Lipid vesicles and membrane fusion

Pulmonary delivery of LNP-mRNAs aerosolised by vibrating mesh nebulizer: An emphasis on variations and in-depth analyses of physicochemical properties

The delivery of lipid nanoparticle (LNP)-mRNAs to the lungs attracts fast increasing interests for vaccination, as the mucosal immunity in the airway can prevent the establishment of an infection rather than only reduce the level of infection associated with systemic immunity triggered via intramuscular injection. The vibrating mesh nebuliser was well utilized to atomize inhalation solutions/suspensions for pulmonary delivery hence employed in this study for aerosolising LNP-mRNAs. In comparison with pre-aerosolised LNP-mRNAs, the post-aerosolised vectors demonstrated a significant increase (t-test, unpaired, p < 0.05) in particle size (215-363 nm vs. 116-130 nm), polydispersity index (PDI: > 0.33 vs. < 0.27), zeta potential (ZP: 11-14 mV vs. 2.6-7.7 mV), and encapsulation efficiency (EE: ∼99 % w/w vs. ∼91 % w/w), indicating a structural alteration upon high-frequency mesh vibration (HFMV). The particle sizes of LNP-mRNAs were further enlarged upon inertial impaction, and the size increments were dependent on the velocities of airflow for impaction and the N/P ratios. The aerosolised mists were fine, with >54 % w/w deposited in lower respiratory tract and >28.5 % w/w further delivered to alveolar regions. Further, a model was created to elucidate the variations of physicochemical properties for LNP-mRNAs upon HFMV and inertial impaction, and it disclosed that the fluidity and shear-induced fusion of LNPs were the fundamental reasons to cause these unfavourable changes particularly the size enlargement. These insights reveal that the effective development of inhaled LNP-mRNAs will rely on shear-less devices, formulation optimizations, inhalable dry powders, and their potential combinations.

Lithium fine tunes lipid membranes through phospholipid binding

Lithium is commonly prescribed for bipolar disorder due to its proven efficacy on patients. Despite this effectiveness, the molecular mechanisms underlying its action remain poorly understood, as it appears to influence numerous unrelated pathways. We propose that these diverse effects may stem from a specific physicochemical event: the binding of lithium cations to phospholipid headgroups. In model membrane systems enabling direct observation of the lithium effects on lipid bilayers, we reveal that lithium binding stiffens the membrane, subsequently altering membrane protein activities. This mechanical impact of lithium links existing rationales, drawing a way to decipher the complex lithium effect in bipolar disorder (BD). To illustrate this global effect of lithium, we use the example of intracellular trafficking, a ubiquitous mechanism involving membrane reorganization in all organelles.

Gymnema saponin-induced lipid flip-flop identifies rigid membrane phenotype of methicillin resistant S. aureus and enhances it's antibiotic susceptibility

Our previous study revealed that lipid flip-flop inducing phytochemicals from Gymnema sylvestre increase membrane permeability of antimicrobials in S. aureus. However, their lipid flipping and membrane permeabilizing effect on methicillin resistant S. aureus (MRSA) membrane that has intrinsically higher aminoacylated lipid content compared to methicillin sensitive S. aureus (MSSA) is poorly characterized. Gymnema saponins, gymnemic acid I and IV significantly increased the antibiotic susceptibility in both MSSA and MRSA. MRSA exhibited a rigid membrane with lipid diffusion coefficient 0.0002 μm2/s compared to the MSSA membrane lipids with diffusion coefficient 1.48 μm2/s. Further, unlike MSSA, MRSA cells inhibited fusion of fluid liposomes with their plasma membrane. In vitro assay on reconstituted membrane vesicles revealed that Gymnema saponins induced 60 % lipid flipping in MSSA membrane compared to only 20 % lipid flipping in MRSA, indicating significantly lower Gymnema saponin-induced trans-bilayer lipid mobility in MRSA. Gymnema saponins induced significantly lower crystal violet uptake, release of cellular protein, cell shrinkage and lysis in MRSA compared to MSSA. Gymnema saponins led to dose-dependent inhibition of lipid-aminoacylation in both MSSA and MRSA making their membranes more negative compared to untreated control cells. In silico analysis reveals binding of both gymnemic acid I and IV to multiple peptide resistance factor (binding energy ∼ 7.5 kCal), the protein responsible for lipid aminoacylation in S. aureus. For the first time, our study reveals that MRSA membrane with higher aminoacyl-PG compared to MSSA shows significantly lower rate of diffusion and trans-bilayer flip-flop of lipids. Further, gymnemic acids are useful probes for identification, characterization and drug sensitization of rigid membrane MRSA phenotypes.

Protein (Lysozyme) Concentration-Dependent Structure, Morphology, and Hysteresis Behavior of a Three-Component (Lysozyme-DMPA-Cholesterol) Protein-Lipid Langmuir Monolayer

Protein (lysozyme)-lipid (DMPA and cholesterol) three-component mixed films (LDC) with varied lysozyme concentration (i.e., LDC_Lx) are investigated at the air-water interface. Elastic modulus-surface pressure (Cs-1-Π) curves derived from Π-A isotherms show that mechanical behavior is strongly dependent on the monolayer composition, and for the same reason, the hysteresis behavior modifies. It is evidenced that the LDC_L0.3 monolayer (lysozyme: 0.3 mg/mL) has significant hysteresis, which is reversible in nature, while the other mixed monolayers do not show such hysteresis behavior. Morphology at the air-water interface via Brewster angle microscopy (BAM) and at the air-solid interface via atomic force microscopy (AFM) shows that the presence of protein in the LDC_Lx monolayer modifies the lateral distribution of molecules, thereby forming a stripe-like pattern at the air-water interface (in optical length scale) with barrier compression or root-like structure on the solid surface at higher Π (in micron length scale), which is not observed in the case of lipid films. Moreover, lysozyme-added LDC_Lx films show an increase in thickness with compression, which is not observed for lipid films, as evidenced from the electron density profiles (EDPs). The morphology modification and thickness variation of LDC_Lx films with compression are most probably due to the reorientation of lysozyme molecules. This structural modification in LDC_Lx films with Π, however, seems to be reversible under expansion, as can be evidenced from the similar in situ morphology observation and similar thickness of the films deposited during both first and second compression. A variation in the strength of interaction forces among film-forming molecules depending on the monolayer composition basically affects the lateral distribution and organizational orientation with surface pressure, thus ultimately influencing macroscopically the monolayer properties such as elastic, hysteresis, morphological, and structural on water and solid surfaces.

