Transformable vesicles for cancer immunotherapy

Immunotherapy that utilizes the human immune system to fight cancer represents a revolutionary method for cancer treatment. Immunotherapeutic agents that trigger the immune response should be carefully delivered to the desired site to maximize immunotherapy effectiveness and minimize side effects. Vesicles offer the possibility of encapsulating both hydrophilic and hydrophobic drugs and thus serve as a promising delivery tool. As multiple irreconcilable requirements exist at different transport stages, developing vesicles transformable in response to given stimuli is of great significance. In this review, we first introduced various vesicle types used for immunotherapy. Furthermore, the typical stimuli that trigger vesicle transformation and the usually generated transformation styles were described. Focusing on three aspects of antigen-presenting cell (APC)/T cell activation, tumor microenvironment (TME) amelioration, and immunogenic cell death (ICD)-induced immunotherapy, we reviewed recently reported transformable vesicles for tumor treatment. Finally, we put forward possible directions for future research and clinical translation.

Transition kinetics of mixed lipid:photosurfactant assemblies studied by time-resolved small angle X-ray scattering

HYPOTHESIS

Photoswitchable surfactants are used in the design of many light-responsive colloids and/or self-assemblies. Photo-isomerization enables to control molecular equilibrium, and triggers transient reorganizations with possibly out-of-equilibrium intermediate states that have been overlooked. Here, we address this question by an in depth structural investigation of intermediate lipid-surfactant assemblies that occur during fast isothermal photo-triggered transition in lipid:surfactant mixtures.

EXPERIMENTS

The structural parameters of mixed assemblies of azobenzene-containing cationic surfactant (AzoTMA) and dioleoylphosphatidylcholine (DOPC) lipids were studied by light scattering and time-resolved small angle X-ray scattering. Structural and compositional information about the assemblies and unimers in bulk were determined at the photostationary states, as well as at intermediate kinetic states formed during UV or blue light illumination.

FINDINGS

DOPC:AzoTMA systems form mixed assemblies representative of phospholipid:cationic surfactant mixtures, that evolve from spheroid, to rod-like micelles, and vesicles with increasing DOPC fraction. Transient assemblies detected during the photo-triggered kinetics are similar to the ones found in stationary states. But changes of AzoTMA unimers in bulk can be considerably faster than mass reorganizations of the mixed assemblies, suggesting that out-of-equilibrium conditions are transiently reached. Mass reorganization of the surfactant-enriched assemblies is much faster than in the lipid enriched ones, providing insight into the role of lipids in a slow reorganization of the assemblies.

Ectoine Effect on Mechanical Properties of Vesicles in Aqueous Solution

The mechanical properties of the vesicles incorporated with ectoine were studied using atomic force microscope (AFM). The vesicles were prepared with dipalmitoylphosphatidylcholine (DPPC) by changing only the ratio of the ectoine to DPPC. After the vesicles were adsorbed on the mica substrate and their morphology were characterized, the plot of an AFM tip displacement versus the tip deflection was acquired by monitoring the behavior of the tip into the vesicle. The breakthrough of the tip into the vesicle was observed to occur twice. Each breakthrough represented a penetration of the tip into the top and bottom portions of the vesicle, respectively. The force data between the pre-contact and the first breakthrough were comparable with the Hertzian model to estimate Young's modulus and the bending modulus of the vesicles. Both moduli decreased proportionally with the increase in the ratio of ectoine to lipid up to 0.5. However, above 0.5, the moduli were slightly changed with the increase. These results of the mechanical properties appear to be due to the osmotic and volumetric effect on the headgroup packing disruption.

