Hydrogen peroxide formation in a surrogate lung fluid by transition metals and quinones present in particulate matter

Characterization of chemical components and cytotoxicity effects of indoor and outdoor fine particulate matter (PM2.5) in Xi'an, China

The chemical and cytotoxicity properties of fine particulate matter (PM_2.5) at indoor and outdoor environment were characterized in Xi'an, China. The mass concentrations of PM_2.5 in urban areas (93.29~96.13 μg m^-3 for indoor and 124.37~154.52 μg m^-3 for outdoor) were higher than suburban (68.40 μg m^-3 for indoor and 96.18 μg m^-3 for outdoor). The PM_2.5 concentrations from outdoor environment due to fossil fuel combustion were higher than indoor environment. An indoor environment without central heating demonstrated higher organic carbon-to-elemental carbon (OC / EC) ratios and n-alkanes values that potentially attributed to residential coal combustion activities. The cell viability of human epithelial lung cells showed dose-dependent decrease, while nitric oxide (NO) and oxidative potential showed dose-dependent increase under exposure to PM_2.5. The variations of bioreactivities could be possibly related to different chemical components from different sources. Moderate (0.4 < R < 0.6) to strong (R > 0.6) correlations were observed between bioreactivities and elemental carbon (EC)/secondary aerosols (NO₃^-, SO₄^2-, and NH₄⁺)/heavy metals (Ni, Cu, and Pb). The findings suggest PM_2.5 is associated with particle induced oxidative potential, which are further responsible for respiratory diseases under chronic exposure.

Use of Dithiothreitol Assay to Evaluate the Oxidative Potential of Atmospheric Aerosols

Oxidative potential (OP) has been proposed as a useful descriptor for the ability of particulate matter (PM) to generate reactive oxygen species (ROS) and consequently induce oxidative stress in biological systems, which has been recognized as one of the most important mechanisms responsible for PM toxicity. The dithiothreitol (DTT) assay is one of the most frequently used techniques to quantify OP because it is low-cost, easy-to-operate, and has high repeatability. With two thiol groups, DTT has been used as a surrogate of biological sulfurs that can be oxidized when exposed to ROS. Within the DTT measurement matrix, OP is defined as the DTT consumption rate. Often, the DTT consumption can be attributed to the presence of transition metals and quinones in PM as they can catalyze the oxidation of DTT through catalytic redox reactions. However, the DTT consumption by non-catalytic PM components has not been fully investigated. In addition, weak correlations between DTT consumption, ROS generation, and cellular responses have been observed in several studies, which also reveal the knowledge gaps between DTT-based OP measurements and their implication on health effects. In this review, we critically assessed the current challenges and limitations of DTT measurement, highlighted the understudied DTT consumption mechanisms, elaborated the necessity to understand both PM-bound and PM-induced ROS, and concluded with research needs to bridge the existing knowledge gaps.

Formation and Evolution of Solvent-Extracted and Nonextractable Environmentally Persistent Free Radicals in Fly Ash of Municipal Solid Waste Incinerators

Environmentally persistent free radicals (EPFRs) are emerging contaminants occurring in combustion-borne particulates and atmospheric particulate matter, but information on their formation and behavior on fly ash from municipal solid waste (MSW) incinerators is scarce. Here, we have found that MSW-associated fly ash samples contain an EPFR concentration of 3-10 × 10¹⁵ spins g^-1, a line width (ΔH_p-p) of ∼8.6 G, and a g-factor of 2.0032-2.0038. These EPFRs are proposed to be mixtures of carbon-centered and oxygen-centered free radicals. Fractionation of the fly ash-associated EPFRs into solvent-extracted and nonextractable radicals suggests that the solvent-extracted part accounts for ∼45-73% of the total amount of EPFRs. Spin densities of solvent-extracted EPFRs correlate positively with the concentrations of Fe, Cu, Mn, Ti, and Zn, whereas similar correlations are comparatively insignificant for nonextractable EPFRs. Under natural conditions, these two types of EPFRs exhibit different stabilization that solvent-extracted EPFRs are relatively unstable, whereas the nonextractable fraction possesses a long life span. Significant correlations between concentrations of solvent-extracted EPFRs and generation of hydroxyl and superoxide radicals are found. Overall, our results suggest that the fractionated solvent-extracted and nonextractable EPFRs may experience different formation and stabilization processes and health effects.

The effects of particle-induced oxidative damage from exposure to airborne fine particulate matter components in the vicinity of landfill sites on Hong Kong

The physical, chemical and bioreactivity characteristics of fine particulate matter (PM_2.5) collected near (<1 km) two landfill sites and downwind urban sites were investigated. The PM_2.5 concentrations were significantly higher in winter than summer. Diurnal variations of PM_2.5 were recorded at both landfill sites. Soot aggregate particles were identified near the landfill sites, which indicated that combustion pollution due to landfill activities was a significant source. High correlation coefficients (r) implied several inorganic elements and water-soluble inorganic ions (vanadium (V), copper (Cu), chloride (Cl^-), nitrate (NO₃^-), sodium (Na) and potassium (K)) were positively associated with wind flow from the landfill sites. Nevertheless, no significant correlations were also identified between these components against DNA damage. Significant associations were observed between DNA damage and some heavy metals such as cadmium (Cd) and lead (Pb), and total Polycyclic Aromatic Hydrocarbons (PAHs) during the summer. The insignificant associations of DNA damage under increased wind frequency from landfills suggested that the PM_2.5 loading from sources such as regional sources was possibly an important contributing factor for DNA damage. This outcome warrants the further development of effective and source-specific landfill management regulations for particulate matter production control to the city.

