Monitoring the interaction of nucleolipoplexes with model membranes

Hydrogen bonding-mediated interaction underlies the enhanced membrane toxicity of chemically transformed polystyrene microplastics by cadmium

The global attention on microplastic pollution and its implications for human health has grown in recent years. Additionally, the co-existence of heavy metals may significantly alter microplastics' physicochemical characteristics, potentially amplifying their overall toxicity-a facet that remains less understood. In this study, we focused the membrane toxicity of modified polystyrene microplastics (PS-MPs) following cadmium (Cd) pretreatment. Our findings revealed that Cd-pretreated PS-MPs exacerbated their toxic effects, including diminished membrane integrity and altered phase fluidity in simulated lipid membrane giant unilamellar vesicles (GUVs), as well as heightened membrane permeability, protein damage, and lipid peroxidation in red blood cells and macrophages. Mechanistically, these augmented membrane toxicities can be partially ascribed to modifications in the surface roughness and hydrophilicity of Cd-pretreated PS-MPs, as well as to interactions between PS-MPs and lipid bilayers. Notably, hydrogen bonds emerged as a crucial mechanism underlying the enhanced interaction of PS-MPs with lipid bilayers.

Design and synthesis of nucleotidyl lipids and their application in the targeted delivery of siG12D for pancreatic cancer therapy

Nucleic acid drugs are attracting significant attention as prospective therapeutics. However, their efficacy is hindered by challenges in penetrating cell membranes and reaching target tissues, limiting their applications. Nucleotidyl lipids, with their specific intermolecular interactions such as H-bonding and π-π stacking, offer a promising solution as gene delivery vehicles. In this study, a novel series of nucleotide-based amphiphiles were synthesized. These lipid molecules possess the ability to self-assemble into spherical vesicles of appropriate size and zeta potential in aqueous solution. Furthermore, their complexes with oligonucleotides demonstrated favorable biocompatibility and exhibited antiproliferative effects against a broad range of cancer cells. Additionally, when combined with the cationic lipid CLD, these complexes displayed promising in vitro performance and in vivo efficacy. By incorporating DSPE-PEGylated cRGD into the formulation, targeted accumulation of siG12D in pancreatic cancer cells increased from approximately 6% to 18%, leading to effective treatment outcomes (intravenous administration, 1 mg/kg). This finding holds significant importance for the liposomal delivery of nucleic acid drugs to extrahepatic tissues.

Interaction of Metallic Nanoparticles With Biomimetic Lipid Liquid Crystalline Cubic Interfaces

In the past decades, events occurring at the nano-bio interface (i.e., where engineered nanoparticles (NPs) meet biological interfaces such as biomembranes) have been intensively investigated, to address the cytotoxicity of nanomaterials and boost their clinical translation. In this field, lamellar synthetic model membranes have been instrumental to disentangle non-specific interactions between NPs and planar biological interfaces. Much less is known on nano-biointeractions occurring at highly curved biological interfaces, such as cubic membranes. These non-lamellar architectures play a crucial -but far from understood-role in several biological processes and occur in cells as a defence mechanism against bacterial and viral pathologies, including coronaviruses infections. Despite its relevance, the interaction of cubic membranes with nano-sized objects (such as viral pathogens, biological macromolecules and synthetic NPs) remains largely unexplored to date. Here, we address the interaction of model lipid cubic phase membranes with two prototypical classes of NPs for Nanomedicine, i.e., gold (AuNPs) and silver NPs (AgNPs). To this purpose, we challenged lipid cubic phase membranes, either in the form of dispersed nanoparticles (i.e., cubosomes) or solid-supported layers of nanometric thickness, with citrate-stabilized AuNPs and AgNPs and monitored the interaction combining bulk techniques (UV-visible spectroscopy, Light and Synchrotron Small-Angle X-ray Scattering) with surface methods (Quartz Crystal Microbalance and Confocal Laser Scanning Microscopy). We show that the composition of the metal core of NPs (i.e., Au vs Ag) modulates their adsorption and self-assembly at cubic interfaces, leading to an extensive membrane-induced clustering of AuNPs, while only to a mild adsorption of isolated AgNPs. Such differences mirror opposite effects at the membrane level, where AuNPs induce lipid extraction followed by a fast disruption of the cubic assembly, while AgNPs do not affect the membrane morphology. Finally, we propose an interaction mechanism accounting for the different behaviour of AuNPs and AgNPs at the cubic interface, highlighting a prominent role of NPs’ composition and surface chemistry in the overall interaction mechanism.

