Dipalmitoylphosphatidylcholine Lipid Research Articles

Cholesterol drives enantiospecific effects of ibuprofen in biomimetic membranes

The interaction between chiral drugs and biomimetic membranes is of interest in biophysical research and biotechnological applications. There is a belief that the membrane composition, particularly the presence of cholesterol, could play a pivotal role in determining enantiospecific effects of pharmaceuticals. Our study explores this topic focusing on the interaction of ibuprofen enantiomers (S- and R-IBP) with cholesterol-containing model membranes. The effects of S- and R-IBP at 20 mol% on bilayer mixtures of dipalmitoylphosphatidylcholine (DPPC) with 0, 10, 20 and 50 mol% cholesterol were investigated using circular dichroism and spin-label electron spin resonance. Morphological changes due to IBP enantiomers were studied with atomic force microscopy on supported cholesterol-containing DPPC monolayers. The results reveal that IBP isoforms significantly and equally interact with pure DPPC lipid assemblies. Cholesterol content, besides modifying the structure and the morphology of the membranes, triggers the drug enantioselectivity at 10 and 20 mol%, with the enantiomers differently adsorbing on membranes and perturbing them. The spectroscopic and the microscopic data indicate that IBP stereospecificity is markedly reduced at equimolar content of Chol mixed with DPPC. This study provides new insights into the role of cholesterol in modulating enantiospecific effects of IBP in lipid membranes.

Investigation of the Membrane Localization and Interaction of Selected Flavonoids by NMR and FTIR Spectroscopy.

In this report, we discuss the effects of undescribed flavone derivatives, HZ4 and SP9, newly isolated from the aerial parts of Hottonia palustris L. and Scleranthus perennis L. on membranes. Interaction of flavonoids with lipid bilayers is important for medicinal applications. The experiments were performed with FTIR and NMR techniques on liposomes prepared from DPPC (dipalmitoylphosphatidylcholine) and EYPC (egg yolk phosphatidylcholine). The data showed that the examined polyphenols incorporate into the polar head group region of DPPC phospholipids at both 25 °C and 45 °C. At the lower temperature, a slight effect in the spectral region of the ester carbonyl group is observed. In contrast, at 45 °C, both compounds bring about the changes in the spectral regions attributed to antisymmetric and symmetric stretching vibrations of CH2 and CH3 moieties. Similarly, as in DPPC lipids, the tested compounds interact with the fingerprint region of the polar head groups of the EYPC lipids and cause its reorganization. The outcomes obtained by NMR analyses confirmed the localization of both flavonoids in the polar heads zone. Unraveled effects of HZ4 and SP9 in respect to lipid bilayers can partly determine their biological activities and are crucial for their usability in medicine as disease-preventing phytochemicals.

Surface-Modified Silver Nanoparticles and Their Encapsulation in Liposomes Can Treat MCF-7 Breast Cancer Cells.

Silver nanoparticles (AgNPs) have emerged as a promising tool for cancer treatment due to their unique physicochemical and biological properties. However, their clinical applications are limited by their potential cytotoxicity caused due to oxidation stress and non-specific cellular uptake pathways. To overcome these barriers, surface modifications of AgNPs have been proposed as an effective strategy to enhance their biocompatibility and specificity toward cancer cells. In this study, AgNPs were synthesised using the chemical reduction method and subsequently conjugated with various capping agents such as Polyvinylpyrrolidone (PVP) and Bovine Serum Albumin (BSA). Further, this study involves the synthesis of liposomes by using dipalmitoyl phosphatidylcholine lipid (DPPC) and cholesterol to increase the biocompatibility and bioavailability of AgNPs to MCF-7 breast cancer cells. In vitro, cytotoxicity studies were performed to determine which surface modification method exhibited the highest cytotoxic effect on the MCF-7 breast cancer cells, which was determined through the MTT assay. The AgNPs conjugated with BSA exhibited the highest cytotoxicity at the lowest dosage, with an IC50 of 2.5 μL/mL. The BSA-AgNPs induced a dose-dependent rise in cytotoxicity through the enhancement of nucleophilic dissolution of the AgNPs in cancer cells. In comparison, the unmodified AgNPs had an IC50 value of 3.0 μL/mL, while the PVP-modified AgNPs had an IC50 of 4.24 μL/mL. AgNPs encapsulated in liposomes had an IC50 value of 5.08 μL/mL, which shows that the encapsulation of AgNPs in liposomes controls their entry into cancer cells. The findings of this research have provided insights into the potential use of surface-modified AgNPs and liposomal encapsulated AgNPs as novel therapeutic tools to overcome the conventional treatment limitations of breast cancer cells.