Physiological response of fish under variable acidic conditions: a molecular approach through the assessment of an eco-physiological marker in the brain

The current study demonstrates oxidative damage and associated neurotoxicity following pH stress in two freshwater carp Labeo rohita and Cirrhinus cirrhosus. Carp (n = 6, 3 replicates) were exposed to four different pH (5.5, 6, 7.5, and 8) against control (pH 6.8 ± 0.05) for 7 days. After completion of treatment, levels of enzymatic (superoxide dismutase [SOD], catalase [CAT], glutathione reductase [GRd]) and non-enzymatic antioxidants (malondialdehyde [MDA], glutathione [GSH]), brain neurological parameters (Na⁺-K⁺ATPase, acetylcholinesterase [AcHE], monoamine oxidase [MAO], and nitric oxide [NO]), xanthine oxidase (XO), heat shock proteins (HSP70 and HSP90), and transcription factor NFkB were measured in carp brain. Variation in the pH caused a significant alteration in the glutathione system (glutathione and glutathione reductase), SOD-CAT system, and stress marker malondialdehyde (MDA). Xanthine oxidase was also induced significantly after pH exposure. Brain neurological parameters (MAO, NO, AChE, and Na⁺-K⁺ATPase) were significantly reduced at each pH-treated carp group though inhibition was highest at lower acidic pH (5.5). Cirrhinus cirrhosus was more affected than that of Labeo rohita. Molecular chaperon HSP70 expression was induced in all pH-treated groups though such induction was more in acid-stressed fish. HSP90 was found to increase only in acid-stressed carp brain. Expression of NFkB was elevated significantly at each treatment group except for pH 7.5. Finally, both acidic and alkaline pH in the aquatic system was found to disturb oxidative balance in carp brain which ultimately affects the neurological activity in carp. However, acidic environment in the aquatic system was more detrimental than the alkaline system regarding oxidative damage and subsequent neurotoxicity in carp brain.

Review of Acellular Assays of Ambient Particulate Matter Oxidative Potential: Methods and Relationships with Composition, Sources, and Health Effects

Oxidative stress is a potential mechanism of action for particulate matter (PM) toxicity and can occur when the body's antioxidant capacity cannot counteract or detoxify harmful effects of reactive oxygen species (ROS) due to an excess presence of ROS. ROS are introduced to the body via inhalation of PM with these species present on and/or within the particles (particle-bound ROS) and/or through catalytic generation of ROS in vivo after inhaling redox-active PM species (oxidative potential, OP). The recent development of acellular OP measurement techniques has led to a surge in research across the globe. In this review, particle-bound ROS techniques are discussed briefly while OP measurements are the focus due to an increasing number of epidemiologic studies using OP measurements showing associations with adverse health effects in some studies. The most common OP measurement techniques, including the dithiothreitol assay, glutathione assay, and ascorbic acid assay, are discussed along with evidence for utility of OP measurements in epidemiologic studies and PM characteristics that drive different responses between assay types (such as species composition, emission source, and photochemistry). Overall, most OP assays respond to metals like copper than can be found in emission sources like vehicles. Some OP assays respond to organics, especially photochemically aged organics, from sources like biomass burning. Select OP measurements have significant associations with certain cardiorespiratory end points, such as asthma, congestive heart disease, and lung cancer. In fact, multiple studies have found that exposure to OP measured using the dithiothreitol and glutathione assays drives higher risk ratios for certain cardiorespiratory outcomes than PM mass, suggesting OP measurements may be integrating the health-relevant fraction of PM and will be useful tools for future health analyses. The compositional impacts, including species and emission sources, on OP could have serious implications for health-relevant PM exposure. Though more work is needed, OP assays show promise for health studies as they integrate the impacts of PM species and properties on catalytic redox reactions into one measurement, and current work highlights the importance of metals, organic carbon, vehicles, and biomass burning emissions to PM exposures that could impact health.

Pulmonary bioaccessibility of trace metals in PM2.5 from different megacities simulated by lung fluid extraction and DGT method

Atmospheric fine particulate matters (PM_2.5) pose significant risks to human health through inhalation, especially in the rapidly developing China due to air pollution. The harmful effects of PM_2.5 are determined not only by its concentrations and hazardous components from diverse sources, but more by their bioavailable fractions actually absorbed by human body. To accurately estimate the inhalation risks of airborne metals, a physiologically based bioaccessibility method combining Simulated Lung Fluid (SLF) extraction and Diffusive Gradients in Thin-films (DGT) approaches was developed, representing the dissolution of particulate metals into lung fluid and the subsequent lung absorption of free metal cations in solution, respectively. The new method was used to compare the lung bioaccessibility of typical trace metals in PM_2.5 from three China megacities (Shanghai and Nanjing in the east, Guangzhou in south) during heavy pollution seasons. Generally, the SLF bioaccessibility (%) simulating the solubility of particulate metals in alveolar lung fluid was in order of Ni > Cd > Mn » Pb, while the succeeding DGT bioaccessibility representing labile metal fractions in solution phase absorbed directly by lung was lower and ranked as Ni ∼ Mn > Cd » Pb, thus Ni and Cd posed relatively higher potential risks owing to their high air pollution level and higher pulmonary bioaccessibility. Due to varied particle sources such as coal combustion and traffic emissions, some airborne metal concentrations (Pb, Ni) showed inconsistent spatial patterns with bulk PM_2.5 concentrations, and also varied bioaccessibility in different regions. The framework for PM_2.5 pollution risk assessments should be refined by considering both aerosol components and associated pollutants' bioaccessibility.

Complexation of Iron and Copper in Ambient Particulate Matter and Its Effect on the Oxidative Potential Measured in a Surrogate Lung Fluid

We investigated the complexation state of atmospheric iron and copper and its impact on the oxidative potential (OP) of ambient PM_2.5 (PM, particulate matter). A novel fractionation scheme was developed to segregate three different fractions of Fe and Cu present in ambient PM_2.5: (i) complexed with hydrophobic organic compounds, (ii) complexed with hydrophilic organic compounds, and (iii) free or inorganic metal fraction. A solid phase extraction (C-18) column was used to separate these fractions. The fractionation scheme applied to the ambient PM_2.5 samples collected from an urban site showed that up to 70-90% of water-soluble Fe and Cu were complexed with the organic compounds. The capability of the complexes of Fe(II) and Cu(II) with Suwanee river fulvic acid (SRFA), a proxy for the atmospheric organic compounds, to generate reactive oxygen species (ROS) (·OH and H₂O₂) in a surrogate lung fluid (SLF) was measured. The complex of Fe-SRFA showed a strong synergistic effect in the generation of ·OH in SLF, while that of Cu-SRFA showed an additive effect. Overall, our results indicate that organic complexation of the metals in ambient PM could significantly alter their OP and needs to be considered while assessing their health impacts.