Advanced Static and Dynamic Fluorescence Microscopy Techniques to Investigate Drug Delivery Systems

In the past decade(s), fluorescence microscopy and laser scanning confocal microscopy (LSCM) have been widely employed to investigate biological and biomimetic systems for pharmaceutical applications, to determine the localization of drugs in tissues or entire organisms or the extent of their cellular uptake (in vitro). However, the diffraction limit of light, which limits the resolution to hundreds of nanometers, has for long time restricted the extent and quality of information and insight achievable through these techniques. The advent of super-resolution microscopic techniques, recognized with the 2014 Nobel prize in Chemistry, revolutionized the field thanks to the possibility to achieve nanometric resolution, i.e., the typical scale length of chemical and biological phenomena. Since then, fluorescence microscopy-related techniques have acquired renewed interest for the scientific community, both from the perspective of instrument/techniques development and from the perspective of the advanced scientific applications. In this contribution we will review the application of these techniques to the field of drug delivery, discussing how the latest advancements of static and dynamic methodologies have tremendously expanded the experimental opportunities for the characterization of drug delivery systems and for the understanding of their behaviour in biologically relevant environments.

Interface interaction between high-siliceous/calcareous mineral granules and model cell membranes dominated by electrostatic force

High-siliceous/calcareous mineral granules may cause cytotoxicity by attaching to cell membranes. In this research, giant (GUVs) and small unilamellar vesicles (SUVs) were used as model membranes for studying the interaction between high-siliceous/calcareous mineral granules (micro calcite, micro quartz, nano calcium carbonate, and nano silica) and artificial membranes. Confocal laser scanning microscopy (CLSM) and fluorescence labeling experiments suggest that nano calcium carbonate (nano CaCO₃) and nano silica (nano SiO₂) induce gelation by disrupting the oppositely charged membranes, indicating the important role of electrostatic forces. Thereby, the mineral granule size affects the electrostatic interactions and thus leading to the damage of the membranes. FTIR spectra and molecular dynamics reveal that mineral granules mainly interact with -PO₂^-, -OH, and -C-N(CH₃)₃⁺ groups in phospholipids. The electrostatic force between nano minerals and phospholipids is greater in the case SiO₂ when compared to CaCO₃. Moreover, nano SiO₂ forms the strongest hydrogen bond with the -PO₂^- group as confirmed by FTIR. Thus, nano SiO₂ causes the greatest damage to membranes. This research provides a deeper understanding of the mechanism regarding the interaction between inhalable mineral granules and cell membranes.

Crystalline phase and surface coating of Al2O3 nanoparticles and their influence on the integrity and fluidity of model cell membranes

Aluminium oxide nanoparticles (Al₂O₃ NPs) potentially cause health hazards after their release into the environment. The crystalline phase of Al₂O₃ NPs determines their surface structure and the number of functional groups. The adsorption of natural organic matter (NOM) or biomolecules on the surface Al₂O₃ NPs also alters their surface properties and subsequent interactions with organisms. In this study, the roles of the Al₂O₃ crystalline phase and the surface coating of the nanoparticles on the membrane integrity and fluidity were investigated. Giant and small unilamellar vesicles (GUVs and SUVs) were prepared as model cell membranes to detect membrane disruption after exposure to Al₂O₃ NPs. Due to amorphous structure and high surface activity of γ-Al₂O₃ NPs, they had a stronger affinity with the membrane and caused more serious membrane rupture than that of α-Al₂O₃ NPs. The deposition of Al₂O₃ NPs on the membrane and the induced membrane disruption were monitored by a quartz crystal microbalance with dissipation (QCM-D) method. HA-coated Al₂O₃ NPs disrupted the SUV layer on the QCM-D sensor, while BSA-coated Al₂O₃ NPs only adhered to the membrane and induced unremarkable vesicle disruption. In addition, untreated γ-Al₂O₃ NPs induced remarkable gelation of a negatively charged membrane, but other types of Al₂O₃ NPs caused negligible membrane phase changes. The outcomes of this study demonstrate that the crystalline phase of the Al₂O₃ NPs affects the integrity and fluidity of cell membranes. The protein coatings on the NPs weaken the NP-membrane interaction, while HA coatings increase the damage of the NP-induced interaction.

