Differential Interactions of Gelatin Nanoparticles with the Major Lipids of Model Lung Surfactant: Changes in the Lateral Membrane Organization

Membrane-Nanoparticle Interactions: The Impact of Membrane Lipids

The growing field of nanotechnology presents opportunity for applications across many sectors. Nanostructures, such as nanoparticles, hold distinct properties based on their size, shape, and chemical modifications that allow them to be utilized in both highly specific as well as broad capacities. As the classification of nanoparticles becomes more well-defined and the list of applications grows, it is imperative that their toxicity be investigated. One such cellular system that is of importance are cellular membranes (biomembranes). Membranes present one of the first points of contact for nanoparticles at the cellular level. This review will address current studies aimed at defining the biomolecular interactions of nanoparticles at the level of the cell membrane, with a specific focus of the interactions of nanoparticles with prominent lipid systems.

The effects of size and surface functionalization of polystyrene nanoplastics on stratum corneum model membranes: An experimental and computational study

Nanoplastics are mainly generated from the decomposition of plastic waste and artificial production and have attracted much attention due to their wide distribution in the environment and the potential risk for humans. As the largest organ of the human body, the skin is inevitably in contact with nanoplastics. Stratum corneum is the first barrier when the skin is exposed to nanoplastics. However, little is known about the interactions between nanoplastics and stratum corneum. Here, the effects of particle size and surface functionalization (amino-modified and carboxy-modified) of polystyrene nanoplastics on the stratum corneum models were studied by Langmuir monolayer and molecular dynamics simulations. An equimolar mixture of ceramide/cholesterol/free fatty acid was used to mimic stratum corneum intercellular lipids. The Langmuir monolayer studies demonstrated that the larger size and surface functionalization of polystyrene nanoplastics significantly reduced the stability of stratum corneum lipid monolayer in a concentration-dependent fashion. Simulation results elucidated that functionalized polystyrene oligomers had a stronger interaction with lipid components of the stratum corneum model membrane. The cell experiments also indicated that functionalized polystyrene nanoplastics, especially for amino-modified polystyrene nanoplastics, had significant cytotoxicity on normal human dermal fibroblast cells. Our results provide fundamental information and the basis for a deeper understanding of the health risks of nanoplastics to humans.

The concentration-dependent effect of hydrocortisone on the structure of model lung surfactant monolayer by using an in silico approach

Understanding the adsorption mechanism of corticosteroids in the lung surfactant requires the knowledge of corticosteroid molecular interactions with lung surfactant monolayer (LSM). We employed coarse-grained molecular dynamics simulation to explore the action of hydrocortisone on an LSM comprised of a phospholipid, cholesterol and surfactant protein. The structural and dynamical morphology of the lung surfactant monolayer at different surface tensions were investigated to assess the monolayer compressibility. The simulations were also conducted at the two extreme ends of breathing cycles: exhalation (0 mN m-1 surface tension) and inhalation (20 mN m-1 surface tension). The impact of surface tension and hydrocortisone concentration on the monolayer compressibility and stability are significant, resulting the monolayer expansion at higher surface tension. However, at low surface tension, the highly compressed monolayer induces monolayer instability in the presence of the drug due to the accumulation of surfactant protein and drug. The constant area per lipid simulation results demonstrate that the surface pressure-area isotherms show a decrease in area-per-lipid with increased drug concentration. The drug-induced expansion causes considerable instability in the monolayer after a specific drug concentration is attained at inhalation breathing condition, whereas, for exhalation breathing, the monolayer gets more compressed, causing the LSM to collapse. The monolayer collapse occurs for inhalation due to the higher drug concentration, whereas for exhalation due to the accumulation of surfactant proteins and drugs. The findings from this study will aid in enhancing the knowledge of molecular interactions of corticosteroid drugs with lung surfactants to treat respiratory diseases.

Vaping additives negatively impact the stability and lateral film organization of lung surfactant model systems

Aims: Inhalation of vaping additives has recently been shown to impair respiratory function, leading to e-cigarette or vaping product use associated with lung injuries. This work was designed to understand the impact of additives (vitamin E, vitamin E acetate, tetrahydrocannabinol and cannabidiol) on model lung surfactants. Materials & methods: Lipid monofilms at the air-water interface and Brewster angle microscopy were used to assess the impact of vaping additives on model lung surfactant films. Results & conclusion: The addition of 5 mol % of vaping additives, and even more so mixtures of vitamins and cannabinoids, negatively impacts lipid packing and film stability, induces material loss upon cycling and significantly reduces functionally relevant lipid domains. This range of detrimental effects could affect proper lung function.

