Liposome-cell interaction: transfer and intracellular release of a trapped fluorescent marker

Enhancing Antimicrobial Peptides from Frog Skin: A Rational Approach

Antimicrobial resistance is a global health threat, which has been worsened by the slow development of new antibiotics. The rational design of natural-derived antimicrobial peptides (AMPs) offers a promising alternative for enhancing the efficacy of AMPs and accelerating drug discovery. This paper describes the rational design of improved peptide derivatives starting from hylin-Pul3, a peptide previously isolated from the frog Boana pulchella, by optimizing its hydrophobicity, cationicity, and amphipathicity. In silico screening identified six promising candidates: dHP3-31, dHP3-50, dHP3-50.137, dHP3-50.190, dHP3-84, and dHP3-84.39. These derivatives exhibited enhanced activity against Gram-negative bacteria, emphasizing the role of cationicity and the strategic arginine incorporation. Hemolytic assays revealed the derivatives' improved selectivity, particularly for the derivatives with "imperfect amphipathicity". In fibroblast assays, dHP3-84 was well-tolerated, while dHP3-84.39 promoted cell proliferation. Antioxidant assays (ABTS assays) highlighted the Trp-containing derivatives' (dHP3-50.137, dHP3-31) significant activity. The lipid membrane interaction studies showed that hylin-Pul3 disrupts membranes directly, while dHP3-84.39, dHP3-50, and dHP3-50.137 promote vesicle aggregation. Conversely, dHP3-84 did not induce membrane disruption or aggregation, suggesting an intracellular mode of action. Machine learning models were effective in predicting bioactivity, as these predicted AMPs showed enhanced selectivity and potency. Among them, dHP3-84 demonstrated broad-spectrum potential. These findings highlight the value of rational design, in silico screening, and structure-activity studies in optimizing AMPs for therapeutic applications.

Interaction of the Antibiotic Rifampicin with Lipid Membranes

Rifampicin is a broad-spectrum antibiotic, active against several bacterial infections such as tuberculosis. It is a relatively large and structurally complex molecule, including numerous polar groups. Although violating several of Lipinski's rules for efficient intestinal absorption, rifampicin shows good oral bioavailability, permeating through cell membranes in the absorption pathway and those of the target organisms. Some hypotheses have been proposed for its efficient membrane permeation, but the details are mostly unknown. In this work, the interaction of rifampicin with POPC lipid bilayers is studied using experimental biophysics methodologies and atomistic molecular dynamics simulations considering the two most prevalent ionic species at physiological pH, the anionic and the zwitterionic forms. The results show that both ionization forms of rifampicin establish favorable interactions with the membrane lipids, in agreement with the relatively high partition coefficient obtained experimentally. The results from MD simulations and isothermal titration calorimetry using different pH buffers show that the piperazine group inserts deeply in the membrane and is accompanied by a stabilization of its neutral form. The bulky nature of rifampicin and its deep insertion in the membrane lead to a strong perturbation in the lipids local order, decreasing the membrane barrier properties as evaluated from the rate of carboxyfluorescein leaching. Altogether, the comparison between the experimental and MD simulations results provides important insight regarding the rifampicin molecular features responsible for its relatively fast membrane permeation. The lipid POPC used in this study was selected as a simple membrane with relevance for different organisms across all kingdoms. Further studies using more complex lipid compositions will provide details on eventual specificities for rifampicin interaction with the membranes of distinct organisms.

Exchange, promiscuity, and orthogonality in de novo designed coiled-coil peptide assemblies

De novo protein design is delivering new peptide and protein structures at a rapid pace. Many of these synthetic polypeptides form well-defined and hyperthermal-stable structures. Generally, however, less is known about the dynamic properties of the de novo designed structures. Here, we explore one aspect of dynamics in a series of de novo coiled-coil peptide assemblies: namely, peptide exchange within and between different oligomers from dimers through to heptamers. First, we develop a fluorescence-based reporter assay for peptide exchange that is straightforward to implement, and, thus, would be useful to others examining similar systems. We apply this assay to explore both homotypic exchange within single species, and heterotypic exchange between coiled coils of different oligomeric states. For the former, we provide a detailed study for a dimeric coiled coil, CC-Di, finding a half-life for exchange of 4.2 ± 0.3 minutes at a peptide concentration of 200 μM. Interestingly, more broadly when assessing exchange across all of the oligomeric states, we find that some of the designs are faithful and only undergo homotypic strand exchange, whereas others are promiscuous and exchange to form unexpected hetero-oligomers. Finally, we develop two design strategies to improve the orthogonality of the different oligomers: (i) using alternate positioning of salt bridge interactions; and (ii) incorporating non-canonical repeats into the designed sequences. In so doing, we reconcile the promiscuity and deliver a set of faithful homo-oligomeric de novo coiled-coil peptides. Our findings have implications for the application of these and other coiled coils as modules in chemical and synthetic biology.

Biocompatible metal-organic frameworks as promising platforms to eradicate HIV reservoirs ex vivo in people living with HIV

The HIV attacks the immune system provoking an infection that is considered a global health challenge. Despite antiretroviral treatments being effective in reducing the plasma viral load in the blood to undetectable levels in people living with HIV (PLWH), the disease is not cured and has become chronic. This happens because of the existence of anatomical and cellular viral reservoirs, mainly located in the lymph nodes and gastrointestinal tract, which are composed of infected CD4+ T cells with a resting memory phenotype and inaccessible to antiretroviral therapy. Herein, a new therapeutic strategy based on nanotechnology is presented. Different combinations of antiretroviral drugs (bictegravir/tenofovir/emtricitabine and nevirapine/tenofovir/emtricitabine) and toll-like receptor agonists were encapsulated into metal-organic frameworks (MOFs) PCN-224 and ZIF-8. The encapsulation efficiencies of all the drugs, as well as their release rate from the carriers, were measured. In vitro studies about the cell viability, the hemocompatibility, and the platelet aggregation of the MOFs were carried out. Epifluorescence microscopy assays confirmed the ability of ZIF-8 to target a carboxyfluorescein probe inside HeLa cell lines and PBMCs. These results pave the way for the use of these structures to eliminate latent HIV reservoirs from anatomical compartments through the activation of innate immune cells, and a higher efficacy of the triplet combinations of antiretroviral drugs.