A closer look into the physical interactions between lipid membranes and layered double hydroxide nanoparticles

Layered double hydroxide nanoparticles (LDH-NPs) constitute promising nanocarriers for drug and gene delivery. Although their cell internalization has been studied, the interaction between LDH-NPs and biological membrane models, such as giant unilamellar vesicles (GUVs), remains unexplored. These vesicles are widely-used membrane models that allow minimizing the complexity and uncertainty associated with biological systems to study the physical interactions in the absence of cell metabolism effects. With such an approach the physicochemical properties of the membrane can be differentiated from the biological functionalities involved in cell internalization and the membrane-mediated internalization can be directly understood. In this work, we describe for the first time the interaction of LDH-NPs with freestanding negatively charged POPC:POPS GUVs by fluorescence microscopy. The experiments were performed with fluorescein labeled LDH-NPs of about 100 nm together with different fluorophores in order to evaluate the NPs interactions with the vesicles as well as their impact on the membrane morphology and permeability. Positively charged LDH-NPs are electrostatically accumulated at the GUVs membrane, altering its lateral phospholipid distribution and increasing the stiffness and permeability of the membrane. The adsorption of albumin (LDH@ALB) or polyacrylic acid (LDH@PA) passivates the surface of LDH-NPs eliminating long-range electrostatic attraction. The absence of membrane-mediated internalization of either LDH@ALB or LDH@PA, represents an advantage in the use of LDH-NPs as drug or nucleic acids nanocarriers, because suitable functionalization will allow an optimal cell targeting.

Adenosine and lipids: A forced marriage or a love match?

Adenosine is a fascinating compound, crucial in many biochemical processes: this ubiquitous nucleoside serves as an essential building block of RNA, is also a component of ATP and regulates numerous pathophysiological mechanisms via binding to four extracellular receptors. Due to its hydrophilic nature, it belongs to a different world than lipids, and has no affinity for them. Since the 1970's, however, new discoveries have emerged and prompted the scientific community to associate adenosine with the lipid family, especially via liposomal preparations and bioconjugation. This seems to be an arranged marriage, but could it turn into a true love match? This review considered all types of unions established between adenosine and lipids. Even though exciting supramolecular structures were observed with adenosine-lipid conjugates, as well as with liposomal preparations which resulted in promising pre-clinical results, the translation of these technologies to the clinic is still limited.

Quantification of C60-induced membrane disruption using a quartz crystal microbalance

Direct contact between fullerene C₆₀ nanoparticles (NPs) and cell membranes is one of mechanisms for its cytotoxicity. In this study, the influence of C₆₀ NPs on lipid membranes was investigated. Giant unilamellar vesicles (GUVs) were used as model cell membranes to observe the membrane disruption after C₆₀ exposure. C₆₀ NPs disrupted the positively charged GUVs but not the negatively charged vesicles, confirming the role of electrostatic forces. To quantify the C₆₀ adhesion on membrane and the induced membrane disruption, a supported lipid bilayer (SLB) and a layer of small unilamellar vesicles (SUVs) were used to cover the sensor of a quartz crystal microbalance (QCM). The mass change on the SLB (Δm_SLB) was caused by the C₆₀ adhesion on the membrane, while the mass change on the SUV layer (Δm_SUV) was the combined result of C₆₀ adhesion (mass increase) and SUV disruption (mass loss). The surface area of SLB (A_SLB) was much smaller than the surface area of SUV (A_SUV), but Δm_SLB was larger than Δm_SUV after C₆₀ deposition, indicating that C₆₀ NPs caused remarkable membrane disruption. Therefore a new method was built to quantify the degree of NP-induced membrane disruption using the values of Δm_SUV/Δm_SLB and A_SUV/A_SLB. In this way, C₆₀ can be compared with other types of NPs to know which one causes more serious membrane disruption. In addition, C₆₀ NPs caused negligible change in the membrane phase, indicating that membrane gelation was not the mechanism of cytotoxicity for C₆₀ NPs. This study provides important information to predict the environmental hazard presented by fullerene NPs and to evaluate the degree of membrane damage caused by different NPs.

Fullerene C₆₀ NPs adhere on lipid membrane due to electrostatic force and cause membrane disruption.

