Phospholipid Monolayers Research Articles

Structural Reorganization of Cell Membrane Models Caused by the Anticancer Antibiotic Doxorubicin

The molecular mechanisms of the interaction of anticancer antibiotic doxorubicin with lipid cell membrane models have been investigated using grazing incidence X-ray diffraction (XRD) and X-ray reflectivity (XRR). The model systems were monolayers of four types of phospholipids, related to the main components of animal cell membranes. New information on the processes of damage of phospholipid monolayer lattice caused by doxorubicin is obtained. It is established that the action of doxorubicin on anionic phospholipid monolayers is determined by the electrostatic interaction: positively charged doxorubicin molecules are incorporated between negatively charged phospholipid functional groups. In the case of neutral phospholipids the key role belongs to the hydrophobic interaction: doxorubicin molecules are coordinated with phospholipid hydrocarbon tails in disordered regions.

Differences in Structural Changes and Pathophysiological Effects of Low-Density Lipoprotein Particles upon Accumulation of Acylhydroperoxy Derivatives in Their Outer Phospholipid Monolayer or upon Modification of Apoprotein B-100 by Natural Dicarbonyls.

Nanoparticles of the lipid-transporting system of the organism, low-density lipoproteins (LDL) of blood plasma, are prone to free radical peroxidation with formation of their main modified forms - oxidized LDL itself (containing hydroperoxy-acyls in phospholipids of the outer layer of particles) and dicarbonyl-modified LDL (apoprotein B-100 in which chemically modified via the Maillard reaction). Based on the study of free radical oxidation kinetics of LDLs, it was found that the existing in the literature designation of "oxidized lipoproteins" is incorrect because it does not reveal the nature of oxidative modification of LDLs. It was shown in this study that the "atherogenic" LDLs (particles of which are actively captured by the cultured macrophages) are not the oxidized LDL (in which LOOH-derivatives of phospholipids are formed by enzymatic oxidation by C-15 lipoxygenase of rabbit reticulocytes), but dicarbonyl-modified LDLs. Important role of the dicarbonyl-modified LDLs in the molecular mechanisms of atherogenesis and endothelial dysfunction is discussed.

Concept of lipid droplet biogenesis

Lipid droplets (LD) are functionally conserved fat storage organelles found in all cell types. LDs have a unique structure comprising of a hydrophobic core of neutral lipids (fat), triacylglycerol (TAG) and cholesterol esters (CE) surrounded by a phospholipid monolayer. LD surface is decorated by a multitude of proteins and enzymes rendering this compartment functional. Accumulating evidence suggests that LDs originate from discrete ER-subdomains, demarcated by the lipodystrophy protein seipin, however, the mechanisms of which are not well understood. LD biogenesis factors together with biophysical properties of the ER membrane orchestrate spatiotemporal regulation of LD nucleation and growth at specific ER subdomains in response to metabolic cues. Defects in LD formation manifests in several human pathologies, including obesity, lipodystrophy, ectopic fat accumulation, and insulin resistance. Here, we review recent advances in understanding the molecular events during initial stages of eukaryotic LD assembly and discuss the critical role of factors that ensure fidelity of this process.

Heterologous expression of MiMLDP, a major lipid droplet protein of the microalga Myrmecia incisa, in Saccharomyces cerevisiae promotes more triacylglycerol storage principally by enlarging lipid droplet size

In some algae, lipid droplets (LDs) are surrounded by phospholipid monolayers containing specialized proteins such as major lipid droplet protein (MLDP), which serves as a principal structural component and makes significant contributions to the enrichment of LDs. In the present study, a new MLDP gene from green alga Myrmecia incisa was reported for the first time, and was comprehensively investigated with respect to its identification, localization and function. The gene product MiMLDP was 35.46 % identical to the reported ortholog in the synonym Lobosphaera incisa. A polyclonal antibody was prepared and the subcellular localization was confirmed to be on the LDs. By flow cytometry and TLC-FID analyses, MiMLDP was demonstrated to improve the accumulation of triacylglycerol. By fusing the coding sequence with eYFP and transforming into yeast strain BY4741, MiMLDP was found to be able to increase the size of LDs and decrease the content of steryl esters, which consequently enhanced the triacylglycerol storage.

