Lipid Vesicles Research Articles

α-Synuclein interaction with POPC/POPS vesicles.

We have investigated the adsorption of the amyloid-forming protein α-Synuclein (αSyn) onto small unilamellar vesicles composed of a mixture of zwitterionic POPC and anionic POPS lipids. αSyn monomers adsorb onto the anionic lipid vesicles where they adopt an α-helical secondary structure. The degree of adsorption depends on the fraction of anionic lipid in the mixed lipid membrane, but one needs to consider the electrostatic shift of the serine pKa with increasing fraction of POPS. The vesicles with adsorbed αSyn monomers are kinetically stable. However, after fibrils have been formed, here triggered by the addition of a small concentration of pre-formed fibrils (seeds), we observed that the average vesicle size increased by approximately a factor of two. This increase in the vesicle size can be explained by vesicle fusion taking place during the fibril formation process.

Pseudo-Phosphorylated Tau Forms Paired Helical Filaments in the Presence of High-Curvature Cholesterol-Containing Lipid Membranes.

The tau protein misfolds in neurodegenerative diseases such as Alzheimer's disease (AD). These pathological tau aggregates are associated with neuronal membranes, but molecular structural information about how disease-like tau fibrils interact with the lipid membrane is scarce. Here, we use solid-state NMR to investigate the structure of a tau construct bearing four AD-relevant phospho-mimetic mutations (4E tau) with cholesterol-containing high-curvature lipid membranes, which mimic the membrane of synaptic vesicles in neurons. We show that 4E tau adopts the AD paired helical filament (PHF) fold in the presence of the membrane at high protein concentrations. Moreover, it inserts into the membrane-water interface with an orientation that suggests possible bridging of multiple lipid vesicles. At lower protein concentrations, moderate chemical shift changes are observed, indicating a perturbation of the PHF structure by the lipids. Removal of the phospho-mimetic mutations led to a qualitatively different β-sheet conformation. These results indicate that posttranslational modifications impact the tau fibril structure more strongly than lipid membranes, but the membrane modulates the conformational equilibria of the aggregates.

Investigating Complexin-Membrane Interactions Using NMR and Optical Methods.

Complexins are a family of small presynaptic proteins that regulate neurotransmitter release at nerve terminals and are highly conserved in evolution. While direct interactions with SNARE proteins are critical for all complexin functions, binding of their disordered C-terminal domains (CTD) to membranes, especially to synaptic vesicle membranes, is essential for the ability of complexin to inhibit vesicle release. Furthermore, while some complexin CTDs possess an endogenous affinity for membranes, other complexin isoforms are subject to lipidation at their C-termini, which is presumed to confer additional membrane binding. Therefore, an in depth understanding of complexin-membrane interactions is required to elucidate the mechanistic basis for their inhibitory activity. Here we describe protocols for characterizing complexin-membrane interactions using solution state nuclear magnetic resonance (NMR) spectroscopy as well as single molecule total-internal reflection fluorescence (TIRF) methods, along with protocols for generating isotopically labeled samples of unmodified and farnesylated complexins and for characterizing synthetic lipid vesicles using dynamic light scattering (DLS).

Effect of osmotic pressure on membrane permeation through antimicrobial peptide-induced pores.

Most antimicrobial peptides (AMPs) induce membrane damage such as pore formation in bacterial cells, resulting in rapid cell death. On the other hand, bacterial cells have a large intracellular turgor pressure, i.e., an osmotic pressure (Π) due to higher osmolarity inside bacterial cells, but the effects of Π on the membrane permeation of the internal contents of lipid vesicles and cells through AMP-induced pores are unknown. Here, we investigated the effect of Π on the membrane permeability of a water-soluble fluorescent probe, AlexaFluor 488 hydrazide (AF488), when passing through peptidyl-glycylleucine-carboxyamide (PGLa)- or magainin 2 (Mag)-induced nanopores in giant unilamellar vesicles (GUVs). For the interaction of PGLa with single GUVs under Π, the onset of pore formation was followed by a gradual increase in the membrane permeability coefficient, MP, until MP reached a steady value, Ps. On the other hand, for the interaction of Mag with single GUVs under Π, the onset of pore formation was rapidly followed by a change of MP to Ps. Small Π values enhanced the Ps values of AF488 passing through the PGLa- or Mag-induced nanopores. The mechanisms underlying the increase of Ps at small Π values were discussed. Based on these results and our previous results that the membrane tension (due to Π) enhances rate of AMP-induced pore formation, we consider the role of turgor pressure in AMP-induced damage in bacterial membranes and the efflux of internal contents.