L-Phenylalanine Partitioning Mechanisms in Model Biological Membranes.

Time-resolved fluorescence spectroscopy in combination with differential scanning calorimetry (DSC) was used to study the chemical interactions that occur when l-phenylalanine is introduced to solutions containing phosphatidylcholine vesicles. Studies reported in this work address open questions about l-Phe's affinity for lipid vesicle bilayers, the effects of l-Phe partitioning on bilayer properties, l-Phe's solvation within a lipid bilayer, and the amount of l-Phe within that local solvation environment. DSC data show that l-Phe reduces the amount of heat necessary to melt saturated phosphatidylcholine bilayers from their gel to liquid-crystalline state but does not change the transition temperature (Tgel-lc). Time-resolved emission shows only a single l-Phe lifetime at low temperatures corresponding to l-Phe remaining solvated in aqueous solution. At temperatures close to Tgel-lc, a second, shorter lifetime appears that is assigned to l-Phe already embedded within the membrane that becomes hydrated as water starts to permeate the lipid bilayer. This new lifetime is attributed to a conformationally restricted rotamer in the bilayer's polar headgroup region and accounts for up to 30% of the emission amplitude. Results reported for dipalmitoylphosphatidylcholine (DPPC, 16:0) lipid vesicles prove to be general, with similar effects observed for dimyristoylphosphatidylcholine (DMPC, 14:0) and distearoylphosphatidylcholine (DSPC, 18:0) vesicles. Taken together, these results create a complete and compelling picture of how l-Phe associates with model biological membranes. Furthermore, this approach to examining amino acid partitioning into membranes and the resulting solvation forces points to new strategies for studying the structure and chemistry of membrane-soluble peptides and selected membrane proteins.

Effect of partial O-methylation in dehydrodieugenol on its antitrypanosomal activity - correlation with the toxicity using cell membrane models

Biseugenol (1), a neolignan with antiprotozoal activity against Trypanosoma cruzi, was partially methylated, and the compound obtained – methyl biseugenol (2) – had its activity evaluated against the extracellular (trypomastigotes) and intracellular (amastigotes) forms of T. cruzi. It was observed that both compounds 1 and 2 exhibited similar effects against trypomastigotes (IC50 of 11.7 and 16.2 μM, respectively), whereas compound 2 displayed higher activity against amastigotes (IC50 = 8.2 μM) in comparison with biseugenol (IC50 = 15.4 μM). Additionally, reduced toxicity against NCTC cells for compound 2 was observed (CC50 > 200 μM), differently from compound 1 with CC50 = 58.0 μM. Aiming to understand better the molecular mechanism of the biological action of compound 2, the prodrug was incorporated into cellular membrane models constituted of Langmuir monolayers of the lipids dipalmitoylphosphatidylcholine (DPPC), dipalmitoylphosphatidylethanolamine (DPPE), dipalmitoylphosphatidylserine (DPPS), and dipalmitoylphosphatidylglycerol (DPPG). The lipid-drug interaction was inferred through tensiometry, surface potential, infrared spectroscopy (PM-IRRAS), and Brewster angle microscopy (BAM). The prodrug expanded DPPC and DPPG monolayers and condensed DPPE ones, as well as presented characteristic behaviors regarding the chemical structure of the lipid considering expansion-compression curves, surface potential-area isotherms, and stability of previously compressed monolayers to relevant-biological surface pressures. PM-IRRAS indicated a molecular disorder for DPPC and DPPS alkyl chains in the presence of the drug. BAM revealed the presence of domains in the DPPG and DPPE monolayers, which was probably induced by the prodrug. These data suggest, in general, that the lipid composition modulates the interaction of compound 2, whose results are expected to correlate to its trypanocidal activity, which involves the plasma membrane of T. cruzi as the primary target, i.e., the first barrier that the compound should encounter to interact with the microorganism.

