Drunken Membranes: Short-Chain Alcohols Alter Fusion of Liposomes to Planar Lipid Bilayers

Effect of invasome composition on membrane fluidity, vesicle stability and skin interactions

Invasomes have been widely exploited to enhance the percutaneous permeation of drugs. On the other hand, few studies have been dedicated to evaluating how their composition impacts the interaction with the skin, vesicle rigidity and stability, which was the focus of this investigation. Light scattering and spectroscopic techniques were considered for vesicle characterization. The addition of cholesterol (CHOL) into the phosphatidylcholine (PC) vesicles led to increased membrane rigidity (from PC:CHOL 5:0.5) and a concentration-dependent disorder effect on skin domains. Nevertheless, these vesicles were showed to be less stable. Ethanol, in turn, resulted in larger and more flexible vesicles, which can be attributed to its preferential distribution in headgroups of PC. The effect of limonene on membrane rigidity was dependent on the vesicle composition. It reduced the rigidity when few constituents were considered, but an opposite effect was observed for vesicles containing PC, CHOL, ethanol and limonene. Competitive effects of limonene and CHOL by the same domains in PC could explain these findings. Limonene was crucial to obtaining more monodisperse vesicles and it showed a synergistic action with CHOL in the disruption of lipid domains in the skin. Invasomes were more stable than liposomes. CHOL-free invasomes showed to be stable for up to 40 days at room temperature.

Drunken lipid membranes, not drunken SNARE proteins, promote fusion in a model of neurotransmitter release

Alcohol affects many neuronal proteins that are upstream or down-stream of synaptic vesicle fusion and neurotransmitter release. Less well studied is alcohol’s effect on the fusion machinery including SNARE proteins and lipid membranes. Using a SNARE-driven fusion assay we show that fusion probability is significantly increased at 0.4% v/v (68 mM) ethanol; but not with methanol up to 10%. Ethanol appears to act directly on membrane lipids since experiments focused on protein properties [circular dichroism spectrometry, site-directed fluorescence interference contrast (sdFLIC) microscopy, and vesicle docking results] showed no significant changes up to 5% ethanol, but a protein-free fusion assay also showed increased lipid membrane fusion rates with 0.4% ethanol. These data show that the effects of high physiological doses of ethanol on SNARE-driven fusion are mediated through ethanol’s interaction with the lipid bilayer of membranes and not SNARE proteins, and that methanol affects lipid membranes and SNARE proteins only at high doses.

Merits and advances of microfluidics in the pharmaceutical field: design technologies and future prospects

Microfluidics is used to manipulate fluid flow in micro-channels to fabricate drug delivery vesicles in a uniform tunable size. Thanks to their designs, microfluidic technology provides an alternative and versatile platform over traditional formulation methods of nanoparticles. Understanding the factors that affect the formulation of nanoparticles can guide the proper selection of microfluidic design and the operating parameters aiming at producing nanoparticles with reproducible properties. This review introduces the microfluidic systems' continuous flow (single-phase) and segmented flow (multiphase) and their different mixing parameters and mechanisms. Furthermore, microfluidic approaches for efficient production of nanoparticles as surface modification, anti-fouling, and post-microfluidic treatment are summarized. The review sheds light on the used microfluidic systems and operation parameters applied to prepare and fine-tune nanoparticles like lipid, poly(lactic-co-glycolic acid) (PLGA)-based nanoparticles as well as cross-linked nanoparticles. The approaches for scale-up production using microfluidics for clinical or industrial use are also highlighted. Furthermore, the use of microfluidics in preparing novel micro/nanofluidic drug delivery systems is presented. In conclusion, the characteristic vital features of microfluidics offer the ability to develop precise and efficient drug delivery nanoparticles.