Tuneable Time Delay in the Burst Release from Oxidation-Sensitive Polymersomes Made by PISA

Reactive polymersomes represent a versatile artificial cargo carrier system that can facilitate an immediate release in response to a specific stimulus. The herein presented oxidation-sensitive polymersomes feature a time-delayed release mechanism in an oxidative environment, which can be precisely adjusted by either tuning the membrane thickness or partial pre-oxidation. These polymeric vesicles are conveniently prepared by PISA allowing the straightforward and effective in situ encapsulation of cargo molecules, as shown for dyes and enzymes. Kinetic studies revealed a critical degree of oxidation causing the destabilization of the membrane, while no release of the cargo is observed beforehand. The encapsulation of glucose oxidase directly transforms these polymersomes into glucose-sensitive vesicles, as small molecules including sugars can passively penetrate their membrane. Considering the ease of preparation, these polymersomes represent a versatile platform for the confinement and burst release of cargo molecules after a precisely adjustable time span in the presence of specific triggers, such as H2 O2 or glucose.

Bimolecular quenching of tryptophan fluorescence in a membrane protein: Evolution of local solvation and environment during folding into a bilayer

Fluorescence spectroscopy, including Stern-Volmer quenching, is a valuable tool for the study of protein dynamics. Changes in protein solvation during the folding reaction of a membrane protein, Outer membrane protein A (OmpA), into lipid bilayers was probed with bimolecular fluorescence quenching with acrylamide quencher. Six single-tryptophan OmpA mutants (W7, W15, W57, W102, W129, and W143) allowed for site-specific investigations at varying locations within the transmembrane β-barrel domain. A sphere-of-action quenching model that combines both static and dynamic components gave rise to Stern-Volmer quenching constants, KD, for OmpA denatured in 8.0 M urea, aggregated in 0.5 M urea, adsorbed onto small unilamellar vesicles (SUVs), and folded in SUVs (t = 6 hrs). The average KD values were KDdenatured(6.4M-1)>KDaggregated5.9M-1>KDadsorbed(1.9M-1)>KDfolded(0.6M-1). With knowledge of the fluorescence lifetimes in the absence of quencher, the bimolecular quenching constants, kq, were derived; the evolution of kq (and therefore KD)during the folding reaction into SUVs (t = 0 hr to t = 6 hrs) revealed desolvation timescales, τdesolv of 41-46 min (W7, W15, W57, W102), 27 min (W129), and 15 min (W143). The evolution of λmax during folding revealed fast and slow components, τenvironmentfast and τenvironmentslow of 7-13 min and 25-84 min, respectively, for all mutants. For the five lipid- facing mutants (W7, W15, W57, W129, and W143), the general trend was τenvironmentfast7-13min<τdesolv15-46min≤τenvironmentslow(25-84min). These results suggest that there is an initial fast step in which there is a large change in polarity to a hydrophobic environment, followed by a slower desolvation process during evolution within the hydrophobic environment. These results complement previous mechanisms of concerted folding and provide insights into site-specific changes in solvation during formation of native β-barrel structure.

PKC-ε regulates vesicle delivery and focal exocytosis for efficient IgG-mediated phagocytosis

Protein kinase C (PKC)-ε is required for membrane addition during IgG-mediated phagocytosis, but its role in this process is ill defined. Here, we performed high-resolution imaging, which reveals that PKC-ε exits the Golgi and enters phagosomes on vesicles that then fuse. TNF and PKC-ε colocalize at the Golgi and on vesicles that enter the phagosome. Loss of PKC-ε and TNF delivery upon nocodazole treatment confirmed vesicular transport on microtubules. That TNF+ vesicles were not delivered in macrophages from PKC-ε null mice, or upon dissociation of the Golgi-associated pool of PKC-ε, implies that Golgi-tethered PKC-ε is a driver of Golgi-to-phagosome trafficking. Finally, we established that the regulatory domain of PKC-ε is sufficient for delivery of TNF+ vesicles to the phagosome. These studies reveal a novel role for PKC-ε in focal exocytosis - its regulatory domain drives Golgi-derived vesicles to the phagosome, whereas catalytic activity is required for their fusion. This is one of the first examples of a PKC requirement for vesicular trafficking and describes a novel function for a PKC regulatory domain. This article has an associated First Person interview with the first author of the paper.