Tracking the Endosomal Escape: A Closer Look at Calcein and Related Reporters

Crossing the cellular membrane and delivering active pharmaceuticals or biologicals into the cytosol of cells is an essential step in the development of nanomedicines. One of the most important intracellular processes regarding the cellular uptake of biologicals is the endolysosomal pathway. Sophisticated nanocarriers have been developed overcoming a major hurdle, the endosomal entrapment, and delivering their cargo to the required site of action. In parallel, in vitro assays have been established analyzing the performance of these nanocarriers. Among them, the release of the membrane-impermeable dye calcein has become a popular and straightforward method. It is accessible for most researchers worldwide, allows for rapid conclusions about the release potential, and enables the study of release mechanisms. This review is intended to provide an overview and guidance for scientists applying the calcein release assay. It comprises a survey of several applications in the study of endosomal escape, considerations of potential pitfalls, challenges and limitations of the assay, and a brief summary of complementary methods. Based on this review, we hope to encourage further research groups to take advantage of the calcein release assay for their own purposes and help to create a database for more efficient cross-correlations between nanocarriers. This article is protected by copyright. All rights reserved.

Effect of Ursolic and Oleanolic Acids on Lipid Membranes: Studies on MRSA and Models of Membranes

Staphylococcus aureus is an opportunistic pathogen and the major causative agent of life-threatening hospital- and community-acquired infections. A combination of antibiotics could be an opportunity to address the widespread emergence of antibiotic-resistant strains, including Methicillin-Resistant S. aureus (MRSA). We here investigated the potential synergy between ampicillin and plant-derived antibiotics (pentacyclic triterpenes, ursolic acid (UA) and oleanolic acid (OA)) towards MRSA (ATCC33591 and COL) and the mechanisms involved. We calculated the Fractional Inhibitory Concentration Index (FICI) and demonstrated synergy. We monitored fluorescence of Bodipy-TR-Cadaverin, propidium iodide and membrane potential-sensitive probe for determining the ability of UA and OA to bind to lipoteichoic acids (LTA), and to induce membrane permeabilization and depolarization, respectively. Both pentacyclic triterpenes were able to bind to LTA and to induce membrane permeabilization and depolarization in a dose-dependent fashion. These effects were not accompanied by significant changes in cellular concentration of pentacyclic triterpenes and/or ampicillin, suggesting an effect mediated through lipid membranes. We therefore focused on membranous effects induced by UA and OA, and we investigated on models of membranes, the role of specific lipids including phosphatidylglycerol and cardiolipin. The effect induced on membrane fluidity, permeability and ability to fuse were studied by determining changes in fluorescence anisotropy of DPH/generalized polarization of Laurdan, calcein release from liposomes, fluorescence dequenching of octadecyl-rhodamine B and liposome-size, respectively. Both UA and OA showed a dose-dependent effect with membrane rigidification, increase of membrane permeabilization and fusion. Except for the effect on membrane fluidity, the effect of UA was consistently higher compared with that obtained with OA, suggesting the role of methyl group position. All together the data demonstrated the potential role of compounds acting on lipid membranes for enhancing the activity of other antibiotics, like ampicillin and inducing synergy. Such combinations offer an opportunity to explore a larger antibiotic chemical space.

Identification and Characteristics of Fusion Peptides Derived From Enveloped Viruses

Membrane fusion events allow enveloped viruses to enter and infect cells. The study of these processes has led to the identification of a number of proteins that mediate this process. These proteins are classified according to their structure, which vary according to the viral genealogy. To date, three classes of fusion proteins have been defined, but current evidence points to the existence of additional classes. Despite their structural differences, viral fusion processes follow a common mechanism through which they exert their actions. Additional studies of the viral fusion proteins have demonstrated the key role of specific proteinogenic subsequences within these proteins, termed fusion peptides. Such peptides are able to interact and insert into membranes for which they hold interest from a pharmacological or therapeutic viewpoint. Here, the different characteristics of fusion peptides derived from viral fusion proteins are described. These criteria are useful to identify new fusion peptides. Moreover, this review describes the requirements of synthetic fusion peptides derived from fusion proteins to induce fusion by themselves. Several sequences of the viral glycoproteins E1 and E2 of HCV were, for example, identified to be able to induce fusion, which are reviewed here.

Avoiding artifacts in liposome leakage measurements via cuvette- and liposome-surface modifications

The barrier properties of lipid membranes are often determined by investigating their solute permeability with the help of spectroscopic methods and the use of liposome-encapsulated self-quenching fluorescent dyes, for example, Carboxyfluorescein (CF). It was shown previously that liposome-surface interactions, and thus the choice of cuvette material, influence the result of such spectroscopic permeability/leakage experiments. In this work, we explore different methods to minimize the artifacts observed in spontaneous leakage measurements performed with cholesterol-containing liposomes. The spontaneous leakage of CF from liposomes with different composition and surface properties is monitored in cuvettes composed of quartz, polystyrene (PS), and Poly(methyl methacrylate) (PMMA). Our results show that significantly different leakage profiles are recorded for the exact same liposome batch depending on the cuvette material used. Quartz Crystal Microbalance with Dissipation Monitoring (QCM-D) experiments indicate that these discrepancies likely arise from side processes occurring at the solution-cuvette interface, mainly, the attaching and spreading of liposomes. Further, we show that in some cases it is possible to minimize liposome-cuvette interactions, and reduce the experimental artifacts, by supplementing the liposomes with polyethylene glycol (PEG)-grafted lipids or gangliosides, and/or by pre-adsorbing free PEG to the cuvette walls. The collected data suggest that quartz cuvettes modified by adsorption of PEG8000 are suitable for spontaneous leakage experiments with POPC:cholesterol-based liposomes, while other cuvette materials perform poorly in the same experiments.