Oxidative Potential by PM2.5 in the North China Plain: Generation of Hydroxyl Radical

Adverse health effects of ambient PM_2.5 ( d_p < 2.5 μm) can be associated with the production of reactive oxygen species (ROS), among which hydroxyl radical (•OH) is the most reactive. However, •OH generated by PM_2.5 has not been quantified and studied in the North China Plain (NCP), which has suffered from heavy air pollution in recent years. In this study, PM_2.5 samples were collected at an urban site (Beijing) and a suburban site (Wangdu), extracted in a cell-free surrogate lung fluid (SLF), and •OH generated in the extracts were quantified. The results show that more •OH is produced on heavily polluted days than that on clean days (2.0 and 1.6 times higher in Beijing and Wangdu, respectively). The production of •OH per unit mass (ng/μg·PM_2.5) decreases with the increase of ambient PM_2.5 concentration because SO₄^2-, NO₃^-, and NH₄⁺ dominate the increased PM_2.5, while these secondary inorganic components do not contribute to the generation of •OH. Trace metals (e.g., Fe, Cu, Se) and carbonaceous species (organic carbon and elemental carbon) correlate well with the •OH production, indicating that particles from combustion sources including coal combustion, vehicle exhaust, and industry contribute more to •OH generation.

Reactive Oxygen Species Formed by Secondary Organic Aerosols in Water and Surrogate Lung Fluid

Reactive oxygen species (ROS) play a central role in adverse health effects of air pollutants. Respiratory deposition of fine air particulate matter can lead to the formation of ROS in epithelial lining fluid, potentially causing oxidative stress and inflammation. Secondary organic aerosols (SOA) account for a large fraction of fine particulate matter, but their role in adverse health effects is unclear. Here, we quantify and compare the ROS yields and oxidative potential of isoprene, β-pinene, and naphthalene SOA in water and surrogate lung fluid (SLF). In pure water, isoprene and β-pinene SOA were found to produce mainly OH and organic radicals, whereas naphthalene SOA produced mainly H₂O₂ and O₂^•-. The total molar yields of ROS of isoprene and β-pinene SOA were 11.8% and 8.2% in water and decreased to 8.5% and 5.2% in SLF, which can be attributed to ROS removal by lung antioxidants. A positive correlation between the total peroxide concentration and ROS yield suggests that organic (hydro)peroxides may play an important role in ROS formation from biogenic SOA. The total molar ROS yields of naphthalene SOA was 1.7% in water and increased to 11.3% in SLF. This strong increase is likely due to redox reaction cycles involving environmentally persistent free radicals (EPFR) or semiquinones, antioxidants, and oxygen, which may promote the formation of H₂O₂ and the adverse health effects of anthropogenic SOA from aromatic precursors.

Dominant Fraction of EPFRs from Nonsolvent-Extractable Organic Matter in Fine Particulates over Xi'an, China

To understand the nature and possible sources of environmentally persistent free radicals (EPFRs) in atmospheric aerosols, the present study used a solvent extraction method to fractionate aerosol components with different polarities and solvent resistance in fine particulate matter (PM_2.5) from Xi'an, China. The characteristics of EPFRs, that is., their concentration, type and lifetime, were obtained based on their electron paramagnetic resonance spectra. The results showed that the EPFRs in the PM_2.5 samples were carbon-centered with a nearby heteroatom ( g = 2.0031) and had a long half-life of more than 3 years. Nearly all of the extractable EPFRs were detected in the water-insoluble organic fraction and showed characteristics indicating that may contain oxygen-centered radical ( g = 2.0038). Most of the total EPFRs in the PM_2.5 were derived from solvent-resistant organic matter (88%), which likely consisted of graphene oxide analogues. The results suggest that previous studies may have missed the major proportion of EPFRs in atmospheric particulates if they only focused on solvent-extractable or metallic oxide-formed EPFRs. Our results showed that the EPFR concentration was significantly and positively correlated with the elemental carbon and NO₂ concentrations, suggesting that traffic emissions may be an important source of EPFRs in PM_2.5 over Xi'an.

TH17-Induced Neutrophils Enhance the Pulmonary Allergic Response Following BALB/c Exposure to House Dust Mite Allergen and Fine Particulate Matter From California and China

Asthma is a global and increasingly prevalent disease. According to the World Health Organization, approximately 235 million people suffer from asthma. Studies suggest that fine particulate matter (PM2.5) can induce innate immune responses, promote allergic sensitization, and exacerbate asthmatic symptoms and airway hyper-responsiveness. Recently, severe asthma and allergic sensitization have been associated with T-helper cell type 17 (TH17) activation. Few studies have investigated the links between PM2.5 exposure, allergic sensitization, asthma, and TH17 activation. This study aimed to determine whether (1) low-dose extracts of PM2.5 from California (PMCA) or China (PMCH) enhance allergic sensitization in mice following exposure to house dust mite (HDM) allergen; (2) eosinophilic or neutrophilic inflammatory responses result from PM and HDM exposure; and (3) TH17-associated cytokines are increased in the lung following exposure to PM and/or HDM. Ten-week-old male BALB/c mice (n = 6-10/group) were intranasally instilled with phosphate-buffered saline (PBS), PM+PBS, HDM, or PM+HDM, on days 1, 3, and 5 (sensitization experiments), and PBS or HDM on days 12-14 (challenge experiments). Pulmonary function, bronchoalveolar lavage cell differentials, plasma immunoglobulin (Ig) protein levels, and lung tissue pathology, cyto-/chemo-kine proteins, and gene expression were assessed on day 15. Results indicated low-dose PM2.5 extracts can enhance allergic sensitization and TH17-associated responses. Although PMCA+HDM significantly decreased pulmonary function, and significantly increased neutrophils, Igs, and TH17-related protein and gene levels compared with HDM, there were no significant differences between HDM and PMCH+HDM treatments. This may result from greater copper and oxidized organic content in PMCA versus PMCH.