Molecular dynamics insight of interaction between the functionalized-carbon nanotube and cancerous cell membrane in doxorubicin delivery

Background and objective:Doxorubicin (DOX) is a known anticancer drug which is widely used in cancer therapy. Carbon nanotubes (CNTs) are among the most promising platforms for smart drug delivery applications. However, due to the toxicity and their low sulubility their application is limited and their functionalization with wide range of biomolecules are suggested. Therefore, the functionalized carbon nanotubes (f-CNT) with carboxyl (CNT-COO) and folic acid (CNT-COO-FA) were investigated as drug-carrier.Methods: Molecular dynamics (MD) simulation along with the Density Functional Theory (DFT) methods are being used to study the drug loading process on functionalized carbon nanotubes.Results: The results indicate that doxorubicin molecules interact more with CNT-COO-FA than CNT-COO. The embedded dipalmitoylphosphatidylcholine (DPPC) lipid bilayer with a folate receptor was considered a cancerous cell’s representative model. Then the drug release from the f-CNTs near the lipid bilayer was simulated. The results showed that CNT-COO-FA with a pH and ligand-sensitive mechanism strongly interacts with cancerous cells, which led to higher drug release, in agreement with the experimental results. The conformational changes of the lipid bilayer and folate receptor during drug release were evaluated. The analysis showed that drug release from CNT-COO-FA has significantly changed lipid bilayer and receptor conformations. The obtained results were interpreted and justified by considering the molecular mechanisms which control the drug delivery in the studied systems.Conclusions: Based on the obtained results, CNT-COO-FA has a better performance during the drug release compared to CNT-COO in delivering doxorubicin. Both pH and ligand sensitive mechanisms are found to be responsible for higher drug delivery efficiency of CNT-COO-FA. In contrast, CNT-COO can only enhance drug delivery efficiently with a pH-sensitive mechanism.

Elucidating lipid conformations in the ripple phase: Machine learning reveals four lipid populations

A new mixed radial-angular, three-particle correlation function method in combination with unsupervised machine learning was applied to examine the emergence of the ripple phase in dipalmitoylphosphatidylcholine (DPPC) lipid bilayers using data from atomistic molecular dynamics simulations of system sizes ranging from 128 to 4096 lipids. Based on the acyl tail conformations, the analysis revealed the presence of four distinct conformational populations of lipids in the ripple phases of the DPPC lipid bilayers. The expected gel-like (ordered; Lo) and fluid-like (disordered; Ld) lipids are found along with their splayed tail equivalents (Lo,s and Ld,s). These lipids differ, based on their gauche distribution and tail packing. The disordered (Ld) and disordered-splayed (Ld,s) lipids spatially cluster in the ripple in the groove side, that is, in an asymmetric manner across the bilayer leaflets. The ripple phase does not contain large numbers of Ld lipids; instead they only exist on the interface of the groove side of the undulation. The bulk of the groove side is a complex coexistence of Lo,Lo,s, and Ld,s lipids. The convex side of the undulation contains predominantly Lo lipids. Thus, the structure of the ripple phase is neither a simple coexistence of ordered and disordered lipids nor a coexistence of ordered interdigitating gel-like (Lo) and ordered-splayed (Lo,s) lipids, but instead a coexistence of an ordered phase and a complex mixed phase. Principal component analysis further confirmed the existence of the four lipid groups.