Dynamic Properties of Pulmonary Lipid Monolayers on the Surfaces of Sodium Polystyrene Sulfonate and Polydiallyldimethylammonium Chloride Solutions

Pulmonary surfactant, which is a complex mixture of lipids and proteins, plays a key role in the functional properties of the respiratory system. Lipids form complexes with proteins to maintain low values of surface tension at continuous compression/expansion deformations. However, interactions that lead to the complexation still remain to be unknown thus significantly hampering the development of synthetic analogs of the natural pulmonary surfactant. In this work, the methods of surface rheology and ellipsometry have been employed to study the dynamic properties of model phospholipid monolayers applied onto the surfaces of synthetic polyelectrolyte solutions. It has been shown, that electrostatic or hydrophobic interactions between lipids and macromolecules are insufficient for the efficient complexation and maintenance of low surface tension values.

Construction and application of artificial lipoproteins using adiposomes

Lipoproteins are complex particles comprised of a neutral lipid core wrapped with a phospholipid monolayer membrane and apolipoproteins on the membrane, which is closely associated with metabolic diseases. To facilitate the elucidation of its formation and dynamics, as well as its applications, we developed an in vitro system in which adiposomes, consisting of a hydrophobic core encircled by a monolayer-phospholipid membrane, were engineered into artificial lipoproteins (ALPs) by recruiting one or more kinds of apolipoproteins, for example, apolipoprotein (Apo) A-I, ApoE, ApoA-IV, and ApoB. In vitro and in vivo studies demonstrated the stability and biological activity of ALPs derived from adiposomes, which resembles native lipoproteins. Of note, adiposomes bearing ApoE were internalized via clathrin-mediated endocytosis following LDLR binding and were delivered to lysosomes. On the other hand, adiposomes bearing ApoA-IV mimicked the existing form of endogenous ApoA-IV and exhibited significant improvement in glucose tolerance in mice. In addition, the construction process was simple, precise, reproducible, as well as easy to adjust for mass production. With this experimental system, different apolipoproteins can be recruited to build ALPs for some biological goals and potential applications in biomedicine.

In-situ grafting of dextran on oil body associated proteins at the oil–water interface through maillard glycosylation: Effect of dextran molecular weight

Oil bodies, which are lipid-storage organelles in plant seeds, are stabilized by monolayer of phospholipids and oil body associated proteins (OBAPs). OBAPs have unique interfacial characteristics but poor water-solubility because they contain long hydrophobic segments. In this paper, dextran with different molecular weights (5, 10, and 20 kDa) was grafted onto the C- and N-terminal ends of OBAPs through in situ Maillard reaction on the surface of oil bodies. Grafting of dextran increases the length of the hydrophilic region of OBAPs, which improves their solubility and function as interfacial stabilizers. Changes in chemical bonds after grafting were observed via confocal-Raman microscopy. After de-lipidization, the physicochemical properties of OBAPs–dextran conjugates were analyzed using solubility and infrared spectroscopy. The interfacial behavior was evaluated using critical micelle concentration and interfacial rheology. The results showed that grafting of dextran improved the solubility of the OBAPs by 20-fold. The contents of α-helix and β-sheet in the OBAPs–dextran conjugates decreased, when compared with OBAPs. The critical micelle concentration of OBAPs–dextran conjugates ranged from 1.20 to 4.92 μg/mL. Grafting of dextran, especially high molecular weight, improved the capacity of the OBAPs to increase the interfacial pressure. Our results provide an efficient and eco-friend method for modification of membrane proteins.