Nanozymes and Their Potential Roles in the Origin of Life.

The origin of life has long been a central scientific challenge, with various hypotheses proposed. The chemical evolution, which supposes that inorganic molecules can transform into organic molecules and subsequent primitive cells, laid the foundation for modern theories. Inorganic minerals are believed to play crucial catalytic roles in the process. However, the harsh reaction conditions of inorganic minerals hinder the accumulation of organic molecules, preventing the efficient transition from inorganic molecules to biomacromolecules. Given the inherent physicochemical properties and enzyme-like activities, this study proposes that nanozymes, nanomaterials with enzyme-like activities, act as efficient prebiotic catalysts in the origin of life. This hypothesis is based on the following: First, unlike traditional minerals, nanominerals can catalyze organic synthesis under milder conditions. Second, nanominerals can not only protect biomolecules from radiation damage but also catalyze polymerization reactions to form functional biomacromolecules and further lipid vesicles. More importantly, nanominerals are abundant in terrestrial and extraterrestrial environments. This perspective will systematically discuss the potential roles of nanozymes in the emergence of life based on the functions of minerals and the characteristics of nanozymes. We hope the research on nanozymes and the origin of life will bridge the gap between inorganic precursors and biomolecules under primitive environments.

Biomimetic astrocyte cell membrane-fused nanovesicles for protecting neurovascular units in hypoxic ischemic encephalopathy

Hypoxic ischemic encephalopathy (HIE) refers to neonatal hypoxic brain injury caused by severe asphyxia during the perinatal period. With a high incidence rate and poor prognosis, HIE accounts for 2.4% of the global disease burden, imposing a heavy burden on families and society. Current clinical treatment for HIE primarily focuses on symptomatic management and supportive care. Therefore, the developments of effective treatment strategies and new drug formulations are critical for improving the prognosis of HIE patients. In order to protect the compromised neurovascular units after HIE, we prepared membrane-fused nanovesicles for delivering rapamycin and si EDN1 (TRCAM@RAPA@si EDN1). Due to the homotypic targeting feature of membrane-fused nanovesicles, we employed astrocyte membranes as synthetic materials to improve the targeting of astrocytes in brain while reducing the clearance of nanovesicles by circulatory system. Additionally, the surface of cell membrane was modified with CXCR3 receptors, enhancing the homing of nanovesicles to infarcted lesions. Lipid vesicles were modified with TK and RVG29 transmembrane peptides, enabling responsive release of internal drugs and blood-brain barrier penetration. Internally loaded rapamycin could promote protective autophagy in astrocytes, improve cellular oxidative stress, while si EDN1 could reduce the expression level of endothelin gene, thereby reducing secondary damage to neurovascular units.Graphical

Identifying the composition of large vesicles in the cytoplasm of oocytes.