Inhibitory Effect of Lanthanides on Native Lipid Flip-Flop

The influence of ytterbium ions (Yb3+), a commonly used paramagnetic NMR chemical shift reagent, on the physical properties and flip-flop kinetics of dipalmitoylphosphatidylcholine (DPPC) planar supported lipid bilayers (PSLBs) was investigated. Langmuir isotherm studies revealed that Yb3+ interacts strongly with the phosphate headgroup of DPPC, evidenced by the increases in shear and compression moduli. Using sum-frequency vibrational spectroscopy, changes in the acyl chain ordering and phase transition temperature were also observed, consistent with Yb3+ interacting with the phosphate headgroup of DPPC. The changes in the physical properties of the membrane were also observed to be concentration dependent, with more pronounced modification observed at low (50 μM) Yb3+ concentrations compared to 6.5 mM Tb3+, suggesting a cross-linking mechanism between adjacent DPPC lipids. Additionally, the changes in membrane packing and phase transition temperatures in the presence of Tris buffer suggested that a putative Yb(Tris)3+ complex forms that coordinates to the PC headgroup. The kinetics of DPPC flip-flop in the gel and liquid crystalline (lc) phases were substantially inhibited in the presence of Yb3+, regardless of the Yb3+ concentration. Analysis of the flip-flop kinetics under the framework of transition state theory revealed that the free energy barrier to flip-flop in both the gel and lc phases was substantial increased over a pure DPPC membrane. In the gel phase, the trend in the free energy barrier appeared to follow the trend in the shear moduli, suggesting that the Yb3+-DPPC headgroup interaction was driving the increase in the activation free energy barrier. In the lc phase, activation free energies of DPPC flip-flop in the presence of 50 μM or 6.5 mM Yb3+ were found to mirror the free energies of TEMPO-DPPC flip-flop, leading to the conclusion that the strong interaction between Yb3+ and the PC headgroup was essentially manifested as a headgroup charge modification. These studies illustrate that the presence of the lanthanide Yb3+ results in significant modification to the lipid membrane physical properties and, more importantly, results in a pronounced inhibition of native lipid flip-flop.

Structural dynamics of chlorpromazine (CPZ) drug with dipalmitoylphosphatidylcholine (DPPC) lipid: a potential drug for SARS-CoV-2

There is an urgent requirement for drug discovery and more importantly drug repositioning due to infectious new Severe Acute Respiratory Syndrome coronavirus 2. As per the recent report published in the journal L'Encéphale in May 2020, there is a planned ReCoVery Study examining the repurposing the chlorpromazine for the treatment of COVID-19. Here, we apply a combined Raman microspectroscopy and DFT-MD approach to investigate the structural dynamics of the Chlorpromazine (CPZ) drug with dipalmitoylphosphatidylcholine (DPPC) lipid bilayer, identifying the specific position of the drug in the DPPC lipid bilayer. The intensity ratios of the Raman peaks I 2935/I 2880, I 1097/I 1064 and I 1097/I 1129 are representative of the interaction of drugs with lipid alkyl chains and furnish conformation of lipid alkyl chains. Raman imaging microscopy for the study of the distribution of CPZ inside the lipid vesicles is reported. We also investigated the influence of order and disorder ratio in the CPZ on the DPPC liposomes prepared on phase transition temperature. HIGHLIGHTS Drug–membrane interactions using micromolar concentrations of both lipid and drugs. Neuroleptic drug and DPPC vesicles composed of DPPC/drug mixtures reveal qualitative differences between the Raman spectra The temperature-controlled Raman microspectroscopic study has demonstrated that below phase-transition temperature, the fatty acid chains of the phospholipids are stiff and packed in a highly ordered array. DFT and MD simulations to understand molecular interactions, structural dynamics, and Raman spectra. Above phase-transition temperature, the chains are disordered and possess more motional freedom. Communicated by Ramaswamy H. Sarma

Incorporation of dehydrodieugenol, a neolignan isolated from Nectandra leucantha (Lauraceae), in lipid Langmuir monolayers as biomembrane models

