Zn2+ Induced Irreversible Aggregation, Stacking, and Leakage of Choline Phosphate Liposomes

Metabolic signatures of population exposure to metal mixtures: A metabolome-wide association study

Numerous studies have explored the health impacts of individual metal exposures, yet the effects of metal mixtures on human endogenous metabolism remain largely unexplored. We aimed to assess the serum metabolic signatures of people exposed to metal mixtures. Serum and urine samples were collected from 186 workers at a steel factory in Anhui, China, in September 2019. Inductively coupled plasma mass spectrometry was used to analyze the concentrations of 23 metal elements. The serum metabolome was determined by liquid chromatography-mass spectrometry (LC-MS). A metabolome-wide association study (MWAS) was performed across the metal exposures and metabolism using quantile g-computation modeling. Pathway enrichment analysis was performed using MetaboAnalyst. We identified 226 metabolites associated with metal mixtures, primarily involving lipid metabolism (glycerophospholipids, sphingolipids), amino acid metabolism (arginine and proline, alanine, aspartate and glutamate metabolism) and caffeine metabolic pathways. Exposure to metal mixtures is mainly associated with alterations in lipid metabolism and amino acid metabolism, particularly in the glycerophospholipid and arginine and proline metabolism pathways.

Chloride intracellular channel (CLIC) proteins function as fusogens

Chloride Intracellular Channel (CLIC) family members uniquely transition between soluble and membrane-associated conformations. Despite decades of extensive functional and structural studies, CLICs' function as ion channels remains debated, rendering our understanding of their physiological role incomplete. Here, we expose the function of CLIC5 as a fusogen. We demonstrate that purified CLIC5 directly interacts with the membrane and induces fusion, as reflected by increased liposomal diameter and lipid and content mixing between liposomes. Moreover, we show that this activity is facilitated by acidic pH, a known trigger for CLICs' transition to a membrane-associated conformation, and that increased exposure of the hydrophobic inter-domain interface is crucial for this process. Finally, mutation of a conserved hydrophobic interfacial residue diminishes the fusogenic activity of CLIC5 in vitro and impairs excretory canal extension in C. elegans in vivo. Together, our results unravel the long-sought physiological role of these enigmatic proteins.

Salt-Induced Adsorption and Rupture of Liposomes on Microplastics

Microplastics have attracted considerable attention because of concerns regarding their environmental risks to living systems. The interaction between the lipid bilayer and microplastics is important for examining the potential harm to biological membranes in the presence of microplastics. In addition, membrane coatings may change the surface and colloidal properties of microplastics. Herein, phosphatidylcholine (PC) lipids, whose headgroup is most common in cell membranes, were used as model lipids. The adsorption and rupture of PC liposomes on microplastics were systematically studied. We found that divalent metal ions, such as Mg2+ and Ca2+, facilitate liposome adsorption onto microplastics and induce 40-55% liposome leakage at 2.5 mM. In contrast, to achieve a similar effect, 300 mM Na+ was required. Adsorption and rupture followed the same metal concentration requirements, suggesting that liposome adsorption was the rate-limiting step. After adsorption with liposomes, microplastics became more hydrophilic and were better dispersed in water. A similar behavior was observed for all five types of tested microplastics, including PP, PE, PVC, PET, and PS. Leakage also occurred in ocean water. This study provides fundamental insights into the interactions between liposomes and microplastics and has implications for the colloidal and transport properties of microplastics.

ISOTHERMAL TITRATION CALORIMETRY (ITC) AS A PROMISING TOOL IN PHARMACEUTICAL NANOTECHNOLOGY

Isothermal titration calorimetry (ITC) is a technique for evaluating the thermodynamic profiles of connection between two molecules, allowing the experimental design of nanoparticles systems with drugs and/or biological molecules. Taking into account the relevance of ITC, we conducted, therefore, an integrative revision of the literature, from 2000 to 2023, on the main purposes of using this technique in pharmaceutical nanotechnology. The search were carried out in the Pubmed, Sciencedirect, Web of Science, and Scifinder databases using the descriptors "Nanoparticles", "Isothermal Titration Calorimetry", and "ITC". We have observed that the ITC technique has been increasingly used in pharmaceutical nanotechnology, seeking to understand the interaction mechanisms in the formation of nanoparticles. Additionally, to understand the behavior of nanoparticles with biological materials (proteins, DNA, cell membranes, among others), thereby helping to understand the behavior of nanocarriers in vivo studies. As a contribution, we intended to reveal the importance of ITC in the laboratory routine, which is itself a quick and easy technique to obtain relevant results that help to optimize the nanosystems formulation process.