Liposomes with Low Levels of Grafted Poly(ethylene glycol) Remain Susceptible to Destabilization by Anti-Poly(ethylene glycol) Antibodies

Binding of anti-PEG antibodies to poly(ethylene glycol) (PEG) on the surface of PEGylated liposomal doxorubicin (PLD) in vitro and in rats can activate complement and cause the rapid release of doxorubicin from the liposome interior. Here, we find that irinotecan liposomes (IL) and L-PLD, which have 16-fold lower levels of 1,2-distearoyl-sn-glycero-3-phosphoethanolamine (DSPE)-PEG2000 in their liposome membrane as compared to PLD, generate less complement activation but remain sensitive to destabilization and drug release by anti-PEG antibodies. Complement activation and liposome destabilization correlated with the theoretically estimated number of antibody molecules bound per liposome. Drug release from liposomes proceeded through the alternative complement pathway but was accelerated by the classical complement pathway. In contrast to PLD destabilization by anti-PEG immunoglobulin G (IgG), which proceeded by the insertion of membrane attack complexes in the lipid bilayer of otherwise intact PLD, anti-PEG IgG promoted the fusion of L-PLD, and IL to form unilamellar and oligo-vesicular liposomes. Anti-PEG immunoglobulin M (IgM) induced drug release from all liposomes (PLD, L-PLD, and IL) via the formation of unilamellar and oligo-vesicular liposomes. Anti-PEG IgG destabilized both PLD and L-PLD in rats, indicating that the reduction of PEG levels on liposomes is not an effective approach to prevent liposome destabilization by anti-PEG antibodies.

Role of Cholesterol in Interaction of Ionic Liquids with Model Lipid Membranes and Associated Permeability

In this work, we explored how the amount of cholesterol in the lipid membrane composed of phosphatidylcholine (POPC) or phosphatidylglycerol (POPG) affects the interaction with 1-dodecyl-3-methylimidazolium bromide ([C12MIM]+Br-) ionic liquids using various biophysical techniques. On interacting with the membrane, [C12MIM]+Br- leads to enhanced membrane permeability and induces membrane fusion, leading to an increase in vesicle size. The 2H-based solid-state NMR investigations of cholesterol-containing lipid membranes reveal that [C12MIM]+Br- decreases the lipid chain order parameters and counteracts the lipid condensation effect of cholesterol to some extent. Therefore, as the amount of cholesterol in the membrane increases, the membrane effect of [C12MIM]+Br- decreases. The effect of [C12MIM]+Br- on the membrane properties is more pronounced for POPC compared to that of POPG membranes. This suggests a dependence of these effects on the electrostatic interactions, indicating that the influence of [C12MIM]+Br- varies based on the lipid composition. The findings suggest that the presence of cholesterol can modulate the effect of [C12MIM]+Br- on membrane properties, with variations observed between POPC and POPG membranes, highlighting the importance of lipid composition. In short, this study provides insights into the intricate interplay between cholesterol, the lipid membrane, and the ionic liquid [C12MIM]+Br-.

A Coronin 1-Derived Peptide Inhibits Membrane Fusion by Modulating Membrane Organization and Dynamics

Membrane fusion is considered the first step in the entry of enveloped viruses into the host cell. Several targeted strategies have been implemented to block viral entry by limiting the fusion protein to form a six-helix bundle, which is a prerequisite for fusion. Nonetheless, the development of broad-spectrum fusion inhibitors is essential to combat emerging and re-emerging viral infections. TG-23, a coronin 1, a tryptophan-aspartate-rich phagosomal protein-derived peptide, demonstrated inhibition of fusion between small unilamellar vesicles (SUVs) by modulating the membrane's physical properties. However, its inhibitory efficacy reduces with an increasing concentration of membrane cholesterol. The present work aims to develop a fusion inhibitor whose efficacy would be unaltered in the presence of membrane cholesterol. A stretch of the tryptophan-aspartic acid-containing peptide with a similar secondary structure and hydrophobicity profile of TG-23 from coronin 1 was synthesized, and its ability to inhibit SUV-SUV fusion with varying concentrations of membrane cholesterol was evaluated. Our results demonstrate that the GG-21 peptide inhibits fusion irrespective of the cholesterol content of the membrane. We have further evaluated the peptide-induced change in the membrane organization and dynamics utilizing arrays of steady-state and time-resolved fluorescence measurements and correlated these results with their effect on fusion. Interestingly, GG-21 displays inhibitory efficacy in a wide variety of lipid compositions despite having a secondary structure and physical properties similar to those of TG-23. Overall, our results advocate that the secondary structure and physical properties of the peptide may not be sufficient to predict its inhibitory efficacy.

Reassembly of the vesicular structure of niosomes after their destruction in a mechanical field

This paper presents, for the first time, evidence for vesicle destruction and payload loss at the stage of purification of niosome dispersions by centrifugation, an important operation in the assembly of vesicular materials. The ability of niosomes of different compositions to reassemble, i.e., to restore the vesicular structure after destruction in the field of centrifugal forces, was demonstrated by dynamic light scattering and fluorescence spectroscopy. The kinetics of reassembly of vesicular structures is determined by the strength of the centrifugal field and the composition of niosomes. In contrast to ternary compositions, where particle size and modality are essentially unchanged after redispersion of the precipitate resulting from centrifugation, niosome dispersions containing anionic dicetyl phosphate includes micron-sized particles after redispersion, which vary in size over a wide range throughout the observation period. The reassembly process is complicated by the presence of charge on the surface of the niosomes. Elastic niosomes - ethosomes have been synthesised which, due to the high deformability of the shells, are less susceptible to destruction in the centrifugal field and retain the contents of the aqueous core. Using the "energy landscape" approximation, it is shown that vesicular structures assembled during hydration and reassembled after their centrifugation occupy different positions in the energetic pathway of their preparation. The results obtained should also be taken into account when determining the entrapment efficiency, since this procedure uses centrifugation to separate the load. It is important to note that the physical stability of niosomes, which is usually considered in terms of the functional activity of particles, is manifest and should be considered at the material preparation stage.

All members of the Arabidopsis DGAT and PDAT acyltransferase families operate during high and low temperatures

The accumulation of triacylglycerol (TAG) in vegetative tissues is necessary to adapt to changing temperatures. It has been hypothesized that TAG accumulation is required as a storage location for maladaptive membrane lipids. The TAG acyltransferase family has five members (DIACYLGLYCEROL ACYLTRANSFERSE1/2/3 and PHOSPHOLIPID:DIACYLGLYCEROL ACYLTRANSFERASE1/2), and their individual roles during temperature challenges have either been described conflictingly or not at all. Therefore, we used Arabidopsis (Arabidopsis thaliana) loss of function mutants in each acyltransferase to investigate the effects of temperature challenge on TAG accumulation, plasma membrane integrity, and temperature tolerance. All mutants were tested under one high- and two low-temperature regimens, during which we quantified lipids, assessed temperature sensitivity, and measured plasma membrane electrolyte leakage. Our findings revealed reduced effectiveness in TAG production during at least one temperature regimen for all acyltransferase mutants compared to the wild type, resolved conflicting roles of pdat1 and dgat1 by demonstrating their distinct temperature-specific actions, and uncovered that plasma membrane integrity and TAG accumulation do not always coincide, suggesting a multifaceted role of TAG beyond its conventional lipid reservoir function during temperature stress.

