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

Mitochondrial Dysfunction Induced by Ambient Fine Particulate Matter and Potential Mechanisms

Air pollution is one of the major environmental threats contributing to the global burden of disease. Among diverse air pollutants, fine particulate matter (PM2.5) poses a significant adverse health impact and causes multi-system damage. As a highly dynamic organelle, mitochondria are essential for cellular energy metabolism and vital for cellular homeostasis and body fitness. Moreover, mitochondria are vulnerable to external insults and common targets for PM2.5-induced cellular damage. The resultant impairment of mitochondrial structure and function initiates the pathogenesis of diverse human diseases. This review mainly summarizes the in vivo and in vitro findings of PM2.5-induced mitochondrial dysfunction and its implication in PM2.5-induced health effects. Furthermore, recent advances toward the underlying mechanisms of PM2.5 and its components-induced mitochondrial dysfunction are also discussed, with an attempt to provide insights into the toxicity of PM2.5 and basic information for devising appropriate intervention strategies.

Vitamin D ameliorates particulate matter induced mitochondrial damages and calcium dyshomeostasis in BEAS-2B human bronchial epithelial cells

BACKGROUND

Mitochondria is prone to oxidative damage by endogenous and exogenous sources of free radicals, including particulate matter (PM). Given the role of mitochondria in inflammatory disorders, such as asthma and chronic obstructive pulmonary disease, we hypothesized that supplementation of vitamin D may play a protective role in PM-induced mitochondrial oxidative damages of human bronchial epithelial BEAS-2B cells.

METHODS

BEAS-2B cells were pretreated with 1,25(OH)2D3, an active form of vitamin D, for 1 h prior to 24-hour exposure to PM (SRM-1648a). Oxidative stress was measured by flow cytometry. Mitochondrial functions including mitochondrial membrane potential, ATP levels, and mitochondrial DNA copy number were analyzed. Additionally, mitochondrial ultrastructure was examined using transmission electron microscopy. Intracellular and mitochondrial calcium concentration changes were assessed using flow cytometry based on the expression of Fluo-4 AM and Rhod-2 AM, respectively. Pro-inflammatory cytokines, including IL-6 and MCP-1, were quantified using ELISA. The expression levels of antioxidants, including SOD1, SOD2, CAT, GSH, and NADPH, were determined.

RESULTS

Our findings first showed that 24-hour exposure to PM led to the overproduction of reactive oxygen species (ROS) derived from mitochondria. PM-induced mitochondrial oxidation resulted in intracellular calcium accumulation, particularly within mitochondria, and alterations in mitochondrial morphology and functions. These changes included loss of mitochondrial membrane integrity, disarrayed cristae, mitochondrial membrane depolarization, reduced ATP production, and increased mitochondrial DNA copy number. Consequently, PM-induced mitochondrial damage triggered the release of certain inflammatory cytokines, such as IL-6 and MCP-1. Similar to the actions of mitochondrial ROS inhibitor MitoTEMPO, 1,25(OH)2D3 conferred protective effects on mtDNA alterations, mitochondrial damages, calcium dyshomeostasis, thereby decreasing the release of certain inflammatory cytokines. We found that greater cellular level of 1,25(OH)2D3 upregulated the expression of enzymatic (SOD1, SOD2, and CAT) and non-enzymatic (GSH and NADPH) antioxidants to modulate cellular redox homeostasis.

CONCLUSION

Our study provides new evidence that 1,25(OH)2D3 acts as an antioxidant, enhancing BEAS-2B antioxidant responses to regulate mitochondrial ROS homeostasis and mitochondrial function, thereby enhancing epithelial defense against air pollution exposure.

Dynamics of Inflammatory and Pathological Changes Induced by Single Exposure of Particulate Matter (PM2.5) in Mice: Potential Implications in COPD

Chronic Obstructive Pulmonary Disease (COPD) is a progressive disorder of lungs marked by chronic bronchitis and emphysema. Particulate matter (PM2.5), a major component of air pollution has been correlated with COPD incidence. The present work aimed to understand dynamics of cellular/molecular players behind PM2.5-mediated COPD pathogenesis in mice by conducting dose and time-course studies. Single intratracheal exposure of PM2.5 at a dose of either 100 or 200 μg induced inflammatory response in lungs at 4 days. Time course studies showed that inflammation once triggered by PM2.5 is progressive in nature as reflected by data on BALF inflammatory cells at 7/14 days. Similarly, various cytokines/chemokines (KC/IL-6/TNF-α/IL-1β/G-CSF/MCP-1) peak at either 7 or 14 days. However, inflammation declined sharply at 21 days. Data on LPO/GSH and activities of SOD/Catalase show induction of continuous oxidative stress in lung tissue. Next, enhanced mtROS in the CD11b+ inflammatory cells confirms the redox imbalance in neutrophils/macrophages. A continuous decline in lung function was observed till 28 days. Further, histological analysis of lung tissues at 28 days confirmed the presence of emphysematous lesions, validating the potency of PM2.5 to cause irreversible damage to lungs through complex interplay of various cellular/molecular players which may be exploited as potential preventive/therapeutic targets.