Biophysical analysis of gelatin and PLGA nanoparticle interactions with complex biomimetic lung surfactant models

Biocompatible materials are increasingly used for pulmonary drug delivery, and it is essential to understand their potential impact on the respiratory system, notably their effect on lung surfactant, a monolayer of lipids and proteins, responsible for preventing alveolar collapse during breathing cycles. We have developed a complex mimic of lung surfactant composed of eight lipids mixed in ratios reported for native lung surfactant. A synthetic peptide based on surfactant protein B was added to better mimic the biological system. This model was used to evaluate the impact of biocompatible gelatin and poly(lactic-co-glycolic acid) nanoparticles. Surface pressure–area isotherms were used to assess lipid packing, film compressibility and stability, whereas the lateral organization was visualized by Brewster angle microscopy. Nanoparticles increased film fluidity and altered the monolayer collapse pressure. Bright protruding clusters formed in their presence indicate a significant impact on the lateral organization of the surfactant film. Altogether, this work indicates that biocompatible materials considered to be safe for drug delivery still need to be assessed for their potential detrimental impact before use in therapeutic applications

Biodegradable nanoparticles drastically alters lateral organization of lung surfactant lipid- peptide model system.

Are Plant-Based Carbohydrate Nanoparticles Safe for Inhalation? Investigating Their Interactions with the Pulmonary Surfactant Using Langmuir Monolayers

Nanoparticle carriers show promise for drug delivery, including by inhalation, where the first barrier for uptake in the lungs is the monolayer pulmonary surfactant membrane that coats the air/alveoli interface and is critical to breathing. It is imperative to establish the fate of potential nanocarriers and their effects on the biophysical properties of the pulmonary surfactant. To this end, the impact of the nanoparticle surface charge on the lateral organization, thickness, and recompressibility of Langmuir monolayers of model phospholipid-only and phospholipid-protein mixtures was investigated using native and modified forms of nanophytoglycogen, a carbohydrate-based dendritic polymer extracted from corn as monodisperse nanoparticles. We show that the native (quasi-neutral) and anionic nanophytoglycogens have little impact on the phase behavior and film properties. By contrast, cationic nanophytoglycogen alters the film morphology and increases the hysteresis associated with the work of breathing due to its electrostatic interaction with the anionic phospholipids in the model systems. These findings specifically highlight the importance of surface charge as a selection criterion for inhaled nanoformulations.

Comparison of Tanaka lipid mixture with natural surfactant Alveofact to study nanoparticle interactions on Langmuir film balance

Upon inhalation, nanoparticles enter the lungs where the pulmonary surfactant forms the first point of contact and plays a pivotal role for the subsequent absorption into the body. This can lead to interactions that alter the biophysical function of the surfactant monolayer. Therefore, a reliable prediction of the interaction is desired. In this study, we compared the behaviour of an artificial surfactant model with that of a natural surfactant upon exposure to chitosan nanoparticles. To simulate the physiology of the lungs, the surfactant monolayers were placed at an air/aqueous interface of a Langmuir film balance. Based on the data obtained from the experiments, the chitosan nanoparticles first integrated into the monolayer of the natural surfactant and then interact strongly with its compounds thereby moving out of the monolayer. The topographic changes in the monolayer were determined by atomic force microscopy analysis. Using this technique, the nanoparticle localisation on the monolayer could be studied. No visible interaction was observed with the artificial surfactant from surface pressure-time isotherms and atomic force microscopy analysis. Incomplete miscibility lead to instability of the artificial surfactant which left behind a DPPC rich monolayer after nanoparticle interaction. It was not stable enough to see a possible interaction (i.e. change in surface pressure) with the nanoparticles directly. These results should help understand the interactions of lipids among themselves and with the nanoparticles. Furthermore, it should help generate an efficient artificial surfactant model and to understand the underlying mechanisms of the nanoparticle interaction with the monolayer.

Investigation of Drug for Pulmonary Administration-Model Pulmonary Surfactant Monolayer Interactions Using Langmuir-Blodgett Monolayer and Molecular Dynamics Simulation: A Case Study of Ketoprofen

