Quinones and aromatic chemical compounds in particulate matter induce mitochondrial dysfunction: implications for ultrafine particle toxicity

Elevated plasma solMER concentrations link ambient PM2.5 and PAHs to myocardial injury and reduced left ventricular systolic function in children

Exposure to fine particulate matter (PM2.5) and polycyclic aromatic hydrocarbons (PAHs) is known to be associated with the polarization of pro-inflammatory macrophages and the development of various cardiovascular diseases. The pro-inflammatory polarization of resident cardiac macrophages (cMacs) enhances the cleavage of membrane-bound myeloid-epithelial-reproductive receptor tyrosine kinase (MerTK) and promotes the formation of soluble MerTK (solMER). This process influences the involvement of cMacs in cardiac repair, thus leading to an imbalance in cardiac homeostasis, myocardial injury, and reduced cardiac function. However, the relative impacts of PM2.5 and PAHs on human cMacs have yet to be elucidated. In this study, we aimed to investigate the effects of PM2.5 and PAH exposure on solMER in terms of myocardial injury and left ventricular (LV) systolic function in healthy children. A total of 258 children (aged three to six years) were recruited from Guiyu (an area exposed to e-waste) and Haojiang (a reference area). Mean daily PM2.5 concentration data were collected to calculate the individual chronic daily intake (CDI) of PM2.5. We determined concentrations of solMER and creatine kinase MB (CKMB) in plasma, and hydroxylated PAHs (OH-PAHs) in urine. LV systolic function was evaluated by stroke volume (SV). Higher CDI values and OH-PAH concentrations were detected in the exposed group. Plasma solMER and CKMB were higher in the exposed group and were associated with a reduced SV. Elevated CDI and 1-hydroxynaphthalene (1-OHNa) were associated with a higher solMER. Furthermore, increased solMER concentrations were associated with a lower SV and higher CKMB. CDI and 1-OHNa were positively associated with CKMB and mediated by solMER. In conclusion, exposure to PM2.5 and PAHs may lead to the pro-inflammatory polarization of cMacs and increase the risk of myocardial injury and systolic function impairment in children. Furthermore, the pro-inflammatory polarization of cMacs may mediate cardiotoxicity caused by PM2.5 and PAHs.

Difference in the cellular response following THP-1 derived phagocytic monocyte cells exposure to commercial aluminum-based adjuvants and aluminum-containing vaccines

BACKGROUND

Aluminum-based adjuvants (ABAs) enhance the immune response following vaccine injection. Their mechanisms of action are not fully understood, and their bio-persistency have been described associated with long-term adverse effects.

METHODS

We evaluated and compared the cellular effects of the two main ABAs and whole vaccines on ATP production, ROS generation and cytokines production (IL-6 and IL-10), using THP-1 cells.

RESULTS

ABAs altered the cell energy metabolism by increasing ROS production after 24 h and reducing ATP production after 48 h. In addition, both ABAs and whole vaccines induced different kinetics of IL-6 production, whereas only ABAs induced IL-10 secretion.

CONCLUSION

This study showed clearly, for a first time, a difference in cellular response to the ABAs and whole vaccines which should be taken into consideration in future studies focusing on the effect of ABA in vaccines. Future studies on ABAs should also pay attention to mitochondrial function alterations following exposure to ABA-containing vaccines.

Effect of spraying air freshener on particulate and volatile organic compounds in vehicles

People in these days spend approximately 6 % of their time in a means of transport. Air fresheners are frequently used in vehicles to mask odors; however, they can cause adverse health effects such as cardiovascular disease, systemic inflammation and autonomic dysfunction. This study aimed to identify the effects of air fresheners on the concentrations of particulate and volatile organic compounds (VOCs) in different vehicle cabins. Scanning mobility and optical particle sizers were used for the particle measurements. VOCs (e.g., BTEX and d-limonene) were collected using a Tenax TA. The products were sprayed for less than a minute. The study assessed three spray products (all trigger types), vehicle size (small, medium, and large), cabin temperature (10 °C, 20 °C, and 25 °C), and in-vehicle ventilation mode (all-off, recirculation, and external inflow modes). The particle concentration increased rapidly during the 1-min spraying of the products. The proportion of nanoparticles in the front seat (67.2 % ± 2.2 %) was 11.1 % ± 2.2 % lower than that in the rear seat (75.6 % ± 2.1 %). The spray product and vehicle size did not significantly affect the particle or VOC concentrations. With an increase in the temperature of the front seat, the proportion of nanoparticles increased by 25.3 % ± 3.2 %. Moreover, the maximum total VOC concentrations (front seat: 364.3 μg/m3; back seat: 241.3 μg/m3) were observed at 20 °C. Under in-vehicle ventilation, recirculation effectively reduced the overall particle concentration within the cabin; however, the generated VOCs circulated. The external inflow proved effective in cabin air purification by reducing the total VOC concentration to 56.0-57.2 % compared with other ventilation modes. These findings provide substantial insight into the persistence of particles and the dynamics of their dispersion, thereby enabling informed decision-making for particle-related risk management.

Toxicity mechanisms of biomass burning aerosols in in vitro hepatic steatosis models

Nonalcoholic fatty liver disease (NAFLD) is a common chronic liver disease that contributes to the global rise in liver-related morbidity and mortality. Wood tar (WT) aerosols are a significant fraction of carbonaceous aerosol originating from biomass smoldering, contributing to air pollution particles smaller than 2.5 mm (PM2.5). Mechanistic biological associations exist between exposure to PM2.5 and increased NAFLD phenotypes in both cell and animal models. Therefore, this study examines whether an existing NAFLD-like condition can enhance the biological susceptibility of liver cells exposed to air pollution in the form of WT material. Liver cells were incubated with lauric or oleic acid (LA, OA, respectively) for 24 h to accumulate lipids and served as an in vitro hepatic steatosis model. When exposed to 0.02 or 0.2 g/L water-soluble WT aerosols, both steatosis model cells showed increased cell death compared to the control cells (blank-treated cells with or without pre-incubation with LA or OA) or compared to WT-treated cells without pre-incubation with LA or OA. Furthermore, alterations in oxidative status included variations in reactive oxygen species (ROS) levels, elevated levels of lipid peroxidation adducts, and decreased expression of antioxidant genes associated with the NRF2 transcription factor. In addition, steatosis model cells exposed to WT had a higher degree of DNA damage than the control cells (blank-treated cells with or without pre-incubation with LA or OA). These results support a possible systemic effect through the direct inflammatory and oxidative stress response following exposure to water-soluble WT on liver cells, especially those predisposed to fatty liver. Furthermore, the liver steatosis model can be influenced by the type of fatty acid used; increased adverse effects of WT on metabolic dysregulation were observed in the LA model to a higher extent compared to the OA model.

Human exposure to diesel exhaust induces CYP1A1 expression and AhR activation without a coordinated antioxidant response

BACKGROUND

Diesel exhaust (DE) induces neutrophilia and lymphocytosis in experimentally exposed humans. These responses occur in parallel to nuclear migration of NF-κB and c-Jun, activation of mitogen activated protein kinases and increased production of inflammatory mediators. There remains uncertainty regarding the impact of DE on endogenous antioxidant and xenobiotic defences, mediated by nuclear factor erythroid 2-related factor 2 (Nrf2) and the aryl hydrocarbon receptor (AhR) respectively, and the extent to which cellular antioxidant adaptations protect against the adverse effects of DE.

METHODS

Using immunohistochemistry we investigated the nuclear localization of Nrf2 and AhR in the epithelium of endobronchial mucosal biopsies from healthy subjects six-hours post exposure to DE (PM10, 300 µg/m3) versus post-filtered air in a randomized double blind study, as a marker of activation. Cytoplasmic expression of cytochrome P450s, family 1, subfamily A, polypeptide 1 (CYP1A1) and subfamily B, Polypeptide 1 (CYP1B1) were examined to confirm AhR activation; with the expression of aldo-keto reductases (AKR1A1, AKR1C1 and AKR1C3), epoxide hydrolase and NAD(P)H dehydrogenase quinone 1 (NQO1) also quantified. Inflammatory and oxidative stress markers were examined to contextualize the responses observed.

RESULTS

DE exposure caused an influx of neutrophils to the bronchial airway surface (p = 0.013), as well as increased bronchial submucosal neutrophil (p < 0.001), lymphocyte (p = 0.007) and mast cell (p = 0.002) numbers. In addition, DE exposure enhanced the nuclear translocation of the AhR and increased the CYP1A1 expression in the bronchial epithelium (p = 0.001 and p = 0.028, respectively). Nuclear translocation of AhR was also increased in the submucosal leukocytes (p < 0.001). Epithelial nuclear AhR expression was negatively associated with bronchial submucosal CD3 numbers post DE (r = -0.706, p = 0.002). In contrast, DE did not increase nuclear translocation of Nrf2 and was associated with decreased NQO1 in bronchial epithelial cells (p = 0.02), without affecting CYP1B1, aldo-keto reductases, or epoxide hydrolase protein expression.

CONCLUSION

These in vivo human data confirm earlier cell and animal-based observations of the induction of the AhR and CYP1A1 by diesel exhaust. The induction of phase I xenobiotic response occurred in the absence of the induction of antioxidant or phase II xenobiotic defences at the investigated time point 6 h post-exposures. This suggests DE-associated compounds, such as polycyclic aromatic hydrocarbons (PAHs), may induce acute inflammation and alter detoxification enzymes without concomitant protective cellular adaptations in human airways.