Context Oocyte vesicles, or vacuoles, have been described using transmission electron microscopy in most species. In sheep and cow oocytes, vesicles constitute up to 30% of the cytoplasm, their volume decreases during maturation and is lower in poorer quality oocytes, suggesting they are important for oocyte competence. However, the composition and function of these organelles is unknown. Aim This study aimed to ascertain the content of oocyte vesicles and examine the effect of different fixation methods on the size and preservation of these organelles. Methods Sheep oocytes were centrifuged to segregate organelles then stained with organelle-specific fluorescent dyes (Nile Red, LysoTracker, Fluo-4-AM and TMRM) and imaged by live cell confocal microscopy. The oocytes were fixed with either glutaraldehyde or paraformaldehyde and prepared for electron microscopy to confirm the distribution of organelles and compare ultrastructure and organelle size. Key results Nile Red staining has identified that vesicles contain lipid that is different to that in the osmium-stained lipid droplets observed by electron microscopy. Lipid droplets and vesicles were significantly smaller when prepared for electron microscopy compared to live cell imaging. Organelles were less likely to be fully segregated following centrifugation in oocytes prior to maturation (20%) compared to oocytes after maturation (77%; P Conclusions Oocyte vesicles are lipid storing organelles that may be important for oocyte quality. Implications This study highlights the importance of lipid for oocyte quality and the need for further research to identify the optimal fatty acid content for in vitro maturation media and oocyte competence.

Enzymatically Polymerized Organic Conductors on Native Lipid Membranes.

The dual capability of conductive polymers to conduct ions and electrons, in combination with their flexible mechanical properties, makes them ideal for bioelectronic applications. This study explores the in situ enzymatic polymerization of water-soluble π-conjugated monomers on native lipid bilayers derived from the F11 cell line, mimicking mammalian neural membranes. Enzymatic polymerization was catalyzed using horseradish peroxidase (HRP) in the presence of oxidant hydrogen peroxide (H2O2) and monitored via electrochemical quartz crystal microbalance with dissipation (EQCM-D) and electrochemical impedance spectroscopy (EIS). Results showed polymerization with HRP. The structural properties of the formed polymer films were characterized ex situ using atomic force microscopy (AFM), while the quality of the F11 native lipid vesicles and bilayer was respectively assessed through dynamic light scattering (DLS) and fluorescence recovery after photobleaching (FRAP) techniques. This work demonstrates, for the first time, the feasibility of the in situ formation of conductive polymers on native lipid membranes, offering a promising approach for the development of minimally invasive neural electrodes to diagnose and treat neurological disorders.

Spontaneous Emergence of Lipid Vesicles in a Coacervate‐Based Compartmentalized System

The spontaneous emergence of lipid vesicles in the absence of evolved biological machinery represents a major challenge for bottom‐up synthetic biology. We show that coacervate microdroplets could create a compartmentalized environment that enriches lipid molecules and facilitates their spontaneous assembly into lipid vesicles. These vesicles can escape from the coacervate microdroplets in a continuous process under non‐equilibrium conditions, resembling a constant production process akin to a "primitive enzyme" factory assembly line. These findings significantly extend our understanding of the intricate interaction between lipid molecules and coacervate microdroplets, shedding light on the emergence of cellular systems and offering a new perspective on the conditions necessary for the development of life on Earth.

Spontaneous Emergence of Lipid Vesicles in a Coacervate-Based Compartmentalized System.

The spontaneous emergence of lipid vesicles in the absence of evolved biological machinery represents a major challenge for bottom-up synthetic biology. We show that coacervate microdroplets could create a compartmentalized environment that enriches lipid molecules and facilitates their spontaneous assembly into lipid vesicles. These vesicles can escape from the coacervate microdroplets in a continuous process under non-equilibrium conditions, resembling a constant production process akin to a "primitive enzyme" factory assembly line. These findings significantly extend our understanding of the intricate interaction between lipid molecules and coacervate microdroplets, shedding light on the emergence of cellular systems and offering a new perspective on the conditions necessary for the development of life on Earth.