Drug transport kinetics of intravascular triggered drug delivery systems

Intravascular triggered drug delivery systems (IV-DDS) for local drug delivery include various stimuli-responsive nanoparticles that release the associated agent in response to internal (e.g., pH, enzymes) or external stimuli (e.g., temperature, light, ultrasound, electromagnetic fields, X-rays). We developed a computational model to simulate IV-DDS drug delivery, for which we quantified all model parameters in vivo in rodent tumors. The model was validated via quantitative intravital microscopy studies with unencapsulated fluorescent dye, and with two formulations of temperature-sensitive liposomes (slow, and fast release) encapsulating a fluorescent dye as example IV-DDS. Tumor intra- and extravascular dye concentration dynamics were extracted from the intravital microscopy data by quantitative image processing, and were compared to computer model results. Via this computer model we explain IV-DDS delivery kinetics and identify parameters of IV-DDS, of drug, and of target tissue for optimal delivery. Two parameter ratios were identified that exclusively dictate how much drug can be delivered with IV-DDS, indicating the importance of IV-DDS with fast drug release (~sec) and choice of a drug with rapid tissue uptake (i.e., high first-pass extraction fraction). The computational model thus enables engineering of improved future IV-DDS based on tissue parameters that can be quantified by imaging.

Ten Hagen et al. developed a computational model to simulate intravascular triggered drug delivery systems (IV-DDS), which they validated using quantitative intravital microscopy in mice. Their model potentially enables the engineering of more efficacious IV-DDS based on parameters that can be quantified by imaging.

Membrane properties of amacrocyclic tetraether bisphosphatidylcholine lipid: Effect of a single membrane-spanning polymethylene cross-linkage between two head groups of ditetradecylphosphatidylcholine membrane

The plasma membranes of archaea are abundant in macrocyclic tetraether lipids that contain a single or double long transmembrane hydrocarbon chains connecting the two glycerol backbones at both ends. In this study, a novel amacrocyclic bisphosphatidylcholine lipid bearing a single membrane-spanning octacosamethylene chain, 1,1'-O-octacosamethylene-2,2'-di-O-tetradecyl-bis-(sn-glycero)-3,3'-diphosphocholine (AC-(di-O-C14PC)₂), was synthesized to elucidate effects of the interlayer cross-linkage on membrane properties based on comparison with its corresponding diether phosphatidylcholine, 1,2-di-O-tetradecyl-sn-glycero-3-phosphocholine (DTPC), that forms bilayer membrane. Several physicochemical techniques demonstrated that while AC-(di-O-C14PC)₂ monolayer, which adopts a particularly high-ordered structure in the gel phase, shows remarkably high thermotropic transition temperature compared to DTPC bilayer, the fluidity of both phospholipids above the transition temperature is comparable. Nonetheless, the fluorescent dye leakage from inside the AC-(di-O-C14PC)₂ vesicles in the fluid phase is highly suppressed. The origin of the membrane properties characteristic of AC-(di-O-C14PC)₂ monolayer is discussed in terms of the single long transmembrane hydrophobic linkage and the diffusional motion of the lipid molecules.

Cellular compartments challenged by membrane photo-oxidation

The lipid composition impacts directly on the structure and function of the cytoplasmic as well as organelle membranes. Depending on the type of membrane, specific lipids are required to accommodate, intercalate, or pack membrane proteins to the proper functioning of the cells/organelles. Rather than being only a physical barrier that separates the inner from the outer spaces, membranes are responsible for many biochemical events such as cell-to-cell communication, protein-lipid interaction, intracellular signaling, and energy storage. Photochemical reactions occur naturally in many biological membranes and are responsible for diverse processes such as photosynthesis and vision/phototaxis. However, excessive exposure to light in the presence of absorbing molecules produces excited states and other oxidant species that may cause cell aging/death, mutations and innumerable diseases including cancer. At the same time, targeting key compartments of diseased cells with light can be a promising strategy to treat many diseases in a clinical procedure called Photodynamic Therapy. Here we analyze the relationships between membrane alterations induced by photo-oxidation and the biochemical responses in mammalian cells. We specifically address the impact of photosensitization reactions in membranes of different organelles such as mitochondria, lysosome, endoplasmic reticulum, and plasma membrane, and the subsequent responses of eukaryotic cells.

Lipid Scrambling Induced by Membrane-Active Substances

The functional roles of the lipid asymmetry of biomembranes are attracting increasing attention. This study characterizes the activity of surfactants to induce transmembrane flip-flop of lipids and thus "scramble" this asymmetry. Detergent-induced lipid scrambling of liposomes mimicking the charge asymmetry of bacterial membranes with 20 mol % of 1-palmitoyl-2-oleoyl-sn-glycero-3-phospho-rac-glycerol in the outer leaflet only was quantified by ζ-potential measurements for octaethylene glycol dodecyl ether (C₁₂EO₈), octyl glucoside (OG), and dodecyl maltoside. Membrane leakage was separately measured by the fluorescence lifetime-based calcein leakage assay and the onset of the membrane-to-micelle transition by isothermal titration calorimetry. Partition coefficients and partial molar areas were obtained as well. For the quickly membrane-permeant C₁₂EO₈ and OG, leakage proceeds at a rather sharp threshold content in the membrane, which is well below the onset of solubilization and little dependent on incubation time; it is accompanied by fast lipid scrambling. However, unlike leakage, flip-flop is a relaxation process that speeds up gradually from taking weeks in the detergent-free membrane to minutes or less in the leaking membrane. Hence, after 24 h of incubation, 10 mol % of C₁₂EO₈ or 50 mol % of OG in the membrane suffice for virtually complete lipid scrambling, whereas leakage remains below 10% for up to 14 mol % of C₁₂EO₈ and 88 mol % of OG. There is thus a concentration window in which lipid scrambling proceeds without leakage. This implies that lipid scrambling must be considered a possible mode of action of antimicrobial peptides and other membrane-active drugs or biomolecules. A related, detergent-based protocol for scrambling the lipid asymmetry of liposomes and maybe cells without compromising their overall integrity would be a very valuable tool to study functions of lipid asymmetry.