Bioenergetic function is decreased in peripheral blood mononuclear cells of veterans with Gulf War Illness

Gulf War Illness (GWI) is a major health problem for approximately 250,000 Gulf War (GW) veterans, but the etiology of GWI is unclear. We hypothesized that mitochondrial dysfunction is an important contributor to GWI, based on the similarity of some GWI symptoms to those occurring in some mitochondrial diseases; the plausibility that certain pollutants to which GW veterans were exposed affect mitochondria; mitochondrial effects observed in studies in laboratory models of GWI; and previous evidence of mitochondrial outcomes in studies in GW veterans. A primary role of mitochondria is generation of energy via oxidative phosphorylation. However, direct assessment of mitochondrial respiration, reflecting oxidative phosphorylation, has not been carried out in veterans with GWI. In this case-control observational study, we tested multiple measures of mitochondrial function and integrity in a cohort of 114 GW veterans, 80 with and 34 without GWI as assessed by the Kansas definition. In circulating white blood cells, we analyzed multiple measures of mitochondrial respiration and extracellular acidification, a proxy for non-aerobic energy generation; mitochondrial DNA (mtDNA) copy number; mtDNA damage; and nuclear DNA damage. We also collected detailed survey data on demographics; deployment; self-reported exposure to pesticides, pyridostigmine bromide, and chemical and biological warfare agents; and current biometrics, health and activity levels. We observed a 9% increase in mtDNA content in blood in veterans with GWI, but did not detect differences in DNA damage. Basal and ATP-linked oxygen consumption were respectively 42% and 47% higher in veterans without GWI, after adjustment for mtDNA amount. We did not find evidence for a compensatory increase in anaerobic energy generation: extracellular acidification was also lower in GWI (12% lower at baseline). A subset of 27 and 26 veterans returned for second and third visits, allowing us to measure stability of mitochondrial parameters over time. mtDNA CN, mtDNA damage, ATP-linked OCR, and spare respiratory capacity were moderately replicable over time, with intraclass correlation coefficients of 0.43, 0.44, 0.50, and 0.57, respectively. Other measures showed higher visit-to-visit variability. Many measurements showed lower replicability over time among veterans with GWI compared to veterans without GWI. Finally, we found a strong association between recalled exposure to pesticides, pyridostigmine bromide, and chemical and biological warfare agents and GWI (p < 0.01, p < 0.01, and p < 0.0001, respectively). Our results demonstrate decreased mitochondrial respiratory function as well as decreased glycolytic activity, both of which are consistent with decreased energy availability, in peripheral blood mononuclear cells in veterans with GWI.

Oxidized and Unsaturated: Key Organic Aerosol Traits Associated with Cellular Reactive Oxygen Species Production in the Southeastern United States

Exposure to ambient fine particulate matter (PM2.5) is associated with millions of premature deaths annually. Oxidative stress through overproduction of reactive oxygen species (ROS) is a possible mechanism for PM2.5-induced health effects. Organic aerosol (OA) is a dominant component of PM2.5 worldwide, yet its role in PM2.5 toxicity is poorly understood due to its chemical complexity. Here, through integrated cellular ROS measurements and detailed multi-instrument chemical characterization of PM in urban southeastern United States, we show that oxygenated OA (OOA), especially more-oxidized OOA, is the main OA type associated with cellular ROS production. We further reveal that highly unsaturated species containing carbon-oxygen double bonds and aromatic rings in OOA are major contributors to cellular ROS production. These results highlight the key chemical features of ambient OA driving its toxicity. As more-oxidized OOA is ubiquitous and abundant in the atmosphere, this emphasizes the need to understand its sources and chemical processing when formulating effective strategies to mitigate PM2.5 health impacts.

Systematic computational toxicity analysis of the ozonolytic degraded compounds of azo dyes: Quantitative structure-activity relationship (QSAR) and adverse outcome pathway (AOP) based approach

The present study identifies and analyses the degraded products of three azo dyes (Reactive Orange 16, Reactive Red 120, and Direct Red 80) and proffers their in silico toxicity predictions. In our previously published work, the synthetic dye effluents were degraded using an ozonolysis-based Advanced Oxidation Process. In the present study, the degraded products of the three dyes were analysed using GC-MS at endpoint strategy and further subjected to in silico toxicity analysis using Toxicity Estimation Software Tool (TEST), Prediction Of TOXicity of chemicals (ProTox-II), and Estimation Programs Interface Suite (EPI Suite). Several physiological toxicity endpoints, such as hepatotoxicity, carcinogenicity, mutagenicity, cellular and molecular interactions, were considered to assess the Quantitative Structure-Activity Relationships (QSAR) and adverse outcome pathways. The environmental fate of the by-products in terms of their biodegradability and possible bioaccumulation was also assessed. Results of ProTox-II suggested that the azo dye degradation products are carcinogenic, immunotoxic, and cytotoxic and displayed toxicity towards Androgen Receptor and Mitochondrial Membrane Potential. TEST results predicted LC50 and IGC50 values for three organisms Tetrahymena pyriformis, Daphnia magna, and Pimephales promelas. EPISUITE software via the BCFBAF module surmises that the degradation products' bioaccumulation (BAF) and bioconcentration factors (BCF) are high. The cumulative inference of the results suggests that most degradation by-products are toxic and need further remediation strategies. The study aims to complement existing tests to predict toxicity and prioritise the elimination/reduction of harmful degradation products of primary treatment procedures. The novelty of this study is that it streamlines in silico approaches to predict the nature of toxicity of degradation by-products of toxic industrial affluents like azo dyes. These approaches can assist the first phase of toxicology assessments for any pollutant for regulatory decision-making bodies to chalk out appropriate action plans for their remediation.

Fate and environmental behaviors of microplastics through the lens of free radical

Microplastics (MPs), as plastics with a size of less than 5 mm, are ubiquitously present in the environment and become an increasing environmental concern. The fate and environmental behavior of MPs are significantly influenced by the presence of free radicals. Free radicals can cause surface breakage, chemical release, change in crystallinity and hydrophilicity, and aggregation of MPs. On the other hand, the generation of free radicals with a high concentration and oxidation potential can effectively degrade MPs. There is a limited review article to bridge the fate and environmental behaviors of MP with free radicals and their reactions. This paper reviews the sources, types, detection methods, generation mechanisms, and influencing factors of free radicals affecting the environmental processes of MPs, the environmental effects of MPs controlled by free radicals, and the degradation strategies of MPs based on free radical-associated technologies. Moreover, this review elaborates on the limitations of the current research and provides ideas for future research on the interactions between MPs and free radicals to better explain their environmental impacts and control their risks. This article aims to keep the reader abreast of the latest development in the fate and environmental behaviors of MP with free radicals and their reactions and to bridge free radical chemistry with MP control methodology.

Trade-off effect of dissolved organic matter on degradation and transformation of micropollutants: A review in water decontamination

The degradation of micropollutants by various treatments is commonly affected by the ubiquitous dissolved organic matter (DOM) in the water environment. To optimize the operating conditions and decomposition efficiency, it is necessary to consider the impacts of DOM. DOM exhibits varied behaviors in diverse treatments, including permanganate oxidation, solar/ultraviolet photolysis, advanced oxidation processes, advanced reduction process, and enzyme biological treatments. Besides, the different sources (i.e., terrestrial and aquatic, etc) of DOM, and operational circumstances (i.e., concentration and pH) fluctuate different transformation efficiency of micropollutants in water. However, so far, systematic explanations and summaries of relevant research and mechanism are rare. This paper reviewed the "trade-off" performances and the corresponding mechanisms of DOM in the elimination of micropollutants, and summarized the similarities and differences for the dual roles of DOM in each of the aforementioned treatments. Inhibition mechanisms typically include radical scavenging, UV attenuation, competition effect, enzyme inactivation, reaction between DOM and micropollutants, and intermediates reduction. Facilitation mechanisms include the generation of reactive species, complexation/stabilization, cross-coupling with pollutants, and electron shuttle. Moreover, electron-drawing groups (i.e., quinones, ketones functional groups) and electron-supplying groups (i.e., phenols) in the DOM are the main contributors to its trade-off effect.

Biodiesel exhaust particle airway toxicity and the role of polycyclic aromatic hydrocarbons

Renewable alternatives to fossil diesel (FD) including fatty acid methyl ester (FAME) biodiesel have become more prevalent. However, toxicity of exhaust material from their combustion, relative to the fuels they are displacing has not been fully characterised. This study was carried out to examine particle toxicity within the lung epithelium and the role for polycyclic aromatic hydrocarbons (PAHs). Exhaust particles from a 20% (v/v) blend of FAME biodiesel had little impact on primary airway epithelial toxicity compared to FD derived particles but did result in an altered profile of PAHs, including an increase in particle bound carcinogenic B[a]P. Higher blends of biodiesel had significantly increased levels of more carcinogenic PAHs, which was associated with a higher level of stress response gene expression including CYP1A1, NQO1 and IL1B. Removal of semi-volatile material from particulates abolished effects on airway cells. Particle size difference and toxic metals were discounted as causative for biological effects. Finally, combustion of a single component fuel (Methyl decanoate) containing the methyl ester molecular structure found in FAME mixtures, also produced more carcinogenic PAHs at the higher fuel blend levels. These results indicate the use of FAME biodiesel at higher blends may be associated with an increased particle associated carcinogenic and toxicity risk.

