantly decrease the intracellular water viscosity. Also, the intracellular water diffusion coefficient obtained from this method were found in good agreement with other reports.

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.

Skin drug delivery using lipid vesicles: A starting guideline for their development

Lipid vesicles can provide a cost-effective enhancement of skin drug absorption when vesicle production process is optimised. It is an important challenge to design the ideal vesicle, since their properties and features are related, as changes in one affect the others. Here, we review the main components, preparation and characterization methods commonly used, and the key properties that lead to highly efficient vesicles for transdermal drug delivery purposes. We stand by size, deformability degree and drug loading, as the most important vesicle features that determine the further transdermal drug absorption. The interest in this technology is increasing, as demonstrated by the exponential growth of publications on the topic. Although long-term preservation and scalability issues have limited the commercialization of lipid vesicle products, freeze-drying and modern escalation methods overcome these difficulties, thus predicting a higher use of these technologies in the market and clinical practice.

A Comprehensive Review of mRNA Vaccines

mRNA vaccines have been demonstrated as a powerful alternative to traditional conventional vaccines because of their high potency, safety and efficacy, capacity for rapid clinical development, and potential for rapid, low-cost manufacturing. These vaccines have progressed from being a mere curiosity to emerging as COVID-19 pandemic vaccine front-runners. The advancements in the field of nanotechnology for developing delivery vehicles for mRNA vaccines are highly significant. In this review we have summarized each and every aspect of the mRNA vaccine. The article describes the mRNA structure, its pharmacological function of immunity induction, lipid nanoparticles (LNPs), and the upstream, downstream, and formulation process of mRNA vaccine manufacturing. Additionally, mRNA vaccines in clinical trials are also described. A deep dive into the future perspectives of mRNA vaccines, such as its freeze-drying, delivery systems, and LNPs targeting antigen-presenting cells and dendritic cells, are also summarized.

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.

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.

Glycyrrhetinic acid proliposomes mediated by mannosylated ligand: Preparation, physicochemical characterization, environmental stability and bioactivity evaluation

Glycyrrhetinic acid is a bioactive compound extracted from licorice that exhibits inhibition effect on various cancers. However, its hydrophobicity results in low bioavailability that limits application. We aim to overcome this barrier, the present research was performed to prepare glycyrrhetinic acid proliposomes mediated mannosylated ligand (mannose-diester lauric diacid-cholesterol, MDC) and to evaluate its physicochemical characterizations, environmental stability and bioactivity. In preliminary optimization studies of glycyrrhetinic acid proliposomes mediated MDC (MDC-GA-PL), four optimum operating parameters, cryoprotectant of glucose and mannitol, the mixed cryoprotectant ratio (glucose/mannitol) of 1:1, a cryoprotectant/egg phosphatidylcholine mass ratio of 10/1, and -60 ℃ pre-freezing temperature, were obtained after investigation. Under the optimum lyophilization conditions, MDC-GA-PL was freeze-dried and reconstituted proliposomes were characterized. These proliposomes showed that MDC-GA-PL were well-dispersible spherical particles with an average particle size of 120.80 nm, a polydispersity index about 0.095, a zeta potential of -33.15 mV, encapsulation efficiency of 85.9% and drug loading of 6.38%. In vitro drug release study showed that glycyrrhetinic acid release of MDC-GA-PL conforms to the Higuchi release model. In addition, these proliposomes were stable during six months at 4 ℃. Moreover, acute toxicity assay revealed no substantial safety concern for MDC-GA-PL. Finally, in vitro bioactivity of proliposomes was evaluated. Cytotoxicity effect and apoptosis efficiency of MDC-GA-PL by HepG2 cells was significantly higher than that of glycyrrhetinic acid proliposomes without MDC, demonstrating that MDC has a desirable effect on liver target. Overall, we have reason to believe that MDC-GA-PL would be a promising target delivery to improve therapeutic against hepatic diseases.

Impact of Surface Polarity on Lipid Assembly under Spatial Confinement

Molecular dynamics (MD) simulations in the MARTINI model are used to study the assembly of 1-palmitoyl-2-oleoylphosphatidylcholine (POPC) molecules under spatial confinement, such as during solvent evaporation from ultrasmall (femtoliter quantity) droplets. The impact of surface polarity on molecular assembly is discussed in detail. To the best of our knowledge, this work represents the first of its kind. Our results reveal that solvent evaporation gives rise to the formation of well-defined stacks of lipid bilayers in a smectic alignment. These smectic mesophases form on both polar and nonpolar surfaces but with a notable distinction. On polar surfaces, the director of the stack is oriented perpendicular to the support surface. By contrast, the stacks orient at an angle on the nonpolar surfaces. The packing of head groups on surfaces and lipid molecular mobility exhibits significant differences as surface polarity changes. The role of glycerol in the assembly and stability is also revealed. The insights revealed from the simulation have a significant impact on additive manufacturing, biomaterials, model membranes, and engineering protocells. For example, POPC assemblies via evaporation of ultrasmall droplets were produced and characterized. The trends compare well with the bilayer stack models. The surface polarity influences the local morphology and structures at the interfaces, which could be rationalized via the molecule-surface interactions observed from simulations.

