Ultrashort Single-Walled Carbon Nanotubes Insert into a Pulmonary Surfactant Monolayer via Self-Rotation: Poration and Mechanical Inhibition

Pulmonary Surfactant Homeostasis Dysfunction Mediates Multiwalled Carbon Nanotubes Induced Lung Fibrosis via Elevating Surface Tension

Multiwalled carbon nanotubes (MWCNTs) have been widely used in many disciplines and raised great concerns about their negative health impacts, especially environmental and occupational exposure. MWCNTs have been reported to induce fibrotic responses; however, the underlying mechanisms remain largely veiled. Here, we reported that MWCNTs inhalation induced lung fibrosis together with decreased lung compliance, increased elastance in the mice model, and elevated surface tension in vitro. Specifically, MWCNTs increased surface tension by impairing the function of the pulmonary surfactant. Mechanistically, MWCNTs induced lamellar body (LB) dysfunction through autophagy dysfunction, which then leads to surface tension elevated by pulmonary surfactant dysfunction in the context of lung fibrosis. This is a study to investigate the molecular mechanism of MWCNTs-induced lung fibrosis and focus on surface tension. A direct mechanistic link among impaired LBs, surface tension, and fibrosis has been established. This finding elucidates the detailed molecular mechanisms of lung fibrosis induced by MWCNTs. It also highlights that pulmonary surfactants are expected to be potential therapeutic targets for the prevention and treatment of lung fibrosis induced by MWCNTs.

Heterogeneous aggregation of carbon and silicon nanoparticles with benzo[a]pyrene modulates their impacts on the pulmonary surfactant film

Inhaled nanoparticles (NPs) can deposit in alveoli where they interact with the pulmonary surfactant (PS) and potentially induce toxicity. Although nano-bio interactions are influenced by the physicochemical properties of NPs, isolated NPs used in previous studies cannot accurately represent those found in atmosphere. Here we used molecular dynamics simulations to investigate the interplay between two types of NPs associated with benzo[a]pyrene (BaP) at the PS film. Silicon NPs (SiNPs), regardless of aggregation and adsorption, directly penetrated through the PS film with minimal disturbance. Meanwhile, BaPs adsorbed on SiNPs were rapidly solubilized by PS, increasing the BaP's bioaccessibility in alveoli. Carbon NPs (CNPs) showed aggregation and adsorption-dependent effects on the PS film. Compared to isolated CNPs, which extracted PS to form biomolecular coronas, aggregated CNPs caused more pronounced PS disruption, especially around irregularly shaped edges. SiNPs in mixture exacerbated the PS perturbation by piercing PS film around the site of CNP interactions. BaPs adsorbed on CNPs were less solubilized and suppressed PS extraction, but aggravated biophysical inhibition by prompting film collapse under compression. These results suggest that for proper assessment of inhalation toxicity of airborne NPs, it is imperative to consider their heterogeneous aggregation and adsorption of pollutants under atmospheric conditions.

Dual role of pulmonary surfactant corona in modulating carbon nanotube toxicity and benzo[a]pyrene bioaccessibility

Inhaled carbon nanotubes (CNTs) can deposit in the deep lung, where they interact with pulmonary surfactant (PS) to form coronas, potentially altering the fate and toxicity profile of CNTs. However, the presence of other contaminants in combination with CNTs may affect these interactions. Here, we used passive dosing and fluorescence-based techniques confirm the partial solubilization of BaPs adsorbed on CNTs by PS in simulated alveolar fluid. MD simulations were performed to elucidate the competition of interactions between BaPs, CNTs, and PS. We found that PS play two opposing roles in altering the toxicity profile of the CNTs. First, the formation of PS coronas reduce CNTs' toxicity by decreasing the hydrophobicity of the CNTs and decreasing their aspect ratio. Second, the interaction with PS increases the bioaccessibility of BaP through interactions with PS, which may exacerbate the inhalation toxicity of CNTs. These findings suggest that the inhalation toxicity of PS-modified CNTs should consider the bioaccessibility of coexisting contaminants, with the CNT size and aggregation state playing an important role.

Lung surfactant as a biophysical assay for inhalation toxicology

Lung surfactant (LS) is a mixture of lipids and proteins that forms a thin film at the gas-exchange surfaces of the alveoli. The components and ultrastructure of LS contribute to its biophysical and biochemical functions in the respiratory system, most notably the lowering of surface tension to facilitate breathing mechanics. LS inhibition can be caused by metabolic deficiencies or the intrusion of endogenous or exogenous substances. While LS has been sourced from animals or synthesized for clinical therapeutics, the biofluid mixture has also gained recent interest as a biophysical model for inhalation toxicity. Various methods can be used to evaluate LS function quantitatively or qualitatively after exposure to potential toxicants. A narrative review of the recent literature was conducted. Studies focused whether LS was inhibited by various environmental contaminants, nanoparticles, or manufactured products. A review is also conducted on synthetic lung surfactants (SLS), which have emerged as a promising alternative to conventional animal-sourced LS. The intrinsic advantages and recent advances of SLS make a strong case for more widespread usage in LS-based toxicological assays.