Modelling lipid rafts formation through chemo-mechanical interplay triggered by receptor-ligand binding

Cell membranes, mediator of many biological mechanisms from adhesion and metabolism up to mutation and infection, are highly dynamic and heterogeneous environments exhibiting a strong coupling between biochemical events and structural re-organisation. This involves conformational changes induced, at lower scales, by lipid order transitions and by the micro-mechanical interplay of lipids with transmembrane proteins and molecular diffusion. Particular attention is focused on lipid rafts, ordered lipid microdomains rich of signalling proteins, that co-localise to enhance substance trafficking and activate different intracellular biochemical pathways. In this framework, the theoretical modelling of the dynamic clustering of lipid rafts implies a full multiphysics coupling between the kinetics of phase changes and the mechanical work performed by transmembrane proteins on lipids, involving the bilayer elasticity. This mechanism produces complex interspecific dynamics in which membrane stresses and chemical potentials do compete by determining different morphological arrangements, alteration in diffusive walkways and coalescence phenomena, with a consequent influence on both signalling potential and intracellular processes. Therefore, after identifying the leading chemo-mechanical interactions, the present work investigates from a modelling perspective the spatio-temporal evolution of raft domains to theoretically explain co-localisation and synergy between proteins' activation and raft formation, by coupling diffusive and mechanical phenomena to observe different morphological patterns and clustering of ordered lipids. This could help to gain new insights into the remodelling of cell membranes and could potentially suggest mechanically based strategies to control their selectivity, by orienting intracellular functions and mechanotransduction.

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

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

Fusion Landscape of Mycobacterial Envelope-Derived Lipid Vesicles with Intact Bacteria Dictates High Intracellular Drug Retention

Membrane vesicles are critical regulators of pathogenic diseases. In tubercular infections, the use of mycobacteria derived vesicles as delivery vehicles to overcome drug resistance and complex treatment regimens has never been attempted. Here, we first address how these vesicles interact with their target cells, especially via membrane fusion. Membrane fusion between alike mycobacterial outer and inner membrane layer-derived lipid vesicles is shown to be driven by the structural, geometrical, and biophysical attributes of constituent lipids. The increased fusion of outer-membrane-derived vesicles with intact bacteria ensures enhanced intracellular drug levels and is presented as a "natural" antitubercular drug delivery vehicle.

Unveiling the functional epitopes of cobra venom cytotoxin by immunoinformatics and epitope-omic analyses

Approximate 70% of cobra venom is composed of cytotoxin (CTX), which is responsible for the dermonecrotic symptoms of cobra envenomation. However, CTX is generally low in immunogenicity, and the antivenom is ineffective in attenuating its in vivo toxicity. Furthermore, little is known about its epitope properties for empirical antivenom therapy. This study aimed to determine the epitope sequences of CTX using the immunoinformatic analyses and epitope-omics profiling. A conserved CTX was used in this study to determine its T-cell and B-cell epitope sequences using immunoinformatic tools and molecular docking simulation with different Human Leukocyte Antigens (HLAs). The potential T-cell and B-cell epitopes were 'KLVPLFY,' 'CPAGKNLCY,' 'MFMVSTPTK,' and 'DVCPKNSLL.' Molecular docking simulations disclosed that the HLA-B62 supertype exhibited the greatest binding affinity towards cobra venom cytotoxin. The namely L7, G18, K19, N20, M25, K33, V43, C44, K46, N47, and S48 of CTX exhibited prominent intermolecular interactions with HLA-B62. The multi-enzymatic-limited-digestion/liquid chromatography-mass spectrometry (MELD/LC-MS) also revealed three potential epitope sequences as 'LVPLFYK,' 'MFMVS,' and 'TVPVKR'. From different epitope mapping approaches, we concluded four potential epitope sites of CTX as 'KLVPLFYK', 'AGKNL', 'MFMVSTPKVPV' and 'DVCPKNSLL'. Site-directed mutagenesis of these epitopes confirmed their locations at the functional loops of CTX. These epitope sequences are crucial to CTX's structural folding and cytotoxicity. The results concluded the epitopes that resided within the functional loops constituted potential targets to fabricate synthetic epitopes for CTX-targeted antivenom production.

Accurate Capture and Identification of Exosomes: Nanoarchitecture of the MXene Heterostructure/Engineered Lipid Layer

Recently, exosome detection has become an important breakthrough in clinical diagnosis. However, the effective capture and accurate identification of cancer exosomes in a complex biomatrix are still a tough task. Especially, the large size and non-conductivity of exosomes are not conducive to highly sensitive electrochemical or electrochemiluminescence (ECL) detection. Therefore, we have developed a Ti₃C₂T_x-Bi₂S_3-x heterostructure/engineered lipid layer-based nanoarchitecture to overcome the limitations. The engineered lipid layer not only specifically captured and efficiently fused CD63 positive exosomes but also showed excellent antifouling property in the biological matrix. Moreover, the MUC1 aptamer-modified Ti₃C₂T_x-Bi₂S_3-x heterostructure further identified and covered the gastric cancer exosomes that have been trapped in the engineered lipid layer. In the self-luminous Faraday cage-type sensing system, the Ti₃C₂T_x-Bi₂S_3-x heterostructure with sulfur vacancies extended the outer Helmholtz plane and amplified the ECL signal. Therefore, this sensor can be used to detect tumor exosomes in ascites of cancer patients without additional purification. It provides a new pathway to detect exosomes and other large-sized vesicles with high sensitivity.

Enhancing Targeted Therapy in Breast Cancer by Ultrasound-Responsive Nanocarriers

Currently, the response to cancer treatments is highly variable, and severe side effects and toxicity are experienced by patients receiving high doses of chemotherapy, such as those diagnosed with triple-negative breast cancer. The main goal of researchers and clinicians is to develop new effective treatments that will be able to specifically target and kill tumor cells by employing the minimum doses of drugs exerting a therapeutic effect. Despite the development of new formulations that overall can increase the drugs’ pharmacokinetics, and that are specifically designed to bind overexpressed molecules on cancer cells and achieve active targeting of the tumor, the desired clinical outcome has not been reached yet. In this review, we will discuss the current classification and standard of care for breast cancer, the application of nanomedicine, and ultrasound-responsive biocompatible carriers (micro/nanobubbles, liposomes, micelles, polymeric nanoparticles, and nanodroplets/nanoemulsions) employed in preclinical studies to target and enhance the delivery of drugs and genes to breast cancer.

Postsynthetic Photocontrol of Giant Liposomes via Fusion-Based Photolipid Doping

We report on photolipid doping of giant unilamellar vesicles (GUVs) via vesicle fusion with small unilamellar photolipid vesicles (pSUVs), which enables retroactive optical control of the membrane properties. We observe that vesicle fusion is light-dependent, if the phospholipids are neutral. Charge-mediated fusion involving anionic and cationic lipid molecules augments the overall fusion performance and doping efficiency, even in the absence of light exposure. Using phosphatidylcholine analogs with one or two azobenzene photoswitches (azo-PC and dazo-PC) affects domain formation, bending stiffness, and shape of the resulting vesicles in response to irradiation. Moreover, we show that optical membrane control can be extended to long wavelengths using red-absorbing photolipids (red-azo-PC). Combined, our findings present an attractive and practical method for the precise delivery of photolipids, which offers new prospects for the optical control of membrane function.