Novel microfluidic swirl mixers for scalable formulation of curcumin loaded liposomes for cancer therapy

Liposomes have been widely used in nanomedicine for the delivery of hydrophobic and hydrophilic anticancer agents. The most common applications of these formulations are vaccines and anticancer formulations (e.g., mRNA, small molecule drugs). However, large-scale production with precise control of size and size distribution of the lipid-based drug delivery systems (DDSs) is one of the major challenges in the pharmaceutical industry. In this study, we used newly designed microfluidic swirl mixers with simple 3D mixing chamber structures to prepare liposomes at a larger scale (up to 320 mL/min or 20 L/h) than the commercially available devices. This design demonstrated high productivity and better control of liposome size and polydispersity index (PDI) than conventional liposome preparation methods. The microfluidic swirl mixer devices were used to produce curcumin-loaded liposomes under different processing conditions which were later characterized and studied in vitro to evaluate their efficiency as DDSs. The obtained results demonstrated that the liposomes can effectively deliver curcumin into cancer cells. Therefore, the microfluidic swirl mixers are promising devices for reproducible and scalable manufacturing of DDSs.

Deciphering Ethanol-Driven Swelling, Rupturing, Aggregation, and Fusion of Lipid Vesicles Using Coarse-Grained Molecular Dynamics Simulations

Traditionally, liquid ethanol is known to enhance the permeability of lipid membranes and causes vesicle aggregation and fusion. However, how the amphiphilic ethanol molecules perturb the lipid vesicles to facilitate their aggregation or fusion has not been addressed at any level of molecular simulations. Herein, not only have we developed a coarse-grained (CG) model for liquid ethanol, its aqueous mixture, and hydrated lipid membranes for molecular dynamics (MD) simulations, but also utilized it to delineate the aggregation and fusion of lipid vesicles using CG-MD simulations with multimillion particles. We have systematically parametrized the force-field for pure ethanol and its interactions with hydrated POPC and POPE model lipid membranes. In this process, we have successfully reproduced the bulk ethanol structure and concentration-dependent density of aqueous ethanol. To quantify the interaction of ethanol with lipid membranes, we have reproduced the transfer free energy of the ethanol molecule across the hydrated bilayers, and the concentration-dependent distribution of ethanol molecules across the lipid bilayers. After having acceptable force-field parameters for ethanol-membrane interactions, we have checked the effect of ethanol toward the vesicles comprising POPC lipids. We observe a rapid increase in the size of the POPC lipid vesicles with increasing amounts of ethanol up to 30 mol %. We unambiguously observe swelling and decrease in the thickness of the POPC vesicles with increasing amounts of ethanol up to 30 mol %, beyond which the vesicles begin to lose their integrity and rupture at higher mol % of ethanol. The fusion study of two vesicles demonstrates that fused vesicles can be obtained from 20 to 30 mol % of ethanol provided that they are brought closer than a critical distance at a particular mol %. The multivesicle simulations show that along with the increase in the sizes of vesicles the propensity of vesicle aggregation increases as the mol % of ethanol increases.

Fast and versatile analysis of liposome encapsulation efficiency by nanoParticle exclusion chromatography

Liposomes are an attractive drug delivery platform for a wide variety of pharmaceutical molecules. Encapsulation efficiency, which refers to the amount of drug contained inside liposomes compared with the total amount of drug, is a critical quality attribute of liposome products, as the free drug in a liposomal formulation may cause toxicity or undesired biodistribution. The determination of encapsulation efficiency requires the measurement of at least two of the three drug populations: total drug, encapsulated drug and free drug. However, direct measurement of the encapsulated drug and free drug remains a challenging analytical task. Nanoparticle exclusion chromatography (nPEC), an emerging high-performance liquid chromatography (HPLC) technique, has shown great potential in separating and quantifying the free drug in liposomal formulations. In this study, nPEC was systematically evaluated for two representative liposomal formulations containing either hydrophilic or hydrophobic small molecule drugs. It is reported for the first time that the insoluble free drug suspended in the aqueous formulation can be directly measured by nPEC. This free drug in the suspension sample was quantified with excellent accuracy and precision. On the other hand, the total drug measurement from dissociated liposomes was confirmed by the benchmark methodology of reversed phase liquid chromatography (RPLC). The facile quantitation of free and total drug in the liposome formulation enables the fast and accurate determination of the encapsulation efficiency, which can be used to guide the formulation development and characterize the product quality.

Protective effect of Terminalia arjuna against alcohol induced oxidative damage of rat erythrocyte membranes

Background

Alcohol is a widely abused drug with many health implications, mainly caused by the oxidative and nitrosative stress on different body parts. Ayurvedic herbalism authenticates the multiple therapeutic applications of Terminalia arjuna bark due to its rich phytochemical repertoire.