The role of electrostatic potential polarization in the translocation of graphene quantum dots across membranes

Graphene quantum dots (GQDs) have shown promising potential applications in the field of biomedicine. To date, understanding the GQD-cell membrane interactions remains a key issue in developing their biomedical applications, such as targeted drug delivery and bio-imaging. In this study, we mainly shed light on the mechanism of how to control the interactions between GQDs and membranes by tuning the electrostatic potential (EP) of GQDs. Charge distributions at the edge sites were adjusted to mimic the modified EP of GQDs, given that the physicochemical properties of GQDs are usually regulated and determined by the grafted groups and doped atoms at edges. We found that the dynamics of GQDs in the GQD-membrane system can be regulated effectively by modulating the EP of GQDs, which is not only determined by the direct GQD-cell interactions but also by the GQD-water interactions. GQDs with non- or less-polarized EP are hydrophobic, and they can easily translocate into the inner membrane from the bulk water because of the decreased GQD-POPC van der Waals interactions and the favorable dehydration process. In the case of a GQD with more polarized EP, the nanomaterial prefers to adsorb onto the membrane surface due to the strong electrostatic attraction between the GQD and lipid headgroups, and especially, the high dehydration free energy of GQDs can even lead to transient detachment from the surface. These findings would be helpful to understand the interactions between GQD-based nanomaterials and cell membranes, facilitating the rational design of GQD-related biomedicines.

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.

Interaction of nano carbon particles and anthracene with pulmonary surfactant: The potential hazards of inhaled nanoparticles

Understanding the alteration of the air-liquid interfacial properties of pulmonary surfactant (PS) in the presence of nanoparticles (NPs) and polycyclic aromatic hydrocarbons (PAHs) is particularly important for pulmonary risk assessment. Here, we investigated the interaction of natural PS (extracted from pig's lungs) with nano carbon particles (NCPs) and anthracene as a representative PAH. Our results showed that PS exhibited a significant solubilization effect on anthracene. Solubilization experiment for the substructures of PS demonstrated that the mixed phospholipid components of PS played the primary role in the solubilization of PS for anthracene. Adsorption experiment indicated that in the mixed system of PS, NCPs, and anthracene, PS can inhibit the adsorption of anthracene on NCPs due to the solubilization, agglomeration, and competitive adsorption. In addition, the surface tension, phase behavior, and foaming ability of PS were obviously altered in the presence of NCPs. These findings indicate that the solubilization effect of PS on anthracene, the inhibitive effect of PS for the adsorption of anthracene on NCPs, and the alternation of air-liquid interfacial properties of PS containing NCPs may increase the pulmonary risk in the exposure of atmospheric environment containing both PAHs and NCPs.

The asbestos-carbon nanotube analogy: An update

Nanotechnology is an emerging industry based on commercialization of materials with one or more dimensions of 100 nm or less. Engineered nanomaterials are currently incorporated into thin films, porous materials, liquid suspensions, or filler/matrix nanocomposites with future applications predicted in energy and catalysis, microelectronics, environmental sensing and remediation, and nanomedicine. Carbon nanotubes are one-dimensional fibrous nanomaterials that physically resemble asbestos fibers. Toxicologic studies in rodents demonstrated that some types of carbon nanotubes can induce mesothelioma, and the World Health Organization evaluated long, rigid multiwall carbon nanotubes as possibly carcinogenic for humans in 2014. This review summarizes key physicochemical similarities and differences between asbestos fibers and carbon nanotubes. The "fiber pathogenicity paradigm" has been extended to include carbon nanotubes as well as other high-aspect-ratio fibrous nanomaterials including metallic nanowires. This paradigm identifies width, length, and biopersistence of high-aspect-ratio fibrous nanomaterials as critical determinants of lung disease, including mesothelioma, following inhalation. Based on recent theoretical modeling studies, a fourth factor, mechanical bending stiffness, will be considered as predictive of potential carcinogenicity. Novel three-dimensional lung tissue platforms provide an opportunity for in vitro screening of a wide range of high aspect ratio fibrous nanomaterials for potential lung toxicity prior to commercialization.

Transport of nanoparticles across pulmonary surfactant monolayer: a molecular dynamics study

Three types of nanoparticles, including hydrophobic nanoparticles, hydrophilic nanoparticles, and hydrophilic nanoparticles coated with lipids, were found by our molecular dynamics simulations to be transported across the pulmonary surfactant monolayer, but via different pathways, which affect their subsequent interactions with target cell membranes.