Membrane Fusion Biophysical Analysis of Fusogenic Liposomes

Liposomes represent important drug carrier vehicles in biological systems. A fusogenic liposomal system composed of equimolar mixtures of the cationic lipid DOTAP and the phospholipid DOPE showed high fusion and delivery efficiencies with cells and lipid vesicles. However, aspects of the thermodynamics involving the interaction of these fusogenic liposomes and biomimetic systems remain unclear. Here, we investigate the fusion of this system with large unilamellar vesicles (LUVs) composed of the zwitterionic lipid POPC and increasing fractions of the anionic lipid POPG and up to 30 mol % cholesterol. The focus here is to concomitantly follow changes in size, zeta-potential, and enthalpy binding upon membrane interaction and fusion. Isothermal titration calorimetry (ITC) data showed that membrane fusion in our system is an exothermic process in the absence of cholesterol, suggesting that electrostatic attraction is the driving force for fusion. An endothermic component appeared and eventually dominated the titration at 30 mol % cholesterol, which we propose is caused by membrane fluidification when cholesterol is diluted upon fusion. The inflection points of the ITC data occurred around 0.5-0.7 POPG/DOTAP for all systems, the same stoichiometry for which zeta-potential and dynamic light scattering measurements showed an increase in size coupled with charge neutralization of the system, which is consistent with the fact that fusion in our system is charge-mediated. Microscopy observations of the final mixtures revealed the presence of giant vesicles, which is a clear indication of fusion, coexisting with intermediate-sized objects that could be the result of both fusion and/or aggregation. The results show that the fusion efficiency of the DOTAP:DOPE fusogenic system is modulated by the charge and membrane packing of the acceptor membrane and explain why the system fuses very efficiently with cells.

Photoinducible Azobenzene trimethylammonium bromide (AzoTAB)-mediated giant vesicle fusion compatible with synthetic protein translation reactions

Lipid giant vesicles represent a versatile minimal model system to study the physicochemical basis of lipid membrane fusion. Membrane fusion processes are also of interest in synthetic cell research, where cell-mimicking behavior often requires dynamically interacting compartments. For these applications, triggered fusion compatible with transcription-translation systems is key in achieving complexity. Recently, a photosensitive surfactant, azobenzene trimethylammonium bromide (AzoTAB), has been reported to induce membrane fusion by a photoinduced conformational change. Using imaging flow cytometer (IFC) and confocal microscopy we quantitatively investigated photoinduced AzoTAB-mediated fusion of 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphatidylcholine vesicles. The IFC analysis result showed that the fusion rate could reach about 40% following AzoTAB addition and UV irradiation in optimized conditions. We confirmed the compatibility between AzoTAB-induced vesicle fusion and a synthetic cell-free protein translation system using green fluorescent protein as reporter. With the techniques presented, cell-sized vesicle fusion can be quantitatively analyzed and optimized, paving the way to controllable synthetic cells with fundamental biological functions like the ability to express proteins from encapsulated plasmids.

Nanomaterials: The New Antimicrobial Magic Bullet

Bacterial infections are a significant cause of mortality and morbidity worldwide, despite decades of use of numerous existing antibiotics and constant efforts by researchers to discover new antibiotics. The emergence of infections associated with antibiotic-resistant bacterial strains, has amplified the pressure to develop additional bactericidal therapies or new unorthodox approaches that can deal with antimicrobial resistance. Nanomaterial-based strategies, particularly those that do not rely on conventional small-molecule antibiotics, offer promise in part due to their ability to dodge existing mechanisms used by drug-resistant bacteria. Therefore, the use of nanomaterial-based formulations has attracted attention in the field of antibiotic therapy. In this Review, we highlight novel and emerging nanomaterial-based formulations along with details about the mechanisms by which nanoparticles can target bacterial infections and antimicrobial resistance. A detailed discussion about types and the activities of nanoparticles is presented, along with how they can be used as either delivery systems or as inherent antimicrobials, or a combination of both. Lastly, we highlight some toxicological concerns for the use of nanoparticles in antibiotic therapies.

Vesicle-based artificial cells: materials, construction methods and applications

The construction of artificial cells with specific cell-mimicking functions helps to explore complex biological processes and cell functions in natural cell systems and provides an insight into the origins of life. Bottom-up methods are widely used for engineering artificial cells based on vesicles by the in vitro assembly of biomimetic materials. In this review, the design of artificial cells with a specific function is discussed, by considering the selection of synthetic materials and construction technologies. First, a range of biomimetic materials for artificial cells is reviewed, including lipid, polymeric and hybrid lipid/copolymer materials. Biomaterials extracted from natural cells are also covered in this part. Then, the formation of microscale, giant unilamellar vesicles (GUVs) is reviewed based on different technologies, including gentle hydration, electro-formation, phase transfer and microfluidic methods. Subsequently, applications of artificial cells based on single vesicles or vesicle networks are addressed for mimicking cell behaviors and signaling processes. Microreactors for synthetic biology and cell-cell communication are highlighted here as well. Finally, current challenges and future trends for the development and applications of artificial cells are described.

Revealing local molecular distribution, orientation, phase separation, and formation of domains in artificial lipid layers: Towards comprehensive characterization of biological membranes

Lipids, together with molecules such as DNA and proteins, are one of the most relevant systems responsible for the existence of life. Selected lipids are able to assembly into various organized structures, such as lipid membranes. The unique properties of lipid membranes determine their complex functions, not only to separate biological environments, but also to participate in regulatory functions, absorption of nutrients, cell-cell communication, endocytosis, cell signaling, and many others. Despite numerous scientific efforts, still little is known about the reason underlying the variability within lipid membranes, and its biochemical significance. In this review, we discuss the structural complexity of lipid membranes, as well as the importance to simplify studied systems in order to understand phenomena occurring in natural, complex membranes. Such systems require a model interface to be analyzed. Therefore, here we focused on analytical studies of artificial systems at various interfaces. The molecular structure of lipid membranes, specifically the nanometric thickens of molecular bilayer, limits in a major extent the choice of highly sensitive methods suitable to study such structures. Therefore, we focused on methods that combine high sensitivity, and/or chemical selectivity, and/or nanometric spatial resolution, such as atomic force microscopy, nanospectroscopy (tip-enhanced Raman spectroscopy, infrared nanospectroscopy), phase modulation infrared reflection-absorption spectroscopy, sum-frequency generation spectroscopy. We summarized experimental and theoretical approaches providing information about molecular structure and composition, lipid spatial distribution (phase separation), organization (domain shape, molecular orientation) of lipid membranes, and real-time visualization of the influence of various molecules (proteins, drugs) on their integrity. An integral part of this review discusses the latest achievements in the field of lipid layer-based biosensors.