Protein diffusion in a bicontinuous microemulsion: inducing sub-diffusion by tuning the water domain size

We study the diffusion of an enhanced green fluorescent protein (GFP+) in bicontinuous sugar-surfactant based microemulsions. The size of the water domains in such systems is controlled by changes of the oil-to-water ratio. Hence, microemulsions allow to produce confinement effects in a controlled way. At high water content the protein is found to exhibit Fickian diffusion. Decreasing the water domain size leads to a slowing down of the protein diffusion and sub-diffusive behavior is obtained on the scale observed by fluorescence correlation spectroscopy. Further decrease of the water domain size finally nearly fixes the GFP+ in these domains and forces it to increasingly follow the breathing mode of the microemulsion matrix.

Methylene blue-containing liposomes as new photodynamic anti-bacterial agents

Novel cationic liposomes containing the photo-activatable drug methylene blue (MB) strongly enhance the antibacterial activity of MB towards Gram-negative bacteria and improve biofilm penetration.

Phospholamban spontaneously reconstitutes into giant unilamellar vesicles where it generates a cation selective channel

Phospholamban (PLN) is a small integral membrane protein, which modulates the activity of the Sarcoplasmic Reticulum Ca(2+)-ATPase (SERCA) of cardiac myocytes. PLN, as a monomer, can directly interact and tune SERCA activity, but the physiological function of the pentameric form is not yet fully understood and still debated. In this work, we reconstituted PLN in Giant Unilamellar Vesicles (GUVs), a simple and reliable experimental model system to monitor the activity of proteins in membranes. By Laser Scanning Confocal Microscopy (LSCM) and Fluorescence Correlation Spectroscopy (FCS) we verified a spontaneous reconstitution of PLN into the phospholipid bilayer. In parallel experiments, we measured with the patch clamp technique canonical ion channel fluctuations, which highlight a preference for Cs(+) over K(+) and do not conduct Ca(2+). The results prove that PLN forms, presumably in its pentameric form, a cation selective ion channel.

Terminal lipophilization of a unique DNA dodecamer by various nucleolipid headgroups: Their incorporation into artificial lipid bilayers and hydrodynamic properties

A series of six cyanine-5-labeled oligonucleotides (LONs 10-15), each terminally lipophilized with different nucleolipid head groups, were synthesized using the recently prepared phosphoramidites 4b-9b. The insertion of the LONs within an artificial lipid bilayer, composed of 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC) and 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphoethanolamine (POPE), was studied by single molecule fluorescence spectroscopy and microscopy with the help of an optically transparent microfluidic sample carrier with perfusion capabilities. The incorporation of the lipo-oligonucleotides into the bilayer was studied with respect to efficiency (maximal bilayer brightness) as well as stability against perfusion (final stable bilayer brightness). Attempts to correlate these parameters with the log P values of the corresponding nucleolipid head groups failed, a result which clearly demonstrates that not only the lipophilicity but mainly the chemical structure and topology of the head group is of decisive importance for the optimal interaction of a lipo-oligonucleotide with an artificial lipid bilayer. Moreover, fluorescence half-live and diffusion time values were measured to determine the diffusion coefficients of the lipo-oligonucleotides.

Effects of SiO2 nanoparticles on phospholipid membrane integrity and fluidity

Silicon nanoparticles (NPs) are widely used nanomaterials and reported to have pathogenicity. Effects of five different SiO2 NPs on the membrane integrity and fluidity were studied using giant unilamellar vesicles (GUVs) as model cell membranes. GUVs were made from 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC) by gentle hydration method, and adjusted to be positively- or negatively-charged by adding charged lipids into vesicles. SiO2 NPs caused more serious damage to oppositely-charged membrane because electrostatic attraction favored the hydrogen bonding to the phospholipids. Increase in NP exposure dose/time and NP sedimentation process aggravated the membrane damage. The membrane phases were evaluated applying the fluorescent probe Laurdan and the calculated generalized polarization (GP) values. Anionic SiO2 NPs increased the GP value and induced membrane gelation. Cationic SiO2 NPs did not change the phase of positively-charged GUV and pure DOPC vesicles, but induced the gelation of negatively-charged GUV. Break of membrane integrity and change in membrane phase are possible mechanisms of cytotoxicity because cellular physiological activities require a separated intracellular environment and a fluid membrane phase to support proteins and regulate molecular transport.

