Preparation of unilamellar liposomes of intermediate size (0.1-0.2 mumol) by a combination of reverse phase evaporation and extrusion through polycarbonate membranes

Rational formulation and industrial manufacturing of lipid-based complex injectables: Landmarks and trends

Lipid-based complex injectables are renowned for their effectiveness in delivering drugs, with many approved products. While significant strides have been made in formulating nanosystems for small molecular weight drugs, a pivotal breakthrough emerged with the recognition of lipid nanoparticles as a promising platform for delivering nucleic acids. This finding has paved the way for tackling long-standing challenges in molecular and delivery aspects (e.g., mRNA stability, intracellular delivery) that have impeded the clinical translation of gene therapy, especially in the realm of immunotherapy. Nonetheless, developing and implementing new lipid-based delivery systems pose significant challenges, as industrial manufacturing of these formulations often involves complex, multi-batch processes, giving rise to issues related to scalability, stability, sterility, and regulatory compliance. To overcome these obstacles, embracing the principles of quality-by-design (QbD) is imperative. Furthermore, adopting cutting-edge manufacturing and process analytical tools (PAT) that facilitate the transition from batch to continuous production is essential. Herein, the key milestones and insights derived from the development of currently approved lipid- nanosystems will be explored. Additionally, a comprehensive and critical overview of the latest technologies and regulatory guidelines that underpin the creation of more efficient, scalable, and flexible manufacturing processes for complex lipid-based nanoformulations will be provided.

Enhancing oral bioavailability of insulin through bilosomes: Implication of charge and chain length on apical sodium-dependent bile acid transporter (ASBT) uptake

This study investigates the impact of charge and chain length of bile salts in the bilosomes on the oral bioavailability of insulin (IN) by examining their uptake via the apical sodium-dependent bile acid transporter (ASBT). Deoxycholic acid bile salt was conjugated with different amino acids to create conjugates with varying charge and chain length, which were then embedded in liposomes. The resulting bilosomes had a particle size <400 nm, a PDI of 0.121 ± 0.03, and an entrapment efficiency of ∼70 %, while maintaining the chemical and conformational integrity of the loaded IN. Bilosomes also provided superior protection in biological fluids without compromising their biophysical attributes. Quantitative studies using the Caco-2 cell line demonstrated that anionic bilosomes were taken up more efficiently through ASBT than cationic bilosomes with 4- and 1.3-fold increase, respectively. Ex-vivo permeability studies corroborated these findings. In-vivo efficacy studies revealed a 1.6-fold increase in the AUC of IN with bilosomes compared to subcutaneous IN. The developed bilosomes were able to reduce blood glucose levels by ∼65 % at 6 h, with a cumulative hypoglycemic value of 35 % and a BAR of ∼30 %. These results suggest that ASBT can be a suitable target for improving the oral bioavailability of bilosomes containing IN.

DNA curtains to visualize chromatin interactions

Recent advances in single molecule imaging have allowed the evolution of biochemical techniques that directly visualize protein-DNA interactions in real-time. These techniques rely on diffraction limited total internal reflection microscopy (TIRFM), and have significantly improved our understanding of RNA transcription, DNA replication, homologous recombination, and general DNA repair in the context of chromatin. Here we described a general single molecule TIRFM technique called DNA curtains to directly visualize how enzymes function on chromatinized DNA. The goal of this manuscript is to introduce the reader to methods to express and reconstitute nucleosomes on long stretches of DNA, and to directly visualize this process using DNA curtains with TIRFM.

Skin drug delivery using lipid vesicles: A starting guideline for their development

Lipid vesicles can provide a cost-effective enhancement of skin drug absorption when vesicle production process is optimised. It is an important challenge to design the ideal vesicle, since their properties and features are related, as changes in one affect the others. Here, we review the main components, preparation and characterization methods commonly used, and the key properties that lead to highly efficient vesicles for transdermal drug delivery purposes. We stand by size, deformability degree and drug loading, as the most important vesicle features that determine the further transdermal drug absorption. The interest in this technology is increasing, as demonstrated by the exponential growth of publications on the topic. Although long-term preservation and scalability issues have limited the commercialization of lipid vesicle products, freeze-drying and modern escalation methods overcome these difficulties, thus predicting a higher use of these technologies in the market and clinical practice.

The Importance of Lipid Conjugation on Anti-Fusion Peptides against Nipah Virus

Nipah virus (NiV) is a recently emerging zoonotic virus that belongs to the Paramyxoviridae family and the Henipavirus genus. It causes a range of conditions, from asymptomatic infection to acute respiratory illness and fatal encephalitis. The high mortality rate of 40 to 90% ranks these viruses among the deadliest viruses known to infect humans. Currently, there is no antiviral drug available for Nipah virus disease and treatment is only supportive. Thus, there is an urgent demand for efficient antiviral therapies. NiV F protein, which catalyzes fusion between the viral and host membranes, is a potential target for antiviral drugs, as it is a key protein in the initial stages of infection. Fusion inhibitor peptides derived from the HRC-domain of the F protein are known to bind to their complementary domain in the protein’s transient intermediate state, preventing the formation of a six-helix bundle (6HB) thought to be responsible for driving the fusion of the viral and cell membranes. Here, we evaluated the biophysical and structural properties of four different C-terminal lipid-tagged peptides. Different compositions of the lipid tags were tested to search for properties that might promote efficacy and broad-spectrum activity. Fluorescence spectroscopy was used to study the interaction of the peptides with biomembrane model systems and human blood cells. In order to understand the structural properties of the peptides, circular dichroism measurements and molecular dynamics simulations were performed. Our results indicate a peptide preference for cholesterol-enriched membranes and a lipid conjugation-driven stabilization of the peptide α-helical secondary structure. This work may contribute for the development of highly effective viral fusion against NiV inhibitors.