Molecular Simulations of PEGylated Biomolecules, Liposomes, and Nanoparticles for Drug Delivery Applications

Since the first polyethylene glycol (PEG)ylated protein was approved by the FDA in 1990, PEGylation has been successfully applied to develop drug delivery systems through experiments, but these experimental results are not always easy to interpret at the atomic level because of the limited resolution of experimental techniques. To determine the optimal size, structure, and density of PEG for drug delivery, the structure and dynamics of PEGylated drug carriers need to be understood close to the atomic scale, as can be done using molecular dynamics simulations, assuming that these simulations can be validated by successful comparisons to experiments. Starting with the development of all-atom and coarse-grained PEG models in 1990s, PEGylated drug carriers have been widely simulated. In particular, recent advances in computer performance and simulation methodologies have allowed for molecular simulations of large complexes of PEGylated drug carriers interacting with other molecules such as anticancer drugs, plasma proteins, membranes, and receptors, which makes it possible to interpret experimental observations at a nearly atomistic resolution, as well as help in the rational design of drug delivery systems for applications in nanomedicine. Here, simulation studies on the following PEGylated drug topics will be reviewed: proteins and peptides, liposomes, and nanoparticles such as dendrimers and carbon nanotubes.

Somuncurins: Bioactive Peptides from the Skin of the Endangered Endemic Patagonian Frog Pleurodema somuncurense

The skin glands of amphibian species hold a major component of their innate immunity, namely a unique set of antimicrobial peptides (AMPs). Although most of them have common characteristics, differences in AMP sequences allow a huge repertoire of biological activity with varying degrees of efficacy. We present the first study of the AMPs from Pleurodema somuncurence (Anura: Leptodactylidae: Leiuperinae). Among the 11 identified mature peptides, three presented antimicrobial activity. Somuncurin-1 (FIIWPLRYRK), somuncurin-2 (FILKRSYPQYY), and thaulin-3 (NLVGSLLGGILKK) inhibited Escherichia coli growth. Somuncurin-1 also showed antimicrobial activity against Staphylococcus aureus. Biophysical membrane model studies revealed that this peptide had a greater permeation effect in prokaryotic-like membranes and capacity to restructure liposomes, suggesting fusogenic activity, which could lead to cell aggregation and disruption of cell morphology. This study contributes to the characterization of peptides with new sequences to enrich the databases for the design of therapeutic agents. Furthermore, it highlights the importance of investing in nature conservation and the power of genetic description as a strategy to identify new compounds.

Biophysical approaches for exploring lipopeptide-lipid interactions

In recent years, lipopeptides (LPs) have attracted a lot of attention in the pharmaceutical industry due to their broad-spectrum of antimicrobial activity against a variety of pathogens and their unique mode of action. This class of compounds has enormous potential for application as an alternative to conventional antibiotics and for pest control. Understanding how LPs work from a structural and biophysical standpoint through investigating their interaction with cell membranes is crucial for the rational design of these biomolecules. Various analytical techniques have been developed for studying intramolecular interactions with high resolution. However, these tools have been barely exploited in lipopeptide-lipid interactions studies. These biophysical approaches would give precise insight on these interactions. Here, we reviewed these state-of-the-art analytical techniques. Knowledge at this level is indispensable for understanding LPs activity and particularly their potential specificity, which is relevant information for safe application. Additionally, the principle of each analytical technique is presented and the information acquired is discussed. The key challenges, such as the selection of the membrane model are also been briefly reviewed.

Versatile symport transporters based on cyclic peptide dimers

We present the synthesis and transmembrane transport properties of a new family of tris-pyridine-decorated cyclic peptides.

Self-reporting of payload release in polymer coatings based on the inner filter effect

New polymeric nanoparticle sensors are developed for monitoring the release of non-fluorescent payloads in coatings by the naked eye.

The activity of the saponin ginsenoside Rh2 is enhanced by the interaction with membrane sphingomyelin but depressed by cholesterol

The membrane activity of some saponins, such as digitonin or alpha-hederin, is usually attributed to their interaction with membrane cholesterol (Chol). This contrasts with our recent publication showing that Chol, contrary to sphingomyelin (SM), can delay the cytotoxicity of the saponin ginsenoside Rh2, challenging the usual view that most saponins mediate their membrane effects through interaction with Chol. The aim of the present study was to elucidate the respective importance of Chol and SM as compared to phosphatidylcholine (PC) species in the membrane-related effects of Rh2. On simple lipid monolayers, Rh2 interacted more favorably with eggSM and DOPC than with Chol and eggPC. Using Large Unilamellar Vesicles (LUVs) of binary or ternary lipid compositions, we showed that Rh2 increased vesicle size, decreased membrane fluidity and induced membrane permeability with the following preference: eggSM:eggPC > eggSM:eggPC:Chol > eggPC:Chol. On Giant Unilamellar Vesicles (GUVs), we evidenced that Rh2 generated positive curvatures in eggSM-containing GUVs and small buds followed by intra-luminal vesicles in eggSM-free GUVs. Altogether, our data indicate that eggSM promotes and accelerates membrane-related effects induced by Rh2 whereas Chol slows down and depresses these effects. This study reconsiders the theory that Chol is the only responsible for the activity of saponins.

Mechanistic Landscape of Membrane-Permeabilizing Peptides

Membrane permeabilizing peptides (MPPs) are as ubiquitous as the lipid bilayer membranes they act upon. Produced by all forms of life, most membrane permeabilizing peptides are used offensively or defensively against the membranes of other organisms. Just as nature has found many uses for them, translational scientists have worked for decades to design or optimize membrane permeabilizing peptides for applications in the laboratory and in the clinic ranging from antibacterial and antiviral therapy and prophylaxis to anticancer therapeutics and drug delivery. Here, we review the field of membrane permeabilizing peptides. We discuss the diversity of their sources and structures, the systems and methods used to measure their activities, and the behaviors that are observed. We discuss the fact that "mechanism" is not a discrete or a static entity for an MPP but rather the result of a heterogeneous and dynamic ensemble of structural states that vary in response to many different experimental conditions. This has led to an almost complete lack of discrete three-dimensional active structures among the thousands of known MPPs and a lack of useful or predictive sequence-structure-function relationship rules. Ultimately, we discuss how it may be more useful to think of membrane permeabilizing peptides mechanisms as broad regions of a mechanistic landscape rather than discrete molecular processes.