Membrane targeting of the Spir·formin actin nucleator complex requires a sequential handshake of polar interactions

Spir and formin (FMN)-type actin nucleators initiate actin polymerization at vesicular membranes necessary for long range vesicular transport processes. Here we studied in detail the membrane binding properties and protein/protein interactions that govern the assembly of the membrane-associated Spir·FMN complex. Using biomimetic membrane models we show that binding of the C-terminal Spir-2 FYVE-type zinc finger involves both the presence of negatively charged lipids and hydrophobic contributions from the turret loop that intrudes the lipid bilayer. In solution, we uncovered a yet unknown intramolecular interaction between the Spir-2 FYVE-type domain and the N-terminal kinase non-catalytic C-lobe domain (KIND) that could not be detected in the membrane-bound state. Interestingly, we found that the intramolecular Spir-2 FYVE/KIND and the trans-regulatory Fmn-2-FSI/Spir-2-KIND interactions are competitive. We therefore characterized co-expressed Spir-2 and Fmn-2 fluorescent protein fusions in living cells by fluorescence cross-correlation spectroscopy. The data corroborate a model according to which Spir-2 exists in two different states, a cytosolic monomeric conformation and a membrane-bound state in which the KIND domain is released and accessible for subsequent Fmn-2 recruitment. This sequence of interactions mechanistically couples membrane binding of Spir to the recruitment of FMN, a pivotal step for initiating actin nucleation at vesicular membranes.

Specific DNA duplex formation at an artificial lipid bilayer: fluorescence microscopy after Sybr Green I staining

The article describes the immobilization of different probe oligonucleotides (4, 7, 10) carrying each a racemic mixture of 2,3-bis(hexadecyloxy)propan-1-ol (1a) at the 5'-terminus on a stable artificial lipid bilayer composed of 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphoethanolamine (POPE) and 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC). The bilayer separates two compartments (cis/trans channel) of an optical transparent microfluidic sample carrier with perfusion capabilities. Injection of unlabeled target DNA sequences (6, 8, or 9), differing in sequence and length, leads in the case of complementarity to the formation of stable DNA duplexes at the bilayer surface. This could be verified by Sybr Green I double strand staining, followed by incubation periods and thorough perfusions, and was visualized by single molecule fluorescence spectroscopy and microscopy. The different bilayer-immobilized complexes consisting of various DNA duplexes and the fluorescent dye were studied with respect to the kinetics of their formation as well as to their stability against perfusion.

Biocompatible cationic lipids for the formulation of liposomal DNA vectors

Ethylphosphocholine lipids are highly biocompatible cationic amphiphiles that can be used for the formulation of liposomal DNA vectors, with negligible toxic effects on cells and organisms. Here we report the characterization of EDPPC (1,2-dipalmitoyl-sn-glycero-O-ethyl-3-phosphocholine chloride) liposomes, containing two different zwitterionic helper lipids, POPC (1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine) and DOPE (1,2-dioleoyl-sn-glycero-3-phosphoethanolamine). Depending on the nature of the helper lipid, a phase separation in the bilayer is found at room temperature, where domains enriched in the cationic component coexist in a relatively large temperature range with regions where the zwitterionic lipids are predominant. We studied DNA complexation, the internal structure of lipoplexes and their docking and fusogenic ability with model target bilayers. The structural and functional modifications caused by DNA binding were studied using Dynamic Light Scattering (DLS), zeta potential, and small and wide angle X-ray scattering (SAXS-WAXS) measurements, while the interaction with membranes was assessed by using Giant Unilamellar Vesicles (GUVs) as model target bilayers. The results presented establish a connection between the physicochemical properties of lipid bilayers, and in particular of lipid demixing, with the phase state of the complexes and their ability to interact with model membranes.

Interaction of nanoparticles with lipid membranes: a multiscale perspective

Freestanding lipid bilayers were challenged with 15 nm Au nanospheres either coated by a citrate layer or passivated by a protein corona. The effect of Au nanospheres on the bilayer morphology, permeability and fluidity presents strong differences or similarities, depending on the observation length scale, from the colloidal to the molecular domains. These findings suggest that the interaction between nanoparticles and lipid membranes should be conveniently treated as a multiscale phenomenon.