Amyloid β Dodecamer Disrupts the Neuronal Membrane More Strongly than the Mature Fibril: Understanding the Role of Oligomers in Neurotoxicity

The amyloid cascade hypothesis states that senile plaques, composed of amyloid β (Aβ) fibrils, play a key role in Alzheimer’s disease (AD). However, recent experiments have shown that Aβ oligomers are more toxic to neurons than highly ordered fibrils. The molecular mechanism underlying this observation remains largely unknown. One of the possible scenarios for neurotoxicity is that Aβ peptides create pores in the lipid membrane that allow Ca²⁺ ions to enter cells, resulting in a signal of cell apoptosis. Hence, one might think that oligomers are more toxic due to their higher ability to create ion channels than fibrils. In this work, we study the effect of Aβ42 dodecamer and fibrils on a neuronal membrane, which is similar to that observed in AD patients, using all-atom molecular dynamics simulations. Due to short simulation times, we cannot observe the formation of pores, but useful insight on the early events of this process has been obtained. Namely, we showed that dodecamer distorts the lipid membrane to a greater extent than fibrils, which may indicate that ion channels can be more easily formed in the presence of oligomers. Based on this result, we anticipate that oligomers are more toxic than mature fibrils, as observed experimentally. Moreover, the Aβ–membrane interaction was found to be governed by the repulsive electrostatic interaction between Aβ and the ganglioside GM1 lipid. We calculated the bending and compressibility modulus of the membrane in the absence of Aβ and obtained good agreement with the experiment. We predict that the dodecamer will increase the compressibility modulus but has little effect on the bending modulus. Due to the weak interaction with the membrane, fibrils insignificantly change the membrane elastic properties.

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.

Effect of using amino acids in the freeze-drying of siRNA lipoplexes on gene knockdown in cells after reverse transfection

Recently, small interfering RNA (siRNA)/cationic liposome complexes (siRNA lipoplexes) have become a crucial research tool for studying gene function. Easy and reliable siRNA transfection with a large set of siRNAs is required for the successful screening of gene function. Reverse (Rev)-transfection with freeze-dried siRNA lipoplexes is validated for siRNA transfection with a large set of siRNAs in a multi-well plate. In our previous study, it was shown that Rev-transfection with siRNA lipoplexes freeze-dried in disaccharides or trisaccharides resulted in long-term stability with a high level of gene-knockdown activity. In the present study, the effects of amino acids used as cryoprotectants in the freeze-drying of siRNA lipoplexes on gene knockdown via Rev-transfection were assessed. A total of 15 types of amino acids were used to prepare freeze-dried siRNA lipoplexes, and it was found that the freeze-drying of siRNA lipoplexes with amino acid concentrations >100 mM strongly suppressed targeted gene expression regardless of the amino acid type; however, some amino acids strongly upregulated or downregulated gene expression in the cells transfected with negative control siRNA. Amongst the amino acids tested, the presence of asparagine showed specific gene-knockdown activity, forming large cakes after freeze-drying and retaining a favorable siRNA lipoplex size after rehydration. These findings provide valuable information regarding amino acids as cryoprotectants for Rev-transfection using freeze-dried siRNA lipoplexes for the efficient delivery of siRNA into cells.

Dehydration induced dynamical heterogeneity and ordering mechanism of lipid bilayers

Understanding the influence of dehydration on the membrane structure is crucial to control membrane functionality related to domain formation and cell fusion under anhydrobiosis conditions. To this end, we perform all-atom molecular dynamic simulations of 1,2-dimyristoyl-sn-glycero-3-phosphocholine dimyristoylphosphatidylcholine lipid membranes at different hydration levels at 308 K. As dehydration increases, the lipid area per head group decreases with an increase in bilayer thickness and lipid order parameters indicating bilayer ordering. Concurrently, translational and rotational dynamics of interfacial water (IW) molecules near membranes slow down. On the onset of bilayer ordering, the IW molecules exhibit prominent features of dynamical heterogeneity evident from non-Gaussian parameters and one-dimensional van Hove correlation functions. At a fully hydrated state, diffusion constants (D) of the IW follow a scaling relation, D∼τ_α ^-1, where the α relaxation time (τ_α) is obtained from self-intermediate scattering functions. However, upon dehydration, the relation breaks and the D of the IW follows a power law behavior as D∼τ_α ^-0.57, showing the signature of glass dynamics. τ_α and hydrogen bond lifetime calculated from intermittent hydrogen bond auto-correlation functions undergo a similar crossover in association with bilayer ordering on dehydration. The bilayer ordering is accompanied with an increase in fraction of caged lipids spanned over the bilayer surface and a decrease in fraction of mobile lipids due to the non-diffusive dynamics. Our analyses reveal that the microscopic mechanism of lipid ordering by dehydration is governed by dynamical heterogeneity. The fundamental understanding from this study can be applied to complex bio-membranes to trap functionally relevant gel-like domains at room temperature.

Storage stability of inhalable, controlled-release powder formulations of ciprofloxacin nanocrystal-containing liposomes

Novel inhalable and controlled release powder formulations of ciprofloxacin nanocrystals inside liposomes (CNL) were recently developed. In the present study, the storage stability of CNL powders consisting of lyoprotectant (i.e. sucrose or lactose), lipids, ciprofloxacin (CIP), and magnesium stearate or isoleucine was investigated. These powders were produced by spray drying, collected in a dry box at <15% relative humidity (RH), then stored at room temperature and either 4 or 20 %RH. Liposomal integrity, CIP encapsulation efficiency (EE), in vitro drug release (IVR), aerosol performance, and solid-state properties were examined over six months. Sucrose CNL powder exhibited consistent liposomal integrity, aerosol performance, and controlled release of CIP over six months of storage at 4 %RH. However, storage of the powder at 20 %RH for the same period caused sucrose crystallization and consequently a significant drop in EE and aerosol performance (p-values < 0.05), along with the IVR of CIP becoming similar to that of the non-crystalline CIP liposomal dispersions (f2 > 50). Lactose CNL maintained superior aerosol performance over the six months irrespective of the storage RH. However, liposomal instability occurred at both RHs within the first month of storage with a significant drop in EE and an increase in liposome size (p-values < 0.05). Moreover, the IVR assay of CIP from lactose CNL showed a less controlled release and a substantial difference (f2 < 50) from its initial value after six months regardless of the storage RHs. In conclusion, dry powder inhalers of CNL were physiochemically stable in sucrose lyoprotectant when stored below 4 %RH at room temperature for six months.