A yearlong monitoring campaign of polycyclic aromatic compounds and other air pollutants at three sites in Sweden: Source identification, in vitro toxicity and human health risk assessment

Air pollution is a complex mixture of gases and particulate matter (PM) with local and non-local emission sources, resulting in spatiotemporal variability in concentrations and composition, and thus associated health risks. To study this in the greater Stockholm area, a yearlong monitoring campaign with in situ measurements of PM₁₀, PM₁, black carbon, NO_x, O₃, and PM₁₀-sampling was performed. The locations included an Urban and a Rural background site and a Highway site. Chemical analysis of PM₁₀ was performed to quantify monthly levels of polycyclic aromatic compounds (PACs), which together with other air pollution data were used for source apportionment and health risk assessment. Organic extracts from PM₁₀ were tested for oxidative potential in human bronchial epithelial cells. Strong seasonal patterns were found for most air pollutants including PACs, with higher levels during the winter months than summer e.g., highest levels of PM₁₀ were detected in March at the Highway site (33.2 μg/m³) and lowest in May at the Rural site (3.6 μg/m³). In general, air pollutant levels at the sites were in the order Highway > Urban > Rural. Multivariate analysis identified several polar PACs, including 6H-Benzo[cd]pyren-6-one, as possible discriminatory markers for these sites. The main sources of particulate pollution for all sites were vehicle exhaust and biomass burning emissions, although diesel exhaust was an important source at the Highway site. In vitro results agreed with air pollutant levels, with higher oxidative potential from the winter samples. Estimated lung cancer cases were in the order PM₁₀ > NO₂ > PACs for all sites, and with less evident seasonal differences than in vitro results. In conclusion, our study presents novel seasonal data for many PACs together with air pollutants more traditionally included in air quality monitoring. Moreover, seasonal differences in air pollutant levels correlated with differences in toxicity in vitro.

Facile synthesis of hollow microtubular COF as enrichment probe for quantitative detection of ultratrace quinones in mice plasma with APGC-MS/MS

A hollow microtubular covalent organic framework (denoted as TatDha-COF) was synthesized by solvothermal method for the enrichment and determination of quinones. The TatDha-COF showed large specific surface area (2057 m² g^-1), good crystal structure, ordered pore size distribution (2.3 nm), stable chemical properties and good reusability. Accordingly, a simple and efficient method based on dispersive solid-phase extraction (d-SPE) and atmospheric pressure gas chromatography tandem mass spectrometry (APGC-MS/MS) was developed for the determination of quinones in complex samples. The established method demonstrated a wide liner range, good linearity (r>0.9990), high enrichment factors (EFs, 24-69-folds) and low detection limits (LODs, 0.200-30.0 pg L^-1, S/N≥3). On this basis, the suggested method was successfully applied to sensitively detect the eight ultratrace quinones in mice plasma. Overall, the established method has provided a powerful tool for the enrichment and detection of ultratrace quinones in complex samples, presenting the promising application of TatDha-COF in sample pretreatment.

The State of the Art and Challenges of In Vitro Methods for Human Hazard Assessment of Nanomaterials in the Context of Safe-by-Design

The Safe-by-Design (SbD) concept aims to facilitate the development of safer materials/products, safer production, and safer use and end-of-life by performing timely SbD interventions to reduce hazard, exposure, or both. Early hazard screening is a crucial first step in this process. In this review, for the first time, commonly used in vitro assays are evaluated for their suitability for SbD hazard testing of nanomaterials (NMs). The goal of SbD hazard testing is identifying hazard warnings in the early stages of innovation. For this purpose, assays should be simple, cost-effective, predictive, robust, and compatible. For several toxicological endpoints, there are indications that commonly used in vitro assays are able to predict hazard warnings. In addition to the evaluation of assays, this review provides insights into the effects of the choice of cell type, exposure and dispersion protocol, and the (in)accurate determination of dose delivered to cells on predictivity. Furthermore, compatibility of assays with challenging advanced materials and NMs released from nano-enabled products (NEPs) during the lifecycle is assessed, as these aspects are crucial for SbD hazard testing. To conclude, hazard screening of NMs is complex and joint efforts between innovators, scientists, and regulators are needed to further improve SbD hazard testing.

Linking Cell Health and Reactive Oxygen Species from Secondary Organic Aerosols Exposure

Oxidative stress is a possible mechanism by which ambient fine particulate matter (PM) exerts adverse biological effects. While multiple biological effects and reactive oxygen species (ROS) production have been observed upon PM exposure, whether the biological effects are ROS-mediated remains unclear. Secondary organic aerosols (SOA) constitute a major fraction of fine PM and can contribute substantially to its toxicity. In this work, we measured three types of cell responses (mitochondrial membrane potential (MMP), caspase 3/7 activity, and ROS) and investigated their associations upon exposure to SOA formed from anthropogenic (naphthalene) and biogenic (α-pinene) precursors. MMP and caspase 3/7 activity (an early indicator of apoptosis) are key indicators of cell health, and changes of them could occur downstream of ROS-mediated pathways. We observed a significant increase in caspase 3/7 activity after SOA exposure, suggesting that apoptosis is an important pathway of cell death induced by SOA. We further found strong associations between a decrease in MMP and increase in caspase 3/7 activity with an increase in cellular ROS level. These results suggest that cell health is largely dependent on the cellular ROS level, highlighting oxidative stress as a key mechanism for biological effects from SOA exposure. Linear regression analyses reveal greater changes of the three cellular responses with increasing carbon oxidation state (OSc) of SOA, suggesting that SOA are more toxic when they are more oxidized. Overall, our work provides critical insights into the associations between cell health and ROS level upon SOA exposure and proposes that OSc could be a suitable proxy to assess the overall SOA toxicity.

Polypropylene nanoplastic exposure leads to lung inflammation through p38-mediated NF-κB pathway due to mitochondrial damage

BACKGROUND

Polypropylene (PP) is used in various products such as disposable containers, spoons, and automobile parts. The disposable masks used for COVID-19 prevention mainly comprise PP, and the disposal of such masks is concerning because of the potential environmental pollution. Recent reports have suggested that weathered PP microparticles can be inhaled, however, the inhalation toxicology of PP microparticles is poorly understood.

RESULTS

Inflammatory cell numbers, reactive oxygen species (ROS) production, and the levels of inflammatory cytokines and chemokines in PP-instilled mice (2.5 or 5 mg/kg) increased significantly compared to with those in the control. Histopathological analysis of the lung tissue of PP-stimulated mice revealed lung injuries, including the infiltration of inflammatory cells into the perivascular/parenchymal space, alveolar epithelial hyperplasia, and foamy macrophage aggregates. The in vitro study indicated that PP stimulation causes mitochondrial dysfunction including mitochondrial depolarization and decreased adenosine triphosphate (ATP) levels. PP stimulation led to cytotoxicity, ROS production, increase of inflammatory cytokines, and cell deaths in A549 cells. The results showed that PP stimulation increased the p-p38 and p-NF-κB protein levels both in vivo and in vitro, while p-ERK and p-JNK remained unchanged. Interestingly, the cytotoxicity that was induced by PP exposure was regulated by p38 and ROS inhibition in A549 cells.

CONCLUSIONS

These results suggest that PP stimulation may contribute to inflammation pathogenesis via the p38 phosphorylation-mediated NF-κB pathway as a result of mitochondrial damage.

Characteristics and health risks of parent, alkylated, and oxygenated PAHs and their contributions to reactive oxygen species from PM2.5 vehicular emissions in the longest tunnel in downtown Xi'an, China

A vehicular emission study was conducted in the longest inner-city tunnel in Xi'an, northwestern China in four time periods (I: 07:30-10:30, II: 11:00-14:00, III: 16:30-19:30, and IV: 20:00-23:00 LST). A sum of 40 PAHs, including parent (p-PAHs), alkylated (a-PAHs), and oxygenated (o-PAHs) in fine particulate matter (PM_2.5) were quantified. The relationships between the PAHs and the formation of reactive oxygen species (ROS) were also studied. The average total quantified PAHs concentration was 236.3 ± 48.3 ng m^-3. The p-PAHs were found to be the most dominated group, accounting for an average of 88.1% of the total quantified PAHs, followed by a-PAHs (6.1%) and o-PAHs (5.8%). On the base of the number of aromatic rings, the groups of ≤5 rings (92.5 ± 1.2%) had higher fractions than the high ones (≥6 rings, 7.5 ± 1.2%) for pPAHs. Diurnal variations of PAHs subgroups exhibited the highest levels in Period III, consistent with the largest traffic counts in evening rush hours. However, less reduction of few PAHs in the night period demonstrates that the emissions of compressed natural gas (CNG) and methanol-fueled vehicles cannot be ignored while their contribution increased. High ROS activity levels were observed in the traffic-dominated samples, implying the potential oxidative damages to humans. Additionally, diurnal variation of the ROS activity was consistent with the total quantified PAHs and toxic equivalency of benzo[a]pyrene. Good correlations (R > 0.6, p < 0.05) were seen between individual groups of PAHs (especially for 3-5 rings p-PAHs, 4 rings a-PAHs, and 2-3 rings o-PAHs) and ROS activity, supporting that the vehicular emitted PAHs possibly initiate oxidative stress. The multiple linear regression analysis further illustrated that chrysene contributed the highest (25.0%) to ROS activity. In addition to highlighting the potential hazards to the PAHs from the vehicular emission, their roles to mitigate the health effects by formations of ROS were firstly reported in northwestern China.