Synergistic and Antagonistic Interactions among the Particulate Matter Components in Generating Reactive Oxygen Species Based on the Dithiothreitol Assay

We assessed the interactions among the particulate matter (PM) components in generating the reactive oxygen species (ROS) based on a dithiothreitol (DTT) assay. We started with the standard solutions of known redox-active substances, i.e., quinones (9,10-phenanthraquinone, 1,2-naphthoquinone, 1,4-naphthoquinone, and 5-hydroxy-1,4-naphthoquinone) and metals [Fe (II), Mn (II), and Cu (II)]. Both DTT consumption and hydroxyl radical (·OH) generation were measured in the DTT assay. The interactions of Fe were additive with quinones in DTT consumption but strongly synergistic in ·OH generation. Cu showed antagonistic interactions with quinones in both DTT consumption and ·OH generation. Mn interacted synergistically with quinones in DTT oxidation but antagonistically in ·OH generation. The nature of the interactions of these metals (Fe, Mn, and Cu) with ambient humic-like substances (HULIS) resembled that with quinones, although the intensity of interactions were weaker in DTT consumption than ·OH generation. Finally, we demonstrated that the DTT consumption capability of ambient PM can be well explained by HULIS, three transition metals (Fe, Mn, and Cu), and their interactions, but ·OH generation involves a contribution (∼50%) from additional compounds (aliphatic species or metals other than Fe, Mn, and Cu) present in the hydrophilic PM fraction. The study highlights the need to account for the interactions between organic compounds and metals, while apportioning the relative contributions of chemical components in the PM oxidative potential.

Sea spray aerosol chemical composition: elemental and molecular mimics for laboratory studies of heterogeneous and multiphase reactions

Schematic representation of the reactive uptake of N₂O₅to a sea spray aerosol particle containing a thick organic film.

Oxygenated VOCs, aqueous chemistry, and potential impacts on residential indoor air composition

Dampness affects a substantial percentage of homes and is associated with increased risk of respiratory ailments; yet, the effects of dampness on indoor chemistry are largely unknown. We hypothesize that the presence of water-soluble gases and their aqueous processing alters the chemical composition of indoor air and thereby affects inhalation and dermal exposures in damp homes. Herein, we use the existing literature and new measurements to examine the plausibility of this hypothesis, summarize existing evidence, and identify key knowledge gaps. While measurements of indoor volatile organic compounds (VOCs) are abundant, measurements of water-soluble organic gases (WSOGs) are not. We found that concentrations of total WSOGs were, on average, 15 times higher inside homes than immediately outside (N = 13). We provide insights into WSOG compounds likely to be present indoors using peer-reviewed literature and insights from atmospheric chemistry. Finally, we discuss types of aqueous chemistry that may occur on indoor surfaces and speculate how this chemistry could affect indoor exposures. Liquid water quantities, identities of water-soluble compounds, the dominant chemistry, and fate of aqueous products are poorly understood. These limitations hamper our ability to determine the effects of aqueous indoor chemistry on dermal and inhalation exposures in damp homes.

Aerosol Health Effects from Molecular to Global Scales

Poor air quality is globally the largest environmental health risk. Epidemiological studies have uncovered clear relationships of gaseous pollutants and particulate matter (PM) with adverse health outcomes, including mortality by cardiovascular and respiratory diseases. Studies of health impacts by aerosols are highly multidisciplinary with a broad range of scales in space and time. We assess recent advances and future challenges regarding aerosol effects on health from molecular to global scales through epidemiological studies, field measurements, health-related properties of PM, and multiphase interactions of oxidants and PM upon respiratory deposition. Global modeling combined with epidemiological exposure-response functions indicates that ambient air pollution causes more than four million premature deaths per year. Epidemiological studies usually refer to PM mass concentrations, but some health effects may relate to specific constituents such as bioaerosols, polycyclic aromatic compounds, and transition metals. Various analytical techniques and cellular and molecular assays are applied to assess the redox activity of PM and the formation of reactive oxygen species. Multiphase chemical interactions of lung antioxidants with atmospheric pollutants are crucial to the mechanistic and molecular understanding of oxidative stress upon respiratory deposition. The role of distinct PM components in health impacts and mortality needs to be clarified by integrated research on various spatiotemporal scales for better evaluation and mitigation of aerosol effects on public health in the Anthropocene.

Effects of urban coarse particles inhalation on oxidative and inflammatory parameters in the mouse lung and colon

Background

Air pollution is a recognized aggravating factor for pulmonary diseases and has notably deleterious effects on asthma, bronchitis and pneumonia. Recent studies suggest that air pollution may also cause adverse effects in the gastrointestinal tract. Accumulating experimental evidence shows that immune responses in the pulmonary and intestinal mucosae are closely interrelated, and that gut-lung crosstalk controls pathophysiological processes such as responses to cigarette smoke and influenza virus infection. Our first aim was to collect urban coarse particulate matter (PM) and to characterize them for elemental content, gastric bioaccessibility, and oxidative potential; our second aim was to determine the short-term effects of urban coarse PM inhalation on pulmonary and colonic mucosae in mice, and to test the hypothesis that the well-known antioxidant N-acetyl-L-cysteine (NAC) reverses the effects of PM inhalation.

Results

The collected PM had classical features of urban particles and possessed oxidative potential partly attributable to their metal fraction. Bioaccessibility study confirmed the high solubility of some metals at the gastric level. Male mice were exposed to urban coarse PM in a ventilated inhalation chamber for 15 days at a concentration relevant to episodic elevation peak of air pollution. Coarse PM inhalation induced systemic oxidative stress, recruited immune cells to the lung, and increased cytokine levels in the lung and colon. Concomitant oral administration of NAC reversed all the observed effects relative to the inhalation of coarse PM.

Conclusions

Coarse PM-induced low-grade inflammation in the lung and colon is mediated by oxidative stress and deserves more investigation as potentiating factor for inflammatory diseases.

Electronic supplementary material

The online version of this article (10.1186/s12989-017-0227-z) contains supplementary material, which is available to authorized users.