Freeze-drying of nanoparticles: How to overcome colloidal instability by formulation and process optimization

Lyophilization of nanoparticle (NP) suspensions is a promising technology to improve stability, especially during long-term storage, and offers new routes of administration in solid state. Although considered as a gentle drying process, freeze-drying is also known to cause several stresses leading to physical instability, e.g. aggregation, fusion, or content leakage. NPs are heterogeneous regarding their physico-chemical properties which renders them different in their sensitivity to lyophilization stress and upon storage. But still basic concepts can be deducted. We summarize basic colloidal stabilization mechanisms of NPs in the liquid and the dried state. Furthermore, we give information about stresses occurring during the freezing and the drying step of lyophilization. Subsequently, we review the most commonly investigated NP types including lipophilic, polymeric, or vesicular NPs regarding their particle properties, stabilization mechanisms in the liquid state, and important freeze-drying process, formulation and storage strategies. Finally, practical advice is provided to facilitate purposeful formulation and process development to achieve NP lyophilizates with high colloidal stability.

Current Approaches of Preservation of Cells During (freeze-) Drying

The widespread application of therapeutic cells requires a successful stabilization of cells for the duration of transport and storage. Cryopreservation is currently considered the gold standard for the storage of active cells; however, (freeze-) drying cells could enable higher shelf life stability at ambient temperatures and facilitate easier transport and storage. During (freeze-) drying, freezing, (primary and secondary) drying and also the reconstitution step pose the risk of potential cell damage. To prevent these damaging processes, a wide range of protecting excipients has emerged, which can be classified, according to their chemical affiliation, into sugars, macromolecules, polyols, antioxidants and chelating agents. As many excipients cannot easily permeate the cell membrane, researchers have established various techniques to introduce especially trehalose intracellularly, prior to drying. This review aims to summarize the main damaging mechanisms during (freeze-) drying and to introduce the most common excipients with further details on their stabilizing properties and process approaches for the intracellular loading of excipients. Additionally, we would like to briefly explain recently discovered advantages of drying microorganisms, sperm, platelets, red blood cells, and eukaryotic cells, paying particular attention to the drying technique and residual moisture content.

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.

Facile preparation of liposome-encapsulated Zn–DTPA from soy lecithin for decorporation of radioactive actinides

Diethylenetriaminepentaacetic acid (DTPA) is an attractive decorporation agent that can enhance the excretion of radioactive actinides such as plutonium, americium, and curium after a radiological incident. However, DTPA is excreted in a short period of time after administration. Several formulations have been developed to improve DTPA pharmacokinetics properties. In this project, liposomes were prepared facilely from soy lecithin as a nanocarrier for pulmonary delivery of Zn–DTPA. Lipid hydration, reverse phase evaporation, and mechanical sonication were three methods evaluated for the preparation of liposome-encapsulated Zn-DTPA (lipo-Zn-DTPA). Mechanical sonication was the method of choice due to simple apparatus and facile preparation. Lipo-Zn–DTPA exhibited a hydrodynamic diameter of 178 ± 2 nm and a spherical shape. The loading capacity and encapsulation efficiency of Zn–DTPA were 41 ± 5 mg/g and 10% ± 1%, respectively. Lyophilization of lipo-Zn–DTPA for extended storage did not affect the amount of encapsulated drug or damage the structure of liposomes. An in vivo cytotoxicity test confirmed no serious adverse effect of Zn–DTPA encapsulated lecithin liposomes in rats.

Membrane and lipid metabolism plays an important role in desiccation resistance in the yeast Saccharomyces cerevisiae

Background

Anhydrobiotes, such as the yeast Saccharomyces cerevisiae, are capable of surviving almost total loss of water. Desiccation tolerance requires an interplay of multiple events, including preserving the protein function and membrane integrity, preventing and mitigating oxidative stress, maintaining certain level of energy required for cellular activities in the desiccated state. Many of these crucial processes can be controlled and modulated at the level of organelle morphology and dynamics. However, little is understood about what organelle perturbations manifest in desiccation-sensitive cells as a consequence of drying or how this differs from organelle biology in desiccation-tolerant organisms undergoing anhydrobiosis.

Results

In this study, electron and optical microscopy was used to examine the dynamic changes of yeast cells during the desiccation process. Dramatic structural changes were observed during the desiccation process, including the diminishing of vacuoles, decrease of lipid droplets, decrease in mitochondrial cristae and increase of ER membrane, which is likely caused by ER stress and unfolded protein response. The survival rate was significantly decreased in mutants that are defective in lipid droplet biosynthesis, or cells treated with cerulenin, an inhibitor of fatty acid synthesis.

Conclusion

Our study suggests that the metabolism of lipid droplets and membrane may play an important role in yeast desiccation tolerance by providing cells with energy and possibly metabolic water. Additionally, the decrease in mitochondrial cristae coupled with a decrease in lipid droplets is indicative of a cellular response to reduce the production of reactive oxygen species.

Mechanisms of Desiccation Tolerance: Themes and Variations in Brine Shrimp, Roundworms, and Tardigrades

Water is critical for the survival of most cells and organisms. Remarkably, a small number of multicellular animals are able to survive nearly complete drying. The phenomenon of anhydrobiosis, or life without water, has been of interest to researchers for over 300 years. In this review we discuss advances in our understanding of protectants and mechanisms of desiccation tolerance that have emerged from research in three anhydrobiotic invertebrates: brine shrimp (Artemia), roundworms (nematodes), and tardigrades (water bears). Discovery of molecular protectants that allow each of these three animals to survive drying diversifies our understanding of desiccation tolerance, and convergent themes suggest mechanisms that may offer a general model for engineering desiccation tolerance in other contexts.

