Structural Features and Pro-Inflammatory Effects of Water-Soluble Organic Matter in Inhalable Fine Urban Air Particles

Positive matrix factorization of seasonally resolved organic aerosol at three different central European background sites based on nuclear magnetic resonance Aerosolomics data

Concentration data derived from 1H NMR analysis of the water-soluble organic compounds from fine aerosol (PM2.5) at three Central European background stations, Košetice, Frýdlant (both in the Czech Republic), and Melpitz (Germany), were used for detailed source apportionment analysis. Two winter and two summer episodes (year 2021) with higher organic concentrations and similar wind directions were selected for NMR analyses. The concentration profiles of 61 water-soluble organic compounds were determined by NMR Aerosolomics and a principal component analysis (PCA) was performed on this dataset. Based on the PCA results, 23 compounds were selected for positive matrix factorization (PMF) analysis in order to identify dominant aerosol sources at rural background sites in Central Europe. Both the PCA and the subsequent PMF analyses clearly distinguished the characteristics of winter and summer aerosol particles. In summer, four factors were identified from PMF and were associated with biogenic aerosol (61-78 %), background aerosol (9-15 %), industrial biomass combustion (7-13 %), and residential heating (5-13 %). In winter, only 3 factors were identified - industrial biomass combustion (33-49 %), residential heating (37-45 %) and a background aerosol (8-30 %). The main difference was observed in the winter season with a stronger contribution of emissions from industrial biomass burning at the Czech stations Košetice and Frýdlant (47-49 %) compared to the Melpitz station (33 %). However, in general, there were negligible differences in identified sources between stations in the given seasons, indicating a certain homogeneity in PM2.5 composition within Central Europe at least during the sampling periods.

Contribution of water-soluble extracts to the oxidative and inflammatory effects of atmospheric aerosols: A critical review

Exposure to atmospheric particulate matter (PM) has been associated with heightened risks of lung cancer, cardiovascular and respiratory diseases. PM exposure also affects the immune system, leading to an increased susceptibility to infections, exacerbating pre-existent inflammatory and allergic lung diseases. Atmospheric PM can primarily impact human health through the generation of reactive oxygen species (ROS) that subsequently induce or exacerbate inflammation. These cytotoxic effects have been related with PM concentration, and its chemical constituents, including metals, solvent extractable organics (e.g., polycyclic aromatic hydrocarbons), and water-soluble ions. Although not receiving much attention, the fine aerosol water-soluble organic matter (WSOM) can account for a substantial portion of the overall fine PM mass and has been shown to present strong oxidative and immunomodulatory effects. Thus, the objective of this review is to provide a comprehensive analysis of the role of the water-soluble fraction of PM, with a specific focus on the contribution of the WSOM component to the cytotoxic properties of atmospheric PM. The chemical properties of the water-soluble PM fraction are briefly discussed, while emphasis is put on how PM size, composition, and temporal variations (e.g., seasonality) can impact the pro-oxidative activity, the modulation of inflammatory response, and the cytotoxicity of the water-soluble PM extracts.

Research progress on the characteristics, sources, and environmental and potential health effects of water-soluble organic compounds in atmospheric particulate matter

Water-soluble organic compounds (WSOCs) have received extensive attention due to their indistinct chemical components, complex sources, negative environmental impact, and potential health effects. To the best of our knowledge, until now, there has been no comprehensive review focused on the research progress of WSOCs. This paper reviewed the studies on chemical constituent and characterization, distribution condition, sources, environmental impact, as well as the potential health effects of WSOCs in the past 13 years. Moreover, the main existing challenges and directions for the future research on WSOCs were discussed from several aspects. Because of the complex composition of WSOCs and many unknown individual components that have not been detected, there is still a need for the identification and quantification of WSOCs. As modern people spend more time in indoor environments, it is meaningful to fill the gaps in the component characteristics and sources of indoor WSOCs. In addition, although in vitro cell experiments have shown that WSOCs could induce cellular oxidative stress and trigger the inflammatory response, the corresponding mechanisms of action need to be further explored. The current population epidemiology research of WSOCs is missing. Prospectively, we propose to conduct a comprehensive and simultaneous analysis strategy for concentration screening, source apportionment, potential health effects, and action mechanisms of WSOCs based on high throughput omics coupled with machine learning simulation and prediction.