Dehydrodieugenol, a neolignan isolated from the Brazilian plant Nectandra leucantha (Lauraceae) with reported antiprotozoal and anticancer activity, was incorporated in Langmuir monolayers of selected lipids as cell membrane models, aiming to comprehend its action mechanism at the molecular level. The interaction of this compound with the lipids dipalmitoylphosphatidylcholine (DPPC), dipalmitoylphosphatidylethanolamine (DPPE), dipalmitoylphosphatidylserine (DPPS), and dipalmitoylphosphatidylglycerol (DPPG) was inferred through tensiometry, infrared spectroscopy, and Brewster angle microscopy. The interactions had different effects depending on the chemical nature of the lipid polar head, with expansion for DPPC monolayers, condensation for DPPE, and expansion (at low surface pressures) followed by the overlap of the isotherms (at high surface pressure values) for DPPS and DPPG. Effects caused by dehydrodieugenol in the negatively charged lipids were distinctive, which was also reflected in the hysteresis assays, surface potential-area isotherms, and rheological measurements. Infrared spectroscopy indicated that the drug interaction with the monolayer affects not only the polar groups, but also the acyl lipid chains for all lipids. These results pointed to the fact that the interaction of the drug with lipid monolayers at the air-water interface is modulated by the lipid composition, mainly considering the polar head of the lipids, as well as the hydrophobicity of the lipids and the drug. As negatively charged lipids pointed to distinctive interaction, we believe this can be related to the antiprotozoal and anticancer properties of the compound.

Accurate and Efficient Estimation of Lennard–Jones Interactions for Coarse-Grained Particles via a Potential Matching Method

The Lennard-Jones (LJ) energy functions are commonly used to describe the nonbonded interactions in bulk coarse-grained (CG) models, which contribute significantly to the stabilization of a local binding configuration or a self-assembly system. In many cases, systematic development of the LJ interaction parameters in a CG model requires a comprehensive sampling of the objective molecules at the all-atom (AA) level, which is therefore extremely time-consuming for large systems. Inspired by the concept of electrostatic potential (ESP), we define the LJ static potential (LJSP), by which the embedding potential energy surface can be constructed analytically. A semianalytic approach, namely, the LJSP matching method, is developed here to derive the CG parameters by minimizing the LJSP difference between the AA and the CG models, which provides a universal way to derive the CG LJ parameters from the AA models without doing presampling. The LJSP matching method is successful not only in deriving the LJ interaction energy landscape in the CG models for proteins, lipids, and DNA but also in reproducing the critical properties such as intermediate structures and enthalpy contributions as exemplified in simulating the self-assembly process of the dipalmitoylphosphatidylcholine (DPPC) lipids.

Interactions between curcumin and cell membrane models by Langmuir monolayers

Studying interactions between potential anticancer drugs and cell membrane models is of great interest to explore the capability of novel drugs in the development of anticancer treatments. Lipid membrane models are useful to understand cellular interactions and to discern drug mechanism action. Here, the interactions of curcumin, as a bioactive natural compound with anti-cancer properties, with both healthy and cancerous or tumor cell membrane models, based on Langmuir monolayers, have been studied. The healthy-cell membrane model is composed of cholesterol 67%, and saturated lipid dipalmitoylphosphatidylcholine 33%. The cancerous-cell-membrane-model is composed of a lower proportion of cholesterol, 25%, and unsaturated lipid sphingomyelin 75%. To compare their interaction with curcumin we report the compression isotherms registered for both lipid membrane models and curcumin in different proportions, their compression moduli and the thermodynamic interaction parameters. From this analysis, we evidence a destabilizing interaction between curcumin and the cancerous cell membrane model in comparison with the healthy one. This interaction is further visualized by micro-Brewster Angle and Atomic Force Microscopies. Our experiments show that the drug enhances cohesion in the healthy membrane model whereas it fluidifies the cancerous cell membrane model causing thermodynamic destabilization. These are useful results to improve the selectivity of the drug avoiding adverse side effects of most current anticancer therapies.

Biocompatible and optically stable hydrophobic fluorescent carbon dots for isolation and imaging of lipid rafts in model membrane.