Iron Speciation in Respirable Particulate Matter and Implications for Human Health

Particulate matter (PM) air pollution poses a major global health risk, but the role of iron (Fe) is not clearly defined because chemistry at the particle-cell interface is often not considered. Detailed spectromicroscopy characterizations of PM_2.5 samples from the San Joaquin Valley, CA identified major Fe-bearing components and estimated their relative proportions. Iron in ambient PM_2.5 was present in spatially and temporally variable mixtures, mostly as Fe(III) oxides and phyllosilicates, but with significant fractions of metallic iron (Fe(0)), Fe(II,III) oxide, and Fe(III) bonded to organic carbon. Fe(0) was present as aggregated, nm-sized particles that comprised up to ∼30% of the Fe spectral fraction. Mixtures reflect anthropogenic and geogenic particles subjected to environmental weathering, but reduced Fe in PM originates from anthropogenic sources, likely as abrasion products. Possible mechanistic pathways involving Fe(0) particles and mixtures of Fe(II) and Fe(III) surface species may generate hydrogen peroxide and oxygen-centered radical species (hydroxyl, hydroperoxyl, or superoxide) in Fenton-type reactions. From a health perspective, PM mixtures with reduced and oxidized Fe will have a disproportionate effect in cellular response after inhalation because of their tendency to shuttle electrons and produce oxidants and electrophiles that induce inflammation and oxidative stress.

Impact of COVID-19 Lockdown on Oxidative Potential of Particulate Matter: Case of Athens (Greece)

This work evaluates the aerosol oxidative potential (OP) and its changes from modified air pollution emissions during the COVID-19 lockdown period in 2020, with the intent of elucidating the contribution of aerosol sources and related components to aerosol OP. For this, daily particulate matter (PM) samples at an urban background site were collected and analyzed with a chemical (acellular) assay based on Dithiothreitol (DTT) during the COVID-19 restriction period in Athens (Greece). The obtained time-series of OP, PM2.5, organic matter (OM) and SO42− of the pre-, post- and lockdown periods were also compared to the data of the same time periods during the years 2017–2019. Even though all traffic-related emissions have been significantly reduced during the lockdown period (by 30%), there is no reduction in water-soluble OP, organics and sulfate concentrations of aerosol during 2020. The results reveal that the decrease in traffic was not sufficient to drive any measurable change on OP, suggesting that other sources—such as biomass burning and secondary aerosol from long-range transport, which remained unchanged during the COVID lockdown—are the main contributors to OP in Athens, Greece.

Association Between Atrial Fibrillation and Occupational Exposure in Firefighters Based on Self-Reported Survey Data

Background Exposure to inhaled smoke, pollutants, volatile organic compounds, and polycyclic aromatic hydrocarbons in the firefighting environment has been associated with detrimental respiratory and cardiovascular effects, making firefighters a unique population with both personal and occupational risk factors for cardiovascular disease. Some of these exposures are also associated with development of atrial fibrillation. We aimed to study the association of atrial fibrillation and occupational exposure in firefighters. Methods and Results A cross-sectional survey was conducted between October 2018 and December 2019. Data were gathered electronically and stored in a secure REDCap database through Louisiana State University Health Shreveport. Firefighters who were members of at least 1 of 5 preselected professional organizations were surveyed via electronic links distributed by the organizations. The survey queried the number of fires fought per year as a measure of occupational exposure, as well as self-reported cardiovascular disease. A total of 10 860 active firefighters completed the survey, of whom 93.5% were men and 95.5% were aged ≤60 years. Firefighters who fought a higher number of fires per year had a significantly higher prevalence of atrial fibrillation (0-5 fires per year 2%, 6-10 fires per year 2.3%, 11-20 fires per year 2.7%, 21-30 fires per year 3%, 31 or more fires per year 4.5%; P<0.001). Multivariable logistic regression showed that a higher number of fires fought per year was associated with an increased risk of atrial fibrillation (odds ratio 1.14 [95% CI, 1.04-1.25]; P=0.006). Conclusions Firefighters may have an increased risk of atrial fibrillation associated with the number of fires they fight per year. Further clinical and translational studies are needed to explore causation and mechanisms.

Towards health-based nano reference values (HNRVs) for occupational exposure: Recommendations from an expert panel

Unique physicochemical characteristics of engineered nanomaterials (ENMs) suggest the need for nanomaterial-specific occupational exposure limits (OELs). Setting these limits remains a challenge. Therefore, the aim of this study was to set out a framework to evaluate the feasibility of deriving advisory health-based occupational limit values for groups of ENMs, based on scientific knowledge. We have used an expert panel approach to address three questions: 1) What ENM-categories should be distinguished to derive advisory health-based occupational limit values (or health-based Nano Reference Values, HNRVs) for groups of ENMs? 2) What evidence would be needed to define values for these categories? And 3) How much effort would it take to achieve this? The panel experts distinguished six possible categories of HNRVs: A) WHO-fiber-like high aspect ratio ENMs (HARNs), B) Non-WHO-fiber-like HARNs and other non-spheroidal ENMs, C) readily soluble spheroidal ENMs, D) biopersistent spheroidal ENMs with unknown toxicity, E) biopersistent spheroidal ENMs with substance-specific toxicity and F) biopersistent spheroidal ENMs with relatively low substance-specific toxicity. For category A, the WHO-fiber-like HARNs, agreement was reached on criteria defining this category and the approach of using health-based risk estimates for asbestos to derive the HNRV. For category B, a quite heterogeneous category, more toxicity data are needed to set an HNRV. For category C, readily soluble spheroidal ENMs, using the OEL of their molecular or ionic counterpart would be a good starting point. For the biopersistent ENMs with unknown toxicity, HNRVs cannot be applied as case-by-case testing is required. For the other biopersistent ENMs in category E and F, we make several recommendations that can facilitate the derivation of these HNRVs. The proposed categories and recommendations as outlined by this expert panel can serve as a reference point for derivation of HNRVs when health-based OELs for ENMs are not yet available.

Potential of NRF2 Pathway in Preventing Developmental and Reproductive Toxicity of Fine Particles

Air pollution is associated with significant adverse health effects. Recent studies support the idea that inhalation of fine particles can instigate extrapulmonary effects on the cardiovascular system through several pathways. The systemic transfer of ultrafine particles (UFPs) or soluble particle components (organic compounds and metals) is of particular concern. An integral role of reactive oxygen species (ROS)-dependent pathways has been suggested in systemic inflammatory responses and vascular dysfunction at the molecular level. Accumulating lines of evidence suggest that fine particles affect fetal development, giving rise to low birth weight and a reduction in fetal growth, and also affect the immune, cardiovascular, and central nervous systems. Oxidative stress plays an important role in fine particles toxicity; pre-treatment with antioxidants partially suppresses the developmental toxicity of fine particles. On the other hand, Nuclear factor erythroid-derived 2-like 2 (Nfe2l2), also known as NRF2, is a transcription factor essential for inducible and/or constitutive expression of phase II and antioxidant enzymes. Studies using Nrf2-knockout mice revealed that NRF2 dysfunction is intimately involved in the pathogenesis of various human diseases. Multiple single nucleotide polymorphisms (SNPs) have been detected in human NRF2 locus. An NRF2 gene SNP (−617C > A; rs6721961), located in the upstream promoter region, affects the transcriptional level of NRF2 and thereby the protein level and downstream gene expression. It has been reported that the SNP-617 is associated with various diseases. The onset and exacerbation of the diseases are regulated by genetic predisposition and environmental factors; some people live in the air-polluted environment but are not affected and remain healthy, suggesting the presence of individual differences in the susceptibility to air pollutants. NRF2 polymorphisms may also be associated with the fetal effects of fine particles exposure. Screening high-risk pregnant women genetically susceptible to oxidative stress and prevention by antioxidant interventions to protect fetal development in air-polluted areas should be considered. This article reviews the recent advances in our understanding of the fetal health effects of fine particles and describes potential chemoprevention via the NRF2 pathway to prevent the developmental and reproductive toxicity of fine particles.

Removal of Environmental Nanoparticles Increases Protein Synthesis and Energy Production in Healthy Humans

Currently, industrial activity causes the environmental release of nanoparticles that have multiple adverse effects on population health. There is a clear correlation between the increase in particulate air pollution and the increases in mortality and morbidity rates in both adults and children, which demonstrates the toxic effects of these particles. However, the effect of particle removal on healthy individuals is unknown. Thus, in this preliminary study, we showed, for the first time, how the filtering equipment that we used significantly reduced a large amount of nanoparticles in a minimum time and induced a reduction of oxidative damage in healthy individuals of both sexes after 25, 50 and 100 days of exposure. These effects led to increased protein synthesis and enhanced mitochondrial efficiency, thus resulting in a highly significant triggering of ATP synthesis. These results not only provide insight into the chronic effects that environmental nanoparticles have on individuals prior to the development of pathologies but also demonstrate a system capable of reversing nanoparticle toxicity and allowing cellular energy recovery.

Mitochondria and traffic-related air pollution linked coronary artery calcification: exploring the missing link

The continuing increase in the exposure to Traffic-related air pollution (TRAP) in the general population is predicted to result in a higher incidence of non-communicable diseases like cardiovascular disease. The chronic exposure of air particulate matter from TRAP upon the vascular system leads to the enhancement of deposition of calcium in the vasculature leading to coronary artery calcification (CAC), triggered by inflammatory reactions and endothelial dysfunction. This calcification forms within the intimal and medial layers of vasculature and the underlying mechanism that connects the trigger from TRAP is not well explored. Several local and systemic factors participate in this active process including inflammatory response, hyperlipidemia, presence of self-programmed death bodies and high calcium-phosphate concentrations. These factors along with the loss of molecules that inhibit calcification and circulating nucleation complexes influence the development of calcification in the vasculature. The loss of defense to prevent osteogenic transition linked to micro organelle dysfunction that includes deteriorated mitochondria, elevated mitochondrial oxidative stress, and defective mitophagy. In this review, we examine the contributory role of mitochondria involved in the mechanism of TRAP linked CAC development. Further we examine whether TRAP is an inducer or trigger for the enhanced progression of CAC.