Monensin Enhanced Generation of Extracellular Vesicles as Transfersomes for Promoting Tumor Penetration of Pyropheophorbide-a from Fusogenic Liposome

The current state of antitumor nanomedicines is severely restricted by poor penetration in solid tumors. It is indicated that extracellular vesicles (EVs) secreted by tumor cells can mediate the intercellular transport of antitumor drug molecules in the tumor microenvironment. However, the inefficient generation of EVs inhibits the application of this approach. Herein, we construct an EV-mediated self-propelled liposome containing monensin as the EV secretion stimulant and photosensitizer pyropheophorbide-a (PPa) as a therapeutic agent. Monensin and PPa are first transferred to the tumor plasma membrane with the help of membrane fusogenic liposomes. By hitchhiking EVs secreted by the outer tumor cells, both drugs are layer-by-layer transferred into the deep region of a solid tumor. Particularly, monensin, serving as a sustainable booster, significantly amplifies the EV-mediated PPa penetration by stimulating EV production. Our results show that this endogenous EV-driven nanoplatform leads to deep tumor penetration and enhanced phototherapeutic efficacy.

Biomimetic Curvature and Tension-Driven Membrane Fusion Induced by Silica Nanoparticles

Fusion events in living cells are intricate phenomena that require the coordinate action of multicomponent protein complexes. However, simpler synthetic tools to control membrane fusion in artificial cells are highly desirable. Native membrane fusion machinery mediates fusion, driving a delicate balance of membrane curvature and tension between two closely apposed membranes. Here, we show that silica nanoparticles (SiO₂ NPs) at a size close to the cross-over between tension-driven and curvature-driven interaction regimes initiate efficient fusion of biomimetic model membranes. Fusion efficiency and mechanisms are studied by Förster resonance energy transfer and confocal fluorescence microscopy. SiO₂ NPs induce a slight increase in lipid packing likely to increase the lateral tension of the membrane. We observe a connection between membrane tension and fusion efficiency. Finally, real-time confocal fluorescence microscopy reveals three distinct mechanistic pathways for membrane fusion. SiO₂ NPs show significant potential for inclusion in the synthetic biology toolkit for membrane remodeling and fusion in artificial cells.

Membrane fusion of phospholipid bilayers under high pressure: Spherical and irreversible growth of giant vesicles

Membrane fusion of giant vesicles (GVs) for binary bilayers of unsaturated phospholipids, dioleoylphosphatidyl-ethanolamine (DOPE) having an ability to promote membrane fusion, and its homolog dioleoylphosphatidylcholine (DOPC) having an ability to form GV, was investigated under atmospheric and high pressure. While DOPC formed GVs in the presence of inorganic salts with a multivalent metal ion under atmospheric pressure, an equimolar mixture of DOPE and DOPC formed GVs both in the absence and the presence of LaCl3. We examined the change in size and shape of the GVs of this binary mixture in the absence and presence of LaCl3 as a function of time under atmospheric and high pressure. The size and shape of the GVs in the absence of LaCl3 under atmospheric and high pressure and those in the presence of LaCl3 under atmospheric pressure hardly changed with time. By contrast, the GV in the presence of LaCl3 under high pressure gradually changed in the size and shape with time on a time scale of several hours. Namely, the GV became larger than the original GV due to accelerated membrane fusion and its shape became more spherical. This pressure-induced membrane fusion was completely irreversible, and the growth rate was correlated with the applied pressure. The reason for the GV growth by applying pressure was considered on the basis of thermodynamic phase diagrams. We concluded that the growth is attributable to a closer packing of lipid molecules in the bilayer resulting from their preference of smaller volumes under high pressure. Furthermore, the molecular mechanism of the pressure-induced membrane fusion was explored by observing the fusion of two GVs with almost the same size. From their morphological changes, we revealed that the fusion is caused by the actions of Laplace and osmotic pressure.

Monitoring the formation of a colloidal lipid gel at the nanoscale: vesicle aggregation driven by a temperature-induced mechanism

Colloidal gels made of lipid vesicles at highly diluted conditions have been recently described. The structure and composition of this type of material could be especially relevant for studies that combine model lipid membranes with proteins, peptides, or enzymes to replicate biological conditions. Details about the nanoscale events that occur during the formation of such gels would motivate their future application. Thus, in this work we investigate the gelation mechanism, which consists of a lipid dispersion of vesicles going through a process that involves freezing and heating. The appropriate combination of techniques (transmission electron microscopy, differential scanning calorimetry and synchrotron small angle X-ray scattering) allowed in-depth analysis of the different events that give rise to the formation of the gel. Results showed how freezing damaged the lipid dispersion, causing a polydisperse suspension of membrane fragments and vesicles upon melting. Heating above the lipids' main phase transition temperature promoted the formation of elongated tubular structures. After cooling, these lipid tubes broke down into vesicles that formed branched aggregates across the aqueous phase, obtaining a material with gel characteristics. These mechanistic insights may also allow finding new ways to interact with lipid vesicles to form structured materials. Future works might complement the presented results with molecular dynamics or nuclear magnetic resonance experiments.

Rapid Capture of Cancer Extracellular Vesicles by Lipid Patch Microarrays

Extracellular vesicles (EVs) contain various bioactive molecules such as DNA, RNA, and proteins, and play a key role in the regulation of cancer progression. Furthermore, cancer-associated EVs carry specific biomarkers and can be used in liquid biopsy for cancer detection. However, it is still technically challenging and time consuming to detect or isolate cancer-associated EVs from complex biofluids (e.g., blood). Here, a novel EV-capture strategy based on dip-pen nanolithography generated microarrays of supported lipid membranes is presented. These arrays carry specific antibodies recognizing EV- and cancer-specific surface biomarkers, enabling highly selective and efficient capture. Importantly, it is shown that the nucleic acid cargo of captured EVs is retained on the lipid array, providing the potential for downstream analysis. Finally, the feasibility of EV capture from patient sera is demonstrated. The demonstrated platform offers rapid capture, high specificity, and sensitivity, with only a small need in analyte volume and without additional purification steps. The platform is applied in context of cancer-associated EVs, but it can easily be adapted to other diagnostic EV targets by use of corresponding antibodies.