The pH-sensitive action of cholesterol-conjugated peptide inhibitors of influenza virus

Influenza viruses are major human pathogens, responsible for respiratory diseases affecting millions of people worldwide, with high morbidity and significant mortality. Infections by influenza can be controlled by vaccines and antiviral drugs. However, this virus is constantly under mutations, limiting the effectiveness of these clinical antiviral strategies. It is therefore urgent to develop new ones. Influenza hemagglutinin (HA) is involved in receptor binding and promotes the pH-dependent fusion of viral and cell endocytic membranes. HA-targeted peptides may emerge as a novel antiviral option to block this viral entry step. In this study, we evaluated three HA-derived (lipo)peptides using fluorescence spectroscopy. Peptide membrane interaction assays were performed at neutral and acidic pH to better resemble the natural conditions in which influenza fusion occurs. We found that peptide affinity towards membranes decreases upon the acidification of the environment. Therefore, the released peptides would be able to bind their complementary domain and interfere with the six-helix bundle formation necessary for viral fusion, and thus for the infection of the target cell. Our results provide new insight into molecular interactions between HA-derived peptides and cell membranes, which may contribute to the development of new influenza virus inhibitors.

Highly sensitive interleukin 6 detection by employing commercially ready liposomes in an LFA format

Recent years have confirmed the ubiquitous applicability of lateral flow assays (LFA) in point-of-care testing (POCT). To make this technology available for low abundance analytes, strategies towards lower limits of detections (LOD), while maintaining the LFA’s ease of use, are still being sought. Here, we demonstrate how liposomes can significantly improve the LOD of traditional gold nanoparticle (AuNP)–based assays while fully supporting a ready-to-use system for commercial application. We fine-tuned liposomes towards photometric and fluorescence performance on the synthesis level and applied them in an established interleukin 6 (IL-6) immunoassay normally using commercial AuNP labels. IL-6’s low abundance (< 10 pg mL⁻¹) and increasing relevance as prognostic marker for infections make it an ideal model analyte. It was found that liposomes with a high encapsulant load (150 mmol L⁻¹ sulforhodamine B (SRB)) easily outperform AuNPs in photometric LFAs. Specifically, liposomes with 350 nm in diameter yield a lower LOD even in complex matrices such as human serum below the clinically relevant range (7 pg mL⁻¹) beating AuNP by over an order of magnitude (81 pg mL⁻¹). When dehydrated on the strip, liposomes maintained their signal performance for over a year even when stored at ambient temperature and indicate extraordinary stability of up to 8 years when stored as liquid. Whereas no LOD improvement was obtained by exploiting the liposomes’ fluorescence, an extraordinary gain in signal intensity was achieved upon lysis which is a promising feature for high-resolution and low-cost detection devices. Minimizing the procedural steps by inherently fluorescent liposomes, however, is not feasible. Finally, liposomes are ready for commercial applications as they are easy to mass-produce and can simply be substituted for the ubiquitously used AuNPs in the POCT market.

Red blood cells: The metamorphosis of a neglected carrier into the natural mothership for artificial nanocarriers

Drug delivery research pursues many types of carriers including proteins and other macromolecules, natural and synthetic polymeric structures, nanocarriers of diverse compositions and cells. In particular, liposomes and lipid nanoparticles represent arguably the most advanced and popular human-made nanocarriers, already in multiple clinical applications. On the other hand, red blood cells (RBCs) represent attractive natural carriers for the vascular route, featuring at least two distinct compartments for loading pharmacological cargoes, namely inner space enclosed by the plasma membrane and the outer surface of this membrane. Historically, studies of liposomal drug delivery systems (DDS) astronomically outnumbered and surpassed the RBC-based DDS. Nevertheless, these two types of carriers have different profile of advantages and disadvantages. Recent studies showed that RBC-based drug carriers indeed may feature unique pharmacokinetic and biodistribution characteristics favorably changing benefit/risk ratio of some cargo agents. Furthermore, RBC carriage cardinally alters behavior and effect of nanocarriers in the bloodstream, so called RBC hitchhiking (RBC-HH). This article represents an attempt for the comparative analysis of liposomal vs RBC drug delivery, culminating with design of hybrid DDSs enabling mutual collaborative advantages such as RBC-HH and camouflaging nanoparticles by RBC membrane. Finally, we discuss the key current challenges faced by these and other RBC-based DDSs including the issue of potential unintended and adverse effect and contingency measures to ameliorate this and other concerns.

Liposomes with cyclodextrin channels and polyethyleneimine (PEI) improves cytoplasmic vaccine delivery and induces anti-cancer immune activity in mice

Cancer vaccines have been developed as an additional method of treatment in the fight against cancer. However, an important barrier to an effective vaccine is the inefficient presentation of exogenous antigen by dendritic cells to cytotoxic CD8 T cells. In this study, DPPC liposomes were modified with channels and loaded with polyethyleneimine (PEI) and 5,6-dimethylxanthenone-4-acetic acid (DMXAA) to produce a vaccine carrier. The liposomes were designed to be pH responsive to facilitate delivery of antigens directly to the cytoplasm of antigen presenting cells, bypassing the cross-presentation pathway and improving cellular immune responses. The lysis of liposomes in acidic cell-free conditions was measured using a validated dynamic light scattering assay in order to gain an insight into the mechanism of PEI-mediated lysis. Dendritic cell stimulation and T cell proliferation was investigated in vitro and the potential of this formulation to stimulate a therapeutic anti-cancer immune response was examined in a murine melanoma model. The modified formulation stimulated T cell activation in vitro and induced a small but significant increase in survival in immunized mice. Overall, liposomes modified with PEI and channels successfully delivered antigen to the cytoplasm of dendritic cells, which subsequently led to the development of an appropriate immune response.

