Increased efficiency of charge-mediated fusion in polymer/lipid hybrid membranes

Assessing the negative impact of chlorantraniliprole, isoxaflutole, and simazine pesticides on phospholipid membrane models and tilapia gill tissues

The indiscriminate and, very often, incorrect use of pesticides in Brazil, as well as in other countries, results in severe levels of environmental pollution and intoxication of human life. Herein, we studied plasma membrane models (monolayer and bilayer) of the phospholipid Dioleoyl-sn-glycerol-3-phosphocholine (DOPC) using Langmuir films, and large (LUVs) and giant (GUVs) unilamellar vesicles, to determine the effect of the pesticides chlorantraniliprole (CLTP), isoxaflutole (ISF), and simazine (SMZ), used in sugarcane. CLTP affects the lipid organization of the bioinspired models of DOPC π-A isotherms, while ISF and SMZ pesticides significantly affect the LUVs and GUVs. Furthermore, the in vivo study of the gill tissue in fish in the presence of pesticides (2.0 × 10-10 mol/L for CLTP, 8.3 × 10-9 mol/L for ISF, and SMZ at 9.9 × 10-9 mol/L) was performed using optical and fluorescence images. This investigation was motivated by the gill lipid membranes, which are vital for regulating transporter activity through transmembrane proteins, crucial for maintaining ionic balance in fish gills. In this way, the presence of phospholipids in gills offers a model for understanding their effects on fish health. Histological results show that exposure to CLTP, ISF, and SMZ may interfere with vital gill functions, leading to respiratory disorders and osmoregulation dysfunction. The results indicate that exposure to pesticides caused severe morphological alterations in fish, which could be correlated with their impact on the bioinspired membrane models. Moreover, the effect does not depend on the exposure period (24h and 96h), showing that animals exposed to pesticides for a short period suffer irreparable damage to gill tissue. In summary, we can conclude that the harm caused by pesticides, both in membrane models and in fish gills, occurs due to contamination of the aquatic system with pesticides. Therefore, water quality is vital for the preservation of ecosystems.

Structurally Dynamic Monocyte-Liposome Hybrid Vesicles as an Anticancer Drug Delivery Vehicle: A Crucial Correlation of Microscopic Elasticity and Ultrafast Dynamics

A biomimetic cell-based carrier system based on monocyte membranes and liposomes has been designed to create a hybrid "Monocyte-LP" which inherits the surface antigens of the monocytes along with the drug encapsulation property of the liposome. Förster resonance energy transfer (FRET) and polarization gated anisotropy measurements show the stiffness of the vesicles obtained from monocyte membranes (Mons), phosphatidylcholine membranes (LP), and Monocyte-LP to follow an increasing order of Mons > Monocyte-LP > LP. The dynamics of interface bound water molecules plays a key role in the elasticity of the vesicles, which in turn imparts higher delivery efficacy to the hybrid Monocyte-LP for a model anticancer drug doxorubicin than the other two vesicles, indicating a critical balance between flexibility and rigidity for an efficient cellular uptake. The present work provides insight on the influence of elasticity of delivery vehicles for enhanced drug delivery.

Protein-Rich Rafts in Hybrid Polymer/Lipid Giant Unilamellar Vesicles

Considerable attention has been dedicated to lipid rafts due to their importance in numerous cell functions such as membrane trafficking, polarization, and signaling. Next to studies in living cells, artificial micrometer-sized vesicles with a minimal set of components are established as a major tool to understand the phase separation dynamics and their intimate interplay with membrane proteins. In parallel, mixtures of phospholipids and certain amphiphilic polymers simultaneously offer an interface for proteins and mimic this segregation behavior, presenting a tangible synthetic alternative for fundamental studies and bottom-up design of cellular mimics. However, the simultaneous insertion of complex and sensitive membrane proteins is experimentally challenging and thus far has been largely limited to natural lipids. Here, we present the co-reconstitution of the proton pump bo3 oxidase and the proton consumer ATP synthase in hybrid polymer/lipid giant unilamellar vesicles (GUVs) via fusion/electroformation. Variations of the current method allow for tailored reconstitution protocols and control of the vesicle size. In particular, mixing of protein-free and protein-functionalized nanosized vesicles in the electroformation film results in larger GUVs, while separate reconstitution of the respiratory enzymes enables higher ATP synthesis rates. Furthermore, protein labeling provides a synthetic mechanism for phase separation and protein sequestration, mimicking lipid- and protein-mediated domain formation in nature. The latter means opens further possibilities for re-enacting phenomena like supercomplex assembly or symmetry breaking and enriches the toolbox of bottom-up synthetic biology.

