Polystyrene perturbs the structure, dynamics, and mechanical properties of DPPC membranes: An experimental and computational study

The size-dependent effects of nanoplastics in mouse primary hepatocytes from cells to molecules

Nanoplastics (NPs) are easily ingested by organisms and their major accumulation organ was determined to be liver. To date, the size-dependent cytotoxicity of NPs on mammalian hepatocytes remains unclear. This study utilized mouse primary hepatocytes and catalase (CAT) as specific receptors to investigate the toxicity of NPs from cells to molecules, focusing on size-dependent effects. Results showed that the larger the particle size of NP at low doses (≤50 mg/L), the most pronounced inhibitory effect on hepatocyte viability. 20 nm NPs significantly inhibit cell viability only at high doses (100 mg/L). Larger NP particles (500 nm and 1000 nm) resulted in a massive release of lactate dehydrogenase (LDH) from the cell (cell membrane damage). Reactive oxygen species (ROS), superoxide dismutase (SOD) and CAT tests suggest that NPs disturbed the cellular antioxidant system. 20 nm NPs show great strength in oxidizing lipids and disrupting mitochondrial function compared to NPs of other particle sizes. The degree of inhibition of CAT activity by different sized NPs was coherent at the cellular and molecular levels, and NP-500 had the most impact. This suggests that the structure and microenvironment of the polypeptide chain in the vicinity of the CAT active site is more susceptible to proximity and alteration by NP-500. In addition, the smaller NPs are capable of inducing relaxation of CAT backbone, disruption of H-bonding and reduction of α-helix content, whereas the larger NPs cause contraction of CAT backbone and increase in α-helix content. All NPs induce CAT fluorescence sensitization and make the chromophore microenvironment hydrophobic. This study provides new insights for NP risk assessment and applications.

Insights into short chain polyethylene penetration of phospholipid bilayers via atomistic molecular dynamics simulations

The escalation of global plastic production, reaching an annual output of 400 million tons, has significantly intensified concerns regarding plastic waste management. This has been exacerbated by improper recycling and disposal practices, contributing to the impending crisis of plastic pollution. Predictions indicate that by 2025, the environment will bear the burden of over ten billion metric tons of accumulated plastic waste. This situation has led to the concerning release of microplastics and nanoplastics (NPs) into the environment as plastic materials degrade, thereby posing risks to both ecosystems and human health. Nanoparticle interactions with living organisms have garnered significant attention due to their potential to disrupt vital biological processes. Of particular interest are lipid membranes, acting as crucial gatekeepers, underscoring the importance of comprehending the intricate process of NP penetration. Molecular dynamics (MD) simulations serve as a robust tool, offering molecular-level insights into these intricate interactions. In this study, we leverage all-atom MD simulations to delve into the interactions between lipid bilayers and polyethylene (PETH) chains of varying lengths. The investigation spans diverse lipid bilayer compositions-ranging from pure POPC to POPC:DPPC mixtures-revealing how PETH accommodates itself, adopts extended conformations, and influences membrane structure and ordering. Significantly, while longer PETH chains demonstrate limited passive diffusion, their potential to penetrate bilayers over extended timescales emerges as a significant revelation. Overall, this research significantly advances our comprehension of NP-membrane interactions, shedding light on the potential environmental and health implications that lie ahead.

Variable Non-Gaussian Transport of Nanoplastic on Supported Lipid Bilayers in Saline Conditions

Nanoplastic-lipid interaction is vital to understanding the nanoscale mechanism of plastic adsorption and aggregation on a lipid membrane surface. However, a single-particle mechanistic picture of the nanoplastic transport process on a lipid surface remains unclear. Here, we report a salt-dependent non-Gaussian transport mechanism of polystyrene particles on a supported 1-palmitoyl-2-oleoyl-glycero-3-phosphocholine (POPC) lipid bilayer surface. Particle stickiness on the POPC surface increases with salt concentration, where the particles stay longer at the surface and diffuse to shorter distances. Additionally, a non-Gaussian diffusion state dominates the transport process at high salt concentrations. Our current study provides insight into the transport mechanism of polystyrene (PS) particles on supported lipid membranes, which is essential to understanding fundamental questions regarding the adsorption mechanisms of nanoplastics on lipid surfaces.