Liposome interaction with macrophages and foam cells for atherosclerosis treatment: effects of size, surface charge and lipid composition

Liposomes are potential drug carriers for atherosclerosis therapy due to low immunogenicity and ease of surface modifications that allow them to have prolonged circulation half-life and specifically target atherosclerotic sites to increase uptake efficiency. However, the effects of their size, charge, and lipid compositions on macrophage and foam cell behaviour are not fully understood. In this study, liposomes of different sizes (60 nm, 100 nm and 180 nm), charges (-40 mV, -20 mV, neutral, +15 mV and +30 mV) and lipid compositions (1,2-dipalmitoyl-sn-glycero-3-phosphatidylcholine, 1,2-dipalmitoyl-sn-glycero-3-phosphocholine, L-a-phosphatidylcholine, and egg sphingomyelin) were synthesized, characterized and exposed to macrophages and foam cells. Compared to 100 nm neutral 1,2-dipalmitoyl-sn-glycero-3-phosphatidylcholine (DPPC) liposomes, flow cytometry and confocal imaging indicated that cationic liposomes and 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DSPC) liposomes were internalized more by both macrophages and foam cells. Through endocytosis inhibition, phagocytosis and clathrin-mediated endocytosis were identified as the dominant mechanisms of uptake. Anionic and DSPC liposomes induced more cholesterol efflux capacity in foam cells. These results provide a guide for the optimal size, charge, and lipid composition of liposomes as drug carriers for atherosclerosis treatment.

Liposome composition in drug delivery design, synthesis, characterization, and clinical application

Liposomal drug delivery represents a highly adaptable therapeutic platform for treating a wide range of diseases. Natural and synthetic lipids, as well as surfactants, are commonly utilized in the synthesis of liposomal drug delivery vehicles. The molecular diversity in the composition of liposomes enables drug delivery with unique physiological functions, such as pH response, prolonged blood circulation, and reduced systemic toxicity. Herein, we discuss the impact of composition on liposome synthesis, function, and clinical utility.

Sorting sub-150-nm liposomes of distinct sizes by DNA-brick-assisted centrifugation

In cells, myriad membrane-interacting proteins generate and maintain curved membrane domains with radii of curvature around or below 50 nm. To understand how such highly curved membranes modulate specific protein functions, and vice versa, it is imperative to use small liposomes with precisely defined attributes as model membranes. Here, we report a versatile and scalable sorting technique that uses cholesterol-modified DNA 'nanobricks' to differentiate hetero-sized liposomes by their buoyant densities. This method separates milligrams of liposomes, regardless of their origins and chemical compositions, into six to eight homogeneous populations with mean diameters of 30-130 nm. We show that these uniform, leak-resistant liposomes serve as ideal substrates to study, with an unprecedented resolution, how membrane curvature influences peripheral (ATG3) and integral (SNARE) membrane protein activities. Compared with conventional methods, our sorting technique represents a streamlined process to achieve superior liposome size uniformity, which benefits research in membrane biology and the development of liposomal drug-delivery systems.

Antileishmanial activity of fullerol and its liposomal formulation in experimental models of visceral leishmaniasis

Visceral leishmaniasis (VL) is a systemic parasitic disease that leads to high rates of morbidity and mortality in humans worldwide. There is a great need to develop new drugs and novel strategies to make chemotherapy for this disease more efficacious and well tolerated. Recent reports on the immunomodulatory effects and the low toxicity of the spherical carbon nanostructure fullerol led us to investigate in vitro and in vivo antileishmanial activity in free and encapsulated forms in liposomes. When assayed against intramacrophagic Leishmania amastigotes, fullerol showed a dose-dependent reduction of the infection index with IC50 of 0.042 mg/mL. When given daily by i.p. route for 20 days (0.05 mg/kg/d) in a murine model of acute VL, fullerol promoted significant reduction in the liver parasite load. To improve the delivery of fullerol to the infection sites, liposomal formulations were prepared by the dehydration-rehydration method. When evaluated in the acute VL model, liposomal fullerol (Lip-Ful) formulations given i.p. at 0.05 and 0.2 mg/kg with 4-days intervals were more effective than the free form, with significant parasite reductions in both liver and spleen. Lip-Ful at 0.2 mg/kg promoted complete parasite elimination in the liver. The antileishmanial activity of Lip-Ful was further confirmed in a chronic model of VL. Lip-Ful was also found to induce secretion of pro-inflammatory TNF-α, IFN-γ and IL-1β cytokines. In conclusion, this work reports for the first time the antileishmanial activity of fullerol and introduces an innovative approach for treatment of VL based on the association of this nanostructure with liposomes.

One-step microfluidics production of enzyme-loaded liposomes for the treatment of inflammatory diseases

The biopharmaceuticals market is constantly growing. Despite their advantages over the conventional drugs, biopharmaceuticals have short biological half-lifes, which can be increased using liposomes. However, the common bulk methods to produce biopharmaceuticals-loaded liposomes result in lost of encapsulation efficiency (E.E.), resulting in an expensive process. Herein, the encapsulation of a therapeutic enzyme in liposomes is proposed, using a glass-capillary microfluidic technique. Cu,Zn- Superoxide dismutase (SOD) is successfully encapsulated into liposomes (SOD@Liposomes). SOD@Liposomes with a mean size of 135 ± 41 nm, a polydispersity index of 0.13 ± 0.01, an E.E. of 59 ± 6 % and an enzyme activity of 82 ± 3 % are obtained. in vivo experiments show, through an ear edema model, that SOD@Liposomes administered by the intravenous route enable an edema inhibition of 65 % ± 8 %, over the 20 % ± 13 % of SOD in its free form. The histopathological analyses show a higher inflammatory cell accumulation on the ear treated with SOD in its free form, than treated with SOD@Liposomes. Overall, this work highlights the potential of microfluidics for the production of enzyme-loaded liposomes with high encapsulation efficiency, with the intrinsic advantages of the low time-consuming and easily upscaling microfluidic assembly method.

Micelle-in-Liposomes for Sustained Delivery of Anticancer Agents That Promote Potent TRAIL-Induced Cancer Cell Apoptosis

Tumor necrosis factor (TNF)-related apoptosis-inducing ligand (TRAIL) induces cancer cell-specific apoptosis and has garnered intense interest as a promising agent for cancer treatment. However, the development of TRAIL has been hampered in part because most human cancer cells are resistant to TRAIL. A few small molecules including natural compounds such as piperlongumine (PL) have been reported to sensitize cancer cells to TRAIL. We prepared a novel type of nanomaterial, micelle-in-liposomes (MILs) for solubilization and delivery of PL. PL-loaded MILs were used to sensitize cancer cells to TRAIL. As visualized by cryo-TEM, micelles were successfully loaded inside the aqueous core of liposomes. The MILs increased the water solubility of PL by ~20 fold. A sustained PL release from MILs in physiologically relevant buffer over 7 days was achieved, indicating that the liposomes prevented premature drug release from the micelles in the MILs. Also demonstrated is a potent synergistic apoptotic effect in cancer cells by PL MILs in conjunction with liposomal TRAIL. MILs provide a new formulation and delivery vehicle for hydrophobic anticancer agents, which can be used alone or in combination with TRAIL to promote cancer cell death.