Surface property and in vitro toxicity effect of insoluble particles given by protein corona: Implication for PM cytotoxicity assessment

In vitro toxicological assessment helps explore key fractions of particulate matter (PM) in association with the toxic mechanism. Previous studies mainly discussed the toxicity effects of the water-soluble and organic-soluble fractions of PM. However, the toxicity of insoluble fractions is relatively poorly understood, and the adsorption of proteins is rarely considered. In this work, the formation of protein corona on the surface of insoluble particles during incubation in a culture medium was investigated. It was found that highly abundant proteins in fetal bovine serum were the main components of the protein corona. The adsorbed proteins increased the dispersion stability of insoluble particles. Meanwhile, the leaching concentrations of some metal elements (e.g., Cu, Zn, and Pb) from PM increased in the presence of proteins. The toxicity effects and potential mechanisms of the PM insoluble particle-protein corona complex on macrophage cells RAW264.7 were discussed. The results revealed that the PM insoluble particle-protein corona complex could influence the phagosome pathway in RAW264.7 cells. Thus, it promoted the intracellular reactive oxygen species generation and induced a greater degree of cell differentiation, significantly altering cell morphology. Consequently, this work sheds new light on the combination of insoluble particles and protein corona in terms of PM cytotoxicity assessment.

Liver Injury Induced by Exposure to Polystyrene Microplastics Alone or in Combination with Cadmium in Mice Is Mediated by Oxidative Stress and Apoptosis

Microplastics (MPs) have been considered an emerging environmental pollutant which, when combined with toxic metals, enter the circulatory system of mammals and eventually cause damage. Therefore, it is important to study the toxicity of the mixture of MPs and heavy metals for evaluating risk assessment of mammals. In the present study, the toxicological effects of different concentrations of polystyrene (PS)-MPs alone or in combination with cadmium chloride (CdCl2) during chronic exposure (8 weeks) were evaluated using intragastric administration in mice. Using comparative analysis, it was revealed that PS-MPs alone or in combination with Cd could destroy the normal structural morphology of liver tissue and increase the levels of two biochemical indicators of liver damage, thereby inducing changes in antioxidant and hyperoxide capacities. In addition, PS-MPs and/or Cd activated the antioxidant signaling pathway Nrf2-Keap1 and affected the endogenous apoptosis signaling pathway p53-Bcl-2/Bax, thus promoting apoptosis. These findings suggested that exposure to MPs alone or in combination with Cd led to adverse effects on the liver. Furthermore, it was revealed that co-exposure to MPs and Cd reduced Cd toxicity, thereby highlighting the possibility MPs may act as carriers of other toxic substances and coordinate with them. Therefore, evaluating the synergistic or anti-agonistic effects of MPs on the toxicity and bioavailability of xenobiotics is in the future critical in environmental toxicological studies.

A state-of-the-science review of using mitochondrial DNA copy number as a biomarker for environmental exposure

Mitochondria are bioenergetic, biosynthetic, and signaling organelles in eukaryotes, and contain their own genomes, mitochondrial DNA (mtDNA), to supply energy to cells by generating ATP via oxidative phosphorylation. Therefore, the threat to mitochondria' integrity and health resulting from environmental exposure could induce adverse health effects in organisms. In this review, we summarized the association between mtDNA copy number (mtDNAcn), and environmental exposures as reported in the literature. We conducted a literature search in the Web of Science using [Mitochondrial DNA copy number] and [Exposure] as two keywords and employed three selection criteria for the final inclusion of 97 papers for review. The consensus of data was that mtDNAcn could be used as a plausible biomarker for cumulative exposures to environmental chemical and physical agents. In order to furtherly expand the application of mtDNAcn in ecological and environmental health research, we suggested a series of algorithms aiming to standardize the calculation of mtDNAcn based on the PCR results in this review. We also discussed the pitfalls of using whole blood/plasma samples for mtDNAcn measurements and regard buccal cells a plausible and practical alternative. Finally, we recognized the importance of better understanding the mechanistic analysis and regulatory mechanism of mtDNAcn, in particular the signals release and regulation pathways. We believe that the development of using mtDNAcn as an exposure biomarker will revolutionize the evaluation of chronic sub-lethal toxicity of chemicals to organisms in ecological and environmental health research that has not yet been implemented.