Towards more accurate bioimaging of drug nanocarriers: turning aggregation-caused quenching into a useful tool

One of the current challenges in the monitoring of drug nanocarriers lies in the difficulties in discriminating the carrier-bound signals from the bulk signals of probes. Environment-responsive probes that enable signal switching are making steps towards a solution to this problem. Aggregation-caused quenching (ACQ), a phenomenon generally regarded as unfavorable in bioimaging, has turned out to be a promising characteristic for achieving environment-responsiveness and eliminating free-probe interference. So-called ACQ probes emit fluorescence when dispersed molecularly within the carrier matrix but quench immediately and absolutely once they are released into the ambient aqueous environment upon the degradation of the nanocarriers. Therefore, the fluorescence observed represents integral nanocarriers. Based on this rationale, the in vivo fates of various nanocarriers have been explored using live imaging equipment, with very interesting findings revealing the role of the particles. The current applications are however restricted to nanocarriers with highly hydrophobic matrices (lipid or polyester nanoparticles) or with a hydrophobic core-hydrophilic shell structure (micelles). The ACQ-based bioimaging strategy is emerging as a promising tool to achieve more accurate bioimaging of drug nanocarriers. This review article provides an overview of the ACQ phenomenon and the rationale for and examples of applications, as well as the limitations of the ACQ-based strategy, with a focus on improving the accuracy of bioimaging of nanoparticles.

Parallel damage in mitochondria and lysosomes is an efficient way to photoinduce cell death

Cells challenged by photosensitized oxidations face strong redox stresses and rely on autophagy to either survive or die. However, the use of macroautophagy/autophagy to improve the efficiency of photosensitizers, in terms of inducing cell death, remains unexplored. Here, we addressed the concept that a parallel damage in the membranes of mitochondria and lysosomes leads to a scenario of autophagy malfunction that can greatly improve the efficiency of the photosensitizer to cause cell death. Specific damage to these organelles was induced by irradiation of cells pretreated with 2 phenothiazinium salts, methylene blue (MB) and 1,9-dimethyl methylene blue (DMMB). At a low concentration level (10 nM), only DMMB could induce mitochondrial damage, leading to mitophagy activation, which did not progress to completion because of the parallel damage in lysosome, triggering cell death. MB-induced photodamage was perceived almost instantaneously after irradiation, in response to a massive and nonspecific oxidative stress at a higher concentration range (2 µM). We showed that the parallel damage in mitochondria and lysosomes activates and inhibits mitophagy, leading to a late and more efficient cell death, offering significant advantage (2 orders of magnitude) over photosensitizers that cause unspecific oxidative stress. We are confident that this concept can be used to develop better light-activated drugs. Abbreviations: ΔΨm: mitochondrial transmembrane inner potential; AAU: autophagy arbitrary units; ATG5, autophagy related 5; ATG7: autophagy related 7; BAF: bafilomycin A1; BSA: bovine serum albumin; CASP3: caspase 3; CF: carboxyfluorescein; CTSB: cathepsin B; CVS: crystal violet staining; DCF: dichlorofluorescein; DCFH2: 2',7'-dichlorodihydrofluorescein; DMMB: 1,9-dimethyl methylene blue; ER: endoplasmic reticulum; HaCaT: non-malignant immortal keratinocyte cell line from adult human skin; HP: hydrogen peroxide; LC3B-II: microtubule associated protein 1 light chain 3 beta-II; LMP: lysosomal membrane permeabilization; LTG: LysoTracker™ Green DND-26; LTR: LysoTracker™ Red DND-99; 3-MA: 3-methyladenine; MB: methylene blue; mtDNA: mitochondrial DNA; MitoSOX™: red mitochondrial superoxide probe; MTDR: MitoTracker™ Deep Red FM; MTO: MitoTracker™ Orange CMTMRos; MT-ND1: mitochondrially encoded NADH:ubiquinone oxidoreductase core subunit 1; MTT: methylthiazolyldiphenyl-tetrazolium bromide; 1O2: singlet oxygen; OH. hydroxil radical; PRKN/parkin: parkin RBR E3 ubiquitin protein ligase; PBS: phosphate-buffered saline; PI: propidium iodide; PDT: photodynamic therapy; PS: photosensitizer; QPCR: gene-specific quantitative PCR-based; Rh123: rhodamine 123; ROS: reactive oxygen species RTN: rotenone; SQSTM1/p62: sequestosome 1; SUVs: small unilamellar vesicles; TBS: Tris-buffered saline.

A light-responsive liposomal agent for MRI contrast enhancement and monitoring of cargo delivery

A liposomal MRI-probe changing relaxivity and releasing cargo upon light irradiation was developed for diagnostics and monitoring of drug delivery.

Photo-Oxidation of Unilamellar Vesicles by a Lipophilic Pterin: Deciphering Biomembrane Photodamage

Pterins are natural products that can photosensitize the oxidation of DNA, proteins, and phospholipids. Recently, a new series of decyl-chain (i.e., lipophilic) pterins were synthesized and their photophysical properties were investigated. These decyl-pterins led to efficient intercalation in large unilamellar vesicles and produced, under UVA irradiation, singlet molecular oxygen, a highly oxidative species that react with polyunsaturated fatty acids (PUFAs) to form hydroperoxides. Here, we demonstrate that the association of 4-(decyloxy)pteridin-2-amine ( O-decyl-Ptr) to lipid membranes is key to its ability to trigger phospholipid oxidation in unilamellar vesicles of phosphatidylcholine rich in PUFAs used as model biomembranes. Our results show that O-decyl-Ptr is at least 1 order of magnitude more efficient photosensitizer of lipids than pterin (Ptr), the unsubstituted derivative of the pterin family, which is more hydrophilic and freely passes across lipid membranes. Lipid peroxidation photosensitized by O-decyl-Ptr was detected by the formation of conjugated dienes and oxidized lipids, such as hydroxy and hydroperoxide derivatives. These primary products undergo a rapid conversion into short-chain secondary products by cleavage of the fatty-acid chains, some of which are due to subsequent photosensitized reactions. As a consequence, a fast increase in membrane permeability is observed. Therefore, lipid oxidation induced by O-decyl-Ptr could promote cell photodamage due to the biomembrane integrity loss, which in turn may trigger cell death.