Liposomes: Advancements and innovation in the manufacturing process

Liposomes are well recognised as effective drug delivery systems, with a range of products approved, including follow on generic products. Current manufacturing processes used to produce liposomes are generally complex multi-batch processes. Furthermore, liposome preparation processes adopted in the laboratory setting do not offer easy translation to large scale production, which may delay the development and adoption of new liposomal systems. To promote advancement and innovation in liposome manufacturing processes, this review considers the range of manufacturing processes available for liposomes, from laboratory scale and scale up, through to large-scale manufacture and evaluates their advantages and limitations. The regulatory considerations associated with the manufacture of liposomes is also discussed. New innovations that support leaner scalable technologies for liposome fabrication are outlined including self-assembling liposome systems and microfluidic production. The critical process attributes that impact on the liposome product attributes are outlined to support potential wider adoption of these innovations.

All-in-one microfluidic assembly of insulin-loaded pH-responsive nano-in-microparticles for oral insulin delivery

Here, a continuous two-step glass-capillary microfluidic technique to produce a multistage oral insulin delivery system is reported. This system represents a promising alternative for the common protein/peptide-loaded liposome formulations.

The Main (Glyco) Phospholipid (MPL) of Thermoplasma acidophilum

The main phospholipid (MPL) of Thermoplasma acidophilum DSM 1728 was isolated, purified and physico-chemically characterized by differential scanning calorimetry (DSC)/differential thermal analysis (DTA) for its thermotropic behavior, alone and in mixtures with other lipids, cholesterol, hydrophobic peptides and pore-forming ionophores. Model membranes from MPL were investigated; black lipid membrane, Langmuir-Blodgett monolayer, and liposomes. Laboratory results were compared to computer simulation. MPL forms stable and resistant liposomes with highly proton-impermeable membrane and mixes at certain degree with common bilayer-forming lipids. Monomeric bacteriorhodopsin and ATP synthase from Micrococcus luteus were co-reconstituted and light-driven ATP synthesis measured. This review reports about almost four decades of research on Thermoplasma membrane and its MPL as well as transfer of this research to Thermoplasma species recently isolated from Indonesian volcanoes.

Topological analysis of the gp41 MPER on lipid bilayers relevant to the metastable HIV-1 envelope prefusion state

The membrane proximal external region (MPER) of HIV-1 envelope glycoprotein (gp) 41 is an attractive vaccine target for elicitation of broadly neutralizing antibodies (bNAbs) by vaccination. However, current details regarding the quaternary structural organization of the MPER within the native prefusion trimer [(gp120/41)₃] are elusive and even contradictory, hindering rational MPER immunogen design. To better understand the structural topology of the MPER on the lipid bilayer, the adjacent transmembrane domain (TMD) was appended (MPER-TMD) and studied. Membrane insertion of the MPER-TMD was sensitive both to the TMD sequence and cytoplasmic residues. Antigen binding of MPER-specific bNAbs, in particular 10E8 and DH511.2_K3, was significantly impacted by the presence of the TMD. Furthermore, MPER-TMD assembly into 10-nm diameter nanodiscs revealed a heterogeneous membrane array comprised largely of monomers and dimers, as enumerated by bNAb Fab binding using single-particle electron microscopy analysis, arguing against preferential trimeric association of native MPER and TMD protein segments. Moreover, introduction of isoleucine mutations in the C-terminal heptad repeat to induce an extended MPER α-helical bundle structure yielded an antigenicity profile of cell surface-arrayed Env variants inconsistent with that found in the native prefusion state. In line with these observations, electron paramagnetic resonance analysis suggested that 10E8 inhibits viral membrane fusion by lifting the MPER N-terminal region out of the viral membrane, mandating the exposure of residues that would be occluded by MPER trimerization. Collectively, our data suggest that the MPER is not a stable trimer, but rather a dynamic segment adapted for structural changes accompanying fusion.

Formulation Strategies for Folate-Targeted Liposomes and Their Biomedical Applications

The folate receptor (FR) is a tumor-associated antigen that can bind with folic acid (FA) and its conjugates with high affinity and ingests the bound molecules inside the cell via the endocytic mechanism. A wide variety of payloads can be delivered to FR-overexpressed cells using folate as the ligand, ranging from small drug molecules to large DNA-containing macromolecules. A broad range of folate attached liposomes have been proven to be highly effective as the targeted delivery system. For the rational design of folate-targeted liposomes, an intense conceptual understanding combining chemical and biomedical points of view is necessary because of the interdisciplinary nature of the field. The fabrication of the folate-conjugated liposomes basically involves the attachment of FA with phospholipids, cholesterol or peptides before liposomal formulation. The present review aims to provide detailed information about the design and fabrication of folate-conjugated liposomes using FA attached uncleavable/cleavable phospholipids, cholesterol or peptides. Advances in the area of folate-targeted liposomes and their biomedical applications have also been discussed.