Oxidative potential of particulate matter 2.5 as predictive indicator of cellular stress

Particulate air pollution being recognized to be responsible for short and long term health effects, regulations for particulate matter with an aerodynamic diameter less than 2.5 (PM_2.5) are more and more restrictive. PM_2.5 regulation is based on mass without taking into account PM_2.5 composition that drives toxicity. Measurement of the oxidative potential (OP) of PM could be an additional PM indicator that would encompass the PM components involved in oxidative stress, the main mechanism of PM toxicity. We compared different methods to evaluate the intrinsic oxidative potential of PM_2.5 sampled in Paris and their ability to reflect the oxidative and inflammatory response in bronchial epithelial cells used as relevant target organ cells. The dithiothreitol depletion assay, the antioxidant (ascorbic acid and glutathione) depletion assay (OP^AO), the plasmid scission assay and the dichlorofluorescein (DCFH) oxidation assay used to characterize the OP of PM_2.5 (10-100 μg/mL) provided positive results of different magnitude with all the PM_2.5 samples used with significant correlation with different metals such as Cu and Zn as well as total polyaromatic hydrocarbons and the soluble organic fraction. The OP^AO assay showed the best correlation with the production of intracellular reactive oxygen species by NCI-H292 cell line assessed by DCFH oxidation and with the expression of anti-oxidant genes (superoxide dismutase 2, heme-oxygenase-1) as well as the proinflammatory response (Interleukin 6) when exposed from 1 to 10 μg/cm². The OP^AO assay appears as the most prone to predict the biological effect driven by PM_2.5 and related to oxidative stress.

Degradation of p-Nitrophenol by Lignin and Cellulose Chars: H2O2-Mediated Reaction and Direct Reaction with the Char

Chars and other black carbons are reactive toward certain compounds. Such reactivity has been attributed to reduction of O₂ by persistent free radicals in the solid to H₂O₂, which then back-reacts with the solid to generate reactive oxygen species (ROS; especially HO^•). We studied the decomposition of p-nitrophenol (PNP) by pure lignin and cellulose chars aged in moist air or a vacuum at room temperature for up to a month. In air, the chars chemisorbed oxygen, a portion of which was liberated as H₂O₂ when the char was submerged in water. The evolved H₂O₂ was simultaneously decomposed by the char. PNP reacted predominantly in the sorbed state and only reduction products (phenol, catechol) were identified. Aging the char in air sharply (within hours) reduced H₂O₂-producing capacity and free radical concentration, but more gradually reduced PNP decay rate over the month-long period. PNP decay was only modestly suppressed (12-30%) by H₂O₂ removal (catalase), and had little effect on the free radical signal (<6 radicals annihilated per 1000 PNP reacted). Contrasting with previous studies, the results show that direct reaction of PNP with char predominates over H₂O₂-dependent reactions, and the vast majority of direct-reacting sites are nonradical in character. Nonradical sites are also responsible in part for H₂O₂ decomposition; in fact, H₂O₂ pretreatment depleted PNP reactive sites. Lignin char was generally more reactive than cellulose char. The Fe impurity in lignin played no role. The results are relevant to the fate of pollutants in black carbon-rich environments and the use of carbons in remediation.

Differential pulmonary effects of wintertime California and China particulate matter in healthy young mice

Airborne particulate matter (PM) is associated with adverse cardiorespiratory effects. To better understand source-orientated PM toxicity, a comparative study of the biological effects of fine PM (diameter≤2.5μm, PM_2.5) collected during the winter season from Shanxi Province, China, and the Central Valley, California, United States, was conducted. The overarching hypothesis for this study was to test whether the chemical composition of PM on an equal mass basis from two urban areas, one in China and one in California, can lead to significantly different effects of acute toxicity and inflammation in the lungs of healthy young mice. Male, 8-week old BALB/C mice received a single 50μg dose of vehicle, Taiyuan PM or Sacramento PM by oropharyngeal aspiration and were sacrificed 24h later. Bronchoalveolar lavage, ELISA and histopathology were performed along with chemical analysis of PM composition. Sacramento PM had a greater proportion of oxidized organic material, significantly increased neutrophil numbers and elevated CXCL-1 and TNF-α protein levels compared to the Taiyuan PM. The findings suggest that Sacramento PM_2.5 was associated with a greater inflammatory response compared to that of Taiyuan PM_2.5 that may be due to a higher oxidice. Male, 8-week old BALB/C mice received a single 50μg dose of vehicle, Taiyuan PM or Sacramento PM by oropharyngeal aspiration and were sacrificed 24h later. Bronchoalveolar lavage, ELISA and histopathology were performed along with chemical analysis of PM composition. Sacramento PM had a greater proportion of oxidized organic material, significantly increased neutrophil numbers and elevated CXCL-1 and TNF-α protein levels compared to the Taiyuan PM. The findings suggest that Sacramento PM_2.5 was associated with a greater inflammatory response compared to that of Taiyuan PM_2.5 that may be due to a higher oxidized state of organic carbon and copper content.

Delayed Nrf2-regulated antioxidant gene induction in response to silica nanoparticles

Silica nanoparticles with iron on their surface cause the production of oxidants and stimulate an inflammatory response in macrophages. Nuclear factor erythroid-derived 2 - like factor 2 (Nrf2) signaling and its regulated antioxidant genes play critical roles in maintaining redox homeostasis. In this study we investigated the regulation of four representative Nrf2-regulated antioxidant genes; i.e., glutamate cysteine ligase (GCL) catalytic subunit (GCLC), GCL modifier subunit (GCLM), heme oxygenase 1 (HO-1), and NAD(P)H:quinone oxidoreductase-1 (NQO-1), by iron-coated silica nanoparticles (SiO2-Fe) in human THP-1 macrophages. We found that the expression of these four antioxidant genes was modified by SiO2-Fe in a time-dependent manner. At 6h, their expression was unchanged except for GCLC, which was reduced compared with controls. At 18h, the expression of these antioxidant genes was significantly increased compared with controls. In contrast, the Nrf2 activator sulforaphane induced all antioxidant genes at as early as 3h. The nuclear translocation of Nrf2 occurred later than that for NF-κB p65 protein and the induction of proinflammatory cytokines (TNFα and IL-1β). NF-κB inhibitor SN50 prevented the reduction of GCLC at 6h and abolished the induction of antioxidant genes at 18h by SiO2-Fe, but did not affect the basal and sulforaphane-induced expression of antioxidant genes, suggesting that NF-κB signaling plays a key role in the induction of Nrf2-mediated genes in response to SiO2-Fe. Consistently, SN50 inhibited the nuclear translocation of Nrf2 caused by SiO2-Fe. In addition, Nrf2 silencing decreased the basal and SiO2-induced expression of the four reprehensive antioxidant genes. Taken together, these data indicated that SiO2-Fe induced a delayed response of Nrf2-regulated antioxidant genes, likely through NF-κB-Nrf2 interactions.

