Aspirin-Induced Ordering and Faster Dynamics of a Cationic Bilayer for Drug Encapsulation.

The lipid dynamics and phase play decisive roles in drug encapsulation and delivery to the intracellular target. Thus, understanding the dynamic and structural alterations of membranes induced by drugs is essential for targeted delivery. To this end, united-atom molecular dynamics simulations of a model bilayer, dioctadecyldimethylammonium bromide (DODAB), are performed in the absence and presence of the usual nonsteroidal anti-inflammatory drug (NSAID), aspirin, at 298, 310, and 345 K. At 298 and 310 K, the bilayers are in the interdigitated two-dimensional square phases, which become rugged in the presence of aspirin, as evident from height fluctuations. At 345 K, the bilayer is in the fluid phase in both the absence and presence of aspirin. Aspirin is preferentially located near the oppositely charged headgroup and creates void space, which leads to an increase in the interdigitation and order parameters. Although the center of mass of lipids experiences structural arrest, they reach the diffusive regime faster and have higher lateral diffusion constants in the presence of aspirin. Results are found to be consistent with recent quasi-elastic neutron scattering studies that reveal that aspirin acts as a plasticizer and enhances lateral diffusion of lipids in both ordered and fluid phases. Different relaxation time scales of the bonds along the alkyl tails of DODAB due to the multitude of lipid motions become faster upon the addition of aspirin. Our results show that aspirin insertion is most favorable at physiological temperature. Thus, the ordered, more stable, and faster DODAB bilayer can be a potential drug carrier for the protected encapsulation of aspirin, followed by targeted and controlled drug release with antibacterial activity in the future.

Cholesterol-Controlled Interaction of Ionic Liquids with Model Cellular Membranes.

While ionic liquids (ILs) are considered as prospective ingredients of new antimicrobial agents, it is important to understand the adverse effects of these molecules on human cells. Since cholesterol is the essential component of a human cell membrane, in the present study, the effect of an imidazolium-based IL has been investigated on the model membrane in the presence of cholesterol. The area per sphingomyelin lipid is found to reduce in the presence of the IL, which is quantified by the area-surface pressure isotherm of the lipid monolayer formed at the air-water interface. The effect is considerably diminished in the cholesterol-containing monolayer. Further, the IL is observed to decrease the rigidity of the cholesterol-free monolayer. Interestingly, the presence of cholesterol does not allow any change in this property of the layer at lower surface pressure. However, at a higher surface pressure, the IL increases the elasticity in the cholesterol-induced condensed phase of the lipid layer. The X-ray reflectivity measurement on a stack of cholesterol-free lipid bilayers proved the formation of IL-induced phase-separated domains in the matrix of a pure lipid phase. These domains are found to be formed by interdigitating the chains of the lipids, producing a thinner membrane. Such a phase is less intense in the cholesterol-containing membrane. All of these results indicate that the IL molecules may deform the cholesterol-free membrane of a bacterial cell, but the same may not be harmful to human beings as cholesterol could restrict the insertion in the cellular membrane of a human cell.

1,3 Dialkylated Imidazolium Ionic Liquid Causes Interdigitated Domains in a Phospholipid Membrane.

Amphiphilic imidazolium-based ionic liquids (ILs) have proven their efficacy in altering the membrane integrity and dynamics. The present article investigates the phase-separated domains in a 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) membrane induced by 1,3 dialkylated imidazolium IL. Isotherm measurements on DPPC monolayers formed at the air-water interface have shown a decrease in the mean molecular area with the addition of this IL. The positive value of the excess Gibbs free energy of mixing indicates an unfavorable mixing of the IL into the lipid. This leads to IL-induced phase-separated domains in the multilayer of the lipid confirmed by the occurrence of two sets of equidistance peaks in the X-ray reflectivity data. The electron density profile along the surface normal obtained by the swelling method shows the bilayer thickness of the newly formed IL-rich phase to be substantially lower (∼34 Å) than the DPPC phase (∼45.8 Å). This IL-rich phase has been confirmed to be interdigitated, showing an enhanced electron density in the tail region due to the overlapping hydrocarbon chains. Differential scanning calorimetry measurements showed that the incorporation of IL enhances the fluidity of the lipid bilayer. Therefore, the study indicates the formation of an interdigitated phase with a lower order compared to the gel phase in the DPPC membrane supplemented with the IL.

Ubiquicidin-Derived Peptides Selectively Interact with the Anionic Phospholipid Membrane.