Chemically Designed Nanoscale Materials for Controlling Cellular Processes

Nanoparticles are widely used in various biomedical applications as drug delivery carriers, imaging probes, single-molecule tracking/detection probes, artificial chaperones for inhibiting protein aggregation, and photodynamic therapy materials. One key parameter of these applications is the ability of the nanoparticles to enter into the cell cytoplasm, target different subcellular compartments, and control intracellular processes. This is particularly the case because nanoparticles are designed to interact with subcellular components for the required biomedical performance. However, cells are protected from their surroundings by the cell membrane, which exerts strict control over entry of foreign materials. Thus, nanoparticles need to be designed appropriately so that they can readily cross the cell membrane, target subcellular compartments, and control intracellular processes.In the past few decades there have been great advancements in understanding the principles of cellular uptake of foreign materials. In particular, it has been shown that internalization of foreign materials (small molecules, macromolecules, nanoparticles) is size-dependent: endocytotic uptake of materials requires sizes greater than 10 nm, and materials with sizes of 10-100 nm usually enter into cells by energy-dependent endocytosis via biomembrane-coated vesicles. Direct access to the cytosol is limited to very specific conditions, and endosomal escape of material appears to be the most practical approach for intracellular processing.In this Account, we describe how cellular uptake and intracellular processing of nanoscale materials can be controlled by appropriate design of size and surface chemistry. We first describe the cell membrane structure and principles of cellular uptake of foreign materials followed by their subcellular trafficking. Next, we discuss the designed surface chemistry of a 5-50 nm particle that offers preferential lipid-raft/caveolae-mediated endocytosis over clathrin-mediated endocytosis with minimum endosomal/lysosomal trafficking or energy-independent direct cell membrane translocation (without endocytosis) followed by cytosolic delivery without endosomal/lysosomal trafficking. In particular, we emphasize that the zwitterionic-lipophilic surface property of a nanoparticle offers preferential interaction with the lipid raft region of the cell membrane followed by lipid raft uptake, whereas a lower number of affinity biomolecules (<25) on the nanoparticle surface offers caveolae/lipid-raft uptake, while an arginine/guanidinium-terminated surface along with a size of <10 nm offers direct cell membrane translocation. Finally, we discuss how nanoprobes can be designed by adapting these surface chemistry and size preference principles so that they can readily enter into the cell, label different subcellular compartments, and control intracellular processes such as trafficking kinetics, exocytosis, autophagy, amyloid aggregation, and clearance of toxic amyloid aggregates. The Account ends with a Conclusions and Outlook where we discuss a vision for the development of subcellular targeting nanodrugs and imaging nanoprobes by adapting to these surface chemistry principles.

Role of VAPB and vesicular profiles in α-synuclein aggregates in multiple system atrophy

The pathological hallmark of multiple system atrophy (MSA) is fibrillary aggregates of α‐synuclein (α‐Syn) in the cytoplasm and nucleus of both oligodendrocytes and neurons. In neurons, α‐Syn localizes to the cytosolic and membrane compartments, including the synaptic vesicles, mitochondria, and endoplasmic reticulum (ER). α‐Syn binds to vesicle‐associated membrane protein‐binding protein B (VAPB) in the ER membrane. Overexpression of wild‐type and familial Parkinson's disease mutant α‐Syn perturbs the association between the ER and mitochondria, leading to ER stress and ultimately neurodegeneration. We examined brains from MSA patients (n = 7) and control subjects (n = 5) using immunohistochemistry and immunoelectron microscopy with antibodies against VAPB and phosphorylated α‐Syn. In controls, the cytoplasm of neurons and glial cells was positive for VAPB, whereas in MSA lesions VAPB immunoreactivity was decreased. The proportion of VAPB‐negative neurons in the pontine nucleus was significantly higher in MSA (13.6%) than in controls (0.6%). The incidence of cytoplasmic inclusions in VAPB‐negative neurons was significantly higher (42.2%) than that in VAPB‐positive neurons (3.6%); 67.2% of inclusion‐bearing oligodendrocytes and 51.1% of inclusion‐containing neurons were negative for VAPB. Immunoelectron microscopy revealed that α‐Syn and VAPB were localized to granulofilamentous structures in the cytoplasm of oligodendrocytes and neurons. Many vesicular structures labeled with anti‐α‐Syn were also observed within the granulofilamentous structures in the cytoplasm and nucleus of both oligodendrocytes and neurons. These findings suggest that, in MSA, reduction of VAPB is involved in the disease process and that vesicular structures are associated with inclusion formation.

Zombie ideas about early endosymbiosis: Which entry mechanisms gave us the "endo" in different endosymbionts?

Recently, a review regarding the mechanics and evolution of mitochondrial fission appeared in Nature. Surprisingly, it stated authoritatively that the mitochondrial outer membrane, in contrast with the inner membrane of bacterial descent, was acquired from the host, presumably during uptake. However, it has been known for quite some time that this membrane was also derived from the Gram-negative, alpha-proteobacterium related precursor of present-day mitochondria. The zombie idea of the host membrane still surrounding the endosymbiont is not only wrong, but more importantly, might hamper the proper conception of possible scenarios of eukaryogenesis. Why? Because it steers the imagination not only with regard to possible uptake mechanisms, but also regarding what went on before. Here I critically discuss both the evidence for the continuity of the bacterial outer membrane, the reasons for the persistence of the erroneous host membrane hypothesis and the wider implications of these misconceptions for the ideas regarding events occurring during the first steps towards the evolution of the eukaryotes and later major eukaryotic differentiations. I will also highlight some of the latest insights regarding different instances of endosymbiont evolution.

Study of the Pathogen Inactivation Mechanism in Salt-Coated Filters

As COVID-19 exemplifies, respiratory diseases transmitted through aerosols or droplets are global threats to public health, and respiratory protection measures are essential first lines of infection prevention and control. However, common face masks are single use and can cause cross-infection due to the accumulated infectious pathogens. We developed salt-based formulations to coat membrane fibers to fabricate antimicrobial filters. Here, we report a mechanistic study on salt-induced pathogen inactivation. The salt recrystallization following aerosol exposure was characterized over time on sodium chloride (NaCl), potassium sulfate (K₂SO₄), and potassium chloride (KCl) powders and coatings, which revealed that NaCl and KCl start to recrystallize within 5 min and K₂SO₄ within 15 min. The inactivation kinetics observed for the H1N1 influenza virus and Klebsiella pneumoniae matched the salt recrystallization well, which was identified as the main destabilizing mechanism. Additionally, the salt-coated filters were prepared with different methods (with and without a vacuum process), which led to salt coatings with different morphologies for diverse applications. Finally, the salt-coated filters caused a loss of pathogen viability independent of transmission mode (aerosols or droplets), against both DI water and artificial saliva suspensions. Overall, these findings increase our understanding of the salt-recrystallization-based technology to develop highly versatile antimicrobial filters.

Liposome Fusion Mediated by Hydrophobic Magnetic Nanoparticles Stabilized with Oleic Acid and Modulated by an External Magnetic Field

Membrane fusion is considered relevant in countless scientific areas and biotechnological processes, ranging from vital life events to biomedicine, pharmaceuticals, and materials engineering, among others. In this study, we employed hydrophobic oleic acid (OA)-coated magnetite (Fe₃O₄) nanoparticles (MNP-OA) as a platform to induce the fusion of 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphatidylcholine liposomes [large unilamellar vesicles (LUVs)] in a colloidal dispersion. This fusion was monitored through dynamic light scattering, turbidimetry, and fluorescence assay using the well-known Tb/dipicolinic acid (DPA) complex formation assay. MNP-OA have shown to be able to induce fusion with the mixing of liposomal inner content with direct dependence on the nanoparticle concentration added to the LUVs. Moreover, changes in the permeability of the liposome bilayer, upon the addition of MNP-OA to liposomes, were evaluated by studying the leakage of carboxyfluorescein and of the co-encapsulated Tb/DPA complex. These assays allowed us to determine that MNP-OA did not significantly modify liposome permeability during the fusion process. Transmission electron microscopy and confocal microscopy revealed that MNP-OA remained embedded in the lipid bilayer without producing membrane rupture, liposome deformation, or destruction. In addition, we evaluated the effect of applying a low-intensity magnetic field to the LUVs/MNP-OA system and observed that the nanoparticles considerably increased their fusogenic activity under this external stimulus, as well as they are capable of responding to low magnetic fields of around 0.45 mT. These results revealed the potential of hydrophobic magnetic nanoparticles, stabilized with OA, to act as a fusogen, thus representing a valuable tool for biotechnological applications.