A Versatile DIY 3D Printed Device for the Preparation of Gian Lipid Vesicles as Model Membranes by Electroformation: Design and Fabrication

Una forma sencilla de estudiar las propiedades de la membrana celular y su interacción con otras moléculas es mediante el uso de sistemas modelo con la misma estructura básica. Estos utilizan unos pocos componentes básicos que simulan las condiciones de la membrana plasmática y se han utilizado ampliamente para estudiar las propiedades de las membranas biológicas. Entre estos sistemas modelo, podemos encontrar mono capas de Langmuir, bicapas soportadas y vesículas lipídicas. Las vesículas lipídicas son particularmente interesantes debido a que su estructura esférica imita a las membranas celulares. Entre los diferentes procedimientos para preparar GUV's (vesículas unilamelares gigantes), la electroformación destaca porque las vesículas producidas por este método son en su mayoría más grandes que 100 nm y unilamelares, lo que las hace fácilmente visibles mediante microscopía óptica convencional. Aunque existen dispositivos comerciales disponibles, generalmente se fabrican equipos personalizados de manera artesanal. Este trabajo describe el diseño y la fabricación de un dispositivo sencillo y versátil impreso en 3D para preparar vesículas lipídicas gigantes utilizando el método de electroformación. El dispositivo ha sido diseñado para fijarse en la platina del microscopio.

Enhanced Stability and In Vitro Biocompatibility of Chitosan-Coated Lipid Vesicles for Indomethacin Delivery.

Lipid vesicles, especially those utilizing biocompatible materials like chitosan (CHIT), hold significant promise for enhancing the stability and release characteristics of drugs such as indomethacin (IND), effectively overcoming the drawbacks associated with conventional drug formulations. This study seeks to develop and characterize novel lipid vesicles composed of phosphatidylcholine and CHIT that encapsulate indomethacin (IND-ves), as well as to evaluate their in vitro hemocompatibility. The systems encapsulating IND were prepared using a molecular droplet self-assembly technique, involving the dissolution of lipids, cholesterol, and indomethacin in ethanol, followed by sonication and the gradual incorporation of a CHIT solution to form stable vesicular structures. The vesicles were characterized in terms of size, morphology, Zeta potential, and encapsulation efficiency and the profile release of drug was assessd. In vitro hemocompatibility was evaluated by measuring erythrocyte lysis and quantifying hemolysis rates. The IND-ves exhibited an entrapment efficiency of 85%, with vesicles averaging 317.6 nm in size, and a Zeta potential of 24 mV, indicating good stability in suspension. In vitro release kinetics demonstrated an extended release profile of IND from the vesicles over 8 h, contrasting with the immediate release observed from plain drug solutions. The hemocompatibility assessment revealed that IND-ves exhibited minimal hemolysis, comparable to control groups, indicating good compatibility with erythrocytes. IND-ves provide a promising approach for modified indomethacin delivery, enhancing stability and hemocompatibility. These findings suggest their potential for effective NSAID delivery, with further in vivo studies required to explore clinical applications.

Lipid Demixing Reduces Energy Barriers for High Curvature Vesicle Budding.

Under standard physiological conditions, budding relies on asymmetries, including differences in leaflet composition, area, and osmotic conditions, and involves large curvature changes in nanoscale lipid vesicles. So far, the combined impact of asymmetry and high curvatures on budding has remained unknown. Here, using continuum elastic theory, the budding pathway is detailed under realistic conditions. The model enables a quantitative description of the budding process and the budded state of both ideally and non-ideally mixed lipid nanoscale vesicles. It shows that budding is less favored in smaller vesicles but lipid demixing can significantly reduce its energy barrier and yet high compositional deviations of more than 7% between the bud and vesicle only occur with phase separation on the bud.

Differential insertion of arginine in saturated and unsaturated lipid vesicles.