The combined effects of phenanthrene and micro-/nanoplastics mixtures on the cellular stress responses of the thick-shell mussel Mytilus coruscus

Pollution with complex mixtures of contaminants including micro- and nano-plastics (MNPs) and organic pollutants like polycyclic aromatic hydrocarbons (PAH) poses a major threat to coastal marine ecosystems. Toxic mechanisms of contaminant mixtures are not well understood in marine organisms. We studied the effects of single and combined exposures to polycyclic aromatic hydrocarbon phenanthrene (Phe) and MNPs mixture with sizes of 70 nm, 5 μm and 100 μm on the immune health and oxidative stress parameters in the thick-shell mussel Mytilus coruscus. Immune cells (hemocytes) were more sensitive to the pollutant-induced oxidative stress than the gills. In hemocytes of co-exposed mussels, elevated mortality, lower lysosomal content, high production of reactive oxygen species (ROS) and decrease mitochondrial were found. Disparate responses of antioxidant enzymes in the hemolymph (e.g. increased superoxide dismutase (SOD) activity without a corresponding increase in catalase (CAT) in Phe exposures and an increase in CAT without a change in SOD in MNPs exposures) suggests misbalance of the antioxidant defense in the pollutant-exposed mussels. Gill lacked pronounced oxidative stress response showing a decline in ROS and antioxidant levels. Tissue-specific single and combined effects of Phe and MNPs suggest variation in bioavailability and/or different sensitivity to these pollutants in the studied tissues. Notably, the combined effects of MNPs and Phe were additive or antagonistic, showing that MNPs do not enhance and occasionally mitigate the toxic effects of Phe on the hemocytes and the gills of the mussels. Overall, our study sheds light on the impact of long-term exposure to MNPs and Phe mixtures on mussels, showing high sensitivity of the immune system and modulation of the Phe toxicity by MNPs co-exposure. These findings that may have implications for understanding the impacts of combined PAH and MNPs pollution on the health of mussel populations from polluted coastal habitats.

Associations between Urinary Concentrations of Polycyclic Aromatic Hydrocarbons and Overactive Bladder in US Adults: Data from the National Health and Nutrition Examination Survey 2005-2016

INTRODUCTION

Polycyclic aromatic hydrocarbons (PAHs) are a group of chemicals that can induce oxidative stress and related cytotoxicity. Whether urinary concentrations of PAHs have effects on overactive bladder (OAB) in the general population is still unclear. This study investigated the associations between urinary PAHs and OAB.

METHODS

7,146 adults aged over 20 who participated in the US National Health and Nutrition Examination Survey 2005-2016 were studied. The impact of the six PAHs on OAB was evaluated by multivariate logistic regression, and percent changes related to different quartiles of those six PAH levels were calculated. Confounders including age, logarithmic urinary creatinine, gender, race, body mass index, educational level, marriage, poverty income ratio, diabetes, hypertension, and metabolic syndrome were controlled.

RESULTS

There is a significant positive correlation between urinary concentrations of the six PAHs we include in the study and the occurrence of OAB. Furthermore, individuals with higher PAH levels also reported a more severe OAB symptom score (OABSS).

CONCLUSIONS

Our findings revealed that adult men in the USA with higher urinary PAHs had a higher risk of OAB incidence. These findings suggest the importance of strong environmental regulation of PAHs to protect population health. However, the underlying mechanisms still need further exploration.

Particulate matter-mediated oxidative stress induces airway inflammation and pulmonary dysfunction through TXNIP/NF-κB and modulation of the SIRT1-mediated p53 and TGF-β/Smad3 pathways in mice

