Artificial Phospholipids and Their Vesicles

Designer phospholipid capping ligands for soft metal halide nanocrystals

The success of colloidal semiconductor nanocrystals (NCs) in science and optoelectronics is inextricable from their surfaces. The functionalization of lead halide perovskite NCs1-5 poses a formidable challenge because of their structural lability, unlike the well-established covalent ligand capping of conventional semiconductor NCs6,7. We posited that the vast and facile molecular engineering of phospholipids as zwitterionic surfactants can deliver highly customized surface chemistries for metal halide NCs. Molecular dynamics simulations implied that ligand-NC surface affinity is primarily governed by the structure of the zwitterionic head group, particularly by the geometric fitness of the anionic and cationic moieties into the surface lattice sites, as corroborated by the nuclear magnetic resonance and Fourier-transform infrared spectroscopy data. Lattice-matched primary-ammonium phospholipids enhance the structural and colloidal integrity of hybrid organic-inorganic lead halide perovskites (FAPbBr3 and MAPbBr3 (FA, formamidinium; MA, methylammonium)) and lead-free metal halide NCs. The molecular structure of the organic ligand tail governs the long-term colloidal stability and compatibility with solvents of diverse polarity, from hydrocarbons to acetone and alcohols. These NCs exhibit photoluminescence quantum yield of more than 96% in solution and solids and minimal photoluminescence intermittency at the single particle level with an average ON fraction as high as 94%, as well as bright and high-purity (about 95%) single-photon emission.

Activating the delivery of a model drug to lipid membrane by encapsulation of cyclodextrin: Combined experimental and molecular docking studies

Drug delivery science is always an important topic as it studies the delivery of therapeutic payloads to the desired target cells without affecting the healthy tissues/cells, thus minimizing drug-induced toxicity. Aiming towards the targeted drug delivery, the present project deals with the delivery of a polarity-sensitive solvatochromic model drug, namely, salt of 8-anilinonaphthalene-1-sulphonic acid (ANSA) to the model bio-membrane (which mimic several aspects of the real cell membrane), more precisely at the lipid-water interface of L-α-Dipalmitoylphosphatidylcholine (DPPC) phospholipid. The drug delivery process has been activated through the binding of dye with cyclodextrin, acting as a drug transporter. Detailed steady-state and time-resolved spectroscopic studies including molecular docking analysis imply the targeted drug delivery of dye, ANSA, towards the lipid-water interface region of lipid bilayers through encapsulation within the cyclodextrin void. Stronger binding interaction of the dye with the lipid bilayers relative to β-cyclodextrin (β-CD) is the foremost reason for the targeted delivery. The present biophysical interaction studies of drug-lipid interaction, thus, may provide a cordial approach for drug formulation and drug delivery.

Sex-Specific Patterns of Diaphragm Phospholipid Content and Remodeling during Aging and in a Model of SELENON-Related Myopathy

Growing evidence shows that the lipid bilayer is a key site for membrane interactions and signal transduction. Surprisingly, phospholipids have not been widely studied in skeletal muscles, although mutations in genes involved in their biosynthesis have been associated with muscular diseases. Using mass spectrometry, we performed a phospholipidomic profiling in the diaphragm of male and female, young and aged, wild type and SelenoN knock-out mice, the murine model of an early-onset inherited myopathy with severe diaphragmatic dysfunction. We identified 191 phospholipid (PL) species and revealed an important sexual dimorphism in PLs in the diaphragm, with almost 60% of them being significantly different between male and female animals. In addition, 40% of phospholipids presented significant age-related differences. Interestingly, SELENON protein absence was responsible for remodeling of 10% PL content, completely different in males and in females. Expression of genes encoding enzymes involved in PL remodeling was higher in males compared to females. These results establish the diaphragm PL map and highlight an important PL remodeling pattern depending on sex, aging and partly on genotype. These differences in PL profile may contribute to the identification of biomarkers associated with muscular diseases and muscle aging.