Rethinking Dithiothreitol-Based Particulate Matter Oxidative Potential: Measuring Dithiothreitol Consumption versus Reactive Oxygen Species Generation

We measured the rate of generation of reactive oxygen species (ROS) [hydroxyl radicals (^•OH) and hydrogen peroxide (H₂O₂)] catalyzed by ambient particulate matter (PM) in the dithiothreitol (DTT) assay. To understand the mechanism of ROS generation, we tested several redox-active substances, such as 9,10-phenanthrenequinone (PQ), 5-hydroxy-1,4-naphthoquinone (5H-1,4NQ), 1,2-naphthoquinone (1,2-NQ), 1,4-naphthoquinone (1,4-NQ), copper(II), manganese(II), and iron (II and III). Both pure compounds and their mixtures show different patterns in DTT oxidation versus ROS generation. The quinones, known to oxidize DTT in the efficiency order of PQ > 5H-1,4NQ > 1,2-NQ > 1,4-NQ, show a different efficiency order (5H-1,4NQ > 1,2-NQ ≈ PQ > 1,4-NQ) in the ROS generation. Cu(II), a dominant metal in DTT oxidation, contributes almost negligibly to the ROS generation. Fe is mostly inactive in DTT oxidation, but shows synergistic effect in ^•OH formation in the presence of other quinones (mixture/sum > 1.5). Ten ambient PM samples collected from an urban site were analyzed, and although DTT oxidation was significantly correlated with H₂O₂ generation (Pearson's r = 0.91), no correlation was observed between DTT oxidation and ^•OH formation. Our results show that measuring both DTT consumption and ROS generation in the DTT assay is important to incorporate the synergistic contribution from different aerosol components and to provide a more inclusive picture of the ROS activity of ambient PM.

Air Pollution and Climate Change Effects on Allergies in the Anthropocene: Abundance, Interaction, and Modification of Allergens and Adjuvants

Air pollution and climate change are potential drivers for the increasing burden of allergic diseases. The molecular mechanisms by which air pollutants and climate parameters may influence allergic diseases, however, are complex and elusive. This article provides an overview of physical, chemical and biological interactions between air pollution, climate change, allergens, adjuvants and the immune system, addressing how these interactions may promote the development of allergies. We reviewed and synthesized key findings from atmospheric, climate, and biomedical research. The current state of knowledge, open questions, and future research perspectives are outlined and discussed. The Anthropocene, as the present era of globally pervasive anthropogenic influence on planet Earth and, thus, on the human environment, is characterized by a strong increase of carbon dioxide, ozone, nitrogen oxides, and combustion- or traffic-related particulate matter in the atmosphere. These environmental factors can enhance the abundance and induce chemical modifications of allergens, increase oxidative stress in the human body, and skew the immune system toward allergic reactions. In particular, air pollutants can act as adjuvants and alter the immunogenicity of allergenic proteins, while climate change affects the atmospheric abundance and human exposure to bioaerosols and aeroallergens. To fully understand and effectively mitigate the adverse effects of air pollution and climate change on allergic diseases, several challenges remain to be resolved. Among these are the identification and quantification of immunochemical reaction pathways involving allergens and adjuvants under relevant environmental and physiological conditions.

Occurrence of synthetic phenolic antioxidants and transformation products in urban and rural indoor dust

In this study, seven synthetic phenolic antioxidant (SPA) analogues were positively found in urban and rural indoor dust samples collected from Shandong province in China, among which the novel 2,4,6-tri-tert-butylphenol (AO 246), 2,6-di-tert-butyl-4-sec-butylphenol (DTBSBP), 2,4-di-tert-butylphenol (DBP) and 4,4'-butylidenebis (2-(1,1-dimethylethyl)-5- methyl-phenol) (AO 44B25) analogues accounted for 29% of total SPA concentrations (∑SPAs). Urban dust showed significantly higher ∑SPA levels (range: 1.56e3 - 2.03e4 ng/g) compared with those in rural indoor dust (668-4.39e3 ng/g, p < 0.05). 2,6-Di-tert-butyl-4-methylphenol (BHT) was the dominate analogue in the urban indoor dust, which constituted of 74% in ΣSPAs. While, varied composition profiles of SPAs were noticed in rural indoor dust, for instance, AO 246 (46%) and BHT (43%) had similar contributions to ∑SPAs. Three BHT transformation products (TPs) were also detected in most of the urban and rural dust samples (>97%), with individual residue level in the same order: 2,6-di-tert-butyl-1,4-benzoquinone (BHT-Q) > 2,6-di-tert-butyl-4-hydroxy- 4-methyl-2,5-cyclo-hexadienone (BHT-quinol) > 3,5-di-tert-butyl-4-hydroxybenzal-dehyde (BHT-CHO). Geometric mean values of total TP concentrations were 555 ng/g and 131 ng/g for urban and rural indoor dust samples, respectively. A preliminary estimated daily intake calculation at dust ingestion scenario suggested additional concerns might be paid to simultaneous exposure of several SPA analogues and TPs besides current focus on BHT exposure risks.

Lung bioaccessibility of contaminants in particulate matter of geological origin

Human exposure to particulate matter (PM) has been associated with adverse health effects. While inhalation exposure to airborne PM is a prominent research subject, exposure to PM of geological origin (i.e., generated from soil/soil-like material) has received less attention. This review discusses the contaminants in PM of geological origin and their relevance for human exposure and then evaluates lung bioaccessibility assessment methods and their use. PM of geological origin can contain toxic elements as well as organic contaminants. Observed/predicted PM lung clearance times are long, which may lead to prolonged contact with lung environment. Thus, certain exposure scenarios warrant the use of in vitro bioaccessibility testing to predict lung bioavailability. Limited research is available on lung bioaccessibility test development and test application to PM of geological origin. For in vitro tests, test parameter variation between different studies and concerns about physiological relevance indicate a crucial need for test method standardization and comparison with relevant animal data. Research is recommended on (1) developing robust in vitro lung bioaccessibility methods, (2) assessing bioaccessibility of various contaminants (especially polycyclic aromatic hydrocarbons (PAHs)) in PM of diverse origin (surface soils, mine tailings, etc.), and (3) risk characterization to determine relative importance of exposure to PM of geological origin.