Objective

To observe the extent of oxidative damage caused to erythrocytes by alcohol and assess the protective ability of T. arjuna bark powder aqueous extract (AETA) against the damage.

Materials and methods

Wister albino rats were categorized into four groups of eight rats per group; first group (control) was fed with glucose, second group was given alcohol at a dose of 20% v/v; 5g alcohol/kg b. wt/day, third group was co-administered with AETA (0.5 g/kg b. wt/day) and alcohol and the fourth group was kept on bark extract alone. Blood samples were collected and evaluated for different biochemical parameters after the completion of the treatment period.

Results

Alcohol significantly increased the erythrocyte membrane protein carbonyl and malondialdehyde (MDA) contents, along with a concomitant decrease in the membrane antioxidant status, when compared to the control group. Chromatographic analysis of the alcohol-treated rat erythrocyte membranes revealed altered membrane individual phospholipid contents and fluidity properties. Alcohol-induced morphological changes in the erythrocytes and its effect on decreasing the resistance of hypotonic shock induced by NaCl are evident from the hemolysis curves. However, AETA administration to alcoholic rats beneficially modulated the membrane properties anvd protected erythrocytes from damage.

Conclusion

Results suggest that AETA protects erythrocytes from alcohol-induced oxidative stress, biophysical, and biochemical changes very effectively.

Development of a Microfluidic-Based Post-Treatment Process for Size-Controlled Lipid Nanoparticles and Application to siRNA Delivery

Microfluidic methodologies for preparation of lipid nanoparticles (LNPs) based on an organic solvent injection method enable precise size control of the LNPs. After preparation of LNPs, the organic solvent injection method needs some post-treatments, such as overnight dialysis or direct dilution with a buffer solution. LNP production using the microfluidic-based organic solvent injection method is dominated by kinetics rather than thermodynamics. Kinetics of ethanol removal from the inner and outer membranes of LNPs could induce a structural change in the membrane that could lead to fusion of LNPs. However, the effects of microfluidic post-treatment on the final size of LNPs have not been sufficiently understood. Herein, we investigated the effect of the post-treatment processes on the final product size of LNPs in detail. A simple baffle device and a model lipid system composed of a neutral phospholipid (1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine, POPC) and cholesterol were used to produce the LNPs. We demonstrated that flow conditions of the post-treatment diluting the remaining ethanol in the LNP suspension affected the final product size of LNPs. Based on the findings, we developed an integrated baffle device composed of an LNP production region and a post-treatment region for a microfluidic-based LNP production system; this integrated baffle device prevented the undesirable aggregation or fusion of POPC LNPs even for the high-lipid-concentration condition. Finally, we applied our concept to small interfering RNA (siRNA) delivery and confirmed that no significant effects due to the continuous process occurred on the siRNA encapsulation efficiency, biological distribution, and knockdown activity. The microfluidic post-treatment method is expected to contribute to the production of LNPs for practical applications and the development of novel LNP-based nanomedicines.

The Impact of Solvent Selection: Strategies to Guide the Manufacturing of Liposomes Using Microfluidics

The aim of this work was to assess the impact of solvent selection on the microfluidic production of liposomes. To achieve this, liposomes were manufactured using small-scale and bench-scale microfluidics systems using three aqueous miscible solvents (methanol, ethanol or isopropanol, alone or in combination). Liposomes composed of different lipid compositions were manufactured using these different solvents and characterised to investigate the influence of solvents on liposome attributes. Our studies demonstrate that solvent selection is a key consideration during the microfluidics manufacturing process, not only when considering lipid solubility but also with regard to the resultant liposome critical quality attributes. In general, reducing the polarity of the solvent (from methanol to isopropanol) increased the liposome particle size without impacting liposome short-term stability or release characteristics. Furthermore, solvent combinations such as methanol/isopropanol mixtures can be used to modify solvent polarity and the resultant liposome particle size. However, the impact of solvent choice on the liposome product is also influenced by the liposome formulation; liposomes containing charged lipids tended to show more sensitivity to solvent selection and formulations containing increased concentrations of cholesterol or pegylated-lipids were less influenced by the choice of solvent. Indeed, incorporation of 14 wt% or more of pegylated-lipid was shown to negate the impact of solvent selection.