Molecular dynamics of vegetable oil extraction and degumming: Analysis of micelles and phospholipid bilayers in different solvents

AbstractUnderstanding the molecular‐level mechanisms of vegetable oil extraction and degumming remains limited. This study aimed to investigate these processes using molecular dynamics (MD), with a focus on the challenges associated with replacing n‐hexane with ethanol. MD simulations with a coarse‐grained force field (Martini 3) were conducted to examine the behavior of phospholipid mono/bilayers with and without triacylglycerol in various solvents, including water, absolute and aqueous ethanol (with 0%–10% water content by weight), and n‐hexane. Trilinolein and phospholipids with 16–18 carbon tails and 0–2 unsaturations were considered. The degree of unsaturation and tail size of phospholipids did not significantly affect bilayer formation in water. However, they influenced bilayer organization, as measured by the order parameter, bilayer thickness, and area. The phospholipid bilayer, composed of 1‐palmitoyl‐2‐oleoyl‐sn‐glycero‐3‐phosphocholine (POPC), exhibited a well‐defined structure in water, partial disruption in ethanol, and complete disruption in n‐hexane. The presence of triacylglycerol had no effect on phospholipid monolayers in water but increased lipid disorder in ethanol. Minor amounts of water in ethanol did not significantly alter the behavior of the lipid layers. MD simulations, combined with artificial intelligence, identified and quantified the formation of micelles during the degumming process, both in conjunction with n‐hexane extraction and independently as a function of water concentration. The volume and number of micelles were strongly influenced by the water content. Molecular dynamics in food engineering is relatively limited and scarce because of the complex nature of the systems. However, this study successfully demonstrates its applicability in this context.

Effect of perfluorotetradecanoic acid on the morphology of a photopolymerizable phospholipid monolayer at the air‐water interface

AbstractFundamental physical chemical properties of a monolayer film comprised of the chiral, photopolymerizable phospholipid 1,2‐bis(10,12‐tricosadiynoyl)‐sn‐glycero‐3‐phosphocholine (Diyne PC) and the impact of a model perfluorocarbon, perfluorotetradecanoic acid (PF), on these film properties have been investigated, both with and without UV photopolymerization. Enantiomerically pure Diyne PC formed compact, stable monolayers at the air‐water interface, exhibited typical phospholipid phase transitions in surface pressure‐area isotherms and yielded micron‐scale, linear domains upon film compression. Photopolymerized films were significantly more expanded in comparison with the unpolymerized films and the resulting domains had a spiral morphology with a strongly preferred spiral direction. Mixing Diyne PC with PF altered the isotherm behavior, with the principal effects being a significant reduction in the plateau region associated with the characteristic LE‐LC phase transition and no larger‐scale spiral domain formation in the monolayers of the mixed films. Results are discussed in the context of interactions between the two different film components and the tendency of perfluorinated surfactants to disperse condensed phase regions of phospholipid‐based monolayer films. Overall, the tendency of PF to disperse condensed regions of the film makes patterning of films in mixed phospholipid‐perfluorocarbon monolayers particularly difficult.

Ostwald Ripening of Triacylglycerol Droplets Embedded in Glass-Supported Phospholipid Bilayers.

Lipid droplets are fat storage organelles that consist of a neutral lipid core surrounded by a phospholipid monolayer. Because of their important biological functions, reconstituting model lipid droplets in synthetic phospholipid membranes is of great interest. In the present study, we investigated the incorporation of triacylglycerol droplets into glass-supported phospholipid bilayers by using fluorescence microscopy. We adsorbed triolein emulsions onto a glass surface that was partially covered with planar bilayers. After adsorption, triolein droplets were found to be immobilized in the bilayer membrane. The volume of each bound droplet varied over time. Large droplets grew, whereas small droplets shrank. Additionally, data on fluorescence recovery after photobleaching obtained for a phospholipid probe indicate that phospholipids on and near triolein droplets were fully mobile. Furthermore, photobleaching data obtained for a triacylglycerol probe indicate that triolein molecules diffused between different droplets along the planar bilayer. These results demonstrate Ostwald ripening, where triolein molecules in a small droplet dissolved in the bilayer, diffused laterally, and eventually bound to the interfaces of larger droplets. We investigated the ripening rate by using the average of the cube root of the fluorescence emission obtained for individual droplets. The ripening slowed after the addition of trilinolein to the triolein phase. Finally, we investigated the time dependence of the size distributions of the triolein droplets. The distribution was initially nearly unimodal and subsequently became bimodal.