Isolation and Phospholipid Enrichment of Muscle Mitochondria and Mitoplasts

The efficient ATP production in mitochondria relies on the highly specific organization of its double membrane. Notably, the inner mitochondrial membrane (IMM) displays a massive surface extension through its folding into cristae, along which concentrate respiratory complexes and oligomers of the ATP synthase. Evidence has accumulated to highlight the importance of a specific phospholipid composition of the IMM to support mitochondrial oxidative phosphorylation. Contribution of specific phospholipids to mitochondrial ATP production is classically studied by modulating the activity of enzymes involved in their synthesis, but the interconnection of phospholipid synthesis pathways often impedes the determination of the precise role of each phospholipid. Here, we describe a protocol to specifically enrich mitochondrial membranes with cardiolipin or phosphatidylcholine, as well as a fluorescence-based method to quantify phospholipid enrichment. This method, based on the fusion of lipid vesicles with isolated mitochondria, may further allow a precise evaluation of phospholipid contribution to mitochondrial functions.

Comparative proteome profiling in exosomes derived from porcine colostrum versus mature milk reveals distinct functional proteomes

Exosomes are membranous vesicles of endocytic origin, recently been considered as major players in cell-cell communication. Milk is highly complex, and diverse biocomponents provide adequate nutrition, transfer immunity, and promote adequate neonate development. Milk exosomes are suggested to have a key role in these processes, yet to be further explored, and the alteration of the exosomes' cargo in different stages of lactation stages is important for understanding the factors relevant in nursing and also for improving milk replacer products both for humans and animals. We isolated exosomes from porcine milk in different lactation stages and analyzed their content using a TMT-based high-resolution quantitative proteomic approach. Exosomes were isolated using ultracentrifugation coupled with size exclusion chromatography to enrich milk-derived exosomes in samples obtained at day 0, 7, and 14 after parturition, and characterized by nanoparticle tracking analysis, transmission electron microscopy, and Western blotting. Quantitative proteomics analysis revealed different proteome profiles for colostrum exosomes and milk exosomes. The functional analysis highlighted pathways related to the regulation of homeostasis to be upregulated in colostrum exosomes, and pathways such as endothelial cell development and lipid metabolism to be upregulated in mature milk exosomes. This study endorses the importance of exosomes as active biocomponents of milk and provides knowledge for future studies exploring their role in the regulation of immunity and growth of the newborn. SIGNIFICANCE: The identified functional proteome and protein-protein interaction networks identified in our study help to elucidate the role of milk exosomes in different lactation periods. The results generated herein are of relevance for the basic understanding of their impact on the infant's development but also for bringing forward the manufacturing of milk replacers.

TANGO1 marshals the early secretory pathway for cargo export

TANGO1 protein facilitates the endoplasmic reticulum (ER) export of large cargoes that cannot be accommodated in 60 nm transport vesicles. It assembles into a ring in the plane of the ER membrane to create a distinct domain. Its lumenal portion collects and sorts folded cargoes while its cytoplasmic domains collar COPII coats, recruit retrograde COPI-coated membranes that fuse within the TANGO1 ring, thus opening a tunnel for cargo transfer from the ER into a growing export conduit. This mode of cargo transfer bypasses the need for vesicular intermediates and is used to export the most abundant and bulky cargoes. The evolution of TANGO1 and its activities defines the difference between yeast and animal early secretory pathways.

Photoresponsive supramolecular strategy for controlled assembly in light-inert double-chain surfactant system

HYPOTHESIS

One of the main advances in double-chain surfactant systems has been their progress from the construction of assemblies to the transformation application in medicine and material science, especially to the drug delivery systems. Thus, it is critical to develop stimuli-responsive assemblies based on double-chain surfactants. We predicted that reversible assembly switching can be achieved by manipulation of the ternary host-guest competitive complexation among β-cyclodextrin (β-CD), surfactants, and designed azobenzene (Azo).

EXPERIMENTS

In this work, Azo was introduced into vesicles using supramolecular assembly strategy. Vesicles are formed only when Azo moieties are in trans-form. UV switching of Azo groups led to fast disruption of the Azo@β-CD complexes and relatively slow disintegration of the vesicles. With the alterative irradiation of UV and Vis light, the photoisomerization of azo group provokes the reversible disassembly and reassembly of vesicles.