Effect of cardiolipin on the antimicrobial activity of a new amphiphilic aminoglycoside derivative on Pseudomonas aeruginosa

Amphiphilic aminoglycoside derivatives are promising new antibacterials active against Gram-negative bacteria such as Pseudomonas aeruginosa, including colistin resistant strains. In this study, we demonstrated that addition of cardiolipin to the culture medium delayed growth of P. aeruginosa, favored asymmetrical growth and enhanced the efficiency of a new amphiphilic aminoglycoside derivative, the 3’,6-dinonylneamine. By using membrane models mimicking P. aeruginosa plasma membrane composition (POPE:POPG:CL), we demonstrated the ability of 3’6-dinonylneamine to induce changes in the biophysical properties of membrane model lipid systems in a cardiolipin dependent manner. These changes include an increased membrane permeability associated with a reduced hydration and a decreased ability of membrane to mix and fuse as shown by monitoring calcein release, Generalized Polarization of Laurdan and fluorescence dequenching of octadecyl rhodamine B, respectively. Altogether, results shed light on how cardiolipin may be critical for improving antibacterial action of new amphiphilic aminoglycoside derivatives.

Biomembrane Permeabilization: Statistics of Individual Leakage Events Harmonize the Interpretation of Vesicle Leakage

The mode of action of membrane-active molecules, such as antimicrobial, anticancer, cell penetrating, and fusion peptides and their synthetic mimics, transfection agents, drug permeation enhancers, and biological signaling molecules (e.g., quorum sensing), involves either the general or local destabilization of the target membrane or the formation of defined, rather stable pores. Some effects aim at killing the cell, while others need to be limited in space and time to avoid serious damage. Biological tests reveal translocation of compounds and cell death but do not provide a detailed, mechanistic, and quantitative understanding of the modes of action and their molecular basis. Model membrane studies of membrane leakage have been used for decades to tackle this issue, but their interpretation in terms of biology has remained challenging and often quite limited. Here we compare two recent, powerful protocols to study model membrane leakage: the microscopic detection of dye influx into giant liposomes and time-correlated single photon counting experiments to characterize dye efflux from large unilamellar vesicles. A statistical treatment of both data sets does not only harmonize apparent discrepancies but also makes us aware of principal issues that have been confusing the interpretation of model membrane leakage data so far. Moreover, our study reveals a fundamental difference between nano- and microscale systems that needs to be taken into account when conclusions about microscale objects, such as cells, are drawn from nanoscale models.

Sterol-recognition ability and membrane-disrupting activity of Ornithogalum saponin OSW-1 and usual 3-O-glycosyl saponins

OSW-1 is a structurally unique steroidal saponin isolated from the bulbs of Ornithogalum saundersiae, and has exhibited highly potent and selective cytotoxicity in tumor cell lines. This study aimed to investigate the molecular mechanism for the membrane-permeabilizing activity of OSW-1 in comparison with those of other saponins by using various spectroscopic approaches. The membrane effects and hemolytic activity of OSW-1 were markedly enhanced in the presence of membrane cholesterol. Binding affinity measurements using fluorescent cholestatrienol and solid-state NMR spectroscopy of a 3-d-cholesterol probe suggested that OSW-1 interacts with membrane cholesterol without forming large aggregates while 3-O-glycosyl saponin, digitonin, forms cholesterol-containing aggregates. The results suggest that OSW-1/cholesterol interaction is likely to cause membrane permeabilization and pore formation without destroying the whole membrane integrity, which could partly be responsible for its highly potent cell toxicity.

Targeting Bacterial Cardiolipin Enriched Microdomains: An Antimicrobial Strategy Used by Amphiphilic Aminoglycoside Antibiotics

Some bacterial proteins involved in cell division and oxidative phosphorylation are tightly bound to cardiolipin. Cardiolipin is a non-bilayer anionic phospholipid found in bacterial inner membrane. It forms lipid microdomains located at the cell poles and division plane. Mechanisms by which microdomains are affected by membrane-acting antibiotics and the impact of these alterations on membrane properties and protein functions remain unclear. In this study, we demonstrated cardiolipin relocation and clustering as a result of exposure to a cardiolipin-acting amphiphilic aminoglycoside antibiotic, the 3′,6-dinonyl neamine. Changes in the biophysical properties of the bacterial membrane of P. aeruginosa, including decreased fluidity and increased permeability, were observed. Cardiolipin-interacting proteins and functions regulated by cardiolipin were impacted by the amphiphilic aminoglycoside as we demonstrated an inhibition of respiratory chain and changes in bacterial shape. The latter effect was characterized by the loss of bacterial rod shape through a decrease in length and increase in curvature. It resulted from the effect on MreB, a cardiolipin dependent cytoskeleton protein as well as a direct effect of 3′,6-dinonyl neamine on cardiolipin. These results shed light on how targeting cardiolipin microdomains may be of great interest for developing new antibacterial therapies.

Thiol-Triggered Release of Intraliposomal Content from Liposomes Made of Extremophile-Inspired Tetraether Lipids

Liposomal drug-delivery systems have been used for delivery of drugs to targeted tissues while reducing unwanted side effects. DOXIL, for instance, is a liposomal formulation of the anticancer agent doxorubicin (DOX) that has been used to address problems associated with nonspecific toxicity of free DOX. However, while this liposomal formulation allows for a more-stable circulation of doxorubicin in the body compared to free drug, the efficacy for cancer therapy is reduced in comparison with systemic injections of free drug. A robust liposomal system that can be triggered to release DOX in cancer cells could mitigate problems associated with reduced drug efficacy. In this work, we present a serum-stable, cholesterol-integrated tetraether lipid comprising of a cleavable disulfide bond, {GcGT(S-S)PC-CH}, that is designed to respond to the reducing environment of the cell to trigger the release intraliposomal content upon cellular uptake by cancer cells. A cell viability assay revealed that DOX- loaded liposomes composed of pure GcGT(S-S)PC-CH lipids were ∼20 times more toxic than DOXIL, with an IC₅₀ value comparable to that of free DOX. The low inherent membrane-leakage properties of GcGT(S-S)PC-CH liposomes in the presence of serum, combined with an intracellular triggered release of encapsulated cargo, represents a promising approach for developing improved drug-delivery formulations for the treatment of cancer and possibly other diseases.