Polar Lipids of Marine Microalgae Nannochloropsis oceanica and Chlorococcum amblystomatis Mitigate the LPS-Induced Pro-Inflammatory Response in Macrophages

Microalgae are recognized as a relevant source of bioactive compounds. Among these bioactive products, lipids, mainly glycolipids, have been shown to present immunomodulatory properties with the potential to mitigate chronic inflammation. This study aimed to evaluate the anti-inflammatory effect of polar lipids isolated from Nannochloropsis oceanica and Chlorococcum amblystomatis. Three fractions enriched in (1) digalactosyldiacylglycerol (DGDG) and sulfoquinovosyldiacylglycerol (SQDG), (2) monogalactosyldiacylglycerol (MGDG), and (3) diacylglyceryl-trimethylhomoserine (DGTS) and phospholipids (PL) were obtained from the total lipid extracts (TE) of N. oceanica and C. amblystomatis, and their anti-inflammatory effect was assessed by analyzing their capacity to counteract nitric oxide (NO) production and transcription of pro-inflammatory genes Nos2, Ptgs2, Tnfa, and Il1b in lipopolysaccharide (LPS)-activated macrophages. For both microalgae, TE and Fractions 1 and 3 strongly inhibited NO production, although to different extents. A strong reduction in the LPS-induced transcription of Nos2, Ptgs2, Tnfa, and Il1b was observed for N. oceanica and C. amblystomatis lipids. The most active fractions were the DGTS-and-PL-enriched fraction from N. oceanica and the DGDG-and-SQDG-enriched fraction from C. amblystomatis. Our results reveal that microalgae lipids have strong anti-inflammatory capacity and may be explored as functional ingredients or nutraceuticals, offering a natural solution to tackle chronic inflammation-associated diseases.

Role of Secondary Organic Matter on Soot Particle Toxicity in Reconstituted Human Bronchial Epithelia Exposed at the Air-Liquid Interface

Secondary organic matter (SOM) formed from gaseous precursors constitutes a major mass fraction of fine particulate matter. However, there is only limited evidence on its toxicological impact. In this study, air-liquid interface cultures of human bronchial epithelia were exposed to different series of fresh and aged soot particles generated by a miniCAST burner combined with a micro smog chamber (MSC). Soot cores with geometric mean mobility diameters of 30 and 90 nm were coated with increasing amounts of SOM, generated from the photo-oxidation of mesitylene and ozonolysis of α-pinene. At 24 h after exposure, the release of lactate dehydrogenase (LDH), indicating cell membrane damage, was measured and proteome analysis, i.e. the release of 102 cytokines and chemokines to assess the inflammatory response, was performed. The data indicate that the presence of the SOM coating and its bioavailability play an important role in cytotoxicity. In particular, LDH release increased with increasing SOM mass/total particle mass ratio, but only when SOM had condensed on the outer surface of the soot cores. Proteome analysis provided further evidence for substantial interference of coated particles with essential properties of the respiratory epithelium as a barrier as well as affecting cell remodeling and inflammatory activity.

Deposition potential of 0.003-10 µm ambient particles in the humidified human respiratory tract: Contribution of new particle formation events in Beijing

Ultrafine particles (UFPs) usually explosive growth during new particle formation (NPF) events. However, the risk of exposure to UFPs on NPF days has been ignored due to the prevalence of mass-based air quality standards. In this study, the daily deposited doses, i.e., the daily deposited particle number dose (D_PNd), mass dose (D_PMd), and surface area dose (D_PSd), of ambient particles in the human respiratory tract in Beijing were evaluated based on the particle number size distribution (3 nm-10 µm) from June 2018 to May 2019 utilizing a Multiple-Path Particle Dosimetry Model (MPPD) after the hygroscopic growth of particles in the respiratory tract had been accounted for. Our observations showed a high frequency (72.6%) of NPF on excellent air quality days, with daily mean PM_2.5 concentrations less than 35 μg m^-3. The daily D_PNd on excellent air quality days was comparable with that on polluted days, although the D_PMd on excellent air quality days was as low as 15.6% of that on polluted days. The D_PNd on NPF days was ~1.3 times that on non-NPF days. The D_PNd in respiratory tract regions decreased in the order: tracheobronchial (TB) > pulmonary (PUL) > extrathoracic (ET) on NPF days, while it was PUL > TB > ET on non-NPF days. The number of deposited nucleation mode particles, which were deposited mainly in the TB region (45%), was 2 times higher on NPF days than that on non-NPF days. Our results demonstrated that the deposition potential due to UFPs in terms of particle number concentrations is high in Beijing regardless of the aerosol mass concentration. More toxicological studies related to UFPs on NPF days, especially those targeting tracheobronchial and pulmonary impairment, are required in the future.