FINDINGS

This photo-responsive supramolecular strategy offered a controllable way to prepare responsive vesicles assembled from complex double-chain surfactants, such as phospholipids, which could be further used in drug delivery systems. This new perspective is instructive for the design and functional use of complex surfactants assembly. Importantly, the study results paved the way for the development of novel light-responsive assembly materials operating in aqueous media and biological field.

Ultrastructural characterization of the tegument in protoscoleces of Echinococcus ortleppi

Cystic echinococcosis is a globally distributed zoonosis caused by cestodes of the Echinococcus granulosus sensu lato (s.l.) complex, with Echinococcus ortleppi mainly involved in cattle infection. Protoscoleces show high developmental plasticity, being able to differentiate into either adult worms or metacestodes within definitive or intermediate hosts, respectively. Their outermost cellular layer is called the tegument, which is important in determining the infection outcome through its immunomodulating activities. Herein, we report an in-depth characterization of the tegument of E. ortleppi protoscoleces performed through a combination of scanning and transmission electron microscopy techniques. Using electron tomography, a three-dimensional reconstruction of the tegumental cellular territories was obtained, revealing a novel structure termed the 'tegumental vesicular body' (TVB). Vesicle-like structures, possibly involved in endocytic/exocytic routes, were found within the TVB as well as in the parasite glycocalyx, distal cytoplasm and close inner structures. Furthermore, parasite antigens (GST-1 and AgB) were unevenly localised within tegumental structures, with both being detected in vesicles found within the TBV. Finally, the presence of host (bovine) IgG was also assessed, suggesting a possible endocytic route in protoscoleces. Our data forms the basis for a better understanding of E. ortleppi and E. granulosus s.l. structural biology.

Fractionating stem cells secretome for Parkinson's disease modeling: Is it the whole better than the sum of its parts?

Human mesenchymal stem cells (hMSCs) secretome has been have been at the forefront of a new wave of possible therapeutic strategies for central nervous system neurodegenerative disorders, as Parkinson's disease (PD). While within its protein fraction, several promising proteins were already identified with therapeutic properties on PD, the potential of hMSCs-secretome vesicular fraction remains to be elucidated. Such highlighting is important, since hMSCs secretome-derived vesicles can act as biological nanoparticles with beneficial effects in different pathological contexts. Therefore, in this work, we have isolated hMSCs secretome vesicular fraction, and assessed their impact on neuronal survival, and differentiation on human neural progenitors' cells (hNPCs), and in a 6-hydroxydopamine (6-OHDA) rat model of PD when compared to hMSCs secretome (as a whole) and its protein derived fraction. From the results, we have found hMSCs vesicular fraction as polydispersity source of vesicles, which when applied in vitro was able to induce hNPCs differentiation at the same levels as the whole secretome, while the protein separated fraction was not able to induce such effect. In the context of PD, although distinct effects were observed, hMSCs secretome and its derived fractions displayed a positive impact on animals' motor and histological performance, thereby indicating that hMSCs secretome and its different fractions may impact different mechanisms and pathways. Overall, we concluded that the use of the secretome collected from hMSCs and its different fractions might be active modulators of different neuroregeneration mechanisms, which could open new therapeutical opportunities for their future use as a treatment for PD.

Membrane partitioning and lipid selectivity of the N-terminal amphipathic H0 helices of endophilin isoforms