Redox-Active Moieties in Dissolved Organic Matter Accelerate the Degradation of Nitroimidazoles in SO4•--Based Oxidation

The presence of dissolved organic matter (DOM) is known to inhibit the degradation of trace organic contaminants (TrOCs) in SO₄^•--based advanced oxidation processes (AOPs) due to filtering of the photochemically active light and radical scavenging effects. This study revealed an unexpected contribution for DOM in the degradation of nitroimidazoles (NZs) in the UV/persulfate AOP. The apparent second-order rate constants of NZs with SO₄^•- increased by 2.05 to 4.77 times in the presence of different DOMs. The increments were linearly related to the total electron capacity of DOM. Quinone and polyphenol moieties were found to play a dominant role. The reactive species generated from SO₄^•-'s oxidation of DOM, including semiquinone radical (SQ^•-) and superoxide (O₂^•-), were found to react with NZs via Michael addition and O₂^•- addition. The second-order rate constants of tinidazole with SQ^•- is determined to be (5.69 ± 0.59) × 10⁶ M^-1 s^-1 by laser flash photolysis. Reactive species potentially generated from DOM may be considered in designing processes for the abatement of different types of TrOCs.

The involvement of DRP1-mediated caspase-1 activation in inflammatory response by urban particulate matter in EA.hy926 human vascular endothelial cells

Atmospheric particulate matter (PM) has been reported to be closely related to cardiovascular adverse events. However, the underlying mode of action remains to be elucidated. Previous studies have documented that PM induces mitochondrial damage and inflammation, the relation between these two biological outcomes is still unclear though. In this study, we used EA.hy926 human vascular endothelial cells and a standard PM, PM SRM1648a to study the potential effects of mitochondrial dysfunction on endothelial inflammatory responses. As a result, PM SRM1648a changes mitochondrial morphology and interrupts mitochondrial dynamics with a persistent tendency of fission in a dose-dependent manner. Additionally, the caspase-1/IL-1β axis is involved in inflammatory responses but not cell pyroptosis in EA.hy926 cells following the exposure to PM SRM1648a. The activation of caspase-1 has implications in inflammation but not pyroptosis, because caspase-1-dependent pyroptosis is not the main modality of cell death in PM SRM1648a-treated EA.hy926 cells. With regard to the association between mitochondrial damage and inflammation in the case of particle stimulation, DRP1-mediated mitochondrial fission is responsible for inflammatory responses as a result of caspase-1 activation. The current study showed that PM SRM1648a has the ability to disturb mitochondrial dynamics, and trigger endothelial inflammation via DRP1/caspase-1/IL-1β regulatory pathway. In a conclusion, mitochondrial fission enables EA.hy926 cells to facilitate caspase-1 activation in response to PM SRM1648a, which is a crucial step for inflammatory reaction in vascular endothelial cells.

Oxidative Potential, Cytotoxicity, and Intracellular Oxidative Stress Generating Capacity of PM10: A Case Study in South of Italy

Long and short-term exposure to atmospheric particulate matter (PM) has detrimental effects on human health. The effective mechanisms leading to PM toxicity are still not fully understood, even if it is known that physical-chemical properties, strongly influenced by sources and atmospheric processes, are known to play an important role. In this work, PM10 samples were collected, at an urban background site in southern Italy, to determine cytotoxicity (using MTT test on A549 cells), genotoxicity (using the comet assay), and intracellular oxidative stress on A549 cells exposed for 24 h to aqueous extracts of PM10 samples. Organic carbon (OC) and elemental carbon (EC) content of PM10 and acellular determination of oxidative potential with DTT assay were performed to compare results of acellular and cellular biological assays. Cellular (OSGCV and MTTV) and acellular (OPDTTV) outcomes, normalized in volume, are well correlated (statistically significant results) with carbon content suggesting that combustion sources play an important role in determining cellular oxidative stress and cytotoxicity of PM10. Even if the number of data is limited, genotoxicity results are well correlated (Pearson r > 0.95) with OSGCV and MTTV, and a weaker, but statistically significant correlation was observed with OPDTTV. OSGCV is well correlated with the cell mortality observed with the MTTV test and a lower, but still statistically significant correlation is observed between MTTV and OPDDTV. A statistically significant correlation was found between OPDTTV and OSGCV results. When the outcomes of the cellular and acellular assay are compared normalized in mass (i.e., intrinsic values), the correlations become significantly weaker suggesting that the different sources acting on the site produces particulate matter with different toxicological potential influencing differently the biological tests studied.

Activation of the Complement System on Human Endothelial Cells by Urban Particulate Matter Triggers Inflammation-Related Protein Production

Exposure to particulate matter (PM) is becoming a major global health issue. The amount and time of exposure to PM are known to be closely associated with cardiovascular diseases. However, the mechanism through which PM affects the vascular system is still not clear. Endothelial cells line the interior surface of blood vessels and actively interact with plasma proteins, including the complement system. Unregulated complement activation caused by invaders, such as pollutants, may promote endothelial inflammation. In the present study, we sought to investigate whether urban PM (UPM) acts on the endothelial environment via the complement system. UPM-treated human endothelial cells with normal human serum showed the deposition of membrane attack complexes (MACs) on the cell surface via the alternative pathway of the complement system. Despite the formation of MACs, cell death was not observed, and cell proliferation was increased in UPM-mediated complement activation. Furthermore, complement activation on endothelial cells stimulated the production of inflammation-related proteins. Our results revealed that UPM could activate the complement system in human endothelial cells and that complement activation regulated inflammatory reaction in microenvironment. These findings provide clues with regard to the role of the complement system in pathophysiologic events of vascular disease elicited by air pollution.

Combined Toxicity of Metal Nanoparticles: Comparison of Individual and Mixture Particles Effect

Toxicity of metal nanoparticles (NPs) are closely associated with increasing intracellular reactive oxygen species (ROS) and the levels of pro-inflammatory mediators. However, NP interactions and surface complexation reactions alter the original toxicity of individual NPs. To date, toxicity studies on NPs have mostly been focused on individual NPs instead of the combination of several species. It is expected that the amount of industrial and highway-acquired NPs released into the environment will further increase in the near future. This raises the possibility that various types of NPs could be found in the same medium, thereby, the adverse effects of each NP either could be potentiated, inhibited or remain unaffected by the presence of the other NPs. After uptake of NPs into the human body from various routes, protein kinases pathways mediate their toxicities. In this context, family of mitogen-activated protein kinases (MAPKs) is mostly efficient. Despite each NP activates almost the same metabolic pathways, the toxicity induced by a single type of NP is different than the case of co-exposure to the combined NPs. The scantiness of toxicological data on NPs combinations displays difficulties to determine, if there is any risk associated with exposure to combined nanomaterials. Currently, in addition to mathematical analysis (Response surface methodology; RSM), the quantitative-structure-activity relationship (QSAR) is used to estimate the toxicity of various metal oxide NPs based on their physicochemical properties and levels applied. In this chapter, it is discussed whether the coexistence of multiple metal NPs alter the original toxicity of individual NP. Additionally, in the part of "Toxicity of diesel emission/exhaust particles (DEP)", the known individual toxicity of metal NPs within the DEP is compared with the data regarding toxicity of total DEP mixture.

BC and 1,4NQ-BC up-regulate the cytokines and enhance IL-33 expression in LPS pretreatment of human bronchial epithelial cells☆

Black carbon (BC) reacts with different substances to form secondary pollutants called aged black carbon, which causes inflammation and lung damage. BC and aged BC may enhance IL-33 in vivo, which may be derived from macrophages. The pro-inflammatory effect of IL-33 makes it essential to determine the source of IL-33, so it guides us to explore how to alleviate lung injury. In this study, a human bronchial epithelial cell line of 16HBE cells was selected, and aged BC (1,4-NQ coated BC and ozone oxidized BC) was used. We found that both BC and aged BC were able to up-regulate the mRNA expression of IL-1β, IL-6, and IL-8 except IL-33. However, the Mitogen-activated protein kinases (MAPKs) and Phosphatidylinositol 3-kinase (PI3K)/Protein kinase B (AKTs) pathways remained inactive. After pretreatment with Lipopolysaccharide (LPS), IL-33 mRNA expression was significantly increased in 16HBE cells and MAPKs and PI3K/AKT were activated. These results suggested that MAPKs and PI3K/AKT pathways were involved in the elevation of IL-33. Furthermore, epithelial cells are unlikely to be the source of lung inflammation caused by elevated IL-33 in BC and aged BC.

Effect of combined exposure to environmental aliphatic electrophiles from plants on Keap1/Nrf2 activation and cytotoxicity in HepG2 cells: A model of an electrophile exposome

Electrophiles, ubiquitously found in the environment, modify thiol groups of sensor proteins, leading to activation of redox signaling pathways such as the Kelch-like ECH-associated protein 1 (Keap1)/nuclear factor E2 related factor 2 (Nrf2) pathway. Nrf2 activation by exposure to single electrophiles has been established. However, the effect of exposure to a combination of electrophiles on Nrf2 activation has not been well evaluated. The current study examined whether combined exposure to electrophiles enhances the modification of thiol groups and Keap1/Nrf2 activation in HepG2 cells. Six electrophiles [1,2-naphthoquinone (1,2-NQ), 1,4-NQ, 1,4-benzoquinone, (E)-2-hexenal (hexenal), (E)-2-decenal, and (E)-2-butenal] were tested for S-modification of albumin in vitro and for cytotoxicity to HepG2 cells. Interestingly, a mixture of the electrophiles enhanced S-modification of albumin and cytotoxicity compared with exposure to each electrophile separately. Herein, we focused on 1,2-NQ, 1,4-NQ, and hexenal to clarify the combined effect of electrophiles on Keap1/Nrf2 activation in HepG2 cells. A concentration addition model revealed that 1,2-NQ and/or 1,4-NQ additively enhanced hexenal-mediated S-modification of GSH in vitro, whereas the cytotoxicity of hexenal was synergistically increased by simultaneous exposure of HepG2 cells to the NQs. Furthermore, an NQ cocktail (2.5 μM each) that does not activate Nrf2 enhanced hexenal-mediated Nrf2 activation. These results suggest that combined exposure to electrophiles at low concentrations induces stronger activation of redox signaling compared with exposure to each electrophile alone and worsens their cytotoxicity.