Tapping lipid droplets: A rich fat diet of intracellular bacterial pathogens.

Lipid droplets (LDs) are dynamic and versatile organelles present in most eukaryotic cells. LDs consist of a hydrophobic core of neutral lipids, a phospholipid monolayer coat, and a variety of associated proteins. LDs are formed at the endoplasmic reticulum and have diverse roles in lipid storage, energy metabolism, membrane trafficking, and cellular signaling. In addition to their physiological cellular functions, LDs have been implicated in the pathogenesis of several diseases, including metabolic disorders, cancer, and infections. A number of intracellular bacterial pathogens modulate and/or interact with LDs during host cell infection. Members of the genera Mycobacterium, Legionella, Coxiella, Chlamydia, and Salmonella exploit LDs as a source of intracellular nutrients and membrane components to establish their distinct intracellular replicative niches. In this review, we focus on the biogenesis, interactions, and functions of LDs, as well as on their role in lipid metabolism of intracellular bacterial pathogens.

Perilipin 3 promotes the formation of membrane domains enriched in diacylglycerol and lipid droplet biogenesis proteins.

Lipid droplets (LDs) serve as intracellular stores of energy-rich neutral lipids. LDs form at discrete sites in the endoplasmic reticulum (ER) and they remain closely associated with the ER during lipogenic growth and lipolytic consumption. Their hydrophobic neutral lipid core is covered by a monolayer of phospholipids, which harbors a specific set of proteins. This LD surface is coated and stabilized by perilipins, a family of soluble proteins that specifically target LDs from the cytosol. We have previously used chimeric fusion proteins between perilipins and integral ER membrane proteins to test whether proteins that are anchored to the ER bilayer could be dragged onto the LD monolayer. Expression of these chimeric proteins induces repositioning of the ER membrane around LDs. Here, we test the properties of membrane-anchored perilipins in cells that lack LDs. Unexpectedly, membrane-anchored perilipins induce expansion and vesiculation of the perinuclear membrane resulting in the formation of crescent-shaped membrane domains that harbor LD-like properties. These domains are stained by LD-specific lipophilic dyes, harbor LD marker proteins, and they transform into nascent LDs upon induction of neutral lipid synthesis. These ER domains are enriched in diacylglycerol (DAG) and in ER proteins that are important for early steps of LD biogenesis, including seipin and Pex30. Formation of the domains in vivo depends on DAG levels, and we show that perilipin 3 (PLIN3) binds to liposomes containing DAG in vitro. Taken together, these observations indicate that perilipin not only serve to stabilize the surface of mature LDs but that they are likely to exert a more active role in early steps of LD biogenesis at ER subdomains enriched in DAG, seipin, and neutral lipid biosynthetic enzymes.

Is lipophilicity the main factor determining the effective drug penetration through lipid membranes? Combined GIXD and PM-IRRAS studies on the example of anthracyclines

Cell membranes constitute the first barrier for the drugs on their way to the cell. Therefore, their penetration determines the effectivity of the treatment and is defined by the drug-lipid interactions. A systematic, comprehensive study to assess the impact of different aspects influencing the effective penetration of model lipid membranes by the drugs including lipophilicity, charge, ability to form dimers as well as stearic hindrance was performed. Four anthracyclines differing in the structure and with lipophilicity increasing in the following order: doxorubicin (DOx) < pirarubicin (THP) < daunorubicin (DNR) < idarubicin (IDA) were chosen to assess their impact on 1,2-dimyristoyl-sn-glycero-3-phospho-L-serine (DMPS) monolayers mimicking cancer cell membranes. The investigation performed at the air–water interface involved the application of multiple surface-sensitive techniques to assess the drug interactions with both polar heads of the phospholipid and the penetration of the acyl chain region. The obtained results allowed us to state that although electrostatic interactions and lipophilicity of the drug are one of the key factors, the ability to form dimers as well as stearic hinderance may strongly prevent from the effective penetration of the phospholipid monolayers even for drugs with higher lipophilicity and therefore have to be also taken into account in the development of new therapeutic agents.