Modeling Polyzwitterion-Based Drug Delivery Platforms: A Perspective of the Current State-of-the-Art and Beyond

Drug delivery platforms are anticipated to have biocompatible and bioinert surfaces. PEGylation of drug carriers is the most approved method since it improves water solubility and colloid stability and decreases the drug vehicles’ interactions with blood components. Although this approach extends their biocompatibility, biorecognition mechanisms prevent them from biodistribution and thus efficient drug transfer. Recent studies have shown (poly)zwitterions to be alternatives for PEG with superior biocompatibility. (Poly)zwitterions are super hydrophilic, mainly stimuli-responsive, easy to functionalize and they display an extremely low protein adsorption and long biodistribution time. These unique characteristics make them already promising candidates as drug delivery carriers. Furthermore, since they have highly dense charged groups with opposite signs, (poly)zwitterions are intensely hydrated under physiological conditions. This exceptional hydration potential makes them ideal for the design of therapeutic vehicles with antifouling capability, i.e., preventing undesired sorption of biologics from the human body in the drug delivery vehicle. Therefore, (poly)zwitterionic materials have been broadly applied in stimuli-responsive “intelligent” drug delivery systems as well as tumor-targeting carriers because of their excellent biocompatibility, low cytotoxicity, insignificant immunogenicity, high stability, and long circulation time. To tailor (poly)zwitterionic drug vehicles, an interpretation of the structural and stimuli-responsive behavior of this type of polymer is essential. To this end, a direct study of molecular-level interactions, orientations, configurations, and physicochemical properties of (poly)zwitterions is required, which can be achieved via molecular modeling, which has become an influential tool for discovering new materials and understanding diverse material phenomena. As the essential bridge between science and engineering, molecular simulations enable the fundamental understanding of the encapsulation and release behavior of intelligent drug-loaded (poly)zwitterion nanoparticles and can help us to systematically design their next generations. When combined with experiments, modeling can make quantitative predictions. This perspective article aims to illustrate key recent developments in (poly)zwitterion-based drug delivery systems. We summarize how to use predictive multiscale molecular modeling techniques to successfully boost the development of intelligent multifunctional (poly)zwitterions-based systems.

A Novel High-Throughput Assay Reveals That the Temperature Induced Increases in Transphosphatidylation of Phospholipase D Are Dependent on the Alcohol Acceptor Concentration

Phospholipase D reacts with alcohols or water, transphosphatidylating or hydrolysing lipids such as phosphatidylcholine, generating phosphatidylalcohols or phosphatidic acid, respectively. The enzyme has been employed in many applications making use of the transphosphatidylation reaction and the enzyme’s tolerance for organic solvents in order to synthesize natural and artificial phospholipids. Yet, its catalytic properties with respect to the transphosphatidylation reaction are not well understood. Here, we introduce a novel high-throughput assay, making use of 96-well plates, that employs Fluorescamine for the detection of transphosphatidylated amino alcohols. This assay allowed to monitor the K_M and V_Max at different temperatures, revealing that the former will be elevated by the temperature, while the latter is increased by a combination of both temperature and alcohol acceptor concentration being elevated, suggesting that increase in temperature may open up a new binding site for the alcohol acceptor.

Ultrasound-Triggered Delivery of Iproplatin from Microbubble-Conjugated Liposomes

The PtIV prodrug iproplatin has been actively loaded into liposomes using a calcium acetate gradient, achieving a 3-fold enhancement in drug concentration compared to passive loading strategies. A strain-promoted cycloaddition reaction (azide- dibenzocyclooctyne) was used to attach iproplatin-loaded liposomes L(Pt) to gas-filled microbubbles (M), forming an ultrasound-responsive drug delivery vehicle [M-L(Pt)]. Ultrasound-triggered release of iproplatin from the microbubble-liposome construct was evaluated in cellulo. Breast cancer (MCF-7) cells treated with both free iproplatin and iproplatin-loaded liposome-microbubbles [M-L(Pt)] demonstrated an increase in platinum concentration when exposed to ultrasound. No appreciable platinum uptake was observed in MCF-7 cells following treatment with L(Pt) only or L(Pt)+ultrasound, suggesting that microbubble-mediated ultrasonic release of platinum-based drugs from liposomal carriers enables greater control over drug delivery.