Thermodynamic Driving Forces for Divalent Cations Binding to Zwitterionic Phospholipid Membranes

We calculated the free energies for calcium, magnesium, and zinc ions binding to a zwitterionic phospholipid bilayer by using molecular dynamics simulations and the enhanced umbrella sampling technique. By decomposing the free energy into entropic and enthalpic contributions, we found that Ca²⁺ has the highest binding affinity and that the overall process is endothermic combined with a secondary exothermic process at higher ion concentrations. The relatively low dehydration free energy of Ca²⁺ allows it to release coordinated water upon binding to the membrane. The dehydrated Ca²⁺ further coordinates with lipids, resulting in a weaker influence on the water orientation and increased entropy. However, when sufficient Ca²⁺ ions are adsorbed, the concentrated cation layer induces a positive electrostatic field, which enhances the energy barrier for further ion binding and orients the adjacent water, resulting in decreased entropy. In contrast, binding of Mg²⁺ and Zn²⁺ is exothermic and less favored because they remain fully hydrated when interacting with lipids.

Multistimuli-Responsive and Antifreeze Aggregation-Induced Emission-Active Gels Based on CuNCs

Multistimuli-responsive fluorescent gelsbased small molecular gelator by supramolecular assembly, possessing excellent dynamic and reversible characteristic, have caused much concern. In this article, aggregation-induced emission-active fluorescence gels (AIE-gels) with chirality were developed by combining Cu nanoclusters (CuNCs) and natural amino acids, l-tryptophan (l-Trp) or d-Tryptophan (d-Trp). In DMSO/H₂O mixed solvents, CuNCs can self-assemble to form intertwined fibersbased nanoparticles with numerous pores by introducing Zn²⁺. Fibers as second networks of heteronetwork structures are characterized with the participation of l-Trp or d-Trp for cross-linking to reinforce mechanical strength and chiral regulation of gel networks. Aggregation-induced emission enhancement (AIEE) of CuNCs endows the gels with excellent fluorescent properties by introducing solvents and gelation process. The fluorescent gels exhibit sufficient fluorescence intensity (FI) at -20 °C to -80 °C and possess sensitive responsibility including gel-sol transition and fluorescence behavior for stimuli of mechanical force, heating, pH, H₂O₂, and ethylene diamine tetraacetic acid (EDTA).

Zn2+ Binds to Phosphatidylserine and Induces Membrane Blebbing

Herein, we show that Zn²⁺ binds to phosphatidylserine (PS) lipids in supported lipid bilayers (SLBs), forming a PS-Zn²⁺ complex with an equilibrium dissociation constant of ∼100 μM. Significantly, Zn²⁺ binding to SLBs containing more than 10 mol % PS induces extensive reordering of the bilayer. This reordering is manifest through bright spots of high fluorescence intensity that can be observed when the bilayer contains a dye-labeled lipid. Measurements using atomic force microscopy (AFM) reveal that these spots represent three-dimensional unilamellar blebs. Bleb formation is ion specific, inducible by exposing the bilayer to μM concentrations of Zn²⁺ but not Mg²⁺, Cu²⁺, Co²⁺, or Mn²⁺. Moreover, Ca²⁺ can induce some blebbing at mM concentrations but not nearly as effectively as Zn²⁺. The interactions of divalent metal cations with PS lipids were further investigated by a combination of vibrational sum frequency spectroscopy (VSFS) and surface pressure-area isotherm measurements. VSFS revealed that Zn²⁺ and Ca²⁺ were bound to the phosphate and carboxylate moieties on PS via contact ion pairing, dehydrating the lipid headgroup, whereas Mg²⁺ and Cu²⁺ were bound without perturbing the hydration of these functional groups. Additionally, Zn²⁺ was found to dramatically reduce the area per lipid in lipid monolayers, while Mg²⁺ and Cu²⁺ did not. Ca²⁺ could also reduce the area per lipid but only when significantly higher surface pressures were applied. These measurements suggest that Zn²⁺ caused lipid blebbing by decreasing the area per lipid on the side of the bilayer to which the salt was exposed. Such findings have implications for blebbing, fusion, oxidation, and related properties of PS-rich membranes in biological systems where Zn²⁺ concentrations are asymmetrically distributed.