Endophilin is an N-BAR protein, which is characterized by a crescent-shaped BAR domain and an amphipathic helix that contributes to the membrane binding of these proteins. The exact function of that H0 helix has been a topic of debate. In mammals, there are five different endophilin isoforms, grouped into A (three members) and B (two members) subclasses, which have been described to differ in their subcellular localization and function. We asked to what extent molecular properties of the H0 helices of these members affect their membrane targeting behavior. We found that all H0 helices of the endophilin isoforms display a two-state equilibrium between disordered and α-helical states in which the helical secondary structure can be stabilized through trifluoroethanol. The helicities in high TFE were strikingly different among the H0 peptides. We investigated H0-membrane partitioning by the monitoring of secondary structure changes via CD spectroscopy. We found that the presence of anionic phospholipids is critical for all H0 helices partitioning into membranes. Membrane partitioning is found to be sensitive to variations in membrane complexity. Overall, the H0 B subfamily displays stronger membrane partitioning than the H0 A subfamily. The H0 A peptide-membrane binding occurs predominantly through electrostatic interactions. Variation among the H0 A subfamily may be attributed to slight alterations in the amino acid sequence. Meanwhile, the H0 B subfamily displays greater specificity for certain membrane compositions, and this may link H0 B peptide binding to endophilin B's cellular function.

Silver nanoparticles stabilized by ramnolipids: Effect of pH

Rhamnolipids are glycolipid biosurfactants that have remarkable physicochemical characteristics, such as the capacity for self-assembly, which makes these biomolecules a promising option for application in nanobiotechnology. Rhamnolipids produced from a low-cost carbon source (glycerol) were used to stabilize silver nanoparticles. Silver nanoparticles (AgNPs) have been the subject of studies due to their physical chemical as well as biological properties, which corroborate their catalytic and antimicrobial activity. We compared nanoparticles obtained with three different pH values during synthesis (5, 7 and 9) in the presence of rhamnolipids. Dynamic light scattering showed that larger particles were formed at pH 5 (78-190 nm) compared to pH 7 (6.5-43 nm) and 9 (5.6-28.1 nm). Moreover, nanoparticle stability (analyzed based on the zeta potential) was enhanced with the increase in pH from 5 to 9 (-29.86 ± 1.04, -37.83 ± 0.90 and -40.33 ± 0.57 mV, respectively). Field emission gun scanning electron microscopy confirmed the round morphology of the silver nanoparticles. The LSPR spectra of AgNP for the pHs studied are conserved. In conclusion, different pH values in the presence of rhamnolipids used in the synthesis of silver nanoparticles directly affect nanoparticle size and stability.

Cholesterol-phospholipid interactions resist the detergent effect of bovine bile

Sphingomyelin (SM) and cholesterol complexation gives rise to detergent-resistant liquid-ordered domains. The persistence of these domains and subsequent mixed micelle formation was examined in the presence of bile under physiological digestive in vitro conditions for vesicles comprising either SM/cholesterol, porcine brain phosphatidylcholine (BPC)/cholesterol, or soy phosphatidylcholine (SPC)/cholesterol bilayers, the latter two systems having no liquid-ordered domains. Micellization of these digested phospholipid multilamellar vesicle systems was confirmed by transmission electron microscopy. Bovine bile was found to consist of large multilamellar sheets which subsumed phospholipid vesicles to form aggregated superstructures. Budding off from these superstructures were vesicle-to-micelle transition intermediates: unilamellar vesicles and cylindrical micelles. The presence of cholesterol (60/40 phospholipid/cholesterol mol/mol) delayed the initial rapid onset of digestion, but not for BPC and SPC vesicle systems. Acyl chain order/disorder before and after vesicle-to-micelle transition of all three phospholipid/cholesterol systems was examined using Raman spectroscopy. The addition of bovine bile to both PC/cholesterol vesicle systems reduced the overall ratio of acyl chain disorder to order. In SM/cholesterol vesicles with ≤ 20% mol cholesterol, only the lateral inter-acyl chain packing was reduced, whereas for SM/cholesterol vesicles with ≥ 30% mol cholesterol, a higher proportion of gauche-to-trans isomerization was apparent, demonstrating that SM/cholesterol complexes modify the acyl chain structure of micelles.