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

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

Combining 25-Hydroxycholesterol with an HIV Fusion Inhibitor Peptide: Interaction with Biomembrane Model Systems and Human Blood Cells

The fusion between the viral and the target cell membrane is a crucial step in the life cycle of enveloped viruses. The blocking of this process is a well-known therapeutic approach that led to the development of the fusion inhibitor peptide enfuvirtide, clinically used against human immunodeficiency virus (HIV) type 1. Despite this significant advance on viral treatment, the appearance of resistance has limited its clinical use. Such a limitation has led to the development of other fusion inhibitor peptides, such as C34, that present the same structural domain as enfuvirtide (heptad repeat sequence) but have different functional domains (pocket-binding domain in the case of C34 and lipid-binding domain in the case of enfuvirtide). Recently, the antiviral properties of 25-hydroxycholesterol were demonstrated, which boosted the interest in this oxysterol. The combination of two distinct antiviral molecules, C34 and 25-hydroxycholesterol, may help to suppress the emergence of resistant viruses. In this work, we characterized the interaction of the C34-25-hydroxycholesterol conjugate with biomembrane model systems and human blood cells. Lipid vesicles and monolayers with defined lipid compositions were used as biomembrane model systems. The conjugate interacts preferentially with membranes rich in sphingomyelin (a lipid enriched in lipid rafts) and presents a poor partition to membranes composed solely of phosphatidylcholine and cholesterol. We hypothesize that cholesterol causes a repulsive effect that is overcome in the presence of sphingomyelin. Importantly, the peptide shows a preference for human peripheral blood mononuclear cells relative to erythrocytes, which shows its potential to target CD4⁺ cells. Antiviral activity results against different wild-type and drug-resistant HIV strains further demonstrated the potential of C34-HC as a good candidate for future studies.

Intrinsic Membrane Permeability to Small Molecules

Spontaneous solute and solvent permeation through membranes is of vital importance to human life, be it gas exchange in red blood cells, metabolite excretion, drug/toxin uptake, or water homeostasis. Knowledge of the underlying molecular mechanisms is the sine qua non of every functional assignment to membrane transporters. The basis of our current solubility diffusion model was laid by Meyer and Overton. It correlates the solubility of a substance in an organic phase with its membrane permeability. Since then, a wide range of studies challenging this rule have appeared. Commonly, the discrepancies have their origin in ill-used measurement approaches, as we demonstrate on the example of membrane CO₂ transport. On the basis of the insight that scanning electrochemical microscopy offered into solute concentration distributions in immediate membrane vicinity of planar membranes, we analyzed the interplay between chemical reactions and diffusion for solvent transport, weak acid permeation, and enzymatic reactions adjacent to membranes. We conclude that buffer reactions must also be considered in spectroscopic investigations of weak acid transport in vesicular suspensions. The evaluation of energetic contributions to membrane translocation of charged species demonstrates the compatibility of the resulting membrane current with the solubility diffusion model. A local partition coefficient that depends on membrane penetration depth governs spontaneous membrane translocation of both charged and uncharged molecules. It is determined not only by the solubility in an organic phase but also by other factors like cholesterol concentration and intrinsic electric membrane potentials.

The T Cell Antigen Receptor α Transmembrane Domain Coordinates Triggering through Regulation of Bilayer Immersion and CD3 Subunit Associations

Initial molecular details of cellular activation following αβT cell antigen receptor (TCR) ligation by peptide-major histocompatibility complexes (pMHC) remain unexplored. We determined the nuclear magnetic resonance (NMR) structure of the TCRα subunit transmembrane (TM) domain revealing a bipartite helix whose segmentation fosters dynamic movement. Positively charged TM residues Arg251 and Lys256 project from opposite faces of the helix, with Lys256 controlling immersion depth. Their modification caused stepwise reduction in TCR associations with CD3ζζ homodimers and CD3εγ plus CD3εδ heterodimers, respectively, leading to an activated transcriptome. Optical tweezers revealed that Arg251 and Lys256 mutations altered αβTCR-pMHC bond lifetimes, while mutations within interacting TCRα connecting peptide and CD3δ CxxC motif juxtamembrane elements selectively attenuated signal transduction. Our findings suggest that mechanical forces applied during pMHC ligation initiate T cell activation via a dissociative mechanism, shifting disposition of those basic sidechains to rearrange TCR complex membrane topology and weaken TCRαβ and CD3 associations.

Kinetically Stable Triglyceride-Based Nanodroplets and Their Interactions with Lipid-Specific Proteins

Understanding of the interactions between proteins and natural and artificially prepared lipid membrane surfaces and embedded nonpolar cores is important in studies of physiological processes and their pathologies and is applicable to nanotechnologies. In particular, rapidly growing interest in cellular droplets defines the need for simplified biomimetic lipid model systems to overcome in vivo complexity and variability. We present a protocol for the preparation of kinetically stable nanoemulsions with nanodroplets composed of sphingomyelin (SM) and cholesterol (Chol), as amphiphilic surfactants, and trioleoylglycerol (TOG), at various molar ratios. To prepare stable SM/Chol-coated monodisperse lipid nanodroplets, we modified a reverse phase evaporation method and combined it with ultrasonication. Lipid composition, ζ-potential, gyration and hydrodynamic radius, shape, and temporal stability of the lipid nanodroplets were characterized and compared to extruded SM/Chol large unilamellar vesicles. Lipid nanodroplets and large unilamellar vesicles with theoretical SM/Chol/TOG molar ratios of 1/1/4.7 and 4/1/11.7 were further investigated for the orientational order of their interfacial water molecules using a second harmonic scattering technique, and for interactions with the SM-binding and Chol-binding pore-forming toxins equinatoxin II and perfringolysin O, respectively. The surface characteristics (ζ-potential, orientational order of interfacial water molecules) and binding of these proteins to the nanodroplet SM/Chol monolayers were similar to those for the SM/Chol bilayers of the large unilamellar vesicles and SM/Chol Langmuir monolayers, in terms of their surface structures. We propose that such SM/Chol/TOG nanoparticles with the required lipid compositions can serve as experimental models for monolayer membrane to provide a system that imitates the natural lipid droplets.