Freeze-Dried Extracellular Vesicles From Adipose-Derived Stem Cells Prevent Hypoxia-Induced Muscle Cell Injury

Cellular therapies have tremendous potential for the successful treatment of major extremity wounds in the combat setting, however, the challenges associated with transplanting stem cells in the prolonged field care (PFC) environment are a critical barrier to progress in treating such injuries. These challenges include not only production and storage but also transport and handling issues. Our goal is to develop a new strategy utilizing extracellular vesicles (EVs) secreted by stem cells that can resolve many of these issues and prevent ischemic tissue injury. While EVs can be preserved by freezing or lyophilization, both processes result in decrease in their bioactivity. Here, we describe optimized procedures for EVs production, isolation, and lyophilization from primary human adipose-derived stem cells (hADSCs). We compared two isolation approaches that were ultrafiltration (UF) using a tangential fluid filtration (TFF) system and differential ultracentrifugation (UC). We also optimized EVs lyophilization in conjunction with trehalose and polyvinylpyrrolidone 40 (PVP40) as lyoprotectants. Bioactivity of EVs was assessed based on reversal of hypoxia-induced muscle cell injury. To this end, primary human myoblasts were subjected to hypoxic conditions for 6 h, and then treated with hADSC-derived EVs at a concentration of 50 μg/mL. Subsequently, muscle cell viability and toxicity were evaluated using MTS and LDH assays, respectively. Overall, nanoparticle tracking data indicated that UF/TFF yields threefold more particles than UC. Lyophilization of EVs resulted in a significantly reduced number of particles, which could be attenuated by adding lyoprotections to the freeze-drying solution. Furthermore, EVs isolated by UF/TFF and freeze-dried in the presence of trehalose significantly increased viability (P < 0.0193). Taken together, our findings suggest that the isolation and preservation methods presented in this study may enhance therapeutic applications of EVs.

Membrane lipids destabilize short interfering ribonucleic acid (siRNA)/polyethylenimine nanoparticles

Cell entry of polymeric nanoparticles (NPs) bearing polynucleotides is an important stage for successful gene delivery. In this work, we addressed the influence of cell membrane lipids on the integrity and configurational changes of NPs composed of short interfering ribonucleic acid (siRNA) and polyethylenimine. We focused on NPs derived from two different PEIs, unmodified low molecular weight PEI and linoleic acid (LA)-substituted PEI, and their interactions with two membrane lipids (zwitterionic 2-oleoyl-1-palmitoyl-sn-glycero-3-phosphocholine (POPC) and anionic 1-palmitoyl-2-oleoyl-sn-glycero-3-phospho-l-serine (POPS)). Our experiments showed that POPS liposomes interacted strongly with both types of NPs, which caused partial dissociation of the NPs. POPC liposomes, however, did not induce any dissociation. Consistent with the experiments, steered molecular dynamics simulations showed a stronger interaction between the NPs and the POPS membrane than between the NPs and the POPC membrane. Lipid substitution on the PEIs enhanced the stability of the NPs during membrane crossing; lipid association between PEIs of the LA-bearing NPs as well as parallel orientation of the siRNAs provided protection against their dissociation (unlike NPs from native PEI). Our observations provide valuable insight into the integrity and structural changes of PEI/siRNA NPs during membrane crossing which will help in the design of more effective carriers for nucleic acid delivery.

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.

Lyophilized liposome-based parenteral drug development: Reviewing complex product design strategies and current regulatory environments

Given the successful entry of several liposomal drug products into market, and some with decades of clinical efficacy, liposomal drug delivery systems have proven capabilities to overcome certain limitations of traditional drug delivery, especially for toxic and biologic drugs. This experience has helped promote new liposomal approaches to emerging drug classes and current therapeutic challenges. All approved liposomal dosage forms are parenteral formulations, a pathway demonstrating greatest safety and efficacy to date. Due to the intrinsic instability of aqueous liposomal dispersions, lyophilization is commonly applied as an important solution to improve liposomal drug stability, and facilitate transportation, storage and improve product shelf-life. While lyophilization is a mature pharmaceutical technology, liposome-specific lyophilization platforms must be developed using particular lyophilization experience and strategies. This review provides an overview of liposome formulation-specific lyophilization approaches for parenteral use, excipients used exclusively in liposomal parenteral products, lyophilized liposome formulation design and process development, long-term storage, and current regulatory guidance for liposome drug products. Readers should capture a comprehensive understanding of formulation and process variables and strategies for developing parenterally administered liposomal drugs.

Preserving the Integrity of Surfactant-Stabilized Microbubble Membranes for Localized Oxygen Delivery