Outer membrane vesicles mediated horizontal transfer of an aerobic denitrification gene between Escherichia coli

Bacterial genetic material can be horizontally transferred between microorganisms via outer membrane vesicles (OMVs) released by bacteria. Up to now, the application of vesicle-mediated horizontal transfer of "degrading genes" in environmental remediation has not been reported. In this study, the nirS gene from an aerobic denitrification bacterium, Pseudomonas stutzeri, was enclosed in a pET28a plasmid, transformed into Escherichia coli (E. coli) DH5α and expressed in E. coli BL21. The E. coli DH5α released OMVs containing the recombination plasmid pET28a-nirS-EGFP. When compared with the free pET28a-nirS-EGFP plasmid's inability to transform, nirS in OMVs could be transferred into E. coli BL21 with the transformation frequency of 2.76 × 10⁶ CFU/g when the dosage of OMVs was 200 µg under natural conditions, and nirS could express successfully in recipient bacteria. Furthermore, the recipient bacteria that received OMVs containing pET28a-nirS-EGFP could produce 18.16 U/mL activity of nitrite reductase.

Consequences of the exposure to bisphenol A in cell membrane models at the molecular level and hamster ovary cells viability

The inadequate disposal and the difficulty in its removal from water treatment systems have made the endocrine disruptor bisphenol A (BPA) a significant hazard for humans and animals. The molecular-level mechanisms of BPA action are not known in detail, which calls for systematic investigations using cell membrane models. This paper shows that BPA affects Langmuir monolayers and giant unilamellar vesicles (GUVs) of 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) used as membrane models, in a concentration-dependent manner and with effects that depend on BPA aggregation. BPA increases DPPC monolayer fluidity in surface pressure isotherms upon interacting with the headgroups through hydrogen bonding, according to polarization-modulated infrared reflection absorption spectroscopy (PM-IRRAS). In DPPC GUVs, BPA induced wrinkling and distortion in the spherical shape of the vesicles, but this was only observed for fresh solutions where it is not aggregated. BPA also decreased the viability of hamster ovary cells (CHO) in in vitro experiments. In contrast, aged, aggregated BPA solutions did not affect the GUVs and even increased CHO viability. These results may be rationalized in terms of size-dependent effects of BPA, which may be relevant for its endocrine-disrupting effects.

Lipid nanovesicles for biomedical applications: 'What is in a name'?

Vesicles, generally defined as self-assembled structures formed by single or multiple concentric bilayers that surround an aqueous core, have been widely used for biomedical applications. They can either occur naturally (e.g. exosomes) or be produced artificially and range from the micrometric scale to the nanoscale. One the most well-known vesicle is the liposome, largely employed as a drug delivery nanocarrier. Liposomes have been modified along the years to improve physicochemical and biological features, resulting in long-circulating, ligand-targeted and stimuli-responsive liposomes, among others. In this process, new nomenclatures were reported in an extensive literature. In many instances, the new names suggest the emergence of a new nanocarrier, which have caused confusion as to whether the vesicles are indeed new entities or could simply be considered modified liposomes. Herein, we discussed the extensive nomenclature of vesicles based on the suffix "some" that are employed for drug delivery and composed of various types and proportions of lipids and others amphiphilic compounds. New names have most often been selected based on changes of vesicle lipid composition, but the payload, structural complexity (e.g. multicompartment) and new/improved proprieties (e.g. elasticity) have also inspired new vesicle names. Based on this discussion, we suggested a rational classification for vesicles.

The influence of secondary processes on the porosity of volcanic rocks: A multiscale analysis using 3D X-ray microtomography

The porosity of volcanic rocks can be strongly affected by secondary processes such as the percolation of water and hydrothermal fluids, thus promoting crystallization of secondary minerals in the pores. With an aim to evaluate the impact of secondary mineral fillings, this paper shows the segmentation of secondary and filled pores based on the micro-CT technique. The mineralogy of the sample was analyzed with optical microscopy. Multiscale analysis was performed to determine the total porosity before and after the processes. The results show the influence on the permeability parameter caused by crystallization.

The effect of prime-and-rinse approach using MDP micellar solutions on extrafibrillar demineralization and dentin bond performance

OBJECTIVE

This study investigated the effects of prime-and-rinse approach using 10-methacryloyloxydecyl dihydrogen phosphate (MDP) micellar solutions on extrafibrillar demineralization and dentin bond performance of etch-and-rinse adhesive.