Shipping Remains a Globally Significant Source of Anthropogenic PN Emissions Even after 2020 Sulfur Regulation

Shipping is the main source of anthropogenic particle emissions in large areas of the globe, influencing climate, air quality, and human health in open seas and coast lines. Here, we determined, by laboratory and on-board measurements of ship engine exhaust, fuel-specific particle number (PN) emissions for different fuels and desulfurization applied in shipping. The emission factors were compared to ship exhaust plume observations and, furthermore, exploited in the assessment of global PN emissions from shipping, utilizing the STEAM ship emission model. The results indicate that most particles in the fresh ship engine exhaust are in ultrafine particle size range. Shipping PN emissions are localized, especially close to coastal lines, but significant emissions also exist on open seas and oceans. The global annual PN produced by marine shipping was 1.2 × 10²⁸ (±0.34 × 10²⁸) particles in 2016, thus being of the same magnitude with total anthropogenic PN emissions in continental areas. The reduction potential of PN from shipping strongly depends on the adopted technology mix, and except wide adoption of natural gas or scrubbers, no significant decrease in global PN is expected if heavy fuel oil is mainly replaced by low sulfur residual fuels. The results imply that shipping remains as a significant source of anthropogenic PN emissions that should be considered in future climate and health impact models.

Melatonin ameliorates PM2.5 -induced cardiac perivascular fibrosis through regulating mitochondrial redox homeostasis

Fine particulate matter (PM2.5 ) exposure is correlated with the risk of developing cardiac fibrosis. Melatonin is a major secretory product of the pineal gland that has been reported to prevent fibrosis. However, whether melatonin affects the adverse health effects of PM2.5 exposure has not been investigated. Thus, this study was aimed to investigate the protective effect of melatonin against PM2.5 -accelerated cardiac fibrosis. The echocardiography revealed that PM2.5 had impaired both systolic and diastolic cardiac function in ApoE-/- mice. Histopathological analysis demonstrated that PM2.5 induced cardiomyocyte hypertrophy and fibrosis, particularly perivascular fibrosis, while the melatonin administration was effective in alleviating PM2.5 -induced cardiac dysfunction and fibrosis in mice. Results of electron microscopy and confocal scanning laser microscope confirmed that melatonin had restorative effects against impaired mitochondrial ultrastructure and augmented mitochondrial ROS generation in PM2.5 -treated group. Further investigation revealed melatonin administration could significantly reverse the PM2.5 -induced phenotypic modulation of cardiac fibroblasts into myofibroblasts. For the first time, our study found that melatonin effectively alleviates PM2.5 -induced cardiac dysfunction and fibrosis via inhibiting mitochondrial oxidative injury and regulating SIRT3-mediated SOD2 deacetylation. Our findings indicate that melatonin could be a therapy medicine for prevention and treatment of air pollution-associated cardiac diseases.

NADPH oxidase and mitochondria are relevant sources of superoxide anion in the oxinflammatory response of macrophages exposed to airborne particulate matter

Exposure to ambient air particulate matter (PM) is associated with increased cardiorespiratory morbidity and mortality. In this context, alveolar macrophages exhibit proinflammatory and oxidative responses as a result of the clearance of particles, thus contributing to lung injury. However, the mechanisms linking these pathways are not completely clarified. Therefore, the oxinflammation phenomenon was studied in RAW 264.7 macrophages exposed to Residual Oil Fly Ash (ROFA), a PM surrogate rich in transition metals. While cell viability was not compromised under the experimental conditions, a proinflammatory phenotype was observed in cells incubated with ROFA 100 μg/mL, characterized by increased levels of TNF-α and NO production, together with PM uptake. This inflammatory response seems to precede alterations in redox metabolism, characterized by augmented levels of H₂O₂, diminished GSH/GSSG ratio, and increased SOD activity. This scenario resulted in increased oxidative damage to phospholipids. Moreover, alterations in mitochondrial respiration were observed following ROFA incubation, such as diminished coupling efficiency and spare respiratory capacity, together with augmented proton leak. These findings were accompanied by a decrease in mitochondrial membrane potential. Finally, NADPH oxidase (NOX) and mitochondria were identified as the main sources of superoxide anion () in our model. These results indicate that PM exposure induces direct activation of macrophages, leading to inflammation and increased reactive oxygen species production through NOX and mitochondria, which impairs antioxidant defense and may cause mitochondrial dysfunction.

Comparative study on gene expression profile in rat lung after repeated exposure to diesel and biodiesel exhausts upstream and downstream of a particle filter

Biodiesel is considered as a valuable and less toxic alternative to diesel. However, cellular and molecular effects of repeated exposure to biodiesel emissions from a recent engine equipped with a diesel particle filter (DPF) remain to be characterized. To gain insights about this point, the lung transcriptional signatures were analyzed for rats (n = 6 per group) exposed to filtered air, 30% rapeseed biodiesel (B30) blend or reference diesel (RF0), upstream and downstream a DPF, for 3 weeks (3 h/day, 5 days/week). Genomic analysis revealed a modest regulation of gene expression level (lower than a 2-fold) by both fuels and a higher number of genes regulated downstream the DPF than upstream, in response to either RF0 or to B30 exhaust emissions. The presence of DPF was found to notably impact the lung gene signature of rats exposed to B30. The number of genes regulated in common by both fuels was low, which is likely due to differences in concentrations of regulated pollutants in exhausts, notably for compound organic volatiles, polycyclic aromatic hydrocarbons, NO or NOx. Nevertheless, we have identified some pathways that were activated for both exhaust emissions, such as integrin-, IGF-1- and Rac-signaling pathways, likely reflecting the effects of gas phase products. By contrast, some canonical pathways relative to "oxidative phosphorylation" and "mitochondrial dysfunction" appear as specific to B30 exhaust emission; the repression of transcripts of mitochondrial respiratory chain in lung of rats exposed to B30 downstream of DPF supports the perturbation of mitochondria function. This study done with a recent diesel engine (compliant with the European IV emission standard) and commercially-available fuels reveals that the diesel blend composition and the presence of an after treatment system may modify lung gene signature of rats repeatedly exposed to exhaust emissions, however in a rather modest manner.

Measurements of Gross α- and β-Activities of Archived PM2.5 and PM10 Teflon Filter Samples

The adverse effects of ambient particulate matter (PM) on human health have been well demonstrated, but the underlying properties responsible for its toxicity are still unclear. We hypothesized that particulate radioactivity, which is due to the attachment of radioactive nuclides on particle surfaces, may be responsible for part of PM toxicity. We measured the gross α- and β-activities for daily PM_2.5 and PM₁₀ filters collected at the Harvard Supersite in downtown Boston from 2005 to 2006 and calculated the radioactivities at the time of air sampling retrospectively based on a previously established formula. We examined the relationship between different radioactivities and compared our measurements to those measured at the Boston EPA RadNet Station. The results showed that the majority of PM₁₀ radioactivity is associated with that of PM_2.5 samples for both α-activity (98%) and β-activity (83%). A strong linear relationship was observed between the α- and β-activities for both PM_2.5 [slope = 0.47 (±0.03); p-value < 0.0001] and PM₁₀ [slope = 0.46 (±0.09); p-value < 0.0001] samples. Measurements at the Harvard Supersite and at EPA RadNet sites are highly correlated for both α-activities [slope = 0.17 (±0.02), p-value < 0.0001] and β-activities [slope = 0.30 (±0.05), p-value < 0.0001]. Additionally, we identified several significant predictors for PM_2.5 α-activities. This novel method we developed to measure α- and β-activities from archived filters will make it possible to assess the retrospective particle radioactivity exposure for future epidemiological studies.

1,4NQ-BC enhances the lung inflammation by mediating the secretion of IL-33 which derived from macrophages

Black carbon (BC) is a product of incomplete combustion of fossil fuels and vegetation. The compelling evidence has demonstrated that it has a close relationship with several respiratory and cardiovascular diseases. BC provides the reactive sites and surfaces to absorb various chemicals, such as polycyclic aromatic hydrocarbons (PAH). Naphthoquinone is a typical PAHs which was found in particulate matter (PM) and 1,4NQ-BC owned high oxidative potential and cytotoxicity. IL-33 is an alarmin which increases innate immunity through Th2 responses. It was reported that IL-33 was a potent inducer of pro-inflammatory cytokines, like IL-6. In our previous study, it was revealed that 1,4NQ-BC instilled intratracheally to mice could trigger the lung inflammation and stimulate the secretion of IL-33 in lung tissue. We found that IL-33 could induce inflammation in lung itself. When the macrophages were eliminated, the secretion of IL-33 was reduced and the pathological damage in the lung was relieved after exposure to 1,4NQ-BC. Both MAPK and PI3K/AKT signal pathways were involved in the process of IL-33 secretion and the lung inflammation induced by 1,4NQ-BC. The findings herein support the notion that after exposure to 1,4NQ-BC, the increased secretion of IL-33 was mainly derived from macrophages through both MAPK and PI3K/AKT signal pathways.