Cholesterol and phosphatidylethanolamine lipids exert opposite effects on membrane modulations caused by the M2 amphipathic helix

Membrane curvature remodeling induced by amphipathic helices (AHs) is essential in many biological processes. Here we studied a model amphipathic peptide, M2AH, derived from influenza A M2. We are interested in how M2AH may promote membrane curvature by altering membrane physical properties. We used atomic force microscopy (AFM) to examine changes in membrane topographic and mechanical properties. We used electron paramagnetic resonance (EPR) spectroscopy to explore changes in lipid chain mobility and chain orientational order. We found that M2AH perturbed lipid bilayers by generating nanoscale pits. The structural data are consistent with lateral expansion of lipid chain packing, resulting in a mechanically weaker bilayer. Our EPR spectroscopy showed that M2AH reduced lipid chain mobility and had a minimal effect on lipid chain orientational order. The EPR data are consistent with the surface-bound state of M2AH that acts as a chain mobility inhibitor. By comparing results from different lipid bilayers, we found that cholesterol enhanced the activity of M2AH in inducing bilayer pits and altering lipid chain mobility. The results were explained by considering specific M2AH-cholesterol recognition and/or cholesterol-induced expansion of interlipid distance. Both AFM and EPR experiments revealed a modest effect of anionic lipids. This highlights that membrane interaction of M2AH is mainly driven by hydrophobic forces. Lastly, we found that phosphatidylethanolamine (PE) lipids inhibited the activity of M2AH. We explained our data by considering interlipid hydrogen-bonding that can stabilize bilayer organization. Our results of lipid-dependent membrane modulations are likely relevant to M2AH-induced membrane restructuring.

Nanomaterial Preparation by Extrusion through Nanoporous Membranes

Template synthesis represents an important class of nanofabrication methods. Herein, recent advances in nanomaterial preparation by extrusion through nanoporous membranes that preserve the template membrane without sacrificing it, which is termed as "non-sacrificing template synthesis," are reviewed. First, the types of nanoporous membranes used in nanoporous membrane extrusion applications are introduced. Next, four common nanoporous membrane extrusion strategies: vesicle extrusion, membrane emulsification, precipitation extrusion, and biological membrane extrusion, are examined. These methods have been utilized to prepare a wide range of nanomaterials, including liposomes, emulsions, nanoparticles, nanofibers, and nanotubes. The principle and historical context of each specific technology are discussed, presenting prominent examples and evaluating their positive and negative features. Finally, the current challenges and future opportunities of nanoporous membrane extrusion methods are discussed.

Selective Membrane Disruption Mechanism of an Antibacterial γ-AApeptide Defined by EPR Spectroscopy

γ-AApeptides are a new class of antibacterial peptidomimetics that are not prone to antibiotic resistance and are highly resistant to protease degradation. It is not clear how γ-AApeptides interact with bacterial membranes and alter lipid assembly, but such information is essential to understanding their antimicrobial activities and guiding future design of more potent and specific antimicrobial agents. Using electron paramagnetic resonance techniques, we characterized the membrane interaction and destabilizing mechanism of a lipo-cyclic-γ-AApeptide (AA1), which has broad-spectrum antibacterial activities. The analyses revealed that AA1 binding increases the membrane permeability of POPC/POPG liposomes, which mimic negatively charged bacterial membranes. AA1 binding also inhibits membrane fluidity and reduces solvent accessibility around the lipid headgroup region. Moreover, AA1 interacts strongly with POPC/POPG liposomes, inducing significant lipid lateral-ordering and membrane thinning. In contrast, minimal membrane property changes were observed upon AA1 binding for liposomes mimicking mammalian cell membranes, which consist of neutral lipids and cholesterol. Our findings suggest that AA1 interacts and disrupts bacterial membranes through a carpet-like mechanism. The results showed that the intrinsic features of γ-AApeptides are important for their ability to disrupt bacterial membranes selectively, the implications of which extend to developing new antibacterial biomaterials.

Mechanisms of Vesicular Stomatitis Virus Inactivation by Protoporphyrin IX, Zinc-Protoporphyrin IX, and Mesoporphyrin IX

Virus resistance to antiviral therapies is an increasing concern that makes the development of broad-spectrum antiviral drugs urgent. Targeting of the viral envelope, a component shared by a large number of viruses, emerges as a promising strategy to overcome this problem. Natural and synthetic porphyrins are good candidates for antiviral development due to their relative hydrophobicity and pro-oxidant character. In the present work, we characterized the antiviral activities of protoprophyrin IX (PPIX), Zn-protoporphyrin IX (ZnPPIX), and mesoporphyrin IX (MPIX) against vesicular stomatitis virus (VSV) and evaluated the mechanisms involved in this activity. Treatment of VSV with PPIX, ZnPPIX, and MPIX promoted dose-dependent virus inactivation, which was potentiated by porphyrin photoactivation. All three porphyrins inserted into lipid vesicles and disturbed the viral membrane organization. In addition, the porphyrins also affected viral proteins, inducing VSV glycoprotein cross-linking, which was enhanced by porphyrin photoactivation. Virus incubation with sodium azide and α-tocopherol partially protected VSV from inactivation by porphyrins, suggesting that singlet oxygen (¹O₂) was the main reactive oxygen species produced by photoactivation of these molecules. Furthermore, ¹O₂ was detected by 9,10-dimethylanthracene oxidation in photoactivated porphyrin samples, reinforcing this hypothesis. These results reveal the potential therapeutic application of PPIX, ZnPPIX, and MPIX as good models for broad antiviral drug design.

Broad spectrum antiviral activity for paramyxoviruses is modulated by biophysical properties of fusion inhibitory peptides

Human paramyxoviruses include global causes of lower respiratory disease like the parainfluenza viruses, as well as agents of lethal encephalitis like Nipah virus. Infection is initiated by viral glycoprotein-mediated fusion between viral and host cell membranes. Paramyxovirus viral fusion proteins (F) insert into the target cell membrane, and form a transient intermediate that pulls the viral and cell membranes together as two heptad-repeat regions refold to form a six-helix bundle structure that can be specifically targeted by fusion-inhibitory peptides. Antiviral potency can be improved by sequence modification and lipid conjugation, and by adding linkers between the protein and lipid components. We exploit the uniquely broad spectrum antiviral activity of a parainfluenza F-derived peptide sequence that inhibits both parainfluenza and Nipah viruses, to investigate the influence of peptide orientation and intervening linker length on the peptides' interaction with transitional states of F, solubility, membrane insertion kinetics, and protease sensitivity. We assessed the impact of these features on biodistribution and antiviral efficacy in vitro and in vivo. The engineering approach based on biophysical parameters resulted in a peptide that is a highly effective inhibitor of both paramyxoviruses and a set of criteria to be used for engineering broad spectrum antivirals for emerging paramyxoviruses.