Spontaneous transfer of small peripheral peptides between supported lipid bilayer and giant unilamellar vesicles

Vesicular trafficking facilitates material transport between membrane-bound organelles. Membrane protein cargos are trafficked for relocation, recycling, and degradation during various physiological processes. In vitro fusion studies utilized synthetic lipid membranes to study the molecular mechanisms of vesicular trafficking and to develop synthetic materials mimicking the biological membrane trafficking. Various fusogenic conditions which can induce vesicular fusion have been used to establish synthetic systems that can mimic biological systems. Despite these efforts, the mechanisms underlying vesicular trafficking of membrane proteins remain limited and robust in vitro methods that can construct synthetic trafficking systems for membrane proteins between large membranes (>1 μm2) are unavailable. Here, we provide data to show the spontaneous transfer of small membrane-bound peptides (∼4 kD) between a supported lipid bilayer (SLB) and giant unilamellar vesicles (GUVs). We found that the contact between the SLB and GUVs led to the occasional but notable transfer of membrane-bound peptides in a physiological saline buffer condition (pH 7.4, 150 mM NaCl). Quantitative and dynamic time-lapse analyses suggested that the observed exchange occurred through the formation of hemi-fusion stalks between the SLB and GUVs. Larger protein cargos with a size of ∼77 kD could not be transferred between the SLB and GUVs, suggesting that the larger-sized cargos limited diffusion across the hemi-fusion stalk, which was predicted to have a highly curved structure. Compositional study showed Ni-chelated lipid head group was the essential component catalyzing the process. Our system serves as an example synthetic platform that enables the investigation of small-peptide trafficking between synthetic membranes and reveals hemi-fused lipid bridge formation as a mechanism of peptide transfer.

Nature-Inspired Thylakoid-Based Photosynthetic Nanoarchitectures for Biomedical Applications

"Drawing inspiration from nature" offers a wealth of creative possibilities for designing cutting-edge materials with improved properties and performance. Nature-inspired thylakoid-based nanoarchitectures, seamlessly integrate the inherent structures and functions of natural components with the diverse and controllable characteristics of nanotechnology. These innovative biomaterials have garnered significant attention for their potential in various biomedical applications. Thylakoids possess fundamental traits such as light harvesting, oxygen evolution, and photosynthesis. Through the integration of artificially fabricated nanostructures with distinct physical and chemical properties, novel photosynthetic nanoarchitectures can be catalytically generated, offering versatile functionalities for diverse biomedical applications. In this article, an overview of the properties and extraction methods of thylakoids are provided. Additionally, the recent advancements in the design, preparation, functions, and biomedical applications of a range of thylakoid-based photosynthetic nanoarchitectures are reviewed. Finally, the foreseeable challenges and future prospects in this field is discussed.

Tunable biomimetic bacterial membranes from binary and ternary lipid mixtures and their application in antimicrobial testing

The reconstruction of accurate yet simplified mimetic models of cell membranes is a very challenging goal of synthetic biology. To date, most of the research focuses on the development of eukaryotic cell membranes, while reconstitution of their prokaryotic counterparts has not been fully addressed, and the proposed models do not reflect well the complexity of bacterial cell envelopes. Here, we describe the reconstitution of biomimetic bacterial membranes with an increasing level of complexity, developed from binary and ternary lipid mixtures. Giant unilamellar vesicles composed of phosphatidylcholine (PC) and phosphatidylethanolamine (PE); PC and phosphatidylglycerol (PG); PE and PG; PE, PG and cardiolipin (CA) at varying molar ratios were successfully prepared by the electroformation method. Each of the proposed mimetic models focuses on reproducing specific membrane features such as membrane charge, curvature, leaflets asymmetry, or the presence of phase separation. GUVs were characterized in terms of size distribution, surface charge, and lateral organization. Finally, the developed models were tested against the lipopeptide antibiotic daptomycin. The obtained results showed a clear dependency of daptomycin binding efficiency on the amount of negatively charged lipid species present in the membrane. We anticipate that the models proposed here can be applied not only in antimicrobial testing but also serve as platforms for studying fundamental biological processes in bacteria as well as their interaction with physiologically relevant biomolecules.