Understanding the Transepithelial Transport and Transbilayer Diffusion of the Antihypertensive Peptide Asn-Cys-Trp: Insights from Caco-2 Cell Monolayers and the DPPC Model Membrane

Understanding the transport mechanism of the peptide Asn-Cys-Trp (NCW) is crucial to improving its intestinal absorption and bioavailability. This study investigated the absorption of NCW through Caco-2 cell monolayers and its interaction with the DPPC bilayers. Results revealed that after a 3 h incubation, the Papp (AP-BL) and Papp (BL-AP) values of NCW at a concentration of 5 mmol/L were (22.24 ± 4.52) × 10-7 and (6.63 ± 2.31) × 10-7 cm/s, respectively, with the transport rates of 1.59 ± 0.32 and 0.62 ± 0.20%, indicating its moderate absorption. NCW was found to be transported via PepT1 and paracellular transport pathways, as evidenced by the significant impact of Gly-Pro and cytochalasin D on the Papp values. Moreover, NCW upregulated ZO-1 mRNA expression. Further investigation of the ZO-1-mediated interaction between NCW and tight junction proteins will contribute to a better understanding of the paracellular transport mechanism of NCW. The interaction between NCW and the DPPC bilayers was predominantly driven by entropy. NCW permeated the bilayers through electrostatic, hydrogen bonding, and hydrophobic interactions, resulting in increased fluidity, flexibility, and disorder as well as phase transition and phase separation of the bilayers.

Nanoplastic contamination: Impact on zebrafish liver metabolism and implications for aquatic environmental health

Nanoplastics (NPs) are increasingly pervasive in the environment, raising concerns about their potential health implications, particularly within aquatic ecosystems. This study investigated the impact of polystyrene nanoparticles (PSN) on zebrafish liver metabolism using liquid chromatography hybrid quadrupole time of flight mass spectrometry (LC-QTOF-MS) based non-targeted metabolomics. Zebrafish were exposed to 50 nm PSN for 28 days at low (L-PSN) and high (H-PSN) concentrations (0.1 and 10 mg/L, respectively) via water. The results revealed significant alterations in key metabolic pathways in low and high exposure groups. The liver metabolites showed different metabolic responses with L-PSN and H-PSN. A total of 2078 metabolite features were identified from the raw data obtained in both positive and negative ion modes, with 190 metabolites deemed statistically significant in both L-PSN and H-PSN groups. Disruptions in lipid metabolism, inflammation, oxidative stress, DNA damage, and amino acid synthesis were identified. Notably, L-PSN exposure induced changes in DNA building blocks, membrane-associated biomarkers, and immune-related metabolites, while H-PSN exposure was associated with oxidative stress, altered antioxidant metabolites, and liver injury. For the first time, L-PSN was found depolymerized in the liver by cytochrome P450 enzymes. Utilizing an analytical approach to the adverse outcome pathway (AOP), impaired lipid metabolism and oxidative stress have been identified as potentially conserved key events (KEs) associated with PSN exposure. These KEs further induced liver inflammation, steatosis, and fibrosis at the tissue and organ level. Ultimately, this could significantly impact biological health. The study highlights the PSN-induced effects on zebrafish liver metabolism, emphasizing the need for a better understanding of the risks associated with NPs contamination in aquatic ecosystems.