Biocatalytic CsPbX3 Perovskite Nanocrystals: A Self-Reporting Nanoprobe for Metabolism Analysis

CsPbX₃ perovskite nanocrystals (NCs), with excellent optical properties, have drawn considerable attention in recent years. However, they also suffer from inherent vulnerability and hydrolysis, causing the new understanding or new applications to be difficultly explored. Herein, for the first time, it is discovered that the phospholipid membrane (PM)-coated CsPbX₃ NCs have intrinsic biocatalytic activity. Different from other peroxidase-like nanozymes relying on extra chromogenic reagents, the PM-CsPbX₃ NCs can be used as a self-reporting nanoprobe, allowing an "add-to-answer" detection model. Notably, the fluorescence of PM-CsPbX₃ NCs can be rapidly quenched by adding H₂ O₂ and then be restored by removing excess H₂ O₂ . Initiated from this unexpected observation, the PM-CsPbX₃ NCs can be explored to prepare multi-color bioinks and metabolite-responsive paper analytical devices, demonstrating the great potential of CsPbX₃ NCs in bioanalysis. This is the first report on the discovery of nanozyme-like property of all-inorganic CsPbX₃ perovskite NCs, which adds another piece to the nanozyme puzzle and opens new avenues for in vitro disease diagnostics.

Phospholipids: Identification and Implication in Muscle Pathophysiology

Phospholipids (PLs) are amphiphilic molecules that were essential for life to become cellular. PLs have not only a key role in compartmentation as they are the main components of membrane, but they are also involved in cell signaling, cell metabolism, and even cell pathophysiology. Considered for a long time to simply be structural elements of membranes, phospholipids are increasingly being viewed as sensors of their environment and regulators of many metabolic processes. After presenting their main characteristics, we expose the increasing methods of PL detection and identification that help to understand their key role in life processes. Interest and importance of PL homeostasis is growing as pathogenic variants in genes involved in PL biosynthesis and/or remodeling are linked to human diseases. We here review diseases that involve deregulation of PL homeostasis and present a predominantly muscular phenotype.

Control of Lipid Bilayer Phases of Cell-Sized Liposomes by Surface-Engineered Plasmonic Nanoparticles

Liquid-ordered (Lo)-phase domains, a cholesterol-rich area on lipid bilayers, have attracted significant attention recently because of their relevance to lipid rafts, the formation/collapse of which is associated with various kinds of information exchange through the plasma membrane. Here, we demonstrate that the formation/collapse of Lo-phase domains in cell-sized liposomes, that is, giant unilamellar vesicles (GUVs), can be controlled with bioactive plasmonic nanoparticles and light. The nanoparticles were prepared by surface modification of gold nanorods (AuNRs) using a cationized mutant of high-density lipoprotein (HDL), which is a natural cholesterol transporter. Upon the addition of surface-engineered AuNRs to GUVs with the mixed domains of Lo and liquid-disorder (Ld) phases, the Lo domains collapsed and solid-ordered (So)-phase domains were formed. The reverse phase transition was achieved photothermally, with the AuNRs loaded with cholesterol. During these transitions, the AuNRs appeared to be selectively localized on the less fluidic domain (Lo or So) in the phase-mixed GUVs. These results indicate that the phase transitions occur through the membrane binding of the AuNRs followed by spontaneous/photothermal transfer of cholesterol between the AuNRs and GUVs. Our strategy to develop bioactive AuNRs potentially enables spatiotemporal control of the formation/collapse of lipid rafts in living cells.

Small-Angle Neutron Scattering Study of Temperature-Induced Structural Changes in Liposomes

Liposomes of specific artificial phospholipids, such as Pad-PC-Pad and Rad-PC-Rad, are mechanically responsive. They can release encapsulated therapeutics via physical stimuli, as naturally present in blood flow of constricted vessel segments. The question is how these synthetic liposomes change their structure in the medically relevant temperature range from 22 to 42 °C. In the present study, small-angle neutron scattering (SANS) was employed to evaluate the temperature-induced structural changes of selected artificial liposomes. For Rad-PC-Rad, Pad-Pad-PC, Sur-PC-Sur, and Sad-PC-Sad liposomes, the SANS data have remained constant because the phase transition temperatures are above 42 °C. For Pad-PC-Pad and Pes-PC-Pes liposomes, whose phase transitions are below 42 °C, the q-plots have revealed temperature-dependent structural changes. The average diameter of Pad-PC-Pad liposomes remained almost constant, whereas the eccentricity decreased by an order of magnitude. Related measurements using transmission electron microscopy at cryogenic temperatures, as well as dynamic light scattering before and after the heating cycles, underpin the fact that the non-spherical liposomes flatten out. The SANS data further indicated that, as a consequence of the thermal loop, the mean bilayer thickness increased by 20%, associated with the loss of lipid membrane interdigitation. Therefore, Pad-PC-Pad liposomes are unsuitable for local drug delivery in the atherosclerotic human blood vessel system. In contrast, Rad-PC-Rad liposomes are thermally stable for applications within the human body.