Liposome-Enhanced Lateral-Flow Assays for Clinical Analyses

Clinical and environmental analyses frequently necessitate rapid, simple, and inexpensive point-of-care or field tests. These semiquantitative tests may be later followed up by confirmatory laboratory-based assays, but provide an initial scenario assessment important for resource mobilization and threat confinement. Lateral-flow assays (LFAs) and dip-stick assays, which are typically antibody-based and yield a visually detectable signal, provide an assay format suiting these applications extremely well. Signal generation is commonly obtained through the use of colloidal gold or latex beads, which yield a colored band either directly proportional or inversely proportional to the concentration of the analyte of interest. Here, dye-encapsulating liposomes as a highly visible alternative are discussed. The semiquantitative LFA biosensor described in this chapter relies on a sandwich immunoassay for the detection of myoglobin in whole blood. After an acute myocardial infarction (AMI) event, several cardiac markers are released into the blood, the most common of which are troponin, creatine kinase MB, C-reactive protein, and myoglobin. Due to its early release, myoglobin has value as an indicator of a recent heart attack amongst conditions which present with similar symptoms and its lack of elevation can effectively rule out a heart attack (Brogan et al., Ann Emerg Med 24:665-671, 1994). The assay described within relies on sandwich complex formation between a membrane immobilized capture monoclonal antibody against myoglobin, a detector biotinylated monoclonal antibody against a different epitope on myoglobin, and streptavidin-conjugated visible dye (sulforhodamine B)-encapsulating liposomes to allow for signal generation.

Evaluation of Extrusion Technique for Nanosizing Liposomes

The aim of the present study was to study the efficiency of different techniques used for nanosizing liposomes. Further, the aim was also to evaluate the effect of process parameters of extrusion techniques used for nanosizing liposomes on the size and size distribution of the resultant liposomes. To compare the efficiency of different nanosizing techniques, the following techniques were used to nanosize the liposomes: extrusion, ultrasonication, freeze-thaw sonication (FTS), sonication and homogenization. The extrusion technique was found to be the most efficient, followed by FTS, ultrasonication, sonication and homogenization. The extruder used in the present study was fabricated using readily available and relatively inexpensive apparatus. Process parameters were varied in extrusion technique to study their effect on the size and size distribution of extruded liposomes. The results obtained indicated that increase in the flow rate of the extrusion process decreased the size of extruded liposomes however the size homogeneity was negatively impacted. Furthermore, the liposome size and distribution was found to decline with decreasing membrane pore size. It was found that by extruding through a filter with a pore size of 0.2 µm and above, the liposomes produced were smaller than the pore size, whereas, when they were extruded through a filter with a pore size of less than 0.2 µm the resultant liposomes were slightly bigger than the nominal pore size. Besides that, increment of extrusion temperature above transition temperature of the pro-liposome had no effect on the size and size distribution of the extruded liposomes. In conclusion, the extrusion technique was reproducible and effective among all the methods evaluated. Furthermore, processing parameters used in extrusion technique would affect the size and size distribution of liposomes. Therefore, the process parameters need to be optimized to obtain a desirable size range and homogeneity, reproducible for various in vivo applications.

Gold Nanoantenna-Mediated Photothermal Drug Delivery from Thermosensitive Liposomes in Breast Cancer

In this work, we demonstrate controlled drug delivery from low-temperature-sensitive liposomes (LTSLs) mediated by photothermal heating from multibranched gold nanoantennas (MGNs) in triple-negative breast cancer (TNBC) cells in vitro. The unique geometry of MGNs enables the generation of mild hyperthermia (∼42 °C) by converting near-infrared light to heat and effectively delivering doxorubicin (DOX) from the LTSLs in breast cancer cells. We confirmed the cellular uptake of MGNs by using both fluorescence confocal Z-stack imaging and transmission electron microscopy (TEM) imaging. We performed a cellular viability assay and live/dead cell fluorescence imaging of the combined therapeutic effects of MGNs with DOX-loaded LTSLs (DOX-LTSLs) and compared them with free DOX and DOX-loaded non-temperature-sensitive liposomes (DOX-NTSLs). Imaging of fluorescent live/dead cell indicators and MTT assay outcomes both demonstrated significant decreases in cellular viability when cells were treated with the combination therapy. Because of the high phase-transition temperature of NTSLs, no drug delivery was observed from the DOX-NTSLs. Notably, even at a low DOX concentration of 0.5 μg/mL, the combination treatment resulted in a higher (33%) cell death relative to free DOX (17% cell death). The results of our work demonstrate that the synergistic therapeutic effect of photothermal hyperthermia of MGNs with drug delivery from the LTSLs can successfully eradicate aggressive breast cancer cells with higher efficacy than free DOX by providing a controlled light-activated approach and minimizing off-target toxicity.

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.

Anionic Liposomes Inhibit Human Immunodeficiency Virus Type 1 (HIV-1) Infectivity in CD4+ A3.01 and H9 Cells

Immunodeficiency viruses undergo fusion with liposomes containing anionic phospholipids (Larsen etal., 1990). We have investigated the effect of liposomes composed of cardiolipin, phosphatidylserine or phosphatidylinositol, on the infectivity of three strains of HIV-1 in A3.01 and H9 cells, measured by p24 (gag) production in the medium. The infectivity of HIV-1 in A3.01 or H9 cells was inhibited by the presence of cardiolipin liposomes during a 2 h infection period, with IC50's of 23.0, 4.8, and 5.0 μM phospholipid, respectively, for the different strains. Liposomes composed of phosphatidylserine or phosphatidylinositol were ineffective under similar conditions. However, prolonged pre-incubation of the virus with these liposomes also inhibited infectivity. Inhibition of virus binding to cells could not account for the inhibition of infectivity. We propose that the fusion products of HIV-1 and anionic liposomes are impaired in their ability to fuse with the plasma membrane.