Changes in membrane biophysical properties induced by the Budesonide/Hydroxypropyl-β-cyclodextrin complex

Budesonide (BUD), a poorly soluble anti-inflammatory drug, is used to treat patients suffering from asthma and COPD (Chronic Obstructive Pulmonary Disease). Hydroxypropyl-β-cyclodextrin (HPβCD), a biocompatible cyclodextrin known to interact with cholesterol, is used as a drug-solubilizing agent in pharmaceutical formulations. Budesonide administered as an inclusion complex within HPβCD (BUD:HPβCD) required a quarter of the nominal dose of the suspension formulation and significantly reduced neutrophil-induced inflammation in a COPD mouse model exceeding the effect of each molecule administered individually. This suggests the role of lipid domains enriched in cholesterol for inflammatory signaling activation. In this context, we investigated the effect of BUD:HPβCD on the biophysical properties of membrane lipids. On cellular models (A549, lung epithelial cells), BUD:HPβCD extracted cholesterol similarly to HPβCD. On large unilamellar vesicles (LUVs), by using the fluorescent probes diphenylhexatriene (DPH) and calcein, we demonstrated an increase in membrane fluidity and permeability induced by BUD:HPβCD in vesicles containing cholesterol. On giant unilamellar vesicles (GUVs) and lipid monolayers, BUD:HPβCD induced the disruption of cholesterol-enriched raft-like liquid ordered domains as well as changes in lipid packing and lipid desorption from the cholesterol monolayers, respectively. Except for membrane fluidity, all these effects were enhanced when HPβCD was complexed with budesonide as compared with HPβCD. Since cholesterol-enriched domains have been linked to membrane signaling including pathways involved in inflammation processes, we hypothesized the effects of BUD:HPβCD could be partly mediated by changes in the biophysical properties of cholesterol-enriched domains.

Nanoescapology: progress toward understanding the endosomal escape of polymeric nanoparticles

Using nanoparticles to deliver drugs to cells has the potential to revolutionize the treatment of many diseases, including HIV, cancer, and diabetes. One of the major challenges facing this field is controlling where the drug is trafficked once the nanoparticle is taken up into the cell. In particular, if drugs remain localized in an endosomal or lysosomal compartment, the therapeutic can be rendered completely ineffective. To ensure the design of more effective delivery systems we must first develop a better understanding of how nanoparticles and their cargo are trafficked inside cells. This needs to be combined with an understanding of what characteristics are required for nanoparticles to achieve endosomal escape, along with methods to detect endosomal escape effectively. This review is focused into three sections: first, an introduction to the mechanisms governing internalization and trafficking in cells, second, a discussion of methods to detect endosomal escape, and finally, recent advances in controlling endosomal escape from polymer- and lipid-based nanoparticles, with a focus on engineering materials to promote endosomal escape. WIREs Nanomed Nanobiotechnol 2017, 9:e1452. doi: 10.1002/wnan.1452 For further resources related to this article, please visit the WIREs website.

NO-Responsive vesicles as a drug delivery system

A NO-response amphiphile was successfully formed into vesicles in aqueous solution, which could encapsulate and control the release of carboxyfluorescein (CF) as a model drug in vitro and in living cells.

Applying Fluorescence Correlation Spectroscopy to Investigate Peptide-Induced Membrane Disruption

There is considerable interest in understanding the interactions of antimicrobial peptides with phospholipid membranes. Fluorescence correlation spectroscopy (FCS) is a powerful experimental technique that can be used to gain insight into these interactions. Specifically, FCS can be used to quantify leakage of fluorescent molecules of different sizes from large unilamellar lipid vesicles, thereby providing a tool for estimating the size of peptide-induced membrane disruptions. If fluorescently labeled lipids are incorporated into the membranes of the vesicles, FCS can also be used to obtain information about whether leakage occurs due to localized membrane perturbations or global membrane destabilization. Here, we outline a detailed step-by-step protocol on how to optimally implement an FCS-based leakage assay. To make the protocol easily accessible to other researchers, it has been supplemented with a number of practical tips and tricks.

Niosomal approach to brain delivery: Development, characterization and in vitro toxicological studies

The majority of active agents do not readily permeate into brain due to the presence of the blood-brain barrier and blood-cerebrospinal fluid barrier. Currently, the most innovative and promising non-invasive strategy in brain delivery is the design and preparation of nanocarriers, which can move through the brain endothelium. Niosomes can perform brain delivery, in fact polysorbates, can act as an anchor for apolipoprotein E from blood plasma. The particles mimic LDL and interact with the LDL receptor leading to the endothelial cells uptake. The efficacy of niosomes for anticancer therapeutic applications was correlated to their physicochemical and drug delivery properties. Dimensions and ζ-potential were characterized using dynamic light scattering and asymmetric flow-field fractionation system. Lipid bilayer was characterized measuring the fluidity, polarity and microviscosity by fluorescent probe spectra evaluation. Morphology and homogeneity were characterized using atomic force microscopy. Physicochemical stability and serum stability (45% v/v fetal bovine and human serum) were evaluated as a function of time using dynamic light scattering. U87-MG human glioblastoma cells were used to evaluate vesicle cytotoxicity and internalisation efficiency. From the obtained data, the systems appear useful to perform a prolonged (modified) release of biological active substances to the central nervous system.

Macrophage Activation by Poly(maleic acid-alt-2-cyclohexyl-1,3-dioxap-5-ene) Encapsulated in Polysaccharide-Coated Liposomes

An increase in the efficiency of macrophage activation has been tried by en capsulating potent polyanionic polymer immunomodulators into polysac charide-coated liposomes. For this purpose, several alternating copolymers of maleic acid (MA) and itaconic acid (IT) with 2-cyclohexyl-1,3-dioxap-5-ene (CDA), styrene (ST), and other monomers have been synthesized and frac tionated.

First, the interaction between the liposomes and polyanionic polymers was investigated. As a result, poly(maleic acid-alt-2-cyclohexyl-1,3-dioxap-5-ene) (MA-CDA) was found to be the best candidate for encapsulating in the liposome while poly(itaconic acid-alt-styrene)(IA-ST) strongly perturbed these vesicles.

Based on these results, MA-CDA was encapsulated in the mannan derivative- coated liposomes and the macrophage activation activity was evaluated from the superoxide production of the activated macrophages in vivo. Compared with the administration of free MA-CDA, the maximum in the superoxide pro duction appeared faster (2 h after injection) and the activity was significantly increased.