Effects of particulate matter on atherosclerosis: a link via high-density lipoprotein (HDL) functionality?

BACKGROUND

Exposure to air pollution has been associated with adverse effects on human health, and ultimately increased morbidity and mortality. This is predominantly due to hazardous effects on the cardiovascular system. Exposure to particulate matter (PM) is considered to be responsible for the most severe effects.

MAIN BODY

Here we summarize current knowledge from existing epidemiological, clinical and animal studies on the influence of PM exposure on high-density lipoprotein (HDL) functionality and the potential initiation and progression of atherosclerosis. We highlight experimental studies that bring support to the causality and point to possible mechanistic links. Recent studies indicate that the functional properties of HDL are more important than the levels per se. Fine (PM_2.5-0.1) and ultrafine (UFP) PM are composed of chemicals as well as biological elements that are redox-active and may trigger pro-inflammatory responses. Experimental studies indicate that these properties and responses may promote HDL dysfunction via oxidative pathways. By affecting protein and lipid components of the HDL particle, its anti-atherosclerotic characteristics including cholesterol efflux capacity, as well as other anti-oxidative and anti-inflammatory features might be impaired.

CONCLUSION

Current literature suggests that PM promotes HDL dysfunction via oxidative pathways. However, as relatively few studies so far have evaluated the impact of particulate air pollution on HDL functionality, more human epidemiological as well as experimental studies are needed to strengthen any possible causal relationship and determine any relevance to atherosclerosis.

Cytotoxicity of PM2.5 vehicular emissions in the Shing Mun Tunnel, Hong Kong

Associations between human exposures to vehicular emissions (VE) and cardiopulmonary diseases have been found, with a dearth of information on particle cytotoxicity. This study exposes human lung alveolar epithelial (A549) cells to PM_2.5 (particulate matter with aerodynamic diameter <2.5 μm) samples collected in a tunnel and investigates the oxidative and inflammatory responses. The cytotoxicity factor (CF) is used to normalize the VE cytotoxicity. The emission factors (EFs) were 27.2 ± 12.0 mg vehicle^-1 km^-1 for PM_2.5 and 4.93 ± 1.67 μg vehicle^-1 km^-1 for measured polycyclic aromatic hydrocarbons (PAHs). Higher EFs were found for high (4-6 rings) than low (2-3 rings) molecular-weight particulate PAHs. PM_2.5 VE caused oxidative stress and inflammation of human lung cells. Organic carbon (OC), element carbon (EC), and several PAHs were significantly (p < 0.05) correlated with bioreactivity. Higher CFs were found when diesel vehicle counts were highest during the morning rush hour, implying that diesel-fueled VE were major contributors to cytotoxic effects. This study provides a broader understanding of the toxicity in an engine-exhaust dominated environment.

Zebrafish CYP1A expression in transgenic Caenorhabditis elegans protects from exposures to benzo[a]pyrene and a complex polycyclic aromatic hydrocarbon mixture

Polycyclic aromatic hydrocarbons (PAHs) are environmental toxicants primarily produced during incomplete combustion; some are carcinogens. PAHs can be safely metabolized or, paradoxically, bioactivated via specific cytochrome P450 (CYP) enzymes to more reactive metabolites, some of which can damage DNA and proteins. Among the CYP isoforms implicated in PAH metabolism, CYP1A enzymes have been reported to both sensitize and protect from PAH toxicity. To clarify the role of CYP1A in PAH toxicity, we generated transgenic Caenorhabditis elegans that express CYP1A at a basal (but not inducible) level. Because this species does not normally express any CYP1 family enzyme, this approach permitted a test of the role of basally expressed CYP1A in PAH toxicity. We exposed C. elegans at different life stages to either the PAH benzo[a]pyrene (BaP) alone, or a real-world mixture dominated by PAHs extracted from the sediment of a highly contaminated site on the Elizabeth River (VA, USA). This site, the former Atlantic Wood Industries, was declared a Superfund site due to coal tar creosote contamination that caused very high levels (in the [mg/mL] range) of high molecular weight PAHs within the sediments. We demonstrate that CYP1A protects against BaP-induced growth delay, reproductive toxicity, and reduction of steady state ATP levels. Lack of sensitivity of a DNA repair (Nucleotide Excision Repair)-deficient strain suggested that CYP1A did not produce significant levels of DNA-reactive metabolites from BaP. The protective effects of CYP1A in Elizabeth River sediment extract (ERSE)-exposed nematodes were less pronounced than those seen in BaP-exposed nematodes; CYP1A expression protected against ERSE-induced reduction of steady-state ATP levels, but not other outcomes of exposure to sediment extracts. Overall, we find that in C. elegans, a basal level of CYP1A activity is protective against the examined PAH exposures.

Comparison of the potential mechanisms for hepatotoxicity of p-dialkoxy chlorobenzenes in rat primary hepatocytes for read-across

Read-across based on only structural similarity is considered to have a risk of error in chemical risk assessment. Under these circumstances, considering biological similarity based on adverse outcome pathways using in vitro omics technologies is expected to enhance the accuracy and robustness of conclusions in read-across. However, due to a lack of practical case studies, key considerations and use of these technologies for data gap filling are not well discussed. Here we extracted and compared the potential mechanisms for hepatotoxicity for structural analogs of p-dialkoxy chlorobenzenes including 1,4-dichloro-2,5-dimethoxybenzene (DDMB), 2,5-dichloro-1,4-diethoxybenzene (DDEB), 2-chloro-1,4-dimethoxybenzene (CDMB), and 1-chloro-2,5-diethoxybenzene (CDEB) using in vitro omics technologies for read-across. To reveal the potential mechanisms for hepatotoxicity, we conducted microarray analysis with rat primary hepatocytes. The results showed that three (DDMB, DDEB, CDEB) of the four chemicals affected similar biological pathways such as peroxisome proliferation, oxidative stress, and mitochondrial dysfunction. Furthermore, these biological pathways are consistent with in vivo hepatotoxicity in the source chemical, DDMB. In contrast, CDMB did not affect a specific toxicological pathway. Taken together, these data show the potential mechanisms for hepatotoxicity for three chemicals (DDMB, DDEB, CDEB) and provide novel insights into grouping chemicals using in vitro toxicogenomics for read-across.

The association between high particulate matter pollution and daily cause-specific hospital admissions: a time-series study in Yichang, China

Particulate matter (PM) air pollution is one of the major causes of morbidity and mortality in China. In this study, we estimated the short-term effects of PM on cause-specific hospitalization in Yichang, China. Daily data for PM level, meteorological factors, and hospital admissions (total hospitalization counts = 391,960) in Yichang between 2015 and 2017 were collected. We conducted a time-series study and applied a generalized additive model to evaluate the association between every 10 μg/m³ increment of PM and percent increase of hospitalization. We found positive and statistically significant associations between PM and hospital admissions for multiple outcomes, including all-cause, total respiratory, total cardiovascular diseases, and disease subcategories (hypertensive disease, coronary heart disease, stroke and the stroke subtype, chronic obstructive pulmonary disease, and lower respiratory infection). Each 10 μg/m³ increase in PM_2.5 at Lag01 (a moving average of Lag0 to Lag1), was significantly associated with an increase of 1.31% (95% CI: 0.79%, 1.83%), 1.12% (95% CI: 0.40%, 1.84%), and 1.14% (95% CI: 0.53%, 1.75%) in hospitalizations for all-cause, CVD, and respiratory, respectively. The association for PM₁₀ with all-cause, CVD, and respiratory admissions was similar but weaker than PM_2.5. The effect on admissions persisted for up to 7 days, and peaked at Lag01. The associations between PM and all-cause hospitalizations were stronger among older individuals and in cold seasons. It is therefore important to continue implementation of emission abatement and other effective measures in Yichang and other cities in China.

Property-Activity Relationship of Black Phosphorus at the Nano-Bio Interface: From Molecules to Organisms

As a novel member of the two-dimensional nanomaterial family, mono- or few-layer black phosphorus (BP) with direct bandgap and high charge carrier mobility is promising in many applications such as microelectronic devices, photoelectronic devices, energy technologies, and catalysis agents. Due to its benign elemental composition (phosphorus), large surface area, electronic/photonic performances, and chemical/biological activities, BP has also demonstrated a great potential in biomedical applications including biosensing, photothermal/photodynamic therapies, controlled drug releases, and antibacterial uses. The nature of the BP-bio interface is comprised of dynamic contacts between nanomaterials (NMs) and biological systems, where BP and the biological system interact. The physicochemical interactions at the nano-bio interface play a critical role in the biological effects of NMs. In this review, we discuss the interface in the context of BP as a nanomaterial and its unique physicochemical properties that may affect its biological effects. Herein, we comprehensively reviewed the recent studies on the interactions between BP and biomolecules, cells, and animals and summarized various cellular responses, inflammatory/immunological effects, as well as other biological outcomes of BP depending on its own physical properties, exposure routes, and biodistribution. In addition, we also discussed the environmental behaviors and potential risks on environmental organisms of BP. Based on accumulating knowledge on the BP-bio interfaces, this review also summarizes various safer-by-design strategies to change the physicochemical properties including chemical stability and nano-bio interactions, which are critical in tuning the biological behaviors of BP. The better understanding of the biological activity of BP at BP-bio interfaces and corresponding methods to overcome the challenges would promote its future exploration in terms of bringing this new nanomaterial to practical applications.