Ultrasound contrast agents consist of stabilized microbubbles. We are developing a surfactant-stabilized microbubble platform with a shell composed of Span 60 (Sorbitan monostearate) and an emulsifying agent, water-soluble vitamin E (α-tocopheryl poly(ethylene glycol) succinate, abbreviated as TPGS), named SE61. The microbubbles act both as an imaging agent and a vehicle for delivering oxygen to hypoxic areas in tumors. For clinical use, it is important that a platform be stable under storage at room temperature. To accomplish this, a majority of biologicals are prepared as freeze-dried powders, which also eliminates the necessity of a cold chain. The interfaces among the surfactants, gas, and liquids are subject to disruption in both the freezing and drying phases. Using thermocouples to monitor temperature profiles, differential scanning calorimetry to determine the phase transitions, and acoustic properties to gauge the degree of microbubble disruption, the effects of the freezing rate and the addition of different concentrations of lyoprotectants were determined. Slower cooling rates achieved by freezing the samples in a -20 °C bath were found to be reproducible and produce contrast agents with acceptable acoustical properties. The ionic strength of the solutions and the concentration of the lyoprotectant determined the glass-transition temperature (Tg') of the frozen sample, which determines at what temperature samples can be dried without collapse. Crucially, we found that the shelf stability of surfactant-shelled oxygen microbubbles can be enhanced by increasing the lyoprotectant (glucose) concentration from 1.8 to 5.0% (w/v), which prevents the melt temperature (Tm) of the TPGS phase from rising above room temperature. The increase in glucose concentration results in a lowering of Tm of the emulsifying agent, preventing a phase change in the liquid-crystalline phase and allowing for more stable bubbles. We believe that preventing this phase change is necessary to producing stabilized freeze-dried microbubbles.

Influence of Bilayer Size and Number in Multi-Bilayer DOPC Simulations at Full and Low Hydration

Biophysical studies of model cell membranes at full and low hydration are usually carried out using scattering measurements on multi-bilayer systems. Molecular simulations of lipid bilayers aimed at reproducing those experimental conditions are usually conducted using single bilayers with different amounts of water. These simulation conditions may lead to artifacts arising from size effects and self-interactions because of periodic boundary conditions. We have tested the influence of the size and number of bilayers on membrane properties using the Lipid14 force field for lipids in molecular dynamics simulations of 1,2-dioleoyl- sn-glycero-3-phosphocholine bilayers at full hydration (44 water molecules per lipid), low hydration (18 water molecules per lipid), and dehydration (9 water molecules per lipid). A number of additional simulations were conducted with the Slipids force field for comparison. We have found that the average area per lipid (APL), thickness, mass density profiles, and acyl tail order parameters are insensitive to the size and the number of bilayers for all hydration states. The Lipid14 force field can also successfully reproduce the experimentally observed decrease in APL and corresponding increase in bilayer thickness upon dehydration, reflecting the increase in ordering as the system becomes more gel-like. Additionally, decreasing hydration levels were associated with a trend away from normal lateral diffusion and toward more subdiffusive regimes across both force fields. In summary, at least for the Lipid14 force field, the use of a single bilayer with 128 phospholipid molecules provides an adequate representation of multi-bilayer systems at varying levels of hydration.

Glucose Can Protect Membranes against Dehydration Damage by Inducing a Glassy Membrane State at Low Hydrations

The physical effects of small sugars on membranes have been studied for decades, primarily because of their membrane stabilization in cold or dehydrated environments. We studied the effects of up to 20 mol% glucose in bilayers made of 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC) at low hydration by combining X-ray diffraction and Molecular Dynamics (MD) simulations. In agreement with previous studies, we observe membrane thinning at low and membrane thickening at high sugar concentrations. Glucose was found to preferentially localize to the outer head region of phospholipid bilayers at all concentrations, and partitioning of sugar in the membranes was found to monotonically increase with increasing sugar concentration. While the number of gauche defects in the lipid acyl tails and the lipid packing in the presence of sugar resembled values of a fluid lipid bilayer, tail dynamics, as assessed by autocorrelation of the carbon atoms in the phospholipid tails, were slowed down significantly with increasing glucose content. Thus, our findings suggest that sugar leads to a a disordered, glassy state of the hydrophobic membrane core. The non-monotonic effect of glucose on membrane thickness was found to be an effect of fluidification at low concentrations and decreased interdigitation in the higher sugar concentration regime.

Do Osmolytes Impact the Structure and Dynamics of Myoglobin?

Osmolytes are small organic compounds that can affect the stability of proteins in living cells. The mechanism of osmolytes' protective effects on protein structure and dynamics has not been fully explained, but in general, two possibilities have been suggested and examined: a direct interaction of osmolytes with proteins (water replacement hypothesis), and an indirect interaction (vitrification hypothesis). Here, to investigate these two possible mechanisms, we studied myoglobin-osmolyte systems using FTIR, UV-vis, CD, and femtosecond IR pump-probe spectroscopy. Interestingly, noticeable changes are observed in both the lifetime of the CO stretch of CO-bound myoglobin and the spectra of UV-vis, CD, and FTIR upon addition of the osmolytes. In addition, the temperature-dependent CD studies reveal that the protein's thermal stability depends on molecular structure, hydrogen-bonding ability, and size of osmolytes. We anticipate that the present experimental results provide important clues about the complicated and intricate mechanism of osmolyte effects on protein structure and dynamics in a crowded cellular environment.

Combined effects of osmotic and hydrostatic pressure on multilamellar lipid membranes in the presence of PEG and trehalose

We studied the interaction of lipid membranes with the disaccharide trehalose (TRH), which is known to stabilize biomembranes against various environmental stress factors. Generally, stress factors include low/high temperature, shear, osmotic and hydrostatic pressure. Small-angle X-ray-scattering was applied in combination with fluorescence spectroscopy and calorimetric measurements to get insights into the influence of trehalose on the supramolecular structure, hydration level, and elastic and thermodynamic properties as well as phase behavior of the model biomembrane DMPC, covering a large region of the temperature, osmotic and hydrostatic pressure phase space. We observed distinct effects of trehalose on the topology of the lipid's supramolecular structure. Trehalose, unlike osmotic pressure induced by polyethylene glycol, leads to a decrease of lamellar order and a swelling of multilamellar vesicles, which is attributable to direct interactions between the membrane and trehalose. Our results revealed a distinct biphasic concentration dependence of the observed effects of trehalose. While trehalose intercalates between the polar head groups at low concentrations, the effects after saturation are dominated by the exclusion of trehalose from the membrane surface.