In this work, the effects of L- Arginine (L-Arg) insertion on saturated and unsaturated lipid membranes were assessed by fluorescence spectroscopy, dynamic light scattering (DLS) and monolayer measurements. The studied systems were composed by DPPC, 16:0 DietherPC, 16:1 Δ9-CisPC, DPPC:Chol, 16:1 Δ9-CisPC:Chol, and 16:1 Δ9-CisPC:DPPC in the presence of increasing concentrations of L-Arg. The information obtained using fluorescence spectral Laurdan properties indicates that L- Arg produces a decrease in the polarizability of saturated lipids congruent with the increase in vesicle size and area per lipid. However, in unsaturated lipids, the polarizability increases without significant changes in size and area per lipid denoting a different mechanism of insertion. The two opposite effects can be modulated by the saturated and unsaturated ratio and are independent of carbonyl groups. This modulation is damped by cholesterol. The differences in the L-Arg insertion can be explained considering that in the presence of the double bond, L-Arg decreases the organized water in the lipid matrix without expanding the bilayer. Instead, in saturated lipid membranes, L-Arg inserts into the acyl chains dragging water and expanding the membrane area.

Microfluidic Dielectrophoretic Purification of Extracellular Vesicles from Plasma Lipoproteins.

Extracellular vesicles (EVs) are small lipid vesicles shed by cells, carrying proteins, nucleic acids, and other molecular fingerprints. EVs have emerged as crucial mediators of cell-to-cell communication and hold great promise as biomarkers for liquid biopsies, enabling disease screening, diagnosis, prognosis, and monitoring. However, conventional EV separation methods are hampered by the presence of lipoproteins (LPs) in plasma samples, which have comparable characteristics and significantly outnumber EVs. These LPs contaminants complicate downstream analysis, compromising the accuracy of EV-based liquid biopsies. In this study, we present a lab-on-a-chip device that utilizes dielectrophoretic (DEP) separation principles to achieve efficient separation of EVs from LPs. Our method starts with a lab-on-a-disc filtration of human blood plasma gathering similar-sized EVs and LPs, followed by on-disc buffer exchange and subsequent injection into a microfluidic chip containing slanted interdigitated microelectrodes. The DEP force is negative for all EV sizes and positive for all LP sizes at 104 Hz and thus EVs are pushed away and collected at the collection outlet, whereas LPs are flowed down to the waste outlet. This two-step EVs isolation method, size-based filtration followed by DEP-based purification, offers a promising solution for enhancing the quality and accuracy of EV-based liquid biopsies.

Interaction of Phenanthroline-Containing Copper Complexes with Model Phospholipid Membranes

Medicinal Inorganic Chemistry has provided oncology with metallodrugs for cancer treatment, including several promising candidate drugs. In particular, copper(II) coordination compounds with phenanthroline stand out as potential anticancer agents. In this work, we used Differential Scanning Calorimetry and Electron Spin Resonance to investigate the interaction of the copper phenanthroline complexes [Cu(phen)]2+ and [Cu(L-dipeptide)(phenanthroline) (L-dipeptide: L-Ala-Gly and L-Ala-Phe)) with model lipid membranes (1,2-dipalmitoyl-sn-glycero-3-phosphocholine, DPPC, and 1,2-dipalmitoyl-sn-glycero-3-phospho-(1′-rac-glycerol) sodium salt, DPPG). Our results showed that the complexes interact with the membrane models, fluidizing them. The [Cu(phen)]2+ presented a different localization than the free ligand phen. The dipeptide modulated the localization of the complex in the membrane and the modifications induced in the physicochemical properties of the lipid vesicles. A stronger interaction with DPPG anionic membranes was observed, which mimic membranes with negatively charged surfaces, as found on several tumor cells.