Exposure to particulate matter is currently recognized as a serious aggravating factor of respiratory diseases. In this study, we investigated the effects of particulate matter (PM) on the respiratory system in BALB/c mice and NCI-H292 cells. PM (0, 2.5, 5 and 20 mg/kg) was administered to mice by intra-tracheal instillation for 7 days. After a 7 day-repeated treatment of PM, we evaluated inflammatory cytokines/cell counts in bronchoalveolar lavage fluid (BALF) and conducted pulmonary histology and functional test. We also investigated the role of TXNIP/NF-κB and SIRT1-mediated p53 and TGF-β/Smad3 pathways in PM-induced airway inflammation and pulmonary dysfunction. PM caused a significant increase in pro-inflammatory cytokines, inflammatory cell counts in bronchoalveolar lavage fluid. PM-mediated oxidative stress down-regulated thioredoxin-1 and up-regulated thioredoxin-interacting protein and activation of nuclear factor-kappa B in the lung tissue and PM-treated NCI-H292 cells. PM suppressed sirtuin1 protein levels and increased p53 acetylation in PM-exposed mice and PM-treated NCI-H292 cells. In addition, PM caused inflammatory cell infiltration and the thickening of alveolar walls by exacerbating the inflammatory response in the lung tissue. PM increased levels of transforming growth factor-β, phosphorylation of Smad3 and activation of α-smooth muscle actin, and collagen type1A2 in PM-exposed mice and PM-treated NCI-H292 cells. In pulmonary function tests, PM exposure impaired pulmonary function resembling pulmonary fibrosis, characterized by increased resistance and elastance of the respiratory system, and resistance, elastance, and damping of lung tissues, whereas decreased compliance of the respiratory system, forced expired volume and forced vital capacity. Overall, PM-mediated oxidative stress caused airway inflammation and pulmonary dysfunction with pulmonary fibrosis via TXNIP pathway/NF-κB activation and modulation of the SIRT1-mediated TGF-β/Smad3 pathways. The results of this study can provide fundamental data on the potential adverse effects and underlying mechanism of pulmonary fibrosis caused by PM exposure as a public health concern. Due to the potential toxicity of PM, people with respiratory disease must be careful with PM exposure.

Biological Impact of Organic Extracts from Urban-Air Particulate Matter: An In Vitro Study of Cytotoxic and Metabolic Effects in Lung Cells

Atmospheric particulate matter (PM) with diameters below 10 µm (PM10) may enter the lungs through inhalation and are linked to various negative health consequences. Emergent evidence emphasizes the significance of cell metabolism as a sensitive target of PM exposure. However, the current understanding of the relationship between PM composition, conventional toxicity measures, and the rewiring of intracellular metabolic processes remains limited. In this work, PM10 sampled at a residential area (urban background, UB) and a traffic-impacted location (roadside, RS) of a Portuguese city was comprehensively characterized in terms of polycyclic aromatic hydrocarbons and plasticizers. Epithelial lung cells (A549) were then exposed for 72 h to PM10 organic extracts and different biological outcomes were assessed. UB and RS PM10 extracts dose-dependently decreased cell viability, induced reactive oxygen species (ROS), decreased mitochondrial membrane potential, caused cell cycle arrest at the G0/G1 phase, and modulated the intracellular metabolic profile. Interestingly, the RS sample, richer in particularly toxic PAHs and plasticizers, had a greater metabolic impact than the UB extract. Changes comprised significant increases in glutathione, reflecting activation of antioxidant defences to counterbalance ROS production, together with increases in lactate, NAD+, and ATP, which suggest stimulation of glycolytic energy production, possibly to compensate for reduced mitochondrial activity. Furthermore, a number of other metabolic variations hinted at changes in membrane turnover and TCA cycle dynamics, which represent novel clues on potential PM10 biological effects.

Sestrin2/Keap1/Nrf2 pathway regulates mucus hypersecretion in pulmonary epithelium induced by traffic-related PM2.5 and water-soluble extracts

The involvement of fine particulate matter (PM2.5) exposure in the progression of asthma has been extensively discussed in epidemiological and experimental evidence, which aroused widespread attention. Asthma is characterized by mucus hypersecretion. This study investigates the underlying toxic mechanism of traffic-related PM2.5 (TRPM2.5) and water-soluble extracts (WSE) on mucus hypersecretion in the lungs of rats with asthma and 16HBE cells. The ovalbumin-induced rats were administrated by instillation of TRPM2.5 and WSE in the trachea once three days for eight times. The results showed that TRPM2.5 and WSE had an adverse impact on mucus secretion. Specifically, conspicuous mucus stains and increased goblet cells in the bronchial epithelium by PAS staining were found in lung tissues of rats with asthma; MUC5AC gene and protein expression levels in lung tissues of rats with asthma and 16HBE cells were elevated. In addition, TRPM2.5 and WSE triggered oxidative damage via upregulation of malondialdehyde and myeloperoxidase as well as activation of the Sestrin2/Keap1/Nrf2 signaling pathway. Conversely, the knockdown of Sestrin2 effectively inhibited TRPM2.5 and WSE-induced mucus hypersecretion, oxidative stress, and Keap1/Nrf2 signaling pathway and its downstream target gene NQO1. Collectively, it was demonstrated that TRPM2.5 and WSE induced mucus hypersecretion mediated by the Sestrin2/Keap1/Nrf2 pathway.

