Cholesterol Hinders the Passive Uptake of Amphiphilic Nanoparticles into Fluid Lipid Membranes

Mass and Stiffness Deconvolution in Nanomechanical Resonators for Precise Mass Measurement and In Vivo Biosensing

Nanomechanical sensors, due to their small size and high sensitivity to the environment, hold significant promise for various sensing applications. These sensors enable rapid, highly sensitive, and selective detection of biological and biochemical entities as well as mass spectrometry by utilizing the frequency shift of nanomechanical resonators. Nanomechanical systems have been employed to measure the mass of cells and biomolecules and study the fundamentals of surface science such as phase transitions and diffusion. Here, we develop a methodology using both experimental measurements and numerical simulations to explore the characteristics of nanomechanical resonators when the detection entities are absorbed on the cantilever surface and quantify the mass, density, and Young's modulus of adsorbed entities. Moreover, based on this proposed concept, we present an experimental method for measuring the mass of molecules and living biological entities in their physiological environment. This approach could find applications in predicting the behavior of bionanoelectromechanical resonators functionalized with biological capture molecules, as well as in label-free, nonfunctionalized micro/nanoscale biosensing and mass spectrometry of living bioentities.

Oseltamivir phosphate interaction with model membranes

Oseltamivir belongs to the neuraminidase inhibitors, developed against the influenza virus, and registered under the trademark Tamiflu. Despite its long-term acquaintance, there is limited information in the literature about its physicochemical and structural properties in a lipid-water system. We present an experimentally determined partition coefficient with structural information on the interaction of oseltamivir with the model membrane, its possible location, and its effect on the membrane thermodynamics. The hydrophobic part of the lipid bilayer is affected to a moderate extent, which was proved by slight changes in thermal and structural properties. Hereby, interaction of oseltamivir with the phospholipid bilayer induces concentration dependent decrease of lateral pressure in the bilayer acyl chain region. Oseltamivir charges the bilayer surface positively, which results in the zeta potential increase and changes in anisotropic properties studied by the polarised light microscopy. At the highest oseltamivir concentrations studied, the multilamellar structure is extensively disturbed, likely due to electrostatic repulsion between the adjacent bilayers.

Cholesterols Induced Distinctive Entry of the Graphene Nanosheet into the Cell Membrane

Graphene nanosheets are highly valued in the biomedical field due to their potential applications in drug delivery, biological imaging, and biosensors. Their biological effects on mammalian cells may be influenced by cholesterols, which are crucial components in cell membranes that take part in many vital processes. Therefore, it is particularly important to investigate the effect of cholesterols on the transport mechanism of graphene nanosheets in the cell membrane as well as the final stable configuration of graphene, which may have an impact on cytotoxicity. In this paper, the molecular details of a graphene nanosheet interacting with a 1,2-dipalmitoyl-sn-glycero-3-phosphorylcholine (DPPC) membrane with cholesterols were studied using molecular dynamics simulations. Results showed that the structure of the graphene nanosheet transits from the cut-in state in a pure DPPC membrane to being sandwiched between two DPPC leaflets when cholesterols reach a certain concentration. The underlying mechanism showed that cholesterols are preferentially adsorbed on the graphene nanosheet, which causes a larger disturbance to the nearby DPPC tails and thus guides the graphene nanosheet into the core of lipid bilayers to form a sandwiched structure. Our results are helpful for understanding the fundamental interaction mechanism between the graphene nanosheet and cell membrane and to explore the potential applications of the graphene nanosheet in biomedical sciences.

Cholesterol-Containing Liposomes Decorated With Au Nanoparticles as Minimal Tunable Fusion Machinery

Membrane fusion is essential for the basal functionality of eukaryotic cells. In physiological conditions, fusion events are regulated by a wide range of specialized proteins, operating with finely tuned local lipid composition and ionic environment. Fusogenic proteins, assisted by membrane cholesterol and calcium ions, provide the mechanical energy necessary to achieve vesicle fusion in neuromediator release. Similar cooperative effects must be explored when considering synthetic approaches for controlled membrane fusion. We show that liposomes decorated with amphiphilic Au nanoparticles (AuLips) can act as minimal tunable fusion machinery. AuLips fusion is triggered by divalent ions, while the number of fusion events dramatically changes with, and can be finely tuned by, the liposome cholesterol content. We combine quartz-crystal-microbalance with dissipation monitoring (QCM-D), fluorescence assays, and small-angle X-ray scattering (SAXS) with molecular dynamics (MD) at coarse-grained (CG) resolution, revealing new mechanistic details on the fusogenic activity of amphiphilic Au nanoparticles (AuNPs) and demonstrating the ability of these synthetic nanomaterials to induce fusion regardless of the divalent ion used (Ca²⁺ or Mg²⁺ ). The results provide a novel contribution to developing new artificial fusogenic agents for next-generation biomedical applications that require tight control of the rate of fusion events (e.g., targeted drug delivery).