Proteomics coupled transcriptomics reveals lipopolysaccharide inhibiting peroxisome proliferator-activated receptors signalling pathway to reduce lipid droplets accumulation in mouse liver.

Lipid droplets (LDs) are multifunctional organelles consisting of a central compartment of non-polar lipids shielded from the cytoplasm by a phospholipid monolayer. The excessive accumulation of LDs in cells is closely related to the development and progression of many diseases in humans and animals, such as liver-related and cardiovascular diseases. Thus, regulating the LDs size and abundance is necessary to maintain metabolic homeostasis. This study found that lipopolysaccharide (LPS) stimulation reduced the LDs content in the mouse liver. We tried to explain the possible molecular mechanisms at the broad protein and mRNA levels, finding that inhibition of the peroxisome proliferator-activated receptors (PPAR) signalling pathway by LPS may be a critical factor in reducing LDs content.

Structural insights into perilipin 3 membrane association in response to diacylglycerol accumulation

Lipid droplets (LDs) are dynamic organelles that contain an oil core mainly composed of triglycerides (TAG) that is surrounded by a phospholipid monolayer and LD-associated proteins called perilipins (PLINs). During LD biogenesis, perilipin 3 (PLIN3) is recruited to nascent LDs as they emerge from the endoplasmic reticulum. Here, we analyze how lipid composition affects PLIN3 recruitment to membrane bilayers and LDs, and the structural changes that occur upon membrane binding. We find that the TAG precursors phosphatidic acid and diacylglycerol (DAG) recruit PLIN3 to membrane bilayers and define an expanded Perilipin-ADRP-Tip47 (PAT) domain that preferentially binds DAG-enriched membranes. Membrane binding induces a disorder to order transition of alpha helices within the PAT domain and 11-mer repeats, with intramolecular distance measurements consistent with the expanded PAT domain adopting a folded but dynamic structure upon membrane binding. In cells, PLIN3 is recruited to DAG-enriched ER membranes, and this requires both the PAT domain and 11-mer repeats. This provides molecular details of PLIN3 recruitment to nascent LDs and identifies a function of the PAT domain of PLIN3 in DAG binding.

Targeted Microbubbles for Drug, Gene, and Cell Delivery in Therapy and Immunotherapy.

Microbubbles are 1-10 μm diameter gas-filled acoustically-active particles, typically stabilized by a phospholipid monolayer shell. Microbubbles can be engineered through bioconjugation of a ligand, drug and/or cell. Since their inception a few decades ago, several targeted microbubble (tMB) formulations have been developed as ultrasound imaging probes and ultrasound-responsive carriers to promote the local delivery and uptake of a wide variety of drugs, genes, and cells in different therapeutic applications. The aim of this review is to summarize the state-of-the-art of current tMB formulations and their ultrasound-targeted delivery applications. We provide an overview of different carriers used to increase drug loading capacity and different targeting strategies that can be used to enhance local delivery, potentiate therapeutic efficacy, and minimize side effects. Additionally, future directions are proposed to improve the tMB performance in diagnostic and therapeutic applications.

One amino acid drives the lipid droplet targeting sequence of a new noncoding RNA-encoded protein to mitochondrion.

Over the past decade, the majority of the mammalian genome considered to be noncoding has been revealed to be able to produce proteins. Many RNA molecules, mis-annotated as noncoding, actually are predicted to code for proteins. Some of those proteins have been identified and verified to play critical roles in multiple biological processes. The lipid droplet (LD) is a unique cellular organelle bound with a phospholipid monolayer membrane, and is closely associated with cellular lipid metabolism and metabolic disorders. However, it is still unclear how a protein targets to LDs. Here we identified a new protein on LDs, LDANP2, which is encoded by noncoding RNA, through a proteomics-based strategy. The key sequence for its localization on LDs, Truncation 3, is predicted to form an amphipathic helix. Surprisingly, the deletion of the first amino acid in Truncation 3 resulted in mitochondrial localization. How the types of amino acids would determine the LD or mitochondrial localizations of the protein was studied. The findings introduce a useful strategy to mine for new proteins and would provide clues to the understanding of how a protein would find its right organelle, with phospholipid monolayer or bilayer membrane.