Efficient self-assembly of heterometallic triangular necklace with strong antibacterial activity

Sophisticated mechanically interlocked molecules (MIMs) with interesting structures, properties and applications have attracted great interest in the field of supramolecular chemistry. We herein report a highly efficient self-assembly of heterometallic triangular necklace 1 containing Cu and Pt metals with strong antibacterial activity. Single-crystal X-ray analysis shows that the finely arranged triangular necklace 1 has two racemic enantiomers in its solid state with intriguing packing motif. The superior antibacterial activity of necklace 1 against both standard and clinically drug-resistant pathogens implies that the presence of Cu(I) center and platinum(II) significantly enhance the bacterium-binding/damaging activity, which is mainly attributed to the highly positively charged nature, the possible synergistic effect of heterometals in the necklace, and the improved stability in culture media. This work clearly discloses the structure-property relationships that the existence of two different metal centers not only facilitates successful construction of heterometallic triangular necklace but also endows it with superior nuclease properties and antibacterial activities.

Precise assembly of heterometallic complexes is a challenge. Here, the authors design a heterometallic triangular necklace through a highly efficient threading-and-ring-closing approach driven by metal-ligand coordination, which shows strong bacterium-binding and cell wall/plasma membrane-disrupting capacity for killing bacterial cells.

Growing a Nucleotide/Lanthanide Coordination Polymer Shell on Liposomes

Coating liposomes with a shell is a useful strategy to increase membrane stability and prevent leakage or fusion. Nucleotide/lanthanide coordination nanoparticles (NPs) are formed by a simple mixing at ambient conditions. Because some lipid headgroups contain lanthanide binding ligands, they may direct the growth of such coordination NPs. Herein, a gadolinium/adenosine monophosphate (Gd³⁺/AMP) shell was formed on liposomes (liposome@Gd³⁺/AMP) using lipids containing phosphoserine (PS) or cholinephosphate (CP) headgroups, while phosphocholine liposomes did not support the shell. Liposome binding Gd³⁺ is confirmed by transmission electron microscopy (TEM). The negatively charged CP and PS liposomes reversed to positive upon Gd³⁺ binding, while other metals such as Ca²⁺ and Zn²⁺ did not reverse the charge. Binding of Gd³⁺ did not leak the PS liposomes. Then, AMP was further added to cross-link Gd³⁺ on the liposome surface. A shell was formed as indicated by TEM, and the content inside the liposome remained for the PS liposomes. While adding Triton X-100 still induced leakage of the encapsulated liposomes, the shell protected the liposomes from leakage induced by ZnO NPs, suggesting a porous structure of the Gd³⁺/AMP shell which allowed penetration of Triton X-100 but not the larger ZnO NPs. This work provides a simple method to coat liposomes, and also offers a fundamental understanding of liposome adsorption of lanthanide ions.

Influence of Trivalent Metal Ions on Lipid Vesicles: Gelation and Fusion Phenomena

In this contribution, we report the interaction of 1,2-dimyristoyl- sn-glycero-3-phosphocholine (DMPC) lipid vesicles with a series of trivalent metal ions of the same group, namely, Al³⁺, Ga³⁺, and In³⁺, to get a distinct view of the effect of size, effective charge, and hydration free energy of these metal ions on lipid vesicles. We employed steady-state and time-resolved spectroscopic techniques including time-resolved anisotropy measurement, confocal imaging, and dynamic light scattering (DLS) measurement to probe the interaction. Our study reveals that all of the three trivalent metal ions induce gelation in lipid vesicles by removing water molecules from the interfacial region. The extent of gelation induced by the metal ions follows the order of In³⁺ > Ga³⁺ ≥ Al³⁺. We explain this observation in light of different free-energy terms. Notably, the degree of interaction for trivalent metal ions is higher as compared to that for divalent metal ions at physiological pH (pH ∼ 7.0). Most importantly, we observe that unlike divalent metal ions, trivalent metal ions dehydrate the lipid vesicles even at lower pH. The DLS measurement and confocal imaging indicate that In³⁺ causes significant aggregation or fusion of the PC vesicles, while Al³⁺ and Ga³⁺ did not induce any aggregation at the experimental concentration. We employ Derjaguin-Landau-Vervey-Overbeek (DLVO) theory to explain the aggregation phenomena induced by In³⁺.