Quantification of intracellular payload release from polymersome nanoparticles

Polymersome nanoparticles (PMs) are attractive candidates for spatio-temporal controlled delivery of therapeutic agents. Although many studies have addressed cellular uptake of solid nanoparticles, there is very little data available on intracellular release of molecules encapsulated in membranous carriers, such as polymersomes. Here, we addressed this by developing a quantitative assay based on the hydrophilic dye, fluorescein. Fluorescein was encapsulated stably in PMs of mean diameter 85 nm, with minimal leakage after sustained dialysis. No fluorescence was detectable from fluorescein PMs, indicating quenching. Following incubation of L929 cells with fluorescein PMs, there was a gradual increase in intracellular fluorescence, indicating PM disruption and cytosolic release of fluorescein. By combining absorbance measurements with flow cytometry, we quantified the real-time intracellular release of a fluorescein at a single-cell resolution. We found that 173 ± 38 polymersomes released their payload per cell, with significant heterogeneity in uptake, despite controlled synchronisation of cell cycle. This novel method for quantification of the release of compounds from nanoparticles provides fundamental information on cellular uptake of nanoparticle-encapsulated compounds. It also illustrates the stochastic nature of population distribution in homogeneous cell populations, a factor that must be taken into account in clinical use of this technology.

Modulated cellular delivery of anti-VEGF siRNA (bevasiranib) by incorporating supramolecular assemblies of hydrophobically modified polyamidoamine dendrimer in stealth liposomes

A novel lipopolymer based system was designed and characterized for cellular delivery of anti-VEGF siRNA in SKBR-3 breast tumor cell line. Polyamidoamine (PAMAM) dendrimers of low generations (G1, G2 and G3) were incorporated into polyethylene glycol (PEG)-stabilized liposomes by following the consecutive steps: (a) synthesis of the cholesterol conjugates (40% molar ratio of cholesterol to primary amines of PAMAM), (b) incorporation of the conjugates in liposome by lipid mixing and (c) microencapsulation of the siRNA using the ethanol drop method. The cholesterol conjugates of PAMAM dendrimers (G1-Chol40%, G2-Chol40% and G3-Chol40%) formed self assembly with low CMC values (<11μg/ml). Not only did G2-Chol40% show the highest lipid mixing among the cholesterol conjugates, but also, had the lowest leakage of encapsulated carboxyfluorescein tracer. Various N(amine))/L(lipid)/P(phosphate) mole ratios were investigated for siRNA condensation by ethidium bromide dye exclusion assay. The optimum N/L/P ratio of 20:33:10 was chosen for microencapsulation of anti-VEGF siRNA by ethanol drop method, showing particle size of 130nm, zeta-potential of +4mV, siRNA loading efficiency and capacity of 96% and 13wt%, and high stability against heparin sulfate (extracellular matrix). TEM shows uniform and discrete oligo- or multi-lamellar vesicular structures. The liposome incorporating G2-Chol40% was successfully internalized into SKBR-3 cells mainly through clathrin-mediated endocytosis, which was able to escape from endosomes and showed a significantly higher sequence-specific inhibition of VEGF expression and cell growth than the respective G2-Chol40%/siRNA dendriplexes. Importantly, the cytotoxicity decreased with incorporation of G2-Chol40% in the liposomes.

MMP2-Sensitive PEG-Lipid Copolymers: A New Type of Tumor-Targeted P-Glycoprotein Inhibitor

Low tumor targetability and multidrug resistance (MDR) are two major impediments to the success of cancer treatments. Nanomaterials which possess high tumor targetability and the ability to reverse the MDR are rare. This report describes a new type of self-assembling polyethylene glycol-phosphoethanolamine-based copolymers (PEG-pp-PE) which showed both the matrix metalloproteinase 2 (MMP2)-sensitive tumor-targeted drug delivery and ability to inhibit the P-glycoprotein (P-gp)-mediated drug efflux. In this study, we synthesized a series of the homologous analogues of PEG-pp-PE copolymers and investigated the influence of their structures, including PEG lengths and peptide linkers, on the drug efflux, and identified the underlying mechanisms. We found that the whole structure (PEG-peptide-lipid) rather than any parts of the copolymers was key for the P-gp inhibition and a delicate balance between the hydrophilic and lipophilic segments of the PEG-pp-PE copolymers was needed for better modulating the P-gp-mediated drug efflux. The best copolymer, PEG2k-pp-PE, showed even higher P-gp inhibition effect than the d-α-tocopherol polyethylene glycol 1000 succinate (TPGS1k). We also found that the P-gp inhibition capability of PEG-pp-PE copolymers was highly associated with the P-gp down-regulation, the increase in the plasma membrane fluidity, and the inhibition of the P-gp ATPase activity. Besides, the excellent physicochemical properties, high drug loading, MMP2-dependent drug release, and improved drug efficacy in the MDR cancer cells suggested that the PEG-pp-PE copolymers might have great potential for building tumor-targeted drug delivery systems for treating drug-resistant cancers.

Negatively Charged Lipids as a Potential Target for New Amphiphilic Aminoglycoside Antibiotics: A BIOPHYSICAL STUDY

Bacterial membranes are highly organized, containing specific microdomains that facilitate distinct protein and lipid assemblies. Evidence suggests that cardiolipin molecules segregate into such microdomains, probably conferring a negative curvature to the inner plasma membrane during membrane fission upon cell division. 3',6-Dinonyl neamine is an amphiphilic aminoglycoside derivative active against Pseudomonas aeruginosa, including strains resistant to colistin. The mechanisms involved at the molecular level were identified using lipid models (large unilamellar vesicles, giant unilamelllar vesicles, and lipid monolayers) that mimic the inner membrane of P. aeruginosa The study demonstrated the interaction of 3',6-dinonyl neamine with cardiolipin and phosphatidylglycerol, two negatively charged lipids from inner bacterial membranes. This interaction induced membrane permeabilization and depolarization. Lateral segregation of cardiolipin and membrane hemifusion would be critical for explaining the effects induced on lipid membranes by amphiphilic aminoglycoside antibiotics. The findings contribute to an improved understanding of how amphiphilic aminoglycoside antibiotics that bind to negatively charged lipids like cardiolipin could be promising antibacterial compounds.