Characterizing the "sweet spot" for the preservation of a T-cell line using osmolytes

This study examined the post-thaw recovery of Jurkat cells cryopreserved in single osmolyte solutions containing sucrose, glycerol or isoleucine, as well as in a combination of the three osmolytes. Cell response was determined using low temperature Raman Spectroscopy and variation in post-thaw recovery with composition was analyzed using statistical modeling. Post-thaw recovery of Jurkat cells in single osmolyte was low. A combination of the osmolytes displayed a non-linear relationship between composition and post-thaw recovery, suggesting that interactions exist between the different solutes. The post-thaw recovery for an optimized multicomponent solution was comparable to that observed using 10% dimethyl sulfoxide and a cooling rate of 1 °C/min. Statistical modeling was used to characterize the importance of each osmolyte in the combination and test for interactions between osmolytes. Higher concentrations of glycerol increase post-thaw recovery and interactions between sucrose and glycerol, as well as sucrose and isoleucine improve post-thaw recovery. Raman images clearly demonstrated that damaging intracellular ice formation was observed more often in the presence of single osmolytes as well as non-optimized multi-component solution compositions.

Mechanism of Overwintering in Trees

Boreal trees possess very high freezing resistance, which is induced by short-day length and low temperatures, in order to survive severe subzero temperatures in winter. During autumn, cooperation of photoreceptors and circadian clock system perceiving photoperiod shortening results in growth cessation, dormancy development, and first induction of freezing resistance. The freezing resistance is further enhanced by subsequent low temperature during seasonal cold acclimation with concomitant changes in various morphological and physiological features including accumulation of sugars and late embryogenesis abundant proteins. The mechanism of adaptation to freezing temperatures differs depending on the type of tissue in boreal trees. For example, bark, cambium, and leaf cells tolerate freezing-induced dehydration by extracellular freezing, whereas xylem parenchyma cells avoid intracellular freezing by deep supercooling. In addition, dormant buds in some trees respond by extraorgan freezing. Boreal trees have evolved overwintering mechanisms such as dormancy and high freezing resistance in order to survive freezing temperatures in winter.

Lyophilization of Liposomal Formulations: Still Necessary, Still Challenging

Nowadays, the freeze-drying of liposome dispersions is still necessary to provide a solid dosage form intended for different routes of administration (i.e., parenteral, oral, nasal and/or pulmonary). However, after decades of studies the optimization of process conditions remains still challenging since the freezing and the dehydration destabilize the vesicle organization with the concomitant drug leakage. Starting from the thermal properties of phospholipids, this work reviews the main formulation and process parameters which can guarantee a product with suitable characteristics and increase the efficiency of the manufacturing process. In particular, an overview of the cryo- and/or lyo-protective mechanisms of several excipients and the possible use of co-solvent mixtures is provided. Attention is also focused on the imaging methods recently proposed to characterize the appearance of freeze-dried products and liposome dispersions upon reconstitution. The combination of such data would allow a better knowledge of the factors causing inter-vials variability in the attempt to improve the quality of the final medicinal product.

Drude Polarizable Force Field for Molecular Dynamics Simulations of Saturated and Unsaturated Zwitterionic Lipids

Additive force fields are designed to account for induced electronic polarization in a mean-field average way, using effective empirical fixed charges. The limitation of this approximation is cause for serious concerns, particularly in the case of lipid membranes, where the molecular environment undergoes dramatic variations over microscopic length scales. A polarizable force field based on the classical Drude oscillator offers a practical and computationally efficient framework for an improved representation of electrostatic interactions in molecular simulations. Building on the first-generation Drude polarizable force field for the dipalmitoylphosphatidylcholine 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) molecule, the present effort was undertaken to improve this initial model and expand the force field to a wider range of phospholipid molecules. New lipids parametrized include dimyristoylphosphatidylcholine (DMPC), dilauroylphosphatidylcholine (DLPC), 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC), 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC), dipalmitoylphosphatidylethanolamine (DPPE), 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphoethanolamine (POPE), and 1,2-dioleoyl-sn-glycero-3-phosphoethanolamine (DOPE). The iterative optimization protocol employed in this effort led to lipid models that achieve a good balance between reproducing quantum mechanical data on model compound representative of phospholipids and reproducing a range of experimental condensed phase properties of bilayers. A parametrization strategy based on a restrained ensemble-maximum entropy methodology was used to help accurately match the experimental NMR order parameters in the polar headgroup region. All the parameters were developed to be compatible with the remainder of the Drude polarizable force field, which includes water, ions, proteins, DNA, and selected carbohydrates.

Disordering Effects of Digitonin on Phospholipid Monolayers

Digitonin, a steroidal saponin obtained from the foxglove plant (Digitalis purpurea), displays a wide spectrum of biological properties and is often used as a model in mechanistic investigations of the biological activity of saponins. In the present study, Langmuir monolayers of zwitterionic (DPPC, DMPE, POPC, POPE, DSPC, DSPE, and DPPE) and ionic (DPPS and DPPG) phospholipids were employed in order to better understand the effect of digitonin on the lipid organization. For this purpose, a combination of surface pressure relaxation, infrared reflection absorption spectroscopy (IRRAS), and fluorescence microscopy measurements was used. The observed increase in surface pressure (Π) suggests that digitonin can adsorb at the air/water interface, both bare and covered with the uncompressed phospholipid monolayers. However, the detailed analysis of IRRAS and fluorescence microscopy data shows that digitonin interacts with the lipid monolayers in a very selective way, and both the headgroup and the lipid tails affect this interaction. Nevertheless, it should be noted that in no case did digitonin cause any disruptive effects on the monolayers. The DPPE and DPPS monolayers get disordered by penetration with digitonin, despite an increase in surface pressure, leading to an unprecedented LC-LE transition. Interestingly, saponin could be easily squeezed out of these monolayers by mechanical compression.