Ubiquicidin (UBI)/ribosomal protein S30 (RS30) is an intracellular protein with antimicrobial activities against various pathogens. UBI (29-41) and UBI (31-38) are two crucial peptides derived from Ubiquicidin, which have shown potential as infection imaging probes. Here, we report the interactions of UBI-derived peptides with anionic and zwitterionic phospholipid membranes. Our isothermal titration calorimetry results show that both peptides selectively interact with the anionic phospholipid membrane (a model bacterial membrane) and reside mainly on the membrane surface. The interaction of UBI-derived peptides with the anionic phospholipid membrane is exothermic and driven by both enthalpy (ΔH) and entropy (ΔS), with the entropic term TΔS being greater than ΔH. This large entropic term can be a result of the aggregation of the anionic vesicles, which is confirmed by dynamic light scattering (DLS) measurements. DLS data show that vesicle aggregation is enhanced with increasing peptide-to-lipid molar ratios (P/L) and is found to be more pronounced in the case of UBI (29-41). DLS results are found to be consistent with independent transmission measurements. To study the effects of UBI-derived peptides on the microscopic dynamics of the model bacterial membrane, quasielastic neutron scattering (QENS) measurements have been carried out. The QENS results show that both peptides restrict the lateral motion of the lipid within the leaflet. UBI (29-41) acts as a stronger stiffening agent, hindering the lateral diffusion of lipids more efficiently than UBI (31-38). To our knowledge, this is the first report illustrating the mechanism of interaction of UBI-derived peptides with model membranes. This study also has implications for the improvement and design of antimicrobial peptide-based infection imaging probes.

Effect of an Antimicrobial Peptide on Lateral Segregation of Lipids: A Structure and Dynamics Study by Neutron Scattering.

Antimicrobial peptides are one of the most promising classes of antibiotic agents for drug-resistant bacteria. Although the mechanisms of their action are not fully understood, many of them are found to interact with the target bacterial membrane, causing different degrees of perturbations. In this work, we directly observed that a short peptide disturbs membranes by inducing lateral segregation of lipids without forming pores or destroying membranes. Aurein 1.2 (aurein) is a 13-amino acid antimicrobial peptide discovered in the frog Litoria genus that exhibits high antibiotic efficacy. Being cationic and amphiphilic, it binds spontaneously to a membrane surface with or without charged lipids. With a small-angle neutron scattering contrast matching technique that is sensitive to lateral heterogeneity in membrane, we found that aurein induces significant lateral segregation in an initially uniform lipid bilayer composed of zwitterionic lipid and anionic lipid. More intriguingly, the lateral segregation was similar to the domain formed below the order-disorder phase-transition temperature. To our knowledge, this is the first direct observation of lateral segregation caused by a peptide. With quasi-elastic neutron scattering, we indeed found that the lipid lateral motion in the fluid phase was reduced even at low aurein concentrations. The reduced lateral mobility makes the membrane prone to additional stresses and defects that change membrane properties and impede membrane-related biological processes. Our results provide insights into how a short peptide kills bacteria at low concentrations without forming pores or destroying membranes. With a better understanding of the interaction, more effective and economically antimicrobial peptides may be designed.

Effects of ionic liquids on biomembranes: A review on recent biophysical studies.

Ionic liquids (ILs) have been emerged as a versatile class of compounds that can be easily tuned to achieve desirable properties for various applications. The ability of ILs to interact with biomembranes has attracted significant interest, as they have been shown to modulate membrane properties in ways that may have implications for various biological processes. This review provides an overview of recent studies that have investigated the interaction between ILs and biomembranes. We discuss the effects of ILs on the physical and chemical properties of biomembranes, including changes in membrane fluidity, permeability, and stability. We also explore the mechanisms underlying the interaction of ILs with biomembranes, such as electrostatic interactions, hydrogen bonding, and van der Waals forces. Additionally, we discuss the future prospects of this field.

A novel recombinant tomato-infecting begomovirus capable of transcomplementing heterologous DNA-B components.