Molecular modeling of the carbohydrate corona formation on a polyvinyl chloride nanoparticle and its impact on the adhesion to lipid bilayers

The pervasive presence of nanoplastics (NPs) in the environment has gained increasing attention due to their accumulation in living organisms. These emerging contaminants inevitably interact with extracellular polymeric substances along respiratory or gastrointestinal tracts, and diverse organic coating on the surface of NPs, known as bio- or eco-corona, is formed. Although its impact on altering the NP properties and potential cell internalization has been extensively examined, studies on its role in NP partitioning in the cell membrane are elusive yet. In this work, molecular dynamics is used to investigate the formation of chitosan (CT) corona centered on a polyvinyl chloride (PVC) nanoparticle and the uptake of the resulting complex onto lipid membranes. Coarse-grained models compatible with the newly developed Martini 3.0 force field are implemented for the two polymers employing the atomistic properties as targets in the parameterization. The reliability of the coarse-grained polymer models is demonstrated by reproducing the structural properties of the PVC melt and of solvated CT strands, as well as by determining the conformation adopted by the latter at the NP surface. Results show that the spontaneous binding of CT chains of high and intermediate protonation degrees led to the formation of soft and hard corona that modulates the interaction of PVC core with model membranes. The structural changes of the corona adsorbed at the lipid-water interface enable a subsequent transfer of the NP to the center of the saturated lipid membranes and a complete or partial transition to a snorkel conformation depending on the hydrophilic/hydrophobic balance in the CT-PVC complex. Overall, the computational investigation of the coarse-grained model system provides implications for understanding how the eco-corona development influences the uptake and implicit toxicology of NPs.

Untangling the Interactions between Anionic Polystyrene Nanoparticles and Lipid Membranes Using Laurdan Fluorescence Spectroscopy and Molecular Simulations

Several classes of synthetic nanoparticles (NPs) induce rearrangements of cell membranes that can affect membrane function. This paper describes the investigation of the interactions between polystyrene nanoparticles and liposomes, which serve as model cell membranes, using a combination of laurdan fluorescence spectroscopy and coarse-grained molecular dynamics (MD) simulations. The relative intensities of the gel-like and fluid fluorescent peaks of laurdan, which is embedded in the liposome membranes, are quantified from the areas of deconvoluted lognormal laurdan fluorescence peaks. This provides significant advantages in understanding polymer-membrane interactions. Our study reveals that anionic polystyrene NPs, which are not cross-linked, induce significant membrane rearrangement compared to other cationic or anionic NPs. Coarse-grained MD simulations demonstrate that polymer chains from the anionic polystyrene NP penetrate the liposome membrane. The inner leaflet remains intact throughout this process, though both leaflets show a decrease in lipid packing that is indicative of significant local rearrangement of the liposome membrane. These results are attributed to the formation of a hybrid gel made up of a combination of polystyrene (PS) and lipids that forces water molecules away from laurdan. Our study concludes that a combination of negative surface charge to interact electrostatically with positive charges on the membrane, a hydrophobic core to provide a thermodynamic preference for membrane association, and the ability to extend non-cross linked polymer chains into the liposome membrane are necessary for NPs to cause a significant rearrangement in the liposomes.

The effects of adsorbed benzo(a)pyrene on dynamic behavior of polystyrene nanoplastics through phospholipid membrane: A molecular simulation study

Nanoplastics (NPs) are mainly generated from the decomposition of plastic waste and industrial production, which have attracted much attention due to the potential risk for humans. The ability of NPs to penetrate different biological barriers has been proved, but the understanding of molecular details is very limited, especially for organic pollutant-NP combinations. Here, we investigated the uptake process of polystyrene NPs (PSNPs) combined with benzo(a)pyrene (BAP) molecules by dipalmitoylphosphatidylcholine (DPPC) bilayers by molecular dynamics (MD) simulations. The results showed that the PSNPs can adsorb and accumulate BAP molecules in water phase and then carried BAP molecules to enter DPPC bilayers. At the same time, the adsorbed BAP promoted the penetration of PSNPs into DPPC bilayers effectively by hydrophobic effect. The process of BAP-PSNP combinations penetrating into DPPC bilayers can be summarized into four steps including adhesion on the DPPC bilayer surface, uptake by the DPPC bilayer, BAP molecules detached from the PSNPs, and the PSNPs depolymerized in the bilayer interior. Furthermore, the amount of adsorbed BAP on PSNPs affected the properties of DPPC bilayers directly, especially the fluidity of DPPC bilayers that determine the physiologic function. Obviously, the combined effect of PSNPs and BAP enhanced the cytotoxicity. This work not only presented a vivid transmembrane process of BAP-PSNP combinations and revealed the nature of the effects of adsorbed benzo(a)pyrene on the dynamic behavior of polystyrene nanoplastics through phospholipid membrane, but also provide some necessary information of the potential damage for organic pollutant-nanoplastic combinations on human health at a molecular level.