A novel particulate matter sampling and cell exposure strategy based on agar membrane for cytotoxicity study

Laboratories use different strategies to sample and extract atmospheric particulate matter (PM), some of which can be very complicated. Due to the absence of a standard protocol, it is difficult to compare the results of PM toxicity assessment across different laboratories. Here, we proposed a novel PM sampling and cell exposure strategy based on agar membrane. The agar membrane, prepared by a simple freeze-drying method, has a relatively flat surface and porous interior. We demonstrated that the agar membrane was a reliable substitute material for PM sampling. Then the PM on the agar membranes was directly extracted with the culture medium by vortex method, and the PM on the polytetrafluoroethylene (PTFE) filters was extracted with water by the traditional ultrasonic method for comparison. The extraction efficiency was evaluated and in vitro cytotoxicity assays were carried out to investigate the toxic effects of PM extracted with two strategies on macrophage cells. The results showed that the PM extracted from agar membranes induced higher cytotoxicity and more differentially expressed proteins. Overall, the novel PM sampling-cell exposure strategy based on the agar membrane is easy to operate, biocompatible and comparable, and has low disturbance, could be an alternative sampling and extraction method for PM toxicity assessment.

Elucidation of alveolar macrophage cell response to coal dusts: Role of ferroptosis in pathogenesis of coal workers' pneumoconiosis

Causal factors underlying coal workers' pneumoconiosis (CWP) have been variously attributed to the presence of carbon, crystalline silica and reduced iron (Fe) minerals, especially pyrite and Fe/Si-amorphous compounds. The aim of this research was to assess the role of iron in CWP and, more specifically, the cytotoxicity of coal dusts with different elemental composition towards alveolar macrophages (AMs). Survival rate of AMs, alteration in the production of pro-inflammatory cytokine TNF-α, MDA (the lipid peroxidation product) and intracellular GSH were assessed using commercial assay kits. The quantitative interaction between iron and GSH was investigated by developing a numerical model. The presence of various reduced Fe minerals (viz. pyrite and siderite) in coal dusts exhibited a consistently acute adverse impact on the viability of AMs and enhanced the production of TNF-α. The presence of the clinically available Fe chelator deferiprone (DFP) and the cytosolic antioxidant glutathione (GSH) significantly increased the viability of AMs exposed to Fe bearing coal dusts, suggesting coal dusts containing reduced Fe minerals were likely contributors to the initial stages of AM cytotoxicity via a ferroptosis related pathway. Chemical kinetic modeling indicated that these results may be attributed to an enhanced consumption of GSH as a result of Fe redox cycling. Fe^IIGSH and GS^• produced from the interaction between ferric Fe and GSH facilitated the production of O₂^•- which further oxidized GSH via a direct reaction between GSH and GS^• or GSO^•. These results suggest that coal dusts containing reduced Fe minerals and Fe compounds may elevate acute inflammation levels in AMs, indicating that crystalline silica may not be the only hazard of concern in mining environments.

On the Water-Soluble Organic Matter in Inhalable Air Particles: Why Should Outdoor Experience Motivate Indoor Studies?

The current understanding of water-soluble organic aerosol (OA) composition, sources, transformations, and effects is still limited to outdoor scenarios. However, the OA is also an important component of particulate matter indoors, whose complexity impairs a full structural and molecular identification. The current limited knowledge on indoor OA, and particularly on its water-soluble organic matter (WSOM) fraction is the basis of this feature paper. Inspired by studies on outdoor OA, this paper discusses and prioritizes issues related to indoor water-soluble OA and their effects on human health, providing a basis for future research in the field. The following three main topics are addressed: (1) what is known about the origin, mass contribution, and health effects of WSOM in outdoor air particles; (2) the current state-of-the-art on the WSOM in indoor air particles, the main challenges and opportunities for its chemical characterization and cytotoxicity evaluation; and (3) why the aerosol WSOM should be considered in future indoor air quality studies. While challenging, studies on the WSOM fraction in air particles are highly necessary to fully understand its origin, fate, toxicity, and long-term risks indoors.

Multidimensional Analytical Characterization of Water-Soluble Organic Aerosols: Challenges and New Perspectives

Water-soluble organic aerosols (OA) are an important component of air particles and one of the key drivers that impact both climate and human health. Understanding the processes involving water-soluble OA depends on how well the chemical composition of this aerosol component is decoded. Yet, obtaining detailed information faces several challenges, including water-soluble OA collection, extraction, and chemical complexity. This review highlights the multidimensional non-targeted analytical strategies that have been developed and employed for providing new insights into the structural and molecular features of water-soluble organic components present in air particles. First, the most prominent high-resolution mass spectrometric methods for near real-time measurements of water-soluble OA and their limitations are discussed. Afterward, a special emphasis is given to the degree of compositional information provided by offline multidimensional analytical techniques, namely excitation–emission (EEM) fluorescence spectroscopy, high-resolution mass spectrometry and two-dimensional nuclear magnetic resonance (NMR) spectroscopy and their hyphenation with chromatographic systems. The major challenges ahead on the application of these multidimensional analytical strategies for OA research are also addressed so that they can be used advantageously in future studies.