Pulmonary administration is widely used for the treatment of lung diseases. The interaction between drug molecules and pulmonary surfactants affects the efficacy of the drug directly. The location and distribution of drug molecules in a model pulmonary surfactant monolayer under different surface pressures can provide vivid information on the interaction between drug molecules and pulmonary surfactants during the pulmonary administration. Ketoprofen is a nonsteroidal anti-inflammatory drug for pulmonary administration. The effect of ketoprofen molecules on the lipid monolayer containing 1,2-dipalmitoyl-sn-glycero-3-phosphatidylcholine (DPPC) and 1,2-dipalmitoyl-sn-glycero-3-phospho-rac-glycerol (DPPG) is studied by surface pressure (π)-area (A) isotherms and compressibility modulus (C_s^-1)-surface pressure (π) isotherms. The location and distribution of ketoprofen molecules in a lipid monolayer under different surface pressures are explored by surface tension, density profile, radial distribution function (RDF), and the potential of mean force (PMF) simulated by molecular dynamics (MD) simulation. The introduction of ketoprofen molecules affects the properties of DPPC/DPPG monolayers and the location and distribution of ketoprofen molecules in monolayers with various surface pressures. The existence of ketoprofen molecules hinders the formation of liquid-condensed (LC) films and decreases the compressibility of DPPC/DPPG monolayers. The location and distribution of ketoprofen molecules in the lipid monolayer are affected by cation-π interaction between the choline group of lipids and the benzene ring of ketoprofen, the steric hindrance of the lipid head groups, and the hydrophobicity of ketoprofen molecule itself, comprehensively. The contact state of lipid head group with water is determined by surface pressure, which affects the interaction between drug molecules and lipids and further dominates the location and distribution of ketoprofen in the lipid monolayer. This work confirms that ketoprofen molecules can affect the property and the inner structure of DPPC/DPPG monolayers during breathing. Furthermore, the results obtained using a mixed monolayer containing two major pulmonary surfactants DPPC/DPPG and ketoprofen molecules will be helpful for the in-depth understanding of the mechanism of inhaled administration therapy.

Bioinspired polymer nanoparticles omit biophysical interactions with natural lung surfactant

Herein, we report the attenuated impact of bioinspired nanoparticles on the essential function of lung surfactant. Colloidal particles made from poly(lactide) caused a significant loss of surfactant protein B (and C) from a natural lung surfactant accompanied by a decline in surface activity under static conditions and surface area cycling. No such perturbation of lung surfactant composition and function was observed for polymer nanoparticles coated with bioinspired poly(2-methacryloyloxyethyl phosphorylcholine) (PMPC). More specifically, increasing the PMPC-coating layer thickness (≥3 nm) and density (dense conformation, distance of individual polymer chains of ≤3 nm) on the polymer nanoparticle surface diminished bioadverse events. PMPC-coated poly(lactide) nanoparticles provoked a less severe perturbation of the utilized lung surfactant when compared to colloidal counterparts coated with poly(ethylene glycol). Overall, a steric shielding of colloidal drug delivery vehicles with bioinspired PMPC can be considered as a valuable approach for the rationale development of biocompatible nanomedicines intended for lung delivery.

Compatibility of PEGylated Polymer Nanoparticles with the Biophysical Function of Lung Surfactant

To minimize an unwanted interference of colloidal drug delivery vehicles with the biophysical functionality of lung surfactant, the surface of polymer nanoparticles was modified with poly(ethylene glycol) (PEGylation). Plain poly(lactide) nanoparticles provoked a statistically relevant decrease in the surface activity of the naturally derived lung surfactant, Alveofact. By contrast, the extent of lung surfactant inhibition induced by PEGylated polymer nanoparticles was significantly attenuated. Here, escalations of the PEG coating layer thickness (>3 nm, with a chain-to-chain distance of ≤4 nm) on the colloidal surface were capable of circumventing bioadverse effects. Accordingly, polymer nanoparticles equipped with PEG chains with a molecular weight above 2-5 kDa were compatible with the biophysical function of Alveofact. Overall, PEGylation of polymer nanoparticles presents a promising approach for the development of inhalation nanomedicines revealing negligible effects on the surface activity of the lining layer present in the deep lungs.

Poloxamer-Decorated Polymer Nanoparticles for Lung Surfactant Compatibility

Lung-delivered polymer nanoparticles provoked dysfunction of the essential lung surfactant system. A steric shielding of the nanoparticle surface with poloxamers could minimize the unwanted interference of polymer nanoparticles with the biophysical function of lung surfactant. The extent of poly(styrene) and poly(lactide) nanoparticle-induced lung surfactant inhibition could be related to the type and content of the applied poloxamer. Escalations of the adsorbed coating layer thickness (>3 nm) as well as concentration (brush- rather than mushroom-like conformation of poly(ethylene glycol), chain-to-chain distance of <5 nm) on the colloidal surface were capable of circumventing bioadverse effects. Accordingly, specific formulations (i.e., poloxamer 188, 338, and 407) avoided a perturbation of the microstructure and surface activity of Alveofact and a depletion of the content of surfactant-associated proteins. Poloxamer-modified polymer nanoparticles represent a promising nanomedicine platform intended for respiratory delivery revealing negligible effects on the biophysical functionality of the lining layer present in the deep lungs.