Structural Modifications of Fructans in Aloe barbadensis Miller (Aloe Vera) Grown under Water Stress

Aloe barbadensis Miller (Aloe vera) has a Crassulaceae acid metabolism which grants the plant great tolerance to water restrictions. Carbohydrates such as acemannans and fructans are among the molecules responsible for tolerating water deficit in other plant species. Nevertheless, fructans, which are prebiotic compounds, have not been described nor studied in Aloe vera, whose leaf gel is known to possess beneficial pharmaceutical, nutritional and cosmetic properties. As Aloe vera is frequently cultivated in semi-arid conditions, like those found in northern Chile, we investigated the effect of water deficit on fructan composition and structure. For this, plants were subjected to different irrigation regimes of 100%, 75%, 50% and 25% field capacity (FC). There was a significant increase in the total sugars, soluble sugars and oligo and polyfructans in plants subjected to water deficit, compared to the control condition (100% FC) in both leaf tips and bases. The amounts of fructans were also greater in the bases compared to the leaf tips in all water treatments. Fructans also increase in degree of polymerization with increasing water deficit. Glycosidic linkage analyses by GC-MS, led to the conclusion that there are structural differences between the fructans present in the leaves of control plants with respect to plants irrigated with 50% and 25% FC. Therefore, in non-stressed plants, the inulin, neo-inulin and neo-levan type of fructans predominate, while in the most stressful conditions for the plant, Aloe vera also synthesizes fructans with a more branched structure, the neofructans. To our knowledge, the synthesis and the protective role of neo-fructans under extreme water deficit has not been previously reported.

Binding of Hemagglutinin and Influenza Virus to a Peptide-Conjugated Lipid Membrane

Hemagglutinin (HA) plays an important role in the first step of influenza virus (IFV) infection because it initiates the binding of the virus to the sialylgalactose linkages of the receptors on the host cells. We herein demonstrate that a HA-binding peptide immobilized on a solid support is available to bind to HA and IFV. We previously obtained a HA-binding pentapeptide (Ala-Arg-Leu-Pro-Arg), which was identified by phage-display selection against HAs from random peptide libraries. This peptide binds to the receptor-binding site of HA by mimicking sialic acid. A peptide-conjugated lipid (pep-PE) was chemically synthesized from the peptide and a saturated phospholipid. A lipid bilayer composed of pep-PE and an unsaturated phospholipid (DOPC) was immobilized on a mica plate; and the interaction between HA and the pep-PE/DOPC membrane was investigated using atomic force microscopy. The binding of IFV to the pep-PE/DOPC membrane was detected by an enzyme-linked immunosorbent assay and real-time reverse transcription PCR. Our results indicate that peptide-conjugated lipids are a useful molecular device for the detection of HA and IFV.

Evaluation of electroporation-induced adverse effects on adipose-derived stem cell exosomes

In the recent years, the possibility of utilizing extracellular vesicles for drug delivery purposes has been investigated in various models, suggesting that these vesicles may have such potential. In addition to the choice of donor cell type for vesicle production, a major obstacle still exists with respect of loading the extracellular vesicles efficiently with the drug of choice. One of the proposed solutions to this problem has been drug loading by electroporation, where small pores are created in the membrane of the extracellular vesicles, hereby allowing for free diffusion of the drug compound into the interior of the vesicle. We investigated the utility of adipose-derived stem cells (ASCs) as an efficient exosome donor cell type with a particular focus on the treatment of glioblastoma multiforme (GBM). In addition, we evaluated electroporation-induced effects on the ASC exosomes with respect to their endogenous potential of stimulating GBM proliferation, and morphological changes to single and multiple ASC exosomes. We found that electroporation does not change the endogenous stimulatory capacity of ASC exosomes on GBM cell proliferation, but mediates adverse morphological changes including aggregation of the exosomes. In order to address this issue, we have successfully optimized the use of a trehalose-containing buffer system as a way of maintaining the structural integrity of the exosomes.

Influence of type and proportion of lyoprotectants on lyophilized ginsenoside Rg3 liposomes

Objectives

To improve stability and shelf life, lyophilized formulations of 20(R)-Ginsenoside Rg3 liposomes (G-Rg3-Ls) were prepared.

Methods

Glucose, trehalose, sucrose, maltose, lactose, mannitol, inositol, hydroxypropyl-β-cyclodextrin and polyethylene glycol were used as single lyoprotectant and then compared in terms of their ability to protect lyophilized G-Rg3-Ls. Further, a glucose–mannitol complex was used to determine the optimal lyophilized preparation. The analysis of lyophilized liposomes or lyoprotectant was further investigated by scanning electron microscopy, thermogravimetry-differential thermal analysis, X-ray diffractometry and Fourier transform infrared spectroscopy. Cytotoxicity assay was used to assess the cyto-inhibition of freshly prepared and lyophilized liposomes.

Key findings

When the ratio of glucose–mannitol to phospholipids was 4 : 2 : 1 (w/w) the lyophilized G-Rg3-Ls exhibited good appearance, high DRR (86.52% ± 5.02%), small change in particle size (45.83 ± 0.50%) and short rehydration reconstruction time (8.3 ± 1.5 s). All indices were considerably better than those of each single protective agent. Results indicated that when the two lyoprotectants were combined, the stabilizing effect of glucose and shaping effect of mannitol were well maintained. The cyto-inhibition of freshly prepared and lyophilized G-Rg3 liposomes showed that lyophilization did not affect the bioactivity of G-Rg3.