Role of amphipathicity and hydrophobicity in the balance between hemolysis and peptide-membrane interactions of three related antimicrobial peptides

Cationic antimicrobial peptides (CAMPs) represent important self defense molecules in many organisms, including humans. These peptides have a broad spectrum of activities, killing or neutralizing many Gram-negative and Gram-positive bacteria. The emergence of multidrug resistant microbes has stimulated research on the development of alternative antibiotics. In the search for new antibiotics, cationic antimicrobial peptides (CAMPs) offer a viable alternative to conventional antibiotics, as they physically disrupt the bacterial membranes, leading to lysis of microbial membranes and eventually cell death. In particular, the group of linear α-helical cationic peptides has attracted increasing interest from clinical as well as basic research during the last decade. In this work, we studied the biophysical and microbiological characteristics of three new designed CAMPs. We modified a previously studied CAMP sequence, in order to increase or diminish the hydrophobic face, changing the position of two lysines or replacing three leucines, respectively. These mutations modified the hydrophobic moment of the resulting peptides and allowed us to study the importance of this parameter in the membrane interactions of the peptides. The structural properties of the peptides were also correlated with their membrane-disruptive abilities, antimicrobial activities and hemolysis of human red blood cells.

Filter-extruded liposomes revisited: a study into size distributions and morphologies in relation to lipid-composition and process parameters

Filter-extrusion is a widely used technique for down-sizing of phospholipid vesicles. In order to gain a detailed insight into size and size distributions of filter-extruded vesicles composed of egg phosphatidyl-choline (with varying fractions of cholesterol)--in relation to extrusion-parameters (pore-size, number of filter passages, and flow-rate), flow field-flow fractionation in conjunction with multi-angle laser light scattering (AF4-MALLS, Wyatt Technology Corp., Santa Barbara, CA) was employed. Liposome size-distributions determined by AF4-MALLS were compared with those of dynamic light scattering and correlated with cryo-transmission electron microscopy and (31)P-NMR-analysis of lamellarity. Both the mean size of liposome and the width of size distribution were found to decrease with sequential extrusion through smaller pore size filters, starting at a size range of ≈70-415 nm upon repeated extrusion through 400 nm pore-filters, eventually ending with a size range from ≈30 to 85 nm upon extrusion through 30 nm pore size filters. While for small pores sizes (50 nm), increased flow rates resulted in smaller vesicles, no significant influence of flow rate on mean vesicle size was seen with larger pores. Cholesterol at increasing mol fractions up to 0.45 yielded bigger vesicles (at identical process conditions). For a cholesterol mol fraction of 0.5 in combination with small filter pore size, a bimodal size distribution was seen indicating cholesterol micro-crystallites. Finally, a protocol is suggested to prepare large (∼ 300 nm) liposomes with rather narrow size distribution, based on the filter extrusion at defined flow-rates in combination with freeze-/thaw-cycling and bench-top centrifugation.

Simultaneous targeting of VEGF-receptors 2 and 3 with immunoliposomes enhances therapeutic efficacy

BACKGROUND

Tumor progression depends on angiogenesis. Vascular endothelial growth factor (VEGF) receptors (VEGFRs) are the main signal transducers that stimulate endothelial cell migration and vessel sprouting. At present, only VEGFR2 is targeted in the clinical practice.

PURPOSE

To develop new, anti-angiogenic nanoparticles (immunoliposomes, ILs), that redirect cytotoxic compounds to tumor-associated vascular cells.

METHODS

Pegylated liposomal doxorubicin (PLD) was targeted against VEGFR2- and VEGFR3-expressing cells by inserting anti-VEGFR2 and/or anti-VEGFR3 antibody fragments into the lipid bilayer membrane of PLD. These constructs were tested in vitro, and in vivo in the Rip1Tag2 mouse model of human cancer.

RESULTS

The combination treatment with anti-VEGFR2-ILs-dox and anti-VEGFR3-ILs-dox was superior to targeting only VEGFR2 cells and provides a highly efficient approach of depleting tumor-associated vasculature. This leads to tumor starvation and pronounced reduction of tumor burden.

CONCLUSION

Nanoparticles against VEGFR2 and -3 expressing tumor-associated endothelial cells represent a promising and novel anti-cancer strategy.

Delivery of oligonucleotides with lipid nanoparticles

Since their inception in the 1980s, oligonucleotide-based (ON-based) therapeutics have been recognized as powerful tools that can treat a broad spectrum of diseases. The discoveries of novel regulatory methods of gene expression with diverse mechanisms of action are still driving the development of novel ON-based therapeutics. Difficulties in the delivery of this class of therapeutics hinder their in vivo applications, which forces drug delivery systems to be a prerequisite for clinical translation. This review discusses the strategy of using lipid nanoparticles as carriers to deliver therapeutic ONs to target cells in vitro and in vivo. A discourse on how chemical and physical properties of the lipid materials could be utilized during formulation and the resulting effects on delivery efficiency constitutes the major part of this review.

TOPK inhibitor induces complete tumor regression in xenograft models of human cancer through inhibition of cytokinesis

TOPK (T-lymphokine-activated killer cell-originated protein kinase) is highly and frequently transactivated in various cancer tissues, including lung and triple-negative breast cancers, and plays an indispensable role in the mitosis of cancer cells. We report the development of a potent TOPK inhibitor, OTS964 {(R)-9-(4-(1-(dimethylamino)propan-2-yl)phenyl)-8-hydroxy-6-methylthieno[2,3-c]quinolin-4(5H)-one}, which inhibits TOPK kinase activity with high affinity and selectivity. Similar to the knockdown effect of TOPK small interfering RNAs (siRNAs), this inhibitor causes a cytokinesis defect and the subsequent apoptosis of cancer cells in vitro as well as in xenograft models of human lung cancer. Although administration of the free compound induced hematopoietic adverse reactions (leukocytopenia associated with thrombocytosis), the drug delivered in a liposomal formulation effectively caused complete regression of transplanted tumors without showing any adverse reactions in mice. Our results suggest that the inhibition of TOPK activity may be a viable therapeutic option for the treatment of various human cancers.