Role of Mitochondria in the Redox Signaling Network and Its Outcomes in High Impact Inflammatory Syndromes

Inflammation is associated with the release of soluble mediators that drive cellular activation and migration of inflammatory leukocytes to the site of injury, together with endothelial expression of adhesion molecules, and increased vascular permeability. It is a stepwise tightly regulated process that has been evolved to cope with a wide range of different inflammatory stimuli. However, under certain physiopathological conditions, the inflammatory response overwhelms local regulatory mechanisms and leads to systemic inflammation that, in turn, might affect metabolism in distant tissues and organs. In this sense, as mitochondria are able to perceive signals of inflammation is one of the first organelles to be affected by a dysregulation in the systemic inflammatory response, it has been associated with the progression of the physiopathological mechanisms. Mitochondria are also an important source of ROS (reactive oxygen species) within most mammalian cells and are therefore highly involved in oxidative stress. ROS production might contribute to mitochondrial damage in a range of pathologies and is also important in a complex redox signaling network from the organelle to the rest of the cell. Therefore, a role for ROS generated by mitochondria in regulating inflammatory signaling was postulated and mitochondria have been implicated in multiple aspects of the inflammatory response. An inflammatory condition that affects mitochondrial function in different organs is the exposure to air particulate matter (PM). Both after acute and chronic pollutants exposure, PM uptake by alveolar macrophages have been described to induce local cell activation and recruitment, cytokine release, and pulmonary inflammation. Afterwards, inflammatory mediators have been shown to be able to reach the bloodstream and induce a systemic response that affects metabolism in distant organs different from the lung. In this proinflammatory environment, impaired mitochondrial function that leads to bioenergetic dysfunction and enhanced production of oxidants have been shown to affect tissue homeostasis and organ function. In the present review, we aim to discuss the latest insights into the cellular and molecular mechanisms that link systemic inflammation and mitochondrial dysfunction in different organs, taking the exposure to air pollutants as a case model.

Potential biomarkers and antagonists for fluoranthene-induced cellular toxicity of bone marrow derived mesenchymal stem cells

Background

Fluoranthene (FR) is a common environmental pollutant that exists in a complex mixture with other polycyclic aromatic hydrocarbons (PAHs). We identified biomarkers for monitoring FR exposure and investigated the rescue effect of FR-induced cellular toxicity via aryl hydrocarbon receptor (AHR) antagonist activity in bone marrow derived mesenchymal stem cells (BM-MSCs).

Methods

Morphological changes, viability, and rescue effects of an AHR antagonist (CH223191) were examined in BM-MSCs after exposure to FR. Cytotoxic effects were assayed using the tetrazolium-based colorimetric assay. Apoptosis was measured by annexin V and propidium iodide dye-based flowcytometry assay, mitochondrial membrane potential assay, and nuclear DNA fragmentation assay. Molecular signaling pathways of apoptosis and autophagy were investigated using immunoblotting. Proteomics were performed in order to reveal the spectra of cellular damage and identify biomarkers for FR exposure.

Results

Exposing BM-MSCs to FR (IC₅₀=50 µM) induced cell death and morphological changes, while the AHR antagonist showed rescue effects. Autophagy was activated and mitochondrial membrane potential was decreased. Proteomic analysis identified 48 deregulated proteins (26 upregulated and 22 downregulated). Among them, annexin A6, pyruvate kinase, UDP-glucose dehydrogenase, and phospholipase A2 could be potential biomarkers for FR exposure.

Conclusion

The exposure of BM-MSCs to FR induced remarkable alterations in cellular biology and the proteome, allowing for identification of novel biomarkers for FR exposure. Furthermore, AHR antagonists might be able to prevent cellular damage due to FR exposure.

Polycyclic aromatic hydrocarbon and hypoxia exposures result in mitochondrial dysfunction in zebrafish

Organisms are routinely subjected to a variety of environmental and chemical perturbations simultaneously. Often, multi-stressor exposures result in unpredictable toxicity that occurs through unidentified mechanisms. Here, we focus on polycyclic aromatic hydrocarbons (PAHs) and hypoxia, two environmental and physiological stressors that are known to co-occur in the environment. The aim of this study was to assess whether interactive mitochondrial dysfunction resulted from co-exposures of PAHs and hypoxia. Zebrafish embryos were co-exposed to non-teratogenic concentrations of an environmental PAH mixture and hypoxia beginning at 6 hpf for an acute period of 24 h and afterwards were given either no recovery period, 45 min, 5 -hs, or 18 -hs of recovery time in clean conditions. Mitochondrial function and integrity were assessed through the use of both in ovo and in vitro assays. Hypoxia exposures resulted in drastic reductions in parameters relating to mitochondrial respiration, ATP turnover, and mitochondrial DNA integrity. PAH exposures affected ATP production and content, as well as mitochondrial membrane dynamics and lactate content. While PAH and hypoxia exposures caused a broad range of effects, there appeared to be very little interaction between the two stressors in the co-exposure group. However, because hypoxia significantly altered mitochondrial function, the possibility remains that these effects may limit an individual's ability to respond to PAH toxicity and therefore could cause downstream interactive effects.

Ambient air pollution, asthma drug response, and telomere length in African American youth

BACKGROUND

Telomere length (TL) can serve as a potential biomarker for conditions associated with chronic oxidative stress and inflammation, such as asthma. Air pollution can induce oxidative stress. Understanding the relationship between TL, asthma, and air pollution is important for identifying risk factors contributing to unhealthy aging in children.

OBJECTIVES

We sought to investigate associations between exposures to ambient air pollutants and TL in African American children and adolescents and to examine whether African ancestry, asthma status, and steroid medication use alter the association.

METHODS

Linear regression was used to examine associations between absolute telomere length (aTL) and estimated annual average residential ozone (O3) and fine particulate matter with a diameter of 2.5 μm or less (PM2.5) exposures in a cross-sectional analysis of 1072 children in an existing asthma case-control study. African ancestry, asthma status, and use of steroid medications were examined as effect modifiers.

RESULTS

Participants' aTLs were measured by using quantitative PCR. A 1-ppb and 1 μg/m3 increase in annual average exposure to O3 and PM2.5 were associated with a decrease in aTL of 37.1 kilo-base pair (kb; 95% CI, -66.7 to -7.4 kb) and 57.1 kb (95% CI, -118.1 to 3.9 kb), respectively. African ancestry and asthma were not effect modifiers; however, exposure to steroid medications modified the relationships between TL and pollutants. Past-year exposure to O3 and PM2.5 was associated with shorter TLs in patients without steroid use.

CONCLUSION

Exposure to air pollution was associated with shorter TLs in nonasthmatic children and adolescents. This was not the case for asthmatic children as a group, but those receiving steroid medication had less shortening than those not using steroids. Reduced exposure to air pollution in childhood might help to preserve TL.

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.

Diesel Exhaust Induces Mitochondrial Dysfunction, Hyperlipidemia, and Liver Steatosis

OBJECTIVE

Air pollution is associated with increased cardiovascular morbidity and mortality, as well as dyslipidemia and metabolic syndrome. Our goal was to dissect the mechanisms involved. Approach and Results: We assessed the effects of exposure to air pollution on lipid metabolism in mice through assessment of plasma lipids and lipoproteins, oxidized fatty acids 9-HODE (9-hydroxyoctadecadienoic) and 13-HODE (13-hydroxyoctadecadienoic), lipid, and carbohydrate metabolism. Findings were corroborated, and mechanisms were further assessed in HepG2 hepatocytes in culture. ApoE knockout mice exposed to inhaled diesel exhaust (DE, 6 h/d, 5 days/wk for 16 weeks) exhibited elevated plasma cholesterol and triglyceride levels, increased hepatic triglyceride content, and higher hepatic levels of 9-HODE and 13-HODE, as compared to control mice exposed to filtered air. A direct effect of DE exposure on hepatocytes was demonstrated by treatment of HepG2 cells with a methanol extract of DE particles followed by loading with oleic acid. As observed in vivo, this led to increased triglyceride content and significant downregulation of ACAD9 mRNA expression. Treatment of HepG2 cells with DE particles and oleic acid did not alter de novo lipogenesis but inhibited total, mitochondrial, and ATP-linked oxygen consumption rate, indicative of mitochondrial dysfunction. Treatment of isolated mitochondria, prepared from mouse liver, with DE particles and oleic acid also inhibited mitochondrial complex activity and β-oxidation.

CONCLUSIONS

DE exposure leads to dyslipidemia and liver steatosis in ApoE knockout mice, likely due to mitochondrial dysfunction and decreased lipid catabolism.

Nrf2 protects against diverse PM2.5 components-induced mitochondrial oxidative damage in lung cells

Nrf2 is an important transcription factor implicated in the oxidative stress response, which has been reported to play an important role in the way by which air pollution particulate matter (PM_2.5) induces adverse health effects. This study investigates the mechanism by which Nrf2 exerts its protective effect in PM_2.5 induced toxicity in lung cells. Lung cells silenced for Nrf2 (shNrf2) demonstrated diverse susceptibility to various PM extracts; water extracts containing high levels of dissolved metals exhibited higher capacity to generate mitochondrial reactive oxygen species (ROS) and hence increased oxidative stress levels. Organic extracts containing high levels of polycyclic aromatic hydrocarbons (PAHs) increased mortality and reduced ROS production in the silenced cells. shNrf2 cells exhibited a higher basal mitochondrial respiration rate compared to the control cells. Following exposure to water extracts, the mitochondrial respiration increased, which was not observed with the organic extracts. shNrf2 cells exposed to the organic extracts showed lower mitochondrial membrane potential and lower mtDNA copy number. Nrf2 may act as a signaling mediator for the mitochondria function following PM_2.5 exposure.