Unraveling the Phase Behavior, Mechanical Stability, and Protein Reconstitution Properties of Polymer-Lipid Hybrid Vesicles

Hybrid vesicles consisting of natural phospholipids and synthetic amphiphilic copolymers have shown remarkable material properties and potential for biotechnology, combining the robustness of polymers with the biocompatibility of phospholipid membranes. To predict and optimize the mixing behavior of lipids and copolymers, as well as understand the interaction between the hybrid membrane and macromolecules like membrane proteins, a comprehensive understanding at the molecular level is essential. This can be achieved by a combination of molecular dynamics simulations and experiments. Here, simulations of POPC and PBD22-b-PEO14 hybrid membranes are shown, uncovering different copolymer configurations depending on the polymer-to-lipid ratio. High polymer concentrations created thicker membranes with an extended polymer conformation, while high lipid content led to the collapse of the polymer chain. High concentrations of polymer were further correlated with a decreased area compression modulus and altered lateral pressure profiles, hypothesized to result in the experimentally observed improvement in membrane protein reconstitution and resistance toward destabilization by detergents. Finally, simulations of a WALP peptide embedded in the bilayer showed that only membranes with up to 50% polymer content favored a transmembrane configuration. These simulations correlate with previous and new experimental results and provide a deeper understanding of the properties of lipid-copolymer hybrid membranes.

High Resolution Membrane Structures within Hybrid Lipid-Polymer Vesicles Revealed by Combining X-Ray Scattering and Electron Microscopy

Hybrid vesicles consisting of phospholipids and block-copolymers are increasingly finding applications in science and technology. Herein, small angle X-ray scattering (SAXS) and cryo-electron tomography (cryo-ET) are used to obtain detailed structural information about hybrid vesicles with different ratios of 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC) and poly(1,2-butadiene-block-ethylene oxide) (PBd₂₂ -PEO₁₄ , M_s  = 1800 g mol^-1 ). Using single particle analysis (SPA) the authors are able to further interpret the information gained from SAXS and cryo-ET experiments, showing that increasing PBd₂₂ -PEO₁₄ mole fraction increases the membrane thickness from 52 Å for a pure lipid system to 97 Å for pure PBd₂₂ -PEO₁₄ vesicles. Two vesicle populations with different membrane thicknesses in hybrid vesicle samples are found. As these lipids and polymers are reported to homogeneously mix, bistability is inferred between weak and strong interdigitation regimes of PBd₂₂ -PEO₁₄ within the hybrid membranes. It is hypothesized that membranes of intermediate structure are not energetically favorable. Therefore, each vesicle exists in one of these two membrane structures, which are assumed to have comparable free energies. The authors conclude that, by combining biophysical methods, accurate determination of the influence of composition on the structural properties of hybrid membranes is achieved, revealing that two distinct membranes structures can coexist in homogeneously mixed lipid-polymer hybrid vesicles.

Encapsulation of cannabidiol in oil-in-water nanoemulsions and nanoemulsion-filled hydrogels: A structure and biological assessment study

HYPOTHESIS

Lipophilic cannabidiol can be solubilized in oil-in water nanoemulsions, which can then be impregnated into chitosan hydrogels forming another colloidal system that will facilitate cannabidiol's release. The delivery from both systems was compared, alongside structural and biological studies, to clarify the effect of the two carriers' structure on the release and toxicity of the systems.

EXPERIMENTS

Oil-in-water nanoemulsions (NEs) and the respective nanoemulsion-filled chitosan hydrogels (NE/HGs) were formulated as carriers of cannabidiol (CBD). Size, polydispersity and stability of the NEs were evaluated and then membrane dynamics, shape and structure of both systems were investigated with EPR spin probing, SAXS and microscopy. Biocompatibility of the colloidal delivery systems was evaluated through cytotoxicity tests over normal human skin fibroblasts. An ex vivo permeation protocol using porcine ear skin was implemented to assess the release of CBD and its penetration through the skin.