The genome of a tomato-infecting begomovirus from Ranchi, India, was cloned, sequenced and analysed. The viral genome shared 88.3% sequence identity with an isolate belonging to the species Tobacco curly shoot virus (TbCSV), and this virus should therefore be considered a member of a new species, tentatively named Tomato leaf curl Ranchi virus (ToLCRnV). The DNA-ß molecule, which had 74.5% sequence identity with tomato leaf curl Bangladesh betasatellite (ToLCBDB), is named tomato leaf curl Ranchi betasatellite (ToLCRnB). Phylogenetic analysis revealed that ToLCRnV is related to tomato leaf curl Bangladesh virus (ToLCBDV), tobacco curly shoot virus (TbCSV) and tomato leaf curl Gujarat virus (ToLCGV). An infectivity study with ToLCRnV established the monopartite nature of the viral genome, whereas inoculation with ToLCRnB resulted in increased symptom severity. ToLCRnV could transreplicate DNA-B of tomato leaf curl Gujarat virus (ToLCGV) and tomato leaf curl New Delhi virus (ToLCNDV), both in N. benthamiana and tomato, although DNA-B accumulation of was less than with the wild-type combinations. ToLCRnB could be efficiently replicated by DNA-A of both ToLCNDV and ToLCGV. A leaf disk assay suggests that DNA-A could transreplicate the homologous DNA-B and DNA-ß more efficiently than the heterologous one.

Antimicrobial Peptides: Vestiges of Past or Modern Therapeutics?

The ubiquitous occurrence of Antimicrobial Peptides (AMPs) in all domains of life emphasizes their crucial role as ancient mediators of host defense. Despite their antiquity and prolonged history of exposure to pathogens, endogenous AMPs continue to serve as effective antibiotics. An "evolutionary arms race" between host and pathogen resulted in structural diversity of AMPs, leading these molecules to retain activity against a wide range of pathogens, including antibiotic-resistant microbes. As the menace of antibiotic resistance continues to render most antibiotics ineffective against pathogens, the search for novel drug candidates has taken the center stage. The ability of AMPs to combat antibiotic-resistant microbes gave rise to a remarkable surge of interest in AMPs as potential therapeutics. Apart from being effective antimicrobials, AMPs have also found application as probes suitable for in-situ diagnosis of infection. Here, we review the evolutionary history of AMPs, their structural diversity, and mechanism of interaction with microbial membranes. We also summarize the role of AMPs as modern pharmaceuticals and challenges to this development.

Enhanced Microscopic Dynamics of a Liver Lipid Membrane in the Presence of an Ionic Liquid.

Ionic liquids (ILs) are an important class of emerging compounds, owing to their widespread industrial applications in high-performance lubricants for food and cellulose processing, despite their toxicity to living organisms. It is believed that this toxicity is related to their actions on the cellular membrane. Hence, it is vital to understand the interaction of ILs with cell membranes. Here, we report on the effects of an imidazolium-based IL, 1-decyl-3-methylimidazolium tetrafluoroborate (DMIM[BF4]), on the microscopic dynamics of a membrane formed by liver extract lipid, using quasielastic neutron scattering (QENS). The presence of significant quasielastic broadening indicates that stochastic molecular motions of the lipids are active in the system. Two distinct molecular motions, (i) lateral motion of the lipid within the membrane leaflet and (ii) localized internal motions of the lipid, are found to contribute to the QENS broadening. While the lateral motion could be described assuming continuous diffusion, the internal motion is explained on the basis of localized translational diffusion. Incorporation of the IL into the liver lipid membrane is found to enhance the membrane dynamics by accelerating both lateral and internal motions of the lipids. This indicates that the IL induces disorder in the membrane and enhances the fluidity of lipids. This could be explained on the basis of its location in the lipid membrane. Results are compared with various other additives and we provide an indication of a possible correlation between the effects of guest molecules on the dynamics of the membrane and its location within the membrane.

Neutron Scattering Studies of the Interplay of Amyloid ß Peptide(1-40) and An Anionic Lipid 1,2-dimyristoyl-sn-glycero-3-phosphoglycerol.

The interaction between lipid bilayers and Amyloid ß peptide (Aß) plays a critical role in proliferation of Alzheimer's disease (AD). AD is expected to affect one in every 85 humans by 2050, and therefore, deciphering the interplay of Aß and lipid bilayers at the molecular level is of profound importance. In this work, we applied an array of neutron scattering methods to study the structure and dynamics of Aß(1-40) interacting 1,2-dimyristoyl-sn-glycero-3-phosphoglycerol (DMPG) bilayers. In the structural investigations of lipid bilayer's response to Aß binding, Small Angle Neutron Scattering and Neutron Membrane Diffraction revealed that the Aß anchors firmly to the highly charged DMPG bilayers in the interfacial region between water and hydrocarbon chain, and it doesn't penetrate deeply into the bilayer. This association mode is substantiated by the dynamics studies with high resolution Quasi-Elastic Neutron Scattering experiments, showing that the addition of Aß mainly affects the slower lateral motion of lipid molecules, especially in the fluid phase, but not the faster internal motion. The results revealed that Aß associates with the highly charged membrane in surface with limited impact on the structure, but the altered membrane dynamics could have more influence on other membrane processes.