Exposure to O3 and NO2 on the interfacial chemistry of the pulmonary surfactant and the mechanism of lung oxidative damage

Exposure to ozone (O3) and nitrogen dioxide (NO2) are related to pulmonary dysfunctions and various lung diseases, but the underlying biochemical mechanisms remain uncertain. Herein, the effect of inhalable oxidizing gas pollutants on the pulmonary surfactant (PS, extracted from porcine lungs), a mixture of active lipids and proteins that plays an important role in maintaining normal respiratory mechanics, is investigated in terms of the interfacial chemistry using in-vitro experiments; and the oxidative stress induced by oxidizing gases in the simulated lung fluid (SLF) supplemented with the PS is explored. The results showed that O3 and NO2 individually increased the surface tension of the PS and reduced its foaming ability; this was accompanied by the surface pressure-area isotherms of the PS monolayers shifting toward lower molecular areas, with O3 exhibiting more severe effects than NO2. Moreover, both O3 and NO2 produced reactive oxygen species (ROS) resulting in lipid peroxidation and protein damage to the PS. The formation of superoxide radicals (O2•-) was correlated with the decomposition of O3 and the reactions of O3 and NO2 with antioxidants in the SLF. These radicals, in the presence of antioxidants, led to the formation of hydrogen peroxide and hydroxyl radicals (•OH). Additionally, the direct oxidation of unsaturated lipids by O3 and NO2 further caused an increase in the ROS content. This change in the ROS chemistry and increased •OH production tentatively explain how inhalable oxidizing gases lead to oxidative stress and adverse health effects. In summary, our results indicated that inhaled O3 and NO2 exposure can significantly alter the interfacial properties of the PS, oxidize its active ingredients, and induce ROS formation in the SLF. The results of this study provide a basis for the elucidation of the potential hazards of inhaled oxidizing gas pollutants in the human respiratory system.

Interactions between inhalable aged microplastics and lung surfactant: Potential pulmonary health risks

The relationship between microplastics (MPs) and human respiratory health has garnered significant attention since inhalation constitutes the primary pathway for atmospheric MP exposure. While recent studies have revealed respiratory risks associated with MPs, virgin MPs used as plastic surrogates in these experiments did not represent the MPs that occur naturally and that undergo aging effects. Thus, the effects of aged MPs on respiratory health remain unknown. We herein analyzed the interaction between inhalable aged MPs with lung surfactant (LS) extracted from porcine lungs vis-à-vis interfacial chemistry employing in-vitro experiments, and explored oxidative damage induced by aged MPs in simulated lung fluid (SLF) and the underlying mechanisms of action. Our results showed that aged MPs significantly increased the surface tension of the LS, accompanied by a diminution in its foaming ability. The stronger adsorptive capacity of the aged MPs toward the phospholipids of LS appeared to produce increased surface tension, while the change in foaming ability might have resulted from a variation in the protein secondary structure and the adsorption of proteins onto MPs. The adsorption of phospholipid and protein components then led to the aggregation of MPs in SLF, where the aged MPs exhibited smaller hydrodynamic diameters in comparison with the unaged MPs, likely interacting with biomolecules in bodily fluids to exacerbate health hazards. Persistent free radicals were also formed on aged MPs, inducing the formation of reactive oxygen species such as superoxide radicals (O2•-), hydrogen peroxide (HOOH), and hydroxyl radicals (•OH); this would lead to LS lipid peroxidation and protein damage and increase the risk of respiratory disease. Our investigation was the first-ever to reveal a potential toxic effect of aged MPs and their actions on the human respiratory system, of great significance in understanding the risk of inhaled MPs on lung health.

The effects of molecular weight and orientation on the membrane permeation and partitioning of polycyclic aromatic hydrocarbons: a computational study

Membrane permeation and the partitioning of polycyclic aromatic hydrocarbons (PAHs) are crucial aspects affecting their carcinogenicity and mutagenicity. However, a clear understanding of these processes is still rare due to the difficulty of determining the details experimentally. Here, the interactions between PAHs and lipid bilayers were studied by molecular simulations, mainly to check the influence of molecular weight and orientation. The liposome-water partition coefficient (K_LW), transmembrane time (τ), and permeability coefficient (P) of the PAHs were calculated by integrating free energy profiles from umbrella sampling. For selected PAHs, the membrane adsorption is a spontaneous process. The preferred location is near the CC bond and the orientation is related to the molecular structure. The P values of all the PAHs are basically the same order of magnitude, which means that the molecular weight contributes little to the process. As for K_LW and τ, they show obvious increases with different molecular weights. Unconstrained simulations showed that a flat orientation on the membrane surface would prevent PAHs from being transported through the membrane. Highly hydrophobic driving forces are not always good for the absorption of PAHs, especially the formation of aggregates. In addition, the orientations and energetic barriers of PAHs near the midplane of the lipid bilayer explain the different transitions of high- and low-weight PAHs. This work provides molecular level details relating to the interactions of PAHs with lipid membranes, with significance for understanding the health effects of PAHs.