An ultrasound-assisted procedure for fast screening of mobile fractions of Cd, Pb and Ni in soil. Insight into method optimization and validation

A fast ultrasound-assisted sequential extraction (UASE) procedure for the determination of cadmium, lead and nickel fractions in soil was developed and fully validated. The working parameters of an ultrasound probe were optimized by comparing the content of metals in soil extracts obtained by the UASE procedure with that obtained by the conventional (with the aid of a vertical rotor) modified Community Bureau of Reference (BCR) procedure. The content of metals in soil fractions was determined by electrothermal atomic absorption spectrometry. The total time of extraction of metals from soil was shorten from 48 h to 27 min (total sonication time). The trueness of the developed method was confirmed by analysis of the certified reference material BCR-701. In order to indicate critical points of the developed UASE method, uncertainties of fractionation results were calculated and compared with those calculated for conventional modified BCR procedure. The method usefulness was tested for the determination of metal fractions in different types of soil collected in the Podlasie Province (Poland). The proposed procedure could be used for fast screening of mobile fractions of several heavy metals in soil.

A bias in the "mass-normalized" DTT response - an effect of non-linear concentration-response curves for copper and manganese

The dithiothreitol (DTT) assay is widely used to measure the oxidative potential of particulate matter. Results are typically presented in mass-normalized units (e.g., pmols DTT lost per minute per microgram PM) to allow for comparison among samples. Use of this unit assumes that the mass-normalized DTT response is constant and independent of the mass concentration of PM added to the DTT assay. However, based on previous work that identified non-linear DTT responses for copper and manganese, this basic assumption (that the mass-normalized DTT response is independent of the concentration of PM added to the assay) should not be true for samples where Cu and Mn contribute significantly to the DTT signal. To test this we measured the DTT response at multiple PM concentrations for eight ambient particulate samples collected at two locations in California. The results confirm that for samples with significant contributions from Cu and Mn, the mass-normalized DTT response can strongly depend on the concentration of PM added to the assay, varying by up to an order of magnitude for PM concentrations between 2 and 34 μg mL^-1. This mass dependence confounds useful interpretation of DTT assay data in samples with significant contributions from Cu and Mn, requiring additional quality control steps to check for this bias. To minimize this problem, we discuss two methods to correct the mass-normalized DTT result and we apply those methods to our samples. We find that it is possible to correct the mass-normalized DTT result, although the correction methods have some drawbacks and add uncertainty to DTT analyses. More broadly, other DTT-active species might also have non-linear concentration-responses in the assay and cause a bias. In addition, the same problem of Cu- and Mn-mediated bias in mass-normalized DTT results might affect other measures of acellular redox activity in PM and needs to be addressed.

Chemical exposure-response relationship between air pollutants and reactive oxygen species in the human respiratory tract

Air pollution can cause oxidative stress and adverse health effects such as asthma and other respiratory diseases, but the underlying chemical processes are not well characterized. Here we present chemical exposure-response relations between ambient concentrations of air pollutants and the production rates and concentrations of reactive oxygen species (ROS) in the epithelial lining fluid (ELF) of the human respiratory tract. In highly polluted environments, fine particulate matter (PM2.5) containing redox-active transition metals, quinones, and secondary organic aerosols can increase ROS concentrations in the ELF to levels characteristic for respiratory diseases. Ambient ozone readily saturates the ELF and can enhance oxidative stress by depleting antioxidants and surfactants. Chemical exposure-response relations provide a quantitative basis for assessing the relative importance of specific air pollutants in different regions of the world, showing that aerosol-induced epithelial ROS levels in polluted megacity air can be several orders of magnitude higher than in pristine rainforest air.

Human bronchial epithelial cell injuries induced by fine particulate matter from sandstorm and non-sandstorm periods: Association with particle constituents

Epidemiological studies have demonstrated the exacerbation of respiratory diseases following sandstorm-derived particulate matter (PM) exposure. The presence of anthropogenic and biological agents on the sandstorm PM and the escalation of PM<2.5μm (PM2.5) pollution in China have led to serious concerns regarding the health effects of PM2.5 during Asian sandstorms. We investigated how changes in PM2.5 composition, as the weather transitioned towards a sandstorm, affected human airway epithelial cells. Six PM2.5 samples covering two sandstorm events and their respective background and transition periods were collected in Baotou, an industrial city near the Gobi Desert in China. PM samples from all three periods had mild cytotoxicity in human bronchial epithelial cell line BEAS-2B, which was positively correlated with the contents of polycyclic aromatic hydrocarbons and several metals. All PM samples potently increased the release of interleukin-6 (IL-6) and interleukin-8 (IL-8). Endotoxin in all samples contributed significantly to the IL-6 response, with only a minor effect on IL-8. Cr was positively correlated with both IL-6 and IL-8 release, while Si was only associated with the increase of IL-6. Our study suggests that local agricultural and industrial surroundings in addition to the sandstorm play important roles in the respiratory effects of sandstorm-derived PM.

Characterization of chemical components and bioreactivity of fine particulate matter (PM2.5) during incense burning

The chemical and bioreactivity properties of fine particulate matter (PM2.5) emitted during controlled burning of different brands of incense were characterized. Incenses marketed as being environmentally friendly emitted lower mass of PM2.5 particulates than did traditional incenses. However, the environmentally friendly incenses produced higher total concentrations of non-volatile polycyclic aromatic hydrocarbons (PAHs) and some oxygenated polycyclic aromatic hydrocarbons (OPAHs). Human alveolar epithelial A549 cells were exposed to the collected PM2.5, followed by determining oxidative stress and inflammation. There was moderate to strong positive correlation (R > 0.60, p < 0.05) between selected PAHs and OPAHs against oxidative-inflammatory responses. Strong positive correlation was observed between interleukin 6 (IL-6) and summation of total Group B2 PAHs/OPAHs (∑7PAHs/ΣOPAHs). The experimental data indicate that emissions from the environmentally friendly incenses contained higher concentrations of several PAH and OPAH compounds than did traditional incense. Moreover, these PAHs and OPAHs were strongly correlated with inflammatory responses. The findings suggest a need to revise existing regulation of such products.