Supplementation of exogenous lipids via liposomes improves coral larvae settlement post-cryopreservation and nano-laser warming

Coral reefs worldwide are receding because of detrimental human activities, and cryopreservation of coral larvae would ensure that their genetic biodiversity is not irremediably lost. In recent years, the vitrification and laser warming of coral propagules has demonstrated promising results. During cryopreservation, cellular membranes undergo substantial reconfigurations that may affect survival. Fat enrichment may alter the physical proprieties of cell membranes and improve resistance to low temperatures. Therefore, the aim of this study was to determine whether supplementation of exogenous lipids using liposomes would improve cryosurvival and further development of the vitrified and laser-warmed coral larvae of Seriatopora caliendrum and Pocillopora verrucosa. A vitrification solution (VS) composed of 2 M ethylene glycol (EG), 1 M propylene glycol (PG), 40% (w/v) Ficoll, and 10% gold nanoparticles (at a final concentration of 1.2 × 10¹⁸ particles/m³ and an optimised emission wavelength of 535 nm) was chosen. Coral larvae were subjected to vitrification with VS incorporating one of four lipid classes: phosphatidylcholine (PC), phosphatidylethanolamine (PE), erucic acid (EA), and linoleic acid (LA). Warming was achieved using a single laser pulse (300 V, 10 ms pulse width, 2 mm laser beam diameter). A significantly higher vitality rate was observed in S. caliendrum larvae subjected to vitrification and laser warming with EA-incorporated VS, and P. verrucosa larvae vitrified and laser warmed using PE-incorporated VS achieved a significantly higher settlement rate. Our study demonstrated that supplementation of exogenous lipids with liposomes enhances coral larvae cryotolerance and improves cryopreservation outcomes. Lipid enrichment may play a key role in cryobanking coral propagules, and in propagule development after thawing.

Pharmacokinetics of inhaled nanotherapeutics for pulmonary delivery

Pulmonary delivery of lipid-based nanotherapeutics by inhalation presents an advantageous alternative to oral and intravenous routes of administration that avoids enzymatic degradation in gastrointestinal tract and hepatic first pass metabolism and also limits off-target adverse side effects upon heathy tissues. For lung-related indications, inhalation provides localized delivery in order to enhance therapeutic efficacy at the site of action. Optimization of physicochemical properties, selected drug and inhalation format can greatly influence the pharmacokinetic behavior of inhaled nanoparticle systems and their payloads. The present review analyzes a wide range of nanoparticle systems, their formulations and consequent effect on pharmacokinetic distribution of delivered active components after inhalation.

Technology used to build and transfer mammalian chromosomes

In the near twenty-year existence of the human and mammalian artificial chromosome field, the technologies for artificial chromosome construction and installation into desired cell types or organisms have evolved with the rest of modern molecular and synthetic biology. Medical, industrial, pharmaceutical, agricultural, and basic research scientists seek the as yet unrealized promise of human and mammalian artificial chromosomes. Existing technologies for both top-down and bottom-up approaches to construct these artificial chromosomes for use in higher eukaryotes are very different but aspire to achieve similar results. New capacity for production of chromosome sized synthetic DNA will likely shift the field towards more bottom-up approaches, but not completely. Similarly, new approaches to install human and mammalian artificial chromosomes in target cells will compete with the microcell mediated cell transfer methods that currently dominate the field.

Isolation of an archaeon at the prokaryote-eukaryote interface

The origin of eukaryotes remains unclear1-4. Current data suggest that eukaryotes may have emerged from an archaeal lineage known as 'Asgard' archaea5,6. Despite the eukaryote-like genomic features that are found in these archaea, the evolutionary transition from archaea to eukaryotes remains unclear, owing to the lack of cultured representatives and corresponding physiological insights. Here we report the decade-long isolation of an Asgard archaeon related to Lokiarchaeota from deep marine sediment. The archaeon-'Candidatus Prometheoarchaeum syntrophicum' strain MK-D1-is an anaerobic, extremely slow-growing, small coccus (around 550 nm in diameter) that degrades amino acids through syntrophy. Although eukaryote-like intracellular complexes have been proposed for Asgard archaea6, the isolate has no visible organelle-like structure. Instead, Ca. P. syntrophicum is morphologically complex and has unique protrusions that are long and often branching. On the basis of the available data obtained from cultivation and genomics, and reasoned interpretations of the existing literature, we propose a hypothetical model for eukaryogenesis, termed the entangle-engulf-endogenize (also known as E3) model.

Amphiphilic ionic liquid induced fusion of phospholipid liposomes

The impact of increasing concentration of imidazolium-based ionic liquids ([C_nMIM]⁺[Br]⁻) on the structural integrity of large unilamellar vesicles (LUVs) made of pure phosphatidylcholine (PC) and phosphatidylglycerol (PG) lipids.

Lipidated Polyaza Crown Ethers as Membrane Anchors for DNA-Controlled Content Mixing between Liposomes

The ability to manipulate and fuse nano-compartmentalized volumes addresses a demand for spatiotemporal control in the field of synthetic biology, for example in the bottom-up construction of (bio)chemical nanoreactors and for the interrogation of enzymatic reactions in confined space. Herein, we mix entrapped sub-attoliter volumes of liposomes (~135 nm diameter) via lipid bilayer fusion, facilitated by the hybridization of membrane-anchored lipidated oligonucleotides. We report on an improved synthesis of the membrane-anchor phosphoramidites that allows for a flexible choice of lipophilic moiety. Lipid-nucleic acid conjugates (LiNAs) with and without triethylene glycol spacers between anchor and the 17 nt binding sequence were synthesized and their fusogenic potential evaluated. A fluorescence-based content mixing assay was employed for kinetic monitoring of fusion of the bulk liposome populations at different temperatures. Data obtained at 50 °C indicated a quantitative conversion of the limiting liposome population into fused liposomes and an unprecedently high initial fusion rate was observed. For most conditions and designs only low leakage during fusion was observed. These results consolidate LiNA-mediated membrane fusion as a robust platform for programming compartmentalized chemical and enzymatic reactions.