Lateral heterogeneity in cell membranes features a variety of compositions that influence their inherent properties. One such biophysical variation is the formation of a membrane or lipid raft, which plays important roles in many cellular processes. The lipid rafts on the cell membrane are mostly identified by specific dyes and heavy metal quantum dots, which have their own drawbacks, such as cytotoxicity, photostability, and incompatibility. To this end, we synthesized special, hydrophobic, fluorescent, photostable, and non-cytotoxic carbon dots (CDs) by solvent-free thermal treatment using non-cytotoxic materials and incorporated into the lipid bilayers of giant unilamellar vesicles (GUVs) made from 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC) and dipalmitoylphosphatidylcholine (DPPC) lipids. A 2:2:1 mixture of DOPC, DPPC, and cholesterol (Chol) develops lipid rafts on the membrane by phase separation. The photophysical properties of the CDs get modulated on incorporation into the lipid rafts that identifies the membrane heterogeneity. The main attempt in this work is to develop a new, simple, cost-effective, and bio-friendly lipid raft marker, which can be used in biological applications, alongside other conventional raft markers, with more advantages.

Effect of biphosphate salt on dipalmitoylphosphatidylcholine bilayer deformation by Tat polypeptide.

Translocation of positively charged cell penetrating peptides (CPP) through cell membrane is important in drug delivery. Here we report all-atom molecular dynamics simulations to investigate how a biphosphate salt in a solvent affects the interaction of a CPP, HIV-1 Tat peptide with model dipalmitoylphosphatidylcholine (DPPC) lipid bilayer. Tat peptide has a large number of basic arginines and a couple of polar glutamines. We observe that in absence of salt, the basic residues of the polypeptide get localized in the vicinity of the membrane without altering the bilayer properties much; polypeptide induce local thinning of the bilayer membrane at the area of localization. In presence of biphosphate salt, the basic residues, dressed by the biphosphate ions, are repelled by the phosphate head groups of the lipid molecules. However, polar glutamine prefers to stay in the vicinity of the bilayer. This leads to larger local bilayer thickness at the contact point by the polar residue and non-uniform bilayer thickness profile. The thickness deformation of bilayer structure disappears upon mutating the polar residue, suggesting importance of the polar residue in bilayer deformation. Our studies point to control bilayer deformation by appropriate peptide sequence and solvent conditions.

Theoretical insights into the uptake of sulfonamides onto phospholipid bilayers: Mechanisms, interaction and toxicity evaluation

Sulfonamides (SAs) are now recognized as the main emerging environmental pollutants in aquatic environments. Although the bioaccumulation capacities of SAs have been confirmed, the pathway for the penetration of the SAs into lipid bilayer has been not fully understood. In this study, the bioaccumulation mechanism of four typical SAs onto the dipalmitoyl phosphatidylcholine (DPPC) lipid bilayer and their effects on the properties of DPPC bilayer were employed and evaluated respectively by using molecular dynamics simulations. Results show that from the viewpoint of thermodynamics, it is favorable for these SAs partitioning to DPPC bilayer. The accommodation of four SAs onto the lipid membrane needs to undergo several processes, which include the contact stage, transformation stage, and absorption stage. Besides, the sulfamethoxazole (SMX) and sulfamethazine (SMZ) show a strong preference for the DPPC phase rather than the interface region while the sulfadiazine (SDZ) and sulfametoxydiazine (SMD) have similar tendencies in the interface region and DPPC phase. Furthermore, the cytotoxicity of SAs is reflected in their ability to affect the electrostatic potential of the membrane and to reduce the thickness of phospholipid bilayers. This molecular-level study provided an insightful understanding of the toxicity and bioaccumulation of SAs.