Impact of triblock copolymers on the biophysical function of naturally-derived lung surfactant

The current study aimed at investigating the general applicability of triblock copolymers consisting of poly(ethylene glycol) and poly(propylene glycol) (Pluronic^®) as excipients for lung delivery. After thorough physicochemical characterization of the diverse polymers, their cytotoxicity was evaluated using alveolar epithelial cells. Next, a naturally-derived lung surfactant was challenged with the distinct triblock copolymers with respect to changes in microstructure, adsorption to the air/liquid interface and dynamic surface tension behavior under bubble pulsation. Biocompatibility assessment of triblock copolymers in A549 cells demonstrated some cytotoxicity, dependent on the hydrophobicity and dose of the substance applied (effective at ≥0.1mg/ml). Supplementing triblock copolymers onto Alveofact^® had an obvious influence on the aggregation state and surface activity (>25 and >5mN/m during adsorption and bubble pulsation, respectively) of the lung surfactant. Interestingly, Pluronic^® F127, a rather hydrophilic triblock copolymer, showed the most intense effect on the microstructure and biophysical performance of Alveofact^®. This is likely due to the synergistic interplay of its low critical micelle concentration and rather high molecular weight, leading to the penetration of lung surfactant film/vesicles and accompanied by a partial replacement of relevant surfactant components from the air/liquid interface. Overall, suitable compositions and concentrations of triblock copolymers were identified with respect to compatibility with the physiological environment of the deep lungs.

Applications of Brewster angle microscopy from biological materials to biological systems

Brewster angle microscopy (BAM) is a powerful technique that allows for real-time visualization of Langmuir monolayers. The lateral organization of these films can be investigated, including phase separation and the formation of domains, which may be of different sizes and shapes depending on the properties of the monolayer. Different molecules or small changes within a molecule such as the molecule's length or presence of a double bond can alter the monolayer's lateral organization that is usually undetected using surface pressure-area isotherms. The effect of such changes can be clearly observed using BAM in real-time, under full hydration, which is an experimental advantage in many cases. While previous BAM reviews focused more on selected compounds or compared the impact of structural variations on the lateral domain formation, this review provided a broader overview of BAM application using biological materials and systems including the visualization of amphiphilic molecules, proteins, drugs, extracts, DNA, and nanoparticles at the air-water interface.

Biophysical Activity of Impaired Lung Surfactant upon Exposure to Polymer Nanoparticles

Colloidal drug carriers could improve the therapy of numerous airway diseases. However, it remains unclear to what extent nanoscale particulate matter affects the biophysical function of the essential surface-active lining layer of the lungs, especially under predisposed conditions of airway diseases. Accordingly, the current study investigated the impact of defined polymer nanoparticles on impaired lung surfactants. Admixtures of plasma proteins (albumin and fibrinogen) to Curosurf led to a controllable decrease in surface activity (i.e., adsorption and minimal surface tension of >25 and >5 mN/m, respectively), which served as models for dysfunctional lung surfactants. Next, Curosurf preincubated with plasma proteins was challenged with negatively- and positively charged poly(lactide) nanoparticles. Negatively charged nanoparticles significantly perturbed the biophysical function of impaired Curosurf in a dose-dependent manner, most-likely due to a binding of essential surfactant components. By contrast, addition of positively charged nanoparticles led to no further loss of surface activity, but a remarkable depletion of plasma protein content. Once adsorbed to the surface of polymer nanoparticles, plasma proteins were hindered to displace relevant surfactant components from the air/liquid interface. Overall, the current study indicated that, depending on their physicochemical properties, colloidal drug carriers could compromise the biophysical function of impaired lung surfactants. Notably, a positive surface charge represents a parameter for the rationale design of polymer nanomedicines causing negligible adverse events on an impaired surface-active lining layer in the lungs.

Design and Cellular Fate of Bioinspired Au-Ag Nanoshells@Hybrid Silica Nanoparticles

Silica-coated gold-silver alloy nanoshells were obtained via a bioinspired approach using gelatin and poly-l-lysine (PLL) as biotemplates for the interfacial condensation of sodium silicate solutions. X-ray photoelectron spectroscopy was used as an efficient tool for the in-depth and complete characterization of the chemical features of nanoparticles during the whole synthetic process. Cytotoxicity assays using HaCaT cells evidenced the detrimental effect of the gelatin nanocoating and significant induction of late apoptosis after silicification. In contrast, PLL-modified nanoparticles had less biological impact that was further improved by the silica layer, and uptake rates of up to 50% of those of the initial particles could be achieved. These results are discussed considering the effect of nanosurface confinement of the biopolymers on their chemical and biological reactivity.