Interactions of particulate matter and pulmonary surfactant: Implications for human health

Particulate matter (PM), which is the primary contributor to air pollution, has become a pervasive global health threat. When PM enters into a respiratory tract, the first body tissues to be directly exposed are the cells of respiratory tissues and pulmonary surfactant. Pulmonary surfactant is a pivotal component to modulate surface tension of alveoli during respiration. Many studies have proved that PM would interact with pulmonary surfactant to affect the alveolar activity, and meanwhile, pulmonary surfactant would be adsorbed to the surface of PM to change the toxic effect of PM. This review focuses on recent studies of the interactions between micro/nanoparticles (synthesized and environmental particles) and pulmonary surfactant (natural surfactant and its models), as well as the health effects caused by PM through a few significant aspects, such as surface properties of PM, including size, surface charge, hydrophobicity, shape, chemical nature, etc. Moreover, in vitro and in vivo studies have shown that PM leads to oxidative stress, inflammatory response, fibrosis, and cancerization in living bodies. By providing a comprehensive picture of PM-surfactant interaction, this review will benefit both researchers for further studies and policy-makers for setting up more appropriate regulations to reduce the adverse effects of PM on public health.

Interaction of pulmonary surfactant with silica and polycyclic aromatic hydrocarbons: Implications for respiratory health

Understanding the interaction between pulmonary surfactant (PS) and inhalable pollutants is vital for risk assessment of respiratory health. Here, PS extracted from porcine lung (EPS) was used to investigate the interaction of PS with nano-silica particles and polycyclic aromatic hydrocarbons (PAHs). Our results demonstrated that silica significantly affected the phase behavior and foaming ability of EPS; EPS and its major components (dipalmitoyl phosphatidylcholine, DPPC; bovine serum albumin, BSA) exhibited great enhancing effect on PAHs solubility, which follows the order: EPS > DPPC > BSA, and it was positively correlated with the hydrophobicity of PAHs. Further experiments demonstrated that mixed phospholipids of EPS were largely responsible for the solubilization of EPS on PAHs. In the presence of EPS, DPPC or BSA, adsorption of PAHs by silica was notably inhibited, indicating competitive adsorption between PAHs and PS components on silica. These findings provide evidence for the surface chemistry by which PS facilitates the solubilization of PAHs and reducing the adsorption of PAHs on silica, which may be helpful for deeply understanding the effects of particulate matter and PAHs on lung health.

Exploring the membrane toxicity of decabromodiphenyl ethane (DBDPE): Based on cell membranes and lipid membranes model

Decabromodiphenyl ethane (DBDPE) is widely used in industry as an alternative to the decabromodiphenyl ether (BDEs). The large-scale use of DBDPE could lead to rapid growth of the human accumulation level of DBDPE. However, the biophysics of accumulation of DBDPE in cell membranes, as one of determinants of DBDPE metabolism is not clear. In the present study, detailed observations of cell lactate dehydrogenase (LDH) and reactive oxygen species (ROS) levels measurements proved that the DBDPE exposure to cell could result in significant cell membrane damage by concentration-dependent manners. The fluorescence anisotropy analysis supported the evidence that high concentration DBDPE bound decreased membrane fluidity significantly. Besides it, a detailed molecular dynamic (MD) simulation was approached to investigate the effects of DBDPE on the DPPC (dipalmitoyl phosphatidylcholine) phospholipid bilayer, which was constructed as the model of cell membrane. The molecular dynamic simulation revealed that DBDPE molecules can easily enter the membrane from the aqueous phase. Under the concentration of a threshold, the DBDPE molecules tended to aggregate inside the DPPC bilayer and caused pore formation. The bound of high concentration of DBDPE could result in significant variations in DPPC bilayer with a less dense, more disorder and rougher layer. The knowledge about DBDPEs interactions with lipid membranes is fundamentally essential to understand the in vivo process of DBDPE and the physical basis for the toxicity of DBDPE in cell membranes.

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.

Penetration of antimicrobial peptides in a lung surfactant model

Molecular dynamics simulations were successfully performed to understand the absorption mechanism of antimicrobial peptides LL-37, CATH-2, and SMAP-29 in a lung surfactant model. The antimicrobial peptides quickly penetrate in the lung surfactant model in dozens or hundreds nanoseconds, but they electrostatically interact with the lipid polar heads during the simulation time of 2 μs. This electrostatic interaction should be the explanation for the inactivation of the antimicrobial peptides when co-administrated with lung surfactant. As they strongly interact with the lipid polar heads of the lung surfactant, there is no positive charge available on the antimicrobial peptide to attack the negatively charged bacteria membrane. In order to avoid the interaction of peptides with the lipid polar heads, sodium cholate was used to form nanoparticles which act as an absorption enhancer of all antimicrobial peptides used in this investigation. The nanoparticles of 150 molecules of sodium cholate with one peptide were inserted on the top of the lung surfactant model. The nanoparticles penetrated into the lung surfactant model, spreading the sodium cholate molecules around the lipid polar heads. The sodium cholate molecules seem to protect the peptides from the interaction with the lipid polar heads, leaving them free to be delivered to the water phase. The penetration of peptides alone or even the peptide nanoparticles with sodium cholate do not collapse the lung surfactant model, indicating to be a promisor drug delivery system to the lung. The implications of this finding are that antimicrobial peptides may only be co-administered with an absorption enhancer such as sodium cholate into lung surfactant in order to avoid inactivation of their antimicrobial activity.

Prednisolone adsorption on lung surfactant models: insights on the formation of nanoaggregates, monolayer collapse and prednisolone spreading

The adsorption of prednisolone on a lung surfactant model was successfully performed using coarse grained molecular dynamics.