Nanoscale Structure and Dynamics of Model Membrane Lipid Raft Systems, Studied by Neutron Scattering Methods

Quasi-elastic neutron scattering (QENS) and small angle neutron scattering (SANS), in combination with isotopic contrast variation, have been used to determine the structure and dynamics of three-component lipid membranes, in the form of vesicles, comprising an unsaturated [palmitoyl-oleoyl-phosphatidylcholine (POPC) or dioleoyl-phosphatidylcholine (DOPC)], a saturated phospholipid (dipalmitoyl-phosphatidylcholine (DPPC)), and cholesterol, as a function temperature and composition. SANS studies showed vesicle membranes composed of a 1:1:1 molar ratio of DPPC:DOPC:cholesterol and a 2:2:1 molar ratio of DPPC:POPC:cholesterol phase separated, forming lipid rafts of ∼18 and ∼7 nm diameter respectively, when decreasing temperature from 308 to 297 K. Phase separation was reversible upon increasing temperature. The larger rafts observed in systems containing DOPC are attributed to the greater mis-match in lipid alkyl chains between DOPC and DPPC, than for POPC and DPPC. QENS studies, over the temperature range 283–323K, showed that the resulting data were best modelled by two Lorentzian functions: a narrow component, describing the “in-plane” lipid diffusion, and a broader component, describing the lipid alkyl chain segmental relaxation. The overall “in-plane” diffusion was found to show a significant reduction upon increasing temperature due to the vesicle membranes transitioning from one containing rafts to one where the component lipids are homogeneously mixed. The use of different isotopic combinations allowed the measured overall reduction of in-plane diffusion to be understood in terms of an increase in diffusion of the saturated DPPC lipid and a corresponding decrease in diffusion of the unsaturated DOPC/POPC lipid. As the rafts are considered to be composed principally of saturated lipid and cholesterol, the breakdown of rafts decreases the exposure of the DPPC to cholesterol whilst increasing the exposure of cholesterol to unsaturated lipid. These results show the sensitivity of lipid diffusion to local cholesterol concentration, and the importance of considering the local, rather that the global composition of a membrane when understanding the diffusion processes of lipids within the membrane. The novel combination of SANS and QENS allows a non-intrusive approach to characterize the structure and dynamics occurring in phase-separated model membranes which are designed to mimic the lateral heterogeneity of lipids seen in cellular membranes–a heterogeneity that can have pathological consequences.

Liposome evaluation in inhibiting pump efflux of NorA of Staphylococcus aureus

Liposomes, in addition to providing greater efficacy to antibiotics, decrease toxicity and increase selectivity. This work has as main objectives the sensitization of the need to solve bacterial resistance to antibiotics, addressing the potential of antibiotics carried by liposome. In the preparation of the liposomes, the lipids dipalmitoyl phosphatidylcholine (DPPC), dipalmitoyl phosphatidylserine (DPPS), and cholesterol (COL) with > 99% purity were used. The Staphylococcus aureus strains used were SA-1199B, which expresses the NorA gene encoding the NorA efflux protein, which expels hydrophilic fluoroquinolones and other drugs intercalating DNA dyes, and the wild strain SA-1199. The liposomes associated with antibiotics in the wild type of strain SA-1199 and the carrier strain of pump 1199B, had a better representation of growth inhibition than the wild type strain SA-1199. Given the potential for inhibition of efflux pump seen in the results, we highlight the creation of new drugs or alteration of existing drugs. They are not recognized by the efflux pumps and removed from the target cell.

How Ethanolic Disinfectants Disintegrate Coronavirus Model Membranes: A Dissipative Particle Dynamics Simulation Study.