Understanding the transformations of nanoplastic onto phospholipid bilayers: Mechanism, microscopic interaction and cytotoxicity assessment

The ubiquitous nanoplastics are now considered emergent pollutants in environments. Bioaccumulation of nanoplastics is an important indicator of their hazard. In this work, molecular dynamics were used to study the uptake of five nanoplastics (polyvinyl chloride (PVC), polystyrene (PS), polylactic acid (PLA), polypropylene (PP), and polyethylene terephthalate (PET)) onto DPPC (dipalmitoylphosphatidylcholine) bilayers. Results suggest that nanoplastics became compact after they were deposited in the human body. For PET, PLA, and PS nanoplastics, a free energy barrier of 4-22 kcal mol^-1 needed to be overcome to transfer these polymers from the interface region to the center of the DPPC bilayer. Besides, the free energy difference of PVC and PP from the bulk H₂O to the surface of DPPC was -18.67 kcal mol^-1 and -25.94 kcal mol^-1, respectively. After uptake, the interaction between nanoplastics and lipid bilayer was dominated by the van der Waals rather than electrostatic interaction. Furthermore, the cytotoxicity of nanoplastics was also evaluated and it is reflected in their ability to decrease the thickness of the lipid bilayer. Overall, this work provides implications for understanding the bioaccumulation and toxicity of nanoplastic at the molecular level.

A review on optimistic development of polymeric nanocomposite membrane on environmental remediation

Current health and environmental concerns about the abundance and drawbacks of municipal wastewater as well as industrial effluent have prompted the development of novel and innovative treatment processes. A global shortage of clean water poses significant challenges to the survival of all life forms. For the removal of both biodegradable and non-biodegradable harmful wastes/pollutants from water, sophisticated wastewater treatment technologies are required. Polymer membrane technology is critical to overcoming this major challenge. Polymer matrix-based nanocomposite membranes are among the most popular in polymer membrane technology in terms of convenience. These membranes and their major components are environmentally friendly, energy efficient, cost effective, operationally versatile, and feasible. This review provides an overview of the drawbacks as well as promising developments in polymer membrane and nanocomposite membranes for environmental remediation, with a focus on wastewater treatment. Additionally, the advantages of nanocomposite membranes such as stability, antimicrobial properties, and adsorption processes have been discussed. The goal of this review was to summarize the remediation of harmful pollutants from water and wastewater/effluent using polymer matrix-based nanocomposite membrane technology, and to highlight its shortcomings and future prospects.

Surface-Functionalized Polystyrene Nanoparticles Alter the Transmembrane Potential via Ion-Selective Pores Maintaining Global Bilayer Integrity

Although nanoplastics have well-known toxic effects toward the environment and living organisms, their molecular toxicity mechanisms, including the nature of nanoparticle-cell membrane interactions, are still under investigation. Here, we employ dynamic light scattering, quartz crystal microbalance with dissipation monitoring, and electrophysiology to investigate the interaction between polystyrene nanoparticles (PS NPs) and phospholipid membranes. Our results show that PS NPs adsorb onto lipid bilayers creating soft inhomogeneous films that include disordered defects. PS NPs form an integral part of the generated channels so that the surface functionalization and charge of the NP determine the pore conductive properties. The large difference in size between the NP diameter and the lipid bilayer thickness (∼60 vs ∼5 nm) suggests a particular and complex lipid-NP assembly that is able to maintain overall membrane integrity. In view of this, we suggest that NP-induced toxicity in cells could operate in more subtle ways than membrane disintegration, such as inducing lipid reorganization and transmembrane ionic fluxes that disrupt the membrane potential.