Conclusions

The application of glucose–mannitol composite lyoprotectants can obtain a good G-Rg3 lyophilized preparation.

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.

Dry state preservation of nucleated cells: progress and challenges

Effective stabilization of nucleated cells for dry storage would be a transformative development in the field of cell-based biosensors and biotechnologic devices, as well as regenerative medicine and other areas in which stem cells have clinical utility. Ultimately, the tremendous promise of cell-based products will only be fully realized when stable long-term storage becomes available without the use of liquid nitrogen and bulky, energetically expensive freezers. Significant progress has been made over the last 10 years toward this goal, but obstacles still remain. Loading cells with the protective disaccharide trehalose has been achieved by several different techniques and has been shown to increase cell survival at low water contents. Likewise, the protective effect of heat shock proteins and other compounds have also been explored alone and in combination with trehalose. In some cases, the benefit of these molecules is seen not initially upon rehydration, but over time during cellular recovery. Other considerations, such as inhibiting apoptosis and utilizing isotonic buffer conditions have also provided stepwise increases in cell viability and function following drying and rehydration. In all these cases, however, a low level of residual water is required to achieve viability after rehydration. The most significant remaining challenge is to protect nucleated cells such that this residual water can be safely removed, thus allowing vitrification of intra- and extracellular trehalose and stable dry state storage at room temperature.

Effect of sucrose as a lyoprotectant on the integrity of paclitaxel-loaded liposomes during lyophilization

CONTEXT

The stability of liposomes in the form of dispersion is a major concern due to drug leakage and fusion or aggregation. The stability can be improved by lyophilization, but the stress induced by the lyophilization process can affect the integrity of liposomes.

OBJECTIVE

The objective of this study was to evaluate the lyoprotective effect of sucrose on drug leakage and vesicle size of paclitaxel-loaded liposomes during the lyophilization process.

MATERIALS AND METHODS

Paclitaxel-loaded liposomal dispersions were prepared with sucrose at several lipid-sugar ratios, and internal-external sugar ratios, and then lyophilized. The entrapped paclitaxel content and vesicle size were monitored before and after lyophilization. The stability of the formulation was evaluated at 5 and 25 °C.

RESULTS

A significant increase in free paclitaxel and vesicle size was observed with the liposomes lyophilized without sucrose. Inclusion of sucrose in the formulation significantly reduced the free paclitaxel concentration and minimized the changes in vesicle size. The extent of protection improved further when sucrose was also present in the internal portion of the bilayer. The lyophilized formulation was stable at 5 °C for 3 months.

DISCUSSION

A significant (p < 0.05) correlation was observed between free paclitaxel content and the average diameter of the liposomes with respect to sucrose concentrations in the formulation. Sucrose protected the liposomes from drug leakage and aggregation/fusion induced by the lyophilization process in a concentration dependent manner.

CONCLUSION

The integrity of paclitaxel-loaded liposomes was preserved during lyophilization by optimal levels of lyoprotectant sucrose in the formulation.

Binding of amphiphilic and triphilic block copolymers to lipid model membranes: the role of perfluorinated moieties

A novel class of symmetric amphi- and triphilic (hydrophilic, lipophilic, fluorophilic) block copolymers has been investigated with respect to their interactions with lipid membranes. The amphiphilic triblock copolymer has the structure PGMA(20)-PPO(34)-PGMA(20) (GP) and it becomes triphilic after attaching perfluoroalkyl moieties (F9) to either end which leads to F(9)-PGMA(20)-PPO(34)-PGMA(20)-F(9) (F-GP). The hydrophobic poly(propylene oxide) (PPO) block is sufficiently long to span a lipid bilayer. The poly(glycerol monomethacrylate) (PGMA) blocks have a high propensity for hydrogen bonding. The hydrophobic and lipophobic perfluoroalkyl moieties have the tendency to phase segregate in aqueous as well as in hydrocarbon environments. We performed differential scanning calorimetry (DSC) measurements on polymer bound lipid vesicles under systematic variation of the bilayer thickness, the nature of the lipid headgroup, and the polymer concentration. The vesicles were composed of phosphatidylcholines (DMPC, DPPC, DAPC, DSPC) or phosphatidylethanolamines (DMPE, DPPE, POPE). We showed that GP as well as F-GP binding have membrane stabilizing and destabilizing components. PPO and F9 blocks insert into the hydrophobic part of the membrane concomitantly with PGMA block adsorption to the lipid headgroup layer. The F9 chains act as additional membrane anchors. The insertion of the PPO blocks of both GP and F-GP could be proven by 2D-NOESY NMR spectroscopy. By fluorescence microscopy we show that F-GP binding increases the porosity of POPC giant unilamellar vesicles (GUVs), allowing the influx of water soluble dyes as well as the translocation of the complete triphilic polymer and its accumulation at the GUV surface. These results open a new route for the rational design of membrane systems with specific properties.

Localization of trehalose in partially hydrated DOPC bilayers: insights into cryoprotective mechanisms

Trehalose, a natural disaccharide with bioprotective properties, is widely recognized for its ability to preserve biological membranes during freezing and dehydration events. Despite debate over the molecular mechanisms by which this is achieved, and that different mechanisms imply quite different distributions of trehalose molecules with respect to the bilayer, there are no direct experimental data describing the location of trehalose within lipid bilayer membrane systems during dehydration. Here, we use neutron membrane diffraction to conclusively show that the trehalose distribution in a dioleoylphosphatidylcholine (DOPC) system follows a Gaussian profile centred in the water layer between bilayers. The absence of any preference for localizing near the lipid headgroups of the bilayers indicates that the bioprotective effects of trehalose at physiologically relevant concentrations are the result of non-specific mechanisms that do not rely on direct interactions with the lipid headgroups.