Liposomal Nanovesicles for Efficient Encapsulation of Staphylococcal Antibiotics

Liposomes are attractive vehicles for localized delivery of antibiotics. There exists, however, a gap in knowledge when it comes to achieving high liposomal loading efficiencies for antibiotics. To address this issue, we investigated three antibiotics of clinical relevance against staphylococcal infections with different hydrophilicity and chemical structure, namely, vancomycin hydrochloride, teicoplanin, and rifampin. We categorized the suitability of different encapsulation techniques on the basis of encapsulation efficiency, lipid requirement (important for avoiding lipid toxicity), and mass yield (percentage of mass retained during the preparation process). The moderately hydrophobic (teicoplanin) and highly hydrophobic (rifampin) antibiotics varied significantly in their encapsulation load (max 23.4 and 15.5%, respectively) and mass yield (max 74.1 and 71.8%, respectively), favoring techniques that maximized partition between the aqueous core and the lipid bilayer or those that produce oligolamellar vesicles, whereas vancomycin hydrochloride, a highly hydrophilic molecule, showed little preference to any of the protocols. In addition, we report significant bias introduced by the choice of analytical method adopted to quantify the encapsulation efficiency (underestimation of up to 24% or overestimation by up to 57.9% for vancomycin and underestimation of up to 61.1% for rifampin) and further propose ultrafiltration and bursting by methanol as the method with minimal bias for quantification of encapsulation efficiency in liposomes. The knowledge generated in this work provides critical insight into the more practical, albeit less investigated, aspects of designing vesicles for localized antibiotic delivery and can be extended to other nanovehicles that may suffer from the same biases in analytical protocols.

The SNAP-25 linker supports fusion intermediates by local lipid interactions

SNAP-25 is an essential component of SNARE complexes driving fast Ca²⁺-dependent exocytosis. Yet, the functional implications of the tandem-like structure of SNAP-25 are unclear. Here, we have investigated the mechanistic role of the acylated “linker” domain that concatenates the two SNARE motifs within SNAP-25. Refuting older concepts of an inert connector, our detailed structure-function analysis in murine chromaffin cells demonstrates that linker motifs play a crucial role in vesicle priming, triggering, and fusion pore expansion. Mechanistically, we identify two synergistic functions of the SNAP-25 linker: First, linker motifs support t-SNARE interactions and accelerate ternary complex assembly. Second, the acylated N-terminal linker segment engages in local lipid interactions that facilitate fusion triggering and pore evolution, putatively establishing a favorable membrane configuration by shielding phospholipid headgroups and affecting curvature. Hence, the linker is a functional part of the fusion complex that promotes secretion by SNARE interactions as well as concerted lipid interplay.

Real-Time Monitoring of Interactions between Solid-Supported Lipid Vesicle Layers and Short- and Medium-Chain Length Alcohols: Ethanol and 1-Pentanol

Lipid bilayers represent the interface between the cell and its environment, serving as model systems for the study of various biological processes. For instance, the addition of small molecules such as alcohols is a well-known process that modulates lipid bilayer properties, being considered as a reference for general anesthetic molecules. A plethora of experimental and simulation studies have focused on alcohol’s effect on lipid bilayers. Nevertheless, most studies have focused on lipid membranes formed in the presence of alcohols, while the effect of n-alcohols on preformed lipid membranes has received much less research interest. Here, we monitor the real-time interaction of short-chain alcohols with solid-supported vesicles of dipalmitoylphosphatidylcholine (DPPC) using quartz crystal microbalance with dissipation monitoring (QCM-D) as a label-free method. Results indicate that the addition of ethanol at different concentrations induces changes in the bilayer organization but preserves the stability of the supported vesicle layer. In turn, the addition of 1-pentanol induces not only changes in the bilayer organization, but also promotes vesicle rupture and inhomogeneous lipid layers at very high concentrations.

Metallosomes for biomedical applications by mixing molybdenum carbonyl metallosurfactants and phospholipids

New photo-CORM metallosomes with low cell toxicity were prepared from organometallic metallosurfactants and phospholipids.