(Invited) Integrated Model System of the Biological Membrane on Solid Surface

The biological membrane comprising lipid bilayer membrane and membrane-associated proteins performs a wide range of cellular functions, including signal transduction and energy conversion. Diseases such as cancer and COVID-19 are mechanistically linked with the biological membrane. An important structural feature of the biological membrane is the combination of two-dimensional (2D) and three-dimensional (3D) architectures that form organized 2D fluid and create compartments in the cell and cell-cell junctions. The dynamic self-assembly of the 2D/ 3D membrane structures and their cooperative functions are important in understanding the biological membranes.Synthetic model membranes such as lipid vesicles and black lipid membrane (BLM) have played important roles in extending our understanding of the biological membrane. They also provide platforms for biosensors and biomedical applications. Substrate supported lipid bilayers (SLBs) are a model membrane supported on a planar solid substrate such as silicon and glass (1). They have some unique features compared with other formats of model membranes. First, they are mechanical stable owing to the solid support. Second, they are accessibility to highly sensitive analytical techniques at the liquid-solid interface. Third, they are amenable to application of micro-fabrication techniques. These features render SLBs highly attractive for the development of devices that utilize artificially mimicked cellular functions.We have been developing an integrated model system of the biological membrane on the solid substrate utilizing a micro-patterned membrane of polymeric and natural lipid bilayers (2). The polymeric bilayer is formed from polymerizable diacetylene-containing phospholipid (DiynePC) and acts as a framework to support embedded lipid membranes. The embedded natural lipid membranes retain important characteristics of the biological membrane such as fluidity, and are used as a model system that reproduces the functions of the biological membrane. Various types of natural lipid membranes and proteins have been incorporated. We incorporated rhodopsin photoreceptor (Rh), a G-protein coupled receptor (GPCR), and its cognate G-protein transducin (Gt) into the patterned model membrane. The 2D diffusion and distribution of Rh and Gt were studied for elucidating the functional roles of lipid membrane environments (3). We also reconstituted natural membranes directly from their sources such as mammalian cell membranes and plant thylakoid membranes (4). Reconstituted thylakoid membrane provides a platform for investigating the functional roles of 2D membrane organizations in the photosynthesis.The 3D compartments formed by the biological membrane are also important for cellular functions. For mimicking the 3D compartments, we have developed a nanometric gap structure on the patterned membrane by attaching the polymeric bilayer with a silicone elastomer (PDMS) using an adhesion layer having a defined thickness (nanogap-junction) (5). Nanogap-junction provides a unique possibility to analyze biological molecules with a vastly heightened signal-noise ratio. Nanogap-junction can be used as a platform to study molecular properties and functions of membrane proteins. It should also provide opportunities to detect biomarker molecules using sandwich immuno-assay on the fluid membrane. The combination of 2D mobility and 3D compartmentalization of the membrane will be exploited to open new possibilities in the biomedical applications.The integrated model membrane reproduces some essential structural, physicochemical, and functional features of the biological membrane. These solid supported model membranes have been mainly studied by the optical methods. However, they should be integrated with electrodes, enabling electrochemical detection of the membrane functions. In combination with advanced fabrication technologies and analytical methods, it should provide novel opportunities in fundamental biological sciences as well as biomedical/ analytical applications such as "single molecule diagnostics". E. Sackmann, Science (Washington), 271, 43 (1996). K. Morigaki, Jpn. J. Appl. Phys., 63, 040801 (2024). Y. Tanimoto, K. Okada, F. Hayashi and K. Morigaki, Biophys. J., 109, 2307 (2015). T. Yoneda, Y. Tanimoto, D. Takagi and K. Morigaki, Langmuir, 36, 5863 (2020). M. Tanabe, K. Ando, R. Komatsu and K. Morigaki, Small, 14, 1802804 (2018).

Iron-Induced Lipid Oxidation Alters Membrane Mechanics Favoring Permeabilization.

Ferroptosis is a form of regulated necrosis characterized by the iron-dependent accumulation of lipid peroxides in cell membranes. However, how lipid oxidation via iron-mediated Fenton reactions affects the biophysical properties of cellular membranes and how these changes contribute to the opening of plasma membrane pores are major questions in the field. Here, we characterized the dynamics of membrane alterations during lipid oxidation induced onsite by Fenton reactions in chemically defined in vitro model membrane systems. We find that lipid vesicle permeabilization kinetically correlates with the appearance of malondialdehyde (MDA), a product of lipid oxidation. Iron-induced lipid oxidation also alters the lateral organization of supported lipid bilayers (SLBs) with lipid phase coexistence in a time-dependent manner, reducing the lipid phase mismatch and the circularity of liquid ordered domains, which indicates a decrease in line tension at the phase boundaries. Further analysis of oxidized SLBs by force spectroscopy reveals a significant decrease in the average membrane breakthrough force upon oxidation, resulting from changes in lipid bilayer organization that make it more susceptible to permeabilization. Our findings suggest that lipid oxidation via iron-mediated Fenton-like reactions induces strong changes in membrane lipid interactions and mechanical properties leading to reduced line tension in the permeabilized state of the bilayer, which promotes membrane pore formation.