METHODS

The micellar solutions were prepared by adding 15% MDP in two ethanol-aqueous (75:25, 55:45 V/V%) solutions, referring to MDP/EtOH₇₅ and MDP/EtOH₅₅. After mid-coronal dentin surfaces were either etched (control) or conditioned with MDP/EtOH₇₅ and MDP/EtOH₅₅ and rinsed, they were applied with adhesive (Adpter Single Bond 2) in dry- or wet-bonding mode and placed with composite resin (Filtek Z350 XT). They were prepared into multiple micro-beams for micro-tensile bond strengths (MTBS) testing after storage in water for 24 h or subjecting to thermocycling. The other pretreated dentin surfaces were analyzed by TF-XRD, ATR-FTIR, HRTEM, FE-SEM, contact angle measurement and nanoindentation testing. The MTBS data was analyzed with two-way ANOVA followed by LSD post-hoc test.

RESULTS

MDP/EtOH₇₅ produced significantly greater MTBS values than MDP/EtOH₅₅ and control after thermocycling aging in dry- or wet-bonding mode (P < 0.05). The ATR-FTIR spectrums shows that ratios of phosphate/monomer (1,034 cm^-1/1,716 cm^-1) on MDP/EtOH₇₅-, MDP/EtOH₅₅-treated dentin surfaces are 0.51 and 0.23, respectively. This is confirmed by HRTEM images and SAED pattern that intrafibrillar minerals were mostly preserved after treatment with MDP/EtOH₇₅. MDP/EtOH₇₅ produced significantly higher elastic modulus and nanohardness on pretreated dentin surface than MDP/EtOH₅₅ (P < 0.05). TF-XRD pattern shows some MDP-Ca salts remained on the primed dentin surface.

SIGNIFICANCE

Prime-and-rinse approach using MDP/EtOH₇₅ micellar solution could produce mostly extrafibrillar demineralization, and greatly increase dentin bond durability in dry- or wet-bonding mode.

Mixed liposomes containing gram-positive bacteria lipids: Lipoteichoic acid (LTA) induced structural changes

Lipoteichoic acid (LTA), a surface associated polymer amphiphile tethered directly to the Gram-positive bacterial cytoplasmic membrane, is a key structural and functional membrane component. Its composition in the membrane is regulated by bacteria under different physiological conditions. How such LTA compositional variations modulate the membrane structural stability and integrity is poorly understood. Here, we have investigated structural changes in mixed liposomes mimicking the lipid composition of Gram-positive bacteria membranes, in which the concentration of Bacillus Subtilis LTA was varied between 0-15 mol%. Small-angle neutron scattering (SANS) and dynamic light scattering (DLS) measurements indicated formation of mixed unilamellar vesicles, presumably stabilized by the negatively charged LTA polyphosphates. The vesicle size increased with the LTA molar concentration up to ∼6.5 mol%, accompanied by a broadened size distribution, and further increasing the LTA concentration led to a decrease in the vesicle size. At 80 °C, SANS analyses showed the formation of larger vesicles with thinner shells. Complementary Cryo-TEM imaging confirmed the vesicle formation and the size increase with LTA addition, as well as the presence of interconnected spherical aggregates of smaller size at higher LTA concentrations. The results are discussed in light of the steric and electrostatic interactions of the bulky LTA molecules with increased chain fluidity at the higher temperature, which affect the molecular packing and interactions, and thus depend on the LTA composition, in the membrane.

Measurements of Exocytosis by Capacitance Recordings and Calcium Uncaging in Mouse Adrenal Chromaffin Cells

Fusion of vesicles with the plasma membrane and liberation of their contents is a multistep process involving several proteins. Correctly assigning the role of specific proteins and reactions in this cascade requires a measurement method with high temporal resolution. Patch-clamp recordings of cell membrane capacitance in combination with calcium measurements, calcium uncaging, and carbon-fiber amperometry allow for the accurate determination of vesicle pool sizes, their fusion kinetics, and their secreted oxidizable content. Here, we will describe this method in a model system for neurosecretion, the adrenal chromaffin cells, which secrete adrenaline.