Converting Nanotoxicity Data to Information Using Artificial Intelligence and Simulation

Decades of nanotoxicology research have generated extensive and diverse data sets. However, data is not equal to information. The question is how to extract critical information buried in vast data streams. Here we show that artificial intelligence (AI) and molecular simulation play key roles in transforming nanotoxicity data into critical information, i.e., constructing the quantitative nanostructure (physicochemical properties)-toxicity relationships, and elucidating the toxicity-related molecular mechanisms. For AI and molecular simulation to realize their full impacts in this mission, several obstacles must be overcome. These include the paucity of high-quality nanomaterials (NMs) and standardized nanotoxicity data, the lack of model-friendly databases, the scarcity of specific and universal nanodescriptors, and the inability to simulate NMs at realistic spatial and temporal scales. This review provides a comprehensive and representative, but not exhaustive, summary of the current capability gaps and tools required to fill these formidable gaps. Specifically, we discuss the applications of AI and molecular simulation, which can address the large-scale data challenge for nanotoxicology research. The need for model-friendly nanotoxicity databases, powerful nanodescriptors, new modeling approaches, molecular mechanism analysis, and design of the next-generation NMs are also critically discussed. Finally, we provide a perspective on future trends and challenges.

Free energy landscape of wrapping of lipid nanocluster by polysaccharides

Wrapping of a 20-mer cholesterol nano-cluster (CHL-nanoC) by two widely different types of β-glucan polysaccharides (23-25 mers) having significantly varying glycosidic linkage patterns and side chains is studied by Well-Tempered MetaDynamics (WT-MetaD) simulations. The problem has its relevance in the faecal sterol and bile acid excretion in humans and the role of dietary fibres in aiding the process and combating dyslipidemia. Additionally, the distinctive collective variables studied here can be extended for modeling of polymer wrapped soft clusters/nano-particles in general. The wrapping ability is observed to be significantly correlated to the bending of the polysaccharide chain, an attribute of the glycosidic linkage type. By biasing two unique collective variables, the radius of gyration of the polysaccharide (R_{g, poly}) and the second order Legendre polynomial of the segment orientation parameter, θ, we could successfully observe the wrapping process. This work compares in detail the physical properties of the polysaccharide encapsulated CHL-nanoC by probing the radius of curvature (R_{curv, poly}) of the polysaccharides, their coordination number with respect to the CHL-nanoC (CN), fractional CHL-nanoC surface coverage and the electrostatic surface potentials of the complex assembly. Results indicate that the β-glucan having 1-4 glycosidic linked monomers with intermittent 1-3 linkage is able to wrap the CHL-nanoC more effectively. The 1-3 glycosidic linked β-glucan with 1-6 glycosidic bonds in side chains is significantly curled up and appears to be less efficient in wrapping the nanoC. This work provides a comparative molecular level picture of mutual interaction between two major dietary polysaccharide variants and lipid globules as indicated by numerous clinical level studies involving mice and human models.

A proposed mathematical description of in vivo nanoparticle delivery

Nanoparticles are promising vehicles for the precise delivery of molecular therapies to diseased sites. Nanoparticles interact with a series of tissues and cells before they reach their target, which causes less than 1% of administered nanoparticles to be delivered to these target sites. Researchers have been studying the nano-bio interactions that mediate nanoparticle delivery to develop guidelines for designing nanoparticles with enhanced delivery properties. In this review article, we describe these nano-bio interactions with a series of mathematical equations that quantitatively define the nanoparticle delivery process. We employ a compartment model framework to describe delivery where nanoparticles are either (1) at the site of administration, (2) in the vicinity of target cells, (3) internalized by the target cells, or (4) sequestered away in off-target sites or eliminated from the body. This framework explains how different biological processes govern nanoparticle transport between these compartments, and the role of intercompartmental transport rates in determining the final nanoparticle delivery efficiency. Our framework provides guiding principles to engineer nanoparticles for improved targeted delivery.