Liposomes as models for membrane integrity

Biological membranes form the boundaries to cells. They are integral to cellular function, retaining the valuable components inside and preventing access of unwanted molecules. Many different classes of molecules demonstrate disruptive properties to the plasma membrane. These include alcohols, detergents and antimicrobial agents. Understanding this disruption and the mechanisms by which it can be mitigated is vital for improved therapeutics as well as enhanced industrial processes where the compounds produced can be toxic to the membrane. This mini-review describes the most common molecules that disrupt cell membranes along with a range of in vitro liposome-based techniques that can be used to monitor and delineate these disruptive processes.

Charge and Coordination Directed Liposome Fusion onto SiO2 and TiO2 Nanoparticles

TiO₂ and SiO₂ are very useful materials for building biointerfaces. A particularly interesting aspect is their interaction with lipid bilayers. Many past research efforts focused on phosphocholine (PC) lipids, which form supported lipid bilayers (SLB) on SiO₂ at physiological conditions but are adsorbed as intact liposomes on TiO₂. Low pH was required to form PC SLBs on TiO₂. This work intends to understand the surface forces and chemistry responsible for such differences. Two charge neutral lipids: 1,2-dioleoyl- sn-glycero-3-phosphocholine (DOPC) and 2-((2,3-bis(oleoyloxy)propyl)dimethylammonio)ethyl ethyl phosphate (DOCPe) and two negatively charged lipids: 1,2-dioleoyl- sn-glycero-3-phospho-l-serine (DOPS) and 2-((2,3-bis(oleoyloxy)propyl)dimethylammonio)ethyl hydrogen phosphate (DOCP) were used. Using calcein leakage assays, adsorption measurement, cryo-TEM, and washing, we concluded that charge is the dominating factor on SiO₂. The two neutral lipids form SLB on SiO₂ at pH 3 and 7, but the two negatively charged ones cannot form. On TiO₂, both charge and coordination chemistry are important. The two anionic lipids formed SLB from pH 3 to 10. DOCP had stronger affinity than DOPS likely due to the tighter terminal phosphate binding of the former. The two neutral liposomes formed SLB only at pH 3, where phosphate interaction and van der Waals force are deemed important. The pH 3 prepared TiO₂ DOPC SLBs are destabilized at neutral pH, indicating the reversible nature of the interaction. This work has provided new insights into two important materials interacting with common liposomes, which are important for reproducible biosensing, device fabrication, and drug delivery applications.

Cu2+-Directed Liposome Membrane Fusion, Positive-Stain Electron Microscopy, and Oxidation

Natural lipid headgroups contain a few types of metal ligands, such as phosphate, amine, and serine, which interact with metal ions differently. Herein, we studied the binding between Cu²⁺ and liposomes with four types of headgroups: phosphocholine (PC), phosphoglycerol (PG), phosphoserine (PS), and cholinephosphate (CP). Using fluorescently headgroup-labeled liposomes, Cu²⁺ strongly quenched the CP and PS liposomes, whereas quenching of PC and PG was weaker. Dynamic light scattering indicated that all of the four liposomes aggregated at high Cu²⁺ concentrations, and ethylenediaminetetraacetic acid (EDTA) only restored the original size of the PC liposome, implying fusion of the other three types of liposomes. The leakage tests revealed that the integrity of PC liposomes was not affected by Cu²⁺, but the other three liposomes leaked. Under TEM, all of the liposomes show a positive-stain feature in the presence of Cu²⁺ and Cu²⁺-stained individual liposomes with a short incubation time (<1 min). The oxidative catalytic property of Cu²⁺ was also tested, and a tight binding by the PS liposome inhibited the activity of Cu²⁺. Finally, a model of interaction for each liposome was proposed, and each one has a different metal-binding and interaction mechanism.