We have developed dissipative particle dynamics models for pure dipalmitoylphosphatidylcholine (DPPC), dioleoylphosphatidylcholine (DOPC), and dimyristoylphosphatidylcholine (DMPC) as well as their binary and ternary mixed membranes, as coronavirus model membranes. The stabilities of pure and mixed membranes, surrounded by aqueous solutions containing up to 70 mol % ethanol (alcoholic disinfectants), have been investigated at room temperature. We found that aqueous solutions containing 5–10 mol % ethanol already have a significant weakening effect on the pure and mixed membranes. The magnitude of the effect depends on the membrane composition and the ethanol concentration. Ethanol permeabilizes the membrane, causing its lateral swelling and thickness shrinking and reducing the orientational order of the hydrocarbon tail of the bilayer. The free energy barrier for the permeation of ethanol in the bilayers is considerably reduced by the ethanol uptake. The rupture-critical ethanol concentrations causing the membrane failure are 20.7, 27.5, and 31.7 mol % in the aqueous phase surrounding pure DMPC, DOPC, and DPPC membranes, respectively. Characterizing the failure of lipid membranes by a machine-learning neural network framework, we found that all mixed binary and/or ternary membranes disrupt when immersed in an aqueous solution containing a rupture-critical ethanol concentration, ranging from 20.7 to 31.7 mol %, depending on the composition of the membrane; the DPPC-rich membranes are more intact, while the DMPC-rich membranes are least intact. Due to the tight packing of long, saturated hydrocarbon tails in DPPC, increasing the DPPC content of the mixed membrane increases its stability against the disinfectant. At high DPPC concentrations, where the DOPC and DMPC molecules are confined between the DPPC lipids, the ordered hydrocarbon tails of DPPC also induce order in the DOPC and DMPC molecules and, hence, stabilize the membrane more. Our simulations on pure and mixed membranes of a diversity of compositions reveal that a maximum ethanol concentration of 32 mol % (55 wt %) in the alcohol-based disinfectants is enough to disintegrate any membrane composed of these three lipids.

Interaction of Cyanine-D112 with Binary Lipid Mixtures: Molecular Dynamics Simulation and Differential Scanning Calorimetry Study.

This comprehensive molecular dynamics (MD) simulation and experimental study investigates the lipid bilayer interactions of dye D112 for potential photodynamic therapy (PDT) applications. PDT involves formation of a reactive oxidant species in the presence of a light sensitive molecule and light, interrupting cellular functions. D112 was developed as a photographic emulsifier, and we hypothesized that its combined cationic and lipophilic nature can render a superior photosensitizing property–crucial in various light therapies. The focus of this study is to elucidate the binding and insertion mechanisms of D112 with mixed lipid bilayers of anionic dipalmitoyl-phosphatidylserine (DPPS) and zwitterionic dipalmitoyl-phosphatidylcholine (DPPC) lipids to resemble cancer cell membranes. Our studies confirm initial electrostatic binding between the positively charged moieties of D112 and negatively charged lipid headgroups. Additionally, MD simulations combined with differential scanning calorimetry (DSC) studies confirm that D112-lipid interactions are governed by enthalpy-driven nonclassical hydrophobic effects in the membrane interior. It was further noted that despite the electrostatic preference of D112 toward the anionic lipids, D112 molecules colocalized on DPPC-rich domains after insertion. Atomistic level MD studies point toward two possible insertion mechanisms for D112: harpoon and flip. Further insights from the simulation showcase the interactions of low and high aggregates of D112 with the bilayer as the concentration of D112 increases in solution. The size of aggregates modulates the orientation and degree of insertion, providing important information for future studies on membrane permeation mechanisms.

Graphene Quantum Dot Assisted Translocation of Daunomycin through an Ordered Lipid Membrane: A Study by Fluorescence Lifetime Imaging Microscopy and Resonance Energy Transfer.

Daunomycin (DN) is a well-known chemotherapy drug frequently used in treating acute myeloid and lymphoblastic leukemia. It needs to be delivered to the therapeutic target by a delivering agent that beats the blood-brain barrier. DN is known to be specifically located at the membrane surface and scantly to the bilayer. Penetration of DN into the membrane bilayer depends on the molecular packing of the lipid. It does not travel promptly to the interior of the cells and needs a carrier to serve the purpose. Here, we have demonstrated, by fluorescence lifetime imaging spectroscopy (FLIM) and resonance energy transfer (RET) phenomenon, that ultrasmall graphene quantum dots (GQDs) can be internalized into the aqueous pool of giant unilamellar vesicles (GUVs) made from dipalmitoylphosphatidylcholine (DPPC) lipids, which, in turn, help in fast translocation of DN through the membrane without any delivery vehicle.