Amphiphilic Gold Nanoparticles: A Biomimetic Tool to Gain Mechanistic Insights into Peptide-Lipid Interactions

Functional peptides are now widely used in a myriad of biomedical and clinical contexts, from cancer therapy and tumor targeting to the treatment of bacterial and viral infections. Underlying this diverse range of applications are the non-specific interactions that can occur between peptides and cell membranes, which, in many contexts, result in spontaneous internalization of the peptide within cells by avoiding energy-driven endocytosis. For this to occur, the amphipathicity and surface structural flexibility of the peptides play a crucial role and can be regulated by the presence of specific molecular residues that give rise to precise molecular events. Nevertheless, most of the mechanistic details regulating the encounter between peptides and the membranes of bacterial or animal cells are still poorly understood, thus greatly limiting the biomimetic potential of these therapeutic molecules. In this arena, finely engineered nanomaterials-such as small amphiphilic gold nanoparticles (AuNPs) protected by a mixed thiol monolayer-can provide a powerful tool for mimicking and investigating the physicochemical processes underlying peptide-lipid interactions. Within this perspective, we present here a critical review of membrane effects induced by both amphiphilic AuNPs and well-known amphiphilic peptide families, such as cell-penetrating peptides and antimicrobial peptides. Our discussion is focused particularly on the effects provoked on widely studied model cell membranes, such as supported lipid bilayers and lipid vesicles. Remarkable similarities in the peptide or nanoparticle membrane behavior are critically analyzed. Overall, our work provides an overview of the use of amphiphilic AuNPs as a highly promising tailor-made model to decipher the molecular events behind non-specific peptide-lipid interactions and highlights the main affinities observed both theoretically and experimentally. The knowledge resulting from this biomimetic approach could pave the way for the design of synthetic peptides with tailored functionalities for next-generation biomedical applications, such as highly efficient intracellular delivery systems.

Multimodal Investigation into the Interaction of Quinacrine with Microcavity-Supported Lipid Bilayers

Quinacrine is a versatile drug that is widely recognized for its antimalarial action through its inhibition of the phospholipase enzyme. It also has antianthelmintic and antiprotozoan activities and is a strong DNA binder that may be used to combat multidrug resistance in cancer. Despite extensive cell-based studies, a detailed understanding of quinacrine's influence on the cell membrane, including permeability, binding, and rearrangement at the molecular level, is lacking. Herein, we apply microcavity-suspended lipid bilayers (MSLBs) as in vitro models of the cell membrane comprising DOPC, DOPC:Chol(3:1), and DOPC:SM:Chol(2:2:1) to investigate the influence of cholesterol and intrinsic phase heterogeneity induced by mixed-lipid composition on the membrane interactions of quinacrine. Using electrochemical impedance spectroscopy (EIS) and surface-enhanced Raman spectroscopy (SERS) as label-free surface-sensitive techniques, we have studied quinacrine interaction and permeability across the different MSLBs. Our EIS data reveal that the drug is permeable through ternary DOPC:SM:Chol and DOPC-only bilayer compositions. In contrast, the binary cholesterol/DOPC membrane arrested permeation, yet the drug binds or intercalates at this membrane as reflected by an increase in membrane impedance. SERS supported the EIS data, which was utilized to gain structural insights into the drug-membrane interaction. Our SERS data also provides a simple but powerful label-free assessment of drug permeation because a significant SERS enhancement of the drug's Raman signature was observed only if the drug accessed the plasmonic interior of the pore cavity passing through the membrane. Fluorescent lifetime correlation spectroscopy (FLCS) provides further biophysical insight, revealing that quinacrine binding increases the lipid diffusivity of DOPC and the ternary membrane while remarkably decreasing the lipid diffusivity of the DOPC:Chol membrane. Overall, because of its adaptability to multimodal approaches, the MSLB platform provides rich and detailed insights into drug-membrane interactions, making it a powerful tool for in vitro drug screening.

Investigation of Cellular Interactions of Lipid-Structured Nanoparticles With Oral Mucosal Epithelial Cells

Lipid-based nanosystems enable intracellular delivery of drugs in the oral cavity for the treatment of local diseases. To rationally design such systems, suitable matrix compositions and particle properties need to be identified, and manufacturing technologies that allow reproducible production have to be applied. This is a prerequisite for the reliable and predictable performance of in-vitro biological studies. Here, we showed that solid lipid nanoparticles (SLN, palmitic acid) and nanostructured lipid carriers (NLC, palmitic acid and oleic acid in different ratios) with a size of 250 nm, a negative zeta potential, and a polydispersity index (PdI) of less than 0.3 can be reproducibly prepared by high-pressure homogenization using quality by design and a predictive model. SLN and NLC were colloidally stable after contact with physiological fluid and did not form agglomerates. The in-vitro studies clearly showed that besides particle size, surface charge and hydrophobicity, matrix composition had a significant effect. More specifically, the addition of the liquid lipid oleic acid increased the cellular uptake capacity without changing the underlying uptake mechanism. Regardless of the matrix composition, caveolin-mediated endocytosis was the major route of uptake, which was confirmed by particle localization in the endoplasmic reticulum. Thus, this work provides useful insights into the optimal composition of lipid carrier systems to enhance the intracellular uptake capacity of drugs into the oral mucosa.