The Glo3 GAP crystal structure supports the molecular niche model for ArfGAPs in COPI coats

Arf GTPase activating (ArfGAP) proteins are critical regulatory and effector proteins in membrane trafficking pathways. Budding yeast contain two ArfGAP proteins (Gcs1 and Glo3) implicated in COPI coat function at the Golgi, and yeast require Glo3 catalytic function for viability. A new X-ray crystal structure of the Glo3 GAP domain was determined at 2.1 Å resolution using molecular replacement methods. The structure reveals a Cys4-family zinc finger motif with an invariant residue (R59) positioned to act as an "arginine finger" during catalysis. Comparisons among eukaryotic GAP domains show a key difference between ArfGAP1 and ArfGAP2/3 family members in the final helix located within the domain. Conservation at both the sequence and structural levels suggest the Glo3 GAP domain interacts with yeast Arf1 switch I and II regions to promote catalysis. Together, the structural data presented here provide additional evidence for placing Glo3 near Arf1 triads within membrane-assembled COPI coats and further support the molecular niche model for COPI coat regulation by ArfGAPs.

Physico-chemical studies of elastic compliance and adsorption of DOPC vesicles and its mixture with charged lipids at fluid/solid interface

Lipid bilayer mechanics is crucial to membrane dynamics and in design of liposomes for delivery applications. In this work, vesicles of 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC) (size from 50 nm to 1 μm) and its mixtures with anionic 1,2-dioleoyl-sn-glycero-3-phospho-(1'-rac-glycerol) sodium salt (DOPG) and cationic dimethyldioctadecylammonium bromide (DODAB), have been studied under shear stress at fluid/solid interface and their elastic compliance evaluated. Results show that the rate of spreading of the smaller vesicles (∼70 nm) is about 1.4 times slower than those of larger ones (∼1 μ) and that DOPC has the highest elastic compliance compared with DOPC + DOPG and DOPC + DODAB vesicles. A direct correlation between the elastic compliance and the size of the vesicles shows larger vesicles are more structurally labile during adsorption and subsequent adhesion to solid surfaces than the smaller ones. Specific role of bound water in DODAB is reflected in the lowest elastic compliance of DODAB compared to other lipids. Results show that during the process of adhesion at the fluid/air interface, the vesicles undergo contraction, thereby transmitting mechanical stresses to their microenvironment, which matches the SAXS electron density profiles that indicates larger vesicles have thicker bilayer membranes with larger volume of water compared to the smaller sized ones.

Effect of salts on size and morphology of extruded dimethyldioctadecylammonium bromide or chloride vesicle for polymeric nanocapsules synthesis via templating emulsion polymerization

In preparing polymer capsules by vesicle templated emulsion polymerization, the initial size and morphology of the biomimetic vesicle template dictate the final size and morphology of the capsules. The presence of salts (NaCl, NaBr and LiCl) influences the size, dispersity (PDI) and morphology of dimethyldioctadecylammonium bromide or chloride (DODAX, X  = Br^- or Cl^-) vesicles, prepared via membrane extrusion. DODAX vesicles in pure water exhibit broad size distributions with PDI of 0.5 and 0.3 for DODAB and DODAC, respectively. Addition of salts in water before (pre-addition) and after (post-addition) extrusion reduces the size and PDI of the vesicles significantly and results in various morphology investigated with cryo-TEM. It is observed that at low salt concentration (≤0.5 mM) in pre-addition, DODAX exists as a nice quasi spherical unilamellar vesicle, suitable for vesicle templated polymerization whereas in post-addition of salt at any concentration, the morphology is dominated by structures not suitable for templating application. The information obtained here is crucial for vesicle templated emulsion polymerization and it will be shown that there is a relationship between vesicle template morphology and final polymer capsule morphology.