Revealing the role of oxidation state in interaction between nitro/amino-derived particulate matter and blood proteins

Surface oxidation states of ultrafine particulate matter can influence the proinflammatory responses and reactive oxygen species levels in tissue. Surface active species of vehicle-emission soot can serve as electron transfer-mediators in mitochondrion. Revealing the role of surface oxidation state in particles-proteins interaction will promote the understanding on metabolism and toxicity. Here, the surface oxidation state was modeled by nitro/amino ligands on nanoparticles, the interaction with blood proteins were evaluated by capillary electrophoresis quantitatively. The nitro shown larger affinity than amino. On the other hand, the affinity to hemoglobin is 10(3) times larger than that to BSA. Further, molecular docking indicated the difference of binding intensity were mainly determined by hydrophobic forces and hydrogen bonds. These will deepen the quantitative understanding of protein-nanoparticles interaction from the perspective of surface chemical state.

Repeated exposures to roadside particulate matter extracts suppresses pulmonary defense mechanisms, resulting in lipid and protein oxidative damage

Exposure to particulate matter (PM) pollution in cities and urban canyons can be harmful to the exposed population. However, the underlying mechanisms that lead to health effects are not yet elucidated. It is postulated that exposure to repeated, small, environmentally relevant concentrations can affect lung homeostasis. This study examines the impact of repeated exposures to urban PM on mouse lungs with focus on inflammatory and oxidative stress parameters. Aqueous extracts from collected urban PM were administered to mice by 5 repeated intra-tracheal instillations (IT). Multiple exposures, led to an increase in cytokine levels in both bronchoalveolar lavage fluid and in the blood serum, indicating a systemic reaction. Lung mRNA levels of antioxidant/phase II detoxifying enzymes decreased by exposure to the PM extract, but not when metals were removed by chelation. Finally, disruption of lung tissue oxidant-inflammatory/defense balance was evidenced by increased levels of lipid and protein oxidation. Unlike response to a single IT exposure to the same dose and source of extract, multiple exposures result in lung oxidative damage and a systemic inflammatory reaction. These could be attributed to compromised capacity to activate the protective Nrf2 tissue defense system. It is suggested that water-soluble metals present in urban PM, potentially from break and tire wear, may constitute major drivers of the pulmonary and systemic responses to multiple exposure to urban PM.

Rates of Hydroxyl Radical Production from Transition Metals and Quinones in a Surrogate Lung Fluid

Hydroxyl radical ((•)OH) is the most reactive, and perhaps most detrimental to health, of the reactive oxygen species. (•)OH production in lungs following inhalation of particulate matter (PM) can result from redox-active chemicals, including iron and copper, but the relative importance of these species is unknown. This work investigates (•)OH production from iron, copper, and quinones, both individually and in mixtures at atmospherically relevant concentrations. Iron, copper, and three of the four quinones (1,2-naphthoquinone, phenanthrenequinone and 1,4-naphthoquinone) produce (•)OH. Mixtures of copper or quinones with iron synergistically produce (•)OH at a rate 20-130% higher than the sum of the rates of the individual redox-active species. We developed a regression equation from 20 mixtures to predict the rate of (•)OH production from the particle composition. For typical PM compositions, iron and copper account for most (•)OH production, whereas quinones are a minor source, although they can contribute if present at very high concentrations. This work shows that Cu contributes significantly to (•)OH production in ambient PM; other work has shown that Cu appears to be the primary driver of HOOH production and dithiothreitol (DTT) loss in ambient PM extracts. Taken together, these results indicate that copper appears to be the most important individual contributor to direct oxidant production from inhaled PM.

Single Exposure to near Roadway Particulate Matter Leads to Confined Inflammatory and Defense Responses: Possible Role of Metals

Inhalation of traffic-associated atmospheric particulate matter (PM2.5) is recognized as a significant health risk. In this study, we focused on a single ("subclinical response") exposure to water-soluble extracts from PM collected at a roadside site in a major European city to elucidate potential components that drive pulmonary inflammatory, oxidative, and defense mechanisms and their systemic impacts. Intratracheal instillation (IT) of the aqueous extracts induced a 24 h inflammatory response characterized by increased broncho-alveolar lavage fluid (BALF) cells and cytokines (IL-6 and TNF-α), increased reactive oxygen species production, but insignificant lipids and proteins oxidation adducts in mouse lungs. This local response was largely self-resolved by 48 h, suggesting that it could represent a subclinical response to everyday-level exposure. Removal of soluble metals by chelation markedly diminished the pulmonary PM-mediated response. An artificial metal solution (MS) recapitulated the PM extract response. The self-resolving nature of the response is associated with activating defense mechanisms (increased levels of catalase and glutathione peroxidase expression), observed with both PM extract and MS. In conclusion, metals present in PM collected near roadways are largely responsible for the observed transient local pulmonary inflammation and oxidative stress. Simultaneous activation of the antioxidant defense response may protect against oxidative damage.

Analytical methods for assessing metal bioaccessibility in airborne particulate matter: A scoping review

In contrast to the existence of standardized methods to assess metal bioaccessibility via the gastrointestinal route, there are no widely-accepted, established in vitro testing protocols to measure elemental solubility in the human lung. This may be attributed, in part, to the difficulty associated with simulating the lung's complex in vivo conditions. The purpose of this review is two-fold: (1) to determine how the bioaccessibility of metals associated with ambient particulate matter (PM) in the human lung has been assessed in the literature, and (2) examine the suitability and biological relevance of applied methods for the measurement of metal bioaccessibility employed to date. The review revealed that limited attention has been paid to the development and application of biologically-relevant in vitro methods to measure elemental solubility in ambient PM as a proxy for bioaccessibility in the human lung. Few studies (n=14) used synthetic lung fluids to simulate in vivo conditions, with only half extracting samples at a biologically-relevant temperature of 37°C. There was limited evidence suggesting that the use of water is less effective as a leaching agent compared to simulated lung fluids. In sum, this scoping review highlights a critical need to develop standardized methods for the systematic assessment of elemental bioaccessibility via the respiratory route. Priority should be placed on the validation of biologically-relevant methods, including the use of leaching agents and extraction parameters used, which allow for testing to be conducted in a reliable, yet cost efficient, manner.