Polystyrene-modified carbon nanotubes: Promising carriers in targeted drug delivery

To design drug-delivery agents for therapeutic and diagnostic applications, understanding the mechanisms by which covalently functionalized carbon nanotubes penetrate and interact with cell membranes is of great importance. Here, we report all-atom molecular dynamics results from polystyrene and carboxyl-terminated polystyrene-modified carbon nanotubes and show their translocation behavior across a model lipid bilayer together with their potential to deliver a molecule of the drug ibuprofen into the cell. Our results indicate that functionalized carbon nanotubes are internalized by the membrane in hundreds of nanoseconds and that drug loading increases the internalization speed further. Both loaded and unloaded tubes cross the closest leaflet of the bilayer by nonendocytic pathways, and for the times studied, the drug molecule remains trapped inside the pristine tube while remaining attached at the end of polystyrene-modified tube. On the other hand, carboxyl-terminated polystyrene functionalization allows the drug to be completely released into the lower leaflet of the bilayer without imposing damage to the membrane. This study shows that polystyrene functionalization is a promising alternative and facilitates drug delivery as a benchmark case.

A Mechanoelastic Glimpse on Hyaluronan-Coated Extracellular Vesicles

Cancer cells secrete extracellular vesicles (EVs) covered with a carbohydrate polymer, hyaluronan (HA), linked to tumor malignancy. Herein, we have unravelled the contour lengths of HA on a single cancer cell-derived EV surface using single-molecule force spectroscopy (SMFS), which divulges the presence of low molecular weight HA (LMW-HA < 200 kDa). We also discovered that these LMW-HA-EVs are significantly more elastic than the normal cell-derived EVs. This intrinsic elasticity of cancer EVs could be directly allied to the LMW-HA abundance and associated labile water network on EV surface as revealed by correlative SMFS, hydration dynamics with fluorescence spectroscopy, and molecular dynamics simulations. This method emerges as a molecular biosensor of the cancer microenvironment.

Anionic nanoplastic exposure induces endothelial leakiness

The global-scale production of plastics has been instrumental in advancing modern society, while the rising accumulation of plastics in landfills, oceans, and anything in between has become a major stressor on environmental sustainability, climate, and, potentially, human health. While mechanical and chemical forces of man and nature can eventually break down or recycle plastics, our understanding of the biological fingerprints of plastics, especially of nanoplastics, remains poor. Here we report on a phenomenon associated with the nanoplastic forms of anionic polystyrene and poly(methyl methacrylate), where their introduction disrupted the vascular endothelial cadherin junctions in a dose-dependent manner, as revealed by confocal fluorescence microscopy, signaling pathways, molecular dynamics simulations, as well as ex vivo and in vivo assays with animal model systems. Collectively, our results implicated nanoplastics-induced vasculature permeability as primarily biophysical-biochemical in nature, uncorrelated with cytotoxic events such as reactive oxygen species production, autophagy, and apoptosis. This uncovered route of paracellular transport has opened up vast avenues for investigating the behaviour and biological effects of nanoplastics, which may offer crucial insights for guiding innovations towards a sustainable plastics industry and environmental remediation.

Pollution caused by nanoplastics: adverse effects and mechanisms of interaction via molecular simulation

The continuous increase in the production of synthetic plastics for decades and the inadequate disposal of plastic waste have resulted in a considerable increase of these materials in aquatic environments, which has developed into a major environmental concern. In addition to conventional parameters, the relevance of the environmental monitoring of microplastics (MPs) and nanoplastics (NPs) has been highlighted by the scientific community due to the potential adverse effects these materials pose to the ecosystem as well as to human health. The literature has registered an increasing interest in understanding the mechanisms, at the molecular level, of the interaction between NPs and other compounds using molecular simulation techniques. The present review aims to: (i) summarize the force fields conventionally used to describe NPs by molecular simulations; (ii) discuss the effects of NPs in the structural and dynamical properties of biological membranes; (iii) evaluate how NPs affect the folding of proteins; (iv) discuss the mechanisms by which NPs adsorb contaminants from the environment. NPs can affect the secondary structure of proteins and change the lateral organization and diffusion of lipid membranes. As a result, they may alter the lipid digestion in the gastrointestinal system representing a risk to the assimilation of the nutrients by humans. The adsorption of contaminants on MPs and NPs can potentiate their harmful effects on human health, due to a possible synergism. Therefore, understanding the mechanisms involved in these interactions is crucial to predict dangerous combinations and outline action strategies that reduce negative impacts on ecosystems and human health. Depending on the chemical properties of contaminants and NPs, electrostatic and/or van der Waals interactions can be more relevant in explaining the adsorption process. Finally, we conclude by highlighting gaps in the literature and the critical aspects for future investigations.