Tyrosine-derived polymeric surfactant nanospheres insert cholesterol in cell membranes

HypothesisThe design of biodegradable tyrosine-derived polymeric surfactants (TyPS) through the use of calculated thermodynamic parameters could lead to phospholipid membrane surface modifiers capable of controlling cellular properties such as viability. Delivery of cholesterol by TyPS nanospheres into membrane phospholipid domains could provide further controlled modulation of membrane physical and biological properties. ExperimentCalculated Hansen solubility parameters (∂T) and hydrophile:lipophile balances (HLB) were applied to design and synthesize a small family of diblock and triblock TyPS with different hydrophobic blocks and PEG hydrophilic blocks. Self-assembled TyPS/cholesterol nanospheres were prepared in aqueous media via co-precipitation. Cholesterol loading and Langmuir film balance surface pressures of phospholipid monolayers were obtained. TyPS and TyPS/cholesterol nanosphere effects on human dermal cell viability were evaluated by cell culture using poly(ethylene glycol) (PEG) and Poloxamer 188 as controls. FindingsStable TyPS nanospheres incorporated between 1% and 5% cholesterol. Triblock TyPS formed nanosphere with dimensions significantly smaller than diblock TyPS nanospheres. In accord calculated thermodynamic parameters, cholesterol binding increased with increasing TyPS hydrophobicity. TyPS inserted into phospholipid monolayer films in a manner consistent with their thermodynamic properties and TyPS/cholesterol nanospheres delivered cholesterol into the films. Triblock TyPS/cholesterol nanospheres increased human dermal cell viability, which was indicative of potentially beneficial TyPS effects on cell membrane surface properties.

Influence of the Antimicrobial LL-37 Peptide on Legionella dumoffii Phospholipids Adsorbed at the Air–Liquid Interface

Legionella dumoffii is an intracellular pathogen of freshwater protozoans capable of infecting and multiplying in mammalian cells, causing a severe respiratory disease called Legionnaires’ disease. The pathomechanism of infection development is very complex and depends on many factors, including the structure and properties of macromolecules that build the components of the L. dumoffii cell envelope. Phospholipids (PLs) forming biological membranes have a significant impact on the integrity of the membrane as well as on the interactions with the host cells. L. dumoffii changes its lipid profile under the influence of external factors, which allows it to adapt to the living environment. One of the factors altering the PL composition is the presence of exogenous choline. The aim of this study was to determine the physicochemical properties of the model bacterial membranes adsorbed at the air–liquid interface (Langmuir monolayers). They were composed of phospholipids isolated from L. dumoffii cultured with (PL+choline) and without (PL−choline) choline. Moreover, the effect of the human cathelicidin (LL-37 peptide) added to the subphase on these monolayers was analyzed in terms of phospholipid–peptide interactions. The results indicated that the monolayers of PL+choline were slightly more condensed than PL−choline. In the presence of LL-37, the elasticity of both monolayers increased; thus, their molecular packing and ordering decreased. The disturbing effect was related to the peptide’s antibacterial activity.

Lipid Droplets from Plants and Microalgae: Characteristics, Extractions, and Applications.

Plant and algal LDs are gaining popularity as a promising non-chemical technology for the production of lipids and oils. In general, these organelles are composed of a neutral lipid core surrounded by a phospholipid monolayer and various surface-associated proteins. Many studies have shown that LDs are involved in numerous biological processes such as lipid trafficking and signaling, membrane remodeling, and intercellular organelle communications. To fully exploit the potential of LDs for scientific research and commercial applications, it is important to develop suitable extraction processes that preserve their properties and functions. However, research on LD extraction strategies is limited. This review first describes recent progress in understanding the characteristics of LDs, and then systematically introduces LD extraction strategies. Finally, the potential functions and applications of LDs in various fields are discussed. Overall, this review provides valuable insights into the properties and functions of LDs, as well as potential approaches for their extraction and utilization. It is hoped that these findings will inspire further research and innovation in the field of LD-based technology.