Bioactive Hybrids Containing Artificial Cell Membranes and Phyto-Gold-Silver Chloride Bio-Nanoparticles.

This research targets the need for eco-friendly strategies in the synthesis of bioactive materials, addressing the importance of valorization of vegetal waste. This study focuses on developing biohybrids containing biomimetic lipid vesicles and phytosynthesized gold-silver chloride nanoparticles (AuAgCl NPs) derived from Achillea millefolium L. extract. By leveraging the natural antioxidant and antimicrobial properties of the plant, the research proposes a sustainable approach to creating materials with potential biomedical applications. The biomimetic membranes were loaded with chlorophyll a, a natural spectral marker. Three types of bioactive materials (biohybrids) were developed by varying the lipid vesicle/AuAgCl NP ratio. Optical (UV-Vis, fluorescence emission, FTIR), structural (XRD), elemental (EDX, XPS), and morphological (TEM) studies were performed to characterize the bio-developed materials. The hydrophobic/hydrophilic characteristics of the samples were investigated by measuring the water contact angle, and their size was estimated by DLS and TEM. Zeta potential measurements were used to evaluate the physical stability of phyto-developed particles. Antioxidant properties of phyto-particles were investigated through the chemiluminescence technique. The obtained biomaterials exhibited high antioxidant activity and antiproliferative activity against HT-29 and B-16 cancer cells. Therapeutic index values were calculated for each biohybrid. Additionally, the bio-prepared hybrids revealed biocidal action against Staphylococcus aureus and Enterococcus faecalis. The phyto-developed biomaterials are promising in biomedical applications, particularly as adjuvants in cancer therapy.

Anti-cancer and anti-microbial drug encapsulated lipid vesicles as drug delivery systems: Calorimetric and spectroscopic study

Lipid-based drug delivery systems (DDS) have attracted considerable interest for their capacity to achieve controlled drug release and encapsulate a variety of drug molecules—hydrophobic, hydrophilic, and amphiphilic—enabling diverse therapeutic applications. The research focuses on the structural and functional aspects of lipid-based vesicles that encapsulate both anti-cancer and anti-microbial drugs. The study employs ultrasensitive isothermal titration calorimetry and differential scanning calorimetry to gain mechanistic insights into the partitioning of drugs in the lipid-based DDS, release mechanisms, and binding interactions with serum proteins after the release.The structural properties of 5-fluorouracil (5-FU) suggest that the drug can partition into the outer region of the bilayer, where it forms hydrogen bonds with the polar heads of the amphiphilic lipid chains. Kanamycin indicates strong partitioning into liposomes as it displays a binding constant of the order of 106. Erythromycin exhibits limited partitioning into the bilayer, as assessed by fitting ITC data using a sequential two-binding site model. The values of change in enthalpy and entropy reflect the interaction nature and desolvation process during the drug's partitioning into liposomes. Thermodynamic signatures and transition temperatures obtained from ITC and DSC studies indicate that no diffusion-based drug release occurs from DPPC and DSPC-based liposomes. The interaction heat between the released drug and carrier serum albumin protein is very low and shows no consistent pattern. This suggests that the drugs are stably encapsulated in the drug delivery system (DDS), with no significant leakage over time. Insights from such studies on the influence of drug molecule structure on its partitioning into various lipid vesicles and further release of the same drugs from it guide in criteria for developing improvised drug delivery systems.