FINDINGS

Incorporation of the NEs in chitosan hydrogels does not significantly affect their structural properties as evidenced through SAXS, EPR and confocal microscopy. These findings indicate the successful development of a novel nanocarrier that preserves the NE structure with the CBD remaining encapsulated in the oil core while providing new rheological properties advantageous over NEs. Moreover, NE/HGs proved to be more efficient as a carrier for the release of CBD. Cell viability assessment revealed high biocompatibility of the proposed colloids.

Phase separation in polymer-based biomimetic structures containing planar membranes

Phase separation in biological membranes is crucial for proper cellular functions, such as signaling and trafficking, as it mediates the interactions of condensates on membrane-bound organelles and transmembrane transport to targeted destination compartments. The separation of a lipid bilayer into phases and the formation of lipid rafts involve the restructuring of molecular localization, their immobilization, and local accumulation. By understanding the processes underlying the formation of lipid rafts in a cellular membrane, it is possible to reconstitute this phenomenon in synthetic biomimetic membranes, such as hybrids of lipids and polymers or membranes composed solely of polymers, which offer an increased physicochemical stability and unlimited possibilities of chemical modification and functionalization. In this article, we relate the main lipid bilayer phase transition phenomenon with respect to hybrid biomimetic membranes, composed of lipids mixed with polymers, and fully synthetic membranes. Following, we review the occurrence of phase separation in biomimetic hybrid membranes based on lipids and/or direct lipid analogs, amphiphilic block copolymers. We further exemplify the phase separation and the resulting properties and applications in planar membranes, free-standing and solid-supported. We briefly list methods leading to the formation of such biomimetic membranes and reflect on their improved overall stability and influence on the separation into different phases within the membranes. Due to the importance of phase separation and compartmentalization in cellular membranes, we are convinced that this compiled overview of this phenomenon will be helpful for any researcher in the biomimicry area.

Effects of Charged Lipids on Giant Unilamellar Vesicle Fusion and Inner Content Mixing via Freeze-Thawing

Fusion between giant unilamellar vesicles (GUVs) can incorporate and mix components of biochemical reactions. Recently, GUV fusion induced by freeze-thawing (F/T) was employed to construct artificial cells that can easily and repeatedly fuse GUVs with efficient content mixing. However, GUVs were ruptured during F/T, and the inner contents leaked. Herein, we investigated the effects of charged lipids on GUV fusion via F/T. The presence of 10 %-50 % (w/w%) negatively charged lipids in GUV membranes, mainly composed of the neutral charged lipid 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC), improved resistance to GUV rupture and decreased inner content leakage. Furthermore, we found that the presence of positively charged lipids in GUV membranes elevated GUV rupture compared with F/T between GUVs containing POPC alone. Modified GUVs may better incorporate nutrients and lipid membranes with less damage following GUV fusion via F/T, providing an improved artificial model.

Zwitterionic Dendrimersomes: A Closer Xenobiotic Mimic of Cell Membranes

Building functional mimics of cell membranes is an important task toward the development of synthetic cells. So far, lipid and amphiphilic block copolymers are the most widely used amphiphiles with the bilayers by the former lacking stability while membranes by the latter are typically characterized by very slow dynamics. Herein, a new type of Janus dendrimer containing a zwitterionic phosphocholine hydrophilic headgroup (JD^PC ) and a 3,5-substituted dihydrobenzoate-based hydrophobic dendron is introduced. JD^PC self-assembles in water into zwitterionic dendrimersomes (z-DSs) that faithfully recapitulate the cell membrane in thickness, flexibility, and fluidity, while being resilient to harsh conditions and displaying faster pore closing dynamics in the event of membrane rupture. This enables the fabrication of hybrid DSs with components of natural membranes, including pore-forming peptides, structure-directing lipids, and glycans to create raft-like domains or onion vesicles. Moreover, z-DSs can be used to create active synthetic cells with life-like features that mimic vesicle fusion and motility as well as environmental sensing. Despite their fully synthetic nature, z-DSs are minimal cell mimics that can integrate and interact with living matter with the programmability to imitate life-like features and beyond.