Overview of recent advances in liposomal nanoparticle-based cancer immunotherapy

The clinical performance of conventional cancer therapy approaches (surgery, radiotherapy, and chemotherapy) has been challenged by tumor metastasis and recurrence that is mainly responsible for cancer-caused mortalities. The cancer immunotherapy is being emerged nowadays as a promising therapeutic modality in order to achieve a highly efficient therapeutic performance while circumventing tumor metastasis and relapse. Liposomal nanoparticles (NPs) may serve as an ideal platform for systemic delivery of the immune modulators. In this review, we summarize the cutting-edge progresses in liposomal NPs for cancer immunotherapy, with focus on dendritic cells, T cells, tumor cells, natural killer cells, and macrophages. The review highlights the major challenges and provides a perspective regarding the clinical translation of liposomal nanoparticle-based immunotherapy.

Chain-Length- and Saturation-Tuned Mechanics of Fluid Nanovesicles Direct Tumor Delivery

Small unilamellar vesicles (SUVs), ubiquitous in organisms, play key and active roles in various biological processes. Although the physical properties of the constituent lipid molecules (i.e., the acyl chain length and saturation) are known to affect the mechanical properties of SUVs and consequently regulate their biological behaviors and functions, the underlying mechanism remains elusive. Here, we combined theoretical modeling and experimental investigation to probe the mechanical behaviors of SUVs with different lipid compositions. The membrane bending rigidity of SUVs increased with increasing chain length and saturation, resulting in differences in the vesicle rigidity and deformable capacity. Furthermore, we tested the tumor delivery capacity of liposomes with low, intermediate, and high rigidity as typical models for SUVs. Interestingly, liposomes with intermediate rigidity exhibited better tumor extracellular matrix diffusion and multicellular spheroid (MCS) penetration and retention than that of their stiffer or softer counterparts, contributing to improved tumor suppression. Stiff SUVs had superior cellular internalization capacity but intermediate tumor delivery efficacy. Stimulated emission depletion microscopy directly showed that the optimal formulation was able to transform to a rod-like shape in MCSs, which stimulated fast transport in tumor tissues. In contrast, stiff liposomes hardly deformed, whereas soft liposomes changed their shape irregularly, which slowed their MCS penetration. Our findings introduce special perspectives from which to map the detailed mechanical properties of SUVs with different compositions, provide clues for understanding the biological functions of SUVs, and suggest that liposome mechanics may be a design parameter for enhancing drug delivery.

Elucidation of the mechanism and energy barrier for anesthetic triggered membrane fusion in model membranes

Membrane fusion is vital for cellular function and is generally mediated via fusogenic proteins and peptides. The mechanistic details and subsequently the transition state dynamics of membrane fusion will be dependent on the type of the fusogenic agent. We have previously established the potential of general anesthetics as a new class of fusion triggering agents in model membranes. We employed two-photon excitation fluorescence cross-correlation spectroscopy (TPE-FCCS) to report on vesicle association kinetics and steady-state fluorescence dequenching assays to monitor lipid mixing kinetics. Using halothane to trigger fusion in 110 nm diameter dioleoylphosphatidylcholine (DOPC) liposomes, we found that lipid rearrangement towards the formation of the fusion stalk was rate limiting. The activation barrier for halothane induced membrane fusion in 110 nm vesicles was found to be ∼40 kJ mol−1. We calculated the enthalpy and entropy of the transition state to be ∼40 kJ mol−1and ∼180 J mol−1K−1, respectively. We have found that the addition of halothane effectively lowers the energy barrier for membrane fusion in less curved vesicles largely due to entropic advantages.

Receptor-Independent Transfer of Low Density Lipoprotein Cargo to Biomembranes

The fundamental task of lipoprotein particles is extracellular transport of cholesterol, lipids, and fatty acids. Besides, cholesterol-rich apoB-containing lipoprotein particles (i.e., low density lipoprotein LDL) are key players in progression of atherosclerotic cardiovascular disease and are associated with familial hypercholesterolemia (FH). So far, lipoprotein particle binding to the cell membrane and subsequent cargo transfer is directly linked to the lipoprotein receptors on the target cell surface. However, our observations showed that lipoprotein particle cargo transport takes place even in the absence of the receptor. This finding suggests that an alternative mechanism for lipoprotein-particle/membrane interaction, besides the receptor-mediated one, exists. Here, we combined several complementary biophysical techniques to obtain a comprehensive view on the nonreceptor mediated LDL-particle/membrane. We applied a combination of atomic force and single-molecule-sensitive fluorescence microscopy (AFM and SMFM) to investigate the LDL particle interaction with membranes of increasing complexity. We observed direct transfer of fluorescently labeled amphiphilic lipid molecules from LDL particles into the pure lipid bilayer. We further confirmed cargo transfer by fluorescence cross-correlation spectroscopy (FCCS) and spectral imaging of environment-sensitive probes. Moreover, the integration of the LDL particle into the membranes was directly visualized by high-speed atomic force microscopy (HS-AFM) and cryo-electron microscopy (cryo-EM). Overall, our data show that lipoprotein particles are able to incorporate into lipid membranes upon contact to transfer their cargo in the absence of specific receptors.

Overcoming the Pitfalls of Cytochrome P450 Immobilization through the Use of Fusogenic Liposomes

This work describes a new nanotechnology-based immobilization strategy for cytochrome P450s (CYPs), the major class of drug metabolizing enzymes. Immobilization of CYPs on solid supports provides a significant leap forward compared with soluble enzyme assays by enabling the implementation of through-flow microreactors for, for example, determination of time-dependent inhibition. Immobilization of the complex CYP membrane-protein system is however particularly challenging as the preservation of the authentic enzyme kinetic parameters requires the full complexity of the lipid environment. The developed strategy is based on the spontaneous fusion of biotinylated fusogenic liposomes with lipid bilayers to facilitate the gentle biotinylation of human liver microsomes that incorporate all main natural CYP isoforms. The same process is also feasible for the biotinylation of recombinant CYPs expressed in insect cells, same as any membrane-bound enzymes in principle. As a result, CYPs could be immobilized on streptavidin-functionalized surfaces, both those of commercial magnetic beads and customized microfluidic arrays, so that the enzyme kinetic parameters remain unchanged, unlike in previously reported immobilization approaches that often suffer from restricted substrate diffusion to the enzyme's active site and steric hindrances. The specificity and robustness of the functionalization method of customized microfluidic CYP assays are also carefully examined.

A new developing class of gene delivery: messenger RNA-based therapeutics

Gene therapy has long been held as having the potential to become a front line treatment for various genetic disorders. However, the direct delivery of nucleic acids to correct a genetic disorder has numerous limitations owing to the inability of naked nucleic acids (DNA and RNA) to traverse the cell membrane. Recently, messenger RNA (mRNA) based delivery has become a more attractive alternative to DNA due to the relatively easier transfection process, higher efficiency and safety profile. As with all gene therapies, the central challenge that remains is the efficient delivery of nucleic acids intracellularly. This review presents the recent progress in mRNA delivery, focusing on comparing the advantages and limitations of non-viral based delivery vectors.