Filling the Gap with Long n-Alkanes: Incorporation of C20 and C30 into Phospholipid Membranes

Investigating how hydrophobic molecules mix with phospholipid bilayers and how they affect membrane properties is commonplace in biophysics. Despite this, a molecular-level empirical description of a membrane model as simple as a phospholipid bilayer with long linear hydrophobic chains incorporated is still missing. Here, we present an unprecedented molecular characterization of the incorporation of two long n-alkanes, n-eicosane (C20) and n-triacontane (C30) with 20 and 30 carbons, respectively, in phosphatidylcholine (PC) bilayers using a combination of experimental techniques (²H NMR, ³¹P NMR, ¹H-¹³C dipolar recoupling solid-state NMR, X-ray scattering, and cryogenic electron microscopy) and atomistic molecular dynamics (MD) simulations. At low hydration, deuterated C20 and C30 yield ²H NMR spectra evidencing anisotropic-motion, which demonstrates their miscibility in PC membranes up to a critical alkane-to-acyl-chain volume fraction, ϕ_c. The acquired ²H NMR spectra of C20 and C30 have notably different lineshapes. At low alkane volume fractions below ϕ_c, CHARMM36 MD simulations predict such ²H NMR spectra qualitatively and thus enable an atomistic-level interpretation of the spectra. Above ϕ_c, the ²H NMR lineshapes become characteristic of motions in the intermediate-regime that, together with the MD simulation results, suggest the onset of immiscibility between the alkane molecules and the acyl chains. For all the systems investigated, the phospholipid molecular structure is unperturbed by the presence of the alkanes. However, at conditions of excess hydration and at surprisingly low alkane fractions below ϕ_c, a peak characteristic of isotropic motion is observed in both the ²H spectra of the alkanes and ³¹P spectra of the phospholipids, strongly indicating that the incorporation of the alkanes induces a reduction on the average radius of the lipid vesicles.

Distribution and translocation of micro- and nanoplastics in fish

Microplastics (MPs) and nanoplastics (NPs) are regarded as emerging particulate contaminants. Here, we first summarize the distribution of plastic particles in fish. Field investigations verify the presence of various kinds of fibrous, spherical, and fragmentary MPs in fish gastrointestinal tract and gills, and specifically in muscle and liver. Laboratory works demonstrate that NPs even penetrate into blood vessels of fish and pass onto next generations. Second, we systematically discuss the translocation ability of MPs and NPs in fish. MPs can enter early-developing fish through adherence, and enter adult fish internal organs by intestine absorption or epidermis infiltration. NPs can not only penetrate into fish embryo blastopores, but also reach adult fish internal organs through blood circulation. Third, the cellular basis for translocation of plastic particles, NPs in particular, into cells are critically reviewed. Endocytosis and paracellular penetration are two main pathways for them to enter cells and intercellular space, respectively. Finally, we compare the chemical and physical properties among various particular pollutants (MPs, NPs, settleable particulate matters, and manufactured nanomaterials) and their translocation processes at different biological levels. In future studies, it is urgent to break through the bottleneck techniques for NPs quantification in field environmental matrix and organisms, re-confirm the existence of MPs and NPs in field organisms, and develop more detailed translocating mechanisms of MPs and NPs by applying cutting-edge tracking techniques.