Artemisia gmelinii Extract Attenuates Particulate Matter-Induced Neutrophilic Inflammation in a Mouse Model of Lung Injury

Particulate matter (PM) induces and augments oxidative stress and inflammation, leading to respiratory diseases. Although Artemisia gmelinii Weber ex Stechm has antioxidant and anti-inflammatory effects, there are no reports on whether Artemisia gmelinii extract (AGE) regulates lung inflammation in a PM-induced model. Thus, we investigated the protective effects of AGE using a PM-induced mouse lung inflammation model. AGE significantly decreased the expression of inflammatory chemokines, neutrophil extracellular trap formation, and the total number of inflammatory cells in the bronchoalveolar lavage fluid (BALF). Furthermore, AGE attenuated lung inflammation through the suppression of the nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB)/mitogen-activated protein kinase (MAPK) signaling pathway, while promoting the nuclear factor erythroid-2-related factor 2 (NRF2)/heme oxygenase-1 (HO-1) signaling pathway in lung tissues. Concordant with these observations, AGE suppressed inflammatory cytokines, chemokines, reactive oxygen species, NETosis, myeloperoxidase, and neutrophil elastase by decreasing the mRNA expression of High mobility group box 1, Runt-related transcription factor 1, and Kruppel-like factor 6 in differentiated HL-60 cells. In summary, our data demonstrated that AGE suppresses PM-induced neutrophil infiltration, lung damage, and pulmonary inflammation by suppressing NF-κB/MAPK signaling pathways and enhancing the NRF2/HO-1 signaling pathway. These findings suggest that AGE administration is an effective approach for preventing and treating PM-induced respiratory inflammation.

Sex-specific association of exposure to air pollutants and Nrf2 gene expression and inflammatory biomarkers in exhaled breath of healthy adolescents

Studies investigating the nuclear factor erythroid 2-related factor 2 (Nrf2) expression levels in the respiratory system of healthy subjects are scarce. Moreover, separate studies on the health-related outcomes of air pollution for each sex are limited. The current panel study investigated sex-specific Nrf2 expression levels and related oxidative stress and inflammatory responses among healthy adolescents exposed to PM2.5, PM10, O3, and PM2.5-bounded metals in a high traffic region. Forty-nine healthy nonsmoking subjects participated in the study for five consecutive months (Nov. 2019 to Feb. 2020). Each subject was asked to provide 1 mL of exhaled breath condensate (EBC). Data were analyzed using linear mixed-effects models. The results showed that PM10, PM2.5, O3, and PM2.5-bounded metals were negatively linked to Nrf2 expression level in EBC of females with -58.3% (95% CI: 79.5, -15.4), -32.1% (95% CI: -50.3, -7.1), -76.2% (95% CI: -92.6, -23.9), and -1.9 (95% CI: -3.4, -0.4), respectively. While our results presented no significant association between the studied pollutants and Nrf2 gene expression in males, significant associations were observed between the pollutants and total nitric oxide (NOx), interleukins 6 (IL-6), and tumor necrosis factor-alpha (TNF-α) in the EBC of females. In the case of males, only EBC cytokines showed a significant association with air pollutants. Overall, this study suggests that exposure to ambient air pollutants may affect the respiratory system with biologically different mechanisms in males and females. PM2.5 concentration had a positive correlation with exhaled TNF-α and IL6 values in females while positive correlation with TNF-α and negative correlation with IL6 values in males. O3 had a negative correlation with TNF-α in males.

Effect Of Atmospheric Particulate Matter On The Functional State Of Mitochondria

The health risks associated with outdoor air pollution are of global concern. Atmospheric air pollution negatively affects a number of key aspects of human health, including the functioning of the respiratory, cardiovascular and central nervous systems, but many issues remain unresolved about the relationship between atmospheric air pollution and the development and course of pathologies. The review analyzes data from Russian and foreign sources on the effect of atmospheric particulate matter on the functional state of mitochondria. The effect of air pollution on structural changes in mitochondria, ATP synthesis, production of reactive oxygen species, damage to mitochondrial DNA, and mitochondrial membrane potential has been shown. The data presented in the review indicate the need for further studies of the functional state of mitochondria under the impact of solid particles in atmospheric air.

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.

Nrf2-/- regulated lung DNA demethylation and CYP2E1 DNA methylation under PM2.5 exposure

Cytochrome P450 (CYP450) can mediate fine particulate matter (PM_2.5) exposure leading to lung injury. Nuclear factor E2-related factor 2 (Nrf2) can regulate CYP450 expression; however, the mechanism by which Nrf2^-/- (KO) regulates CYP450 expression via methylation of its promoter after PM_2.5 exposure remains unclear. Here, Nrf2^-/- (KO) mice and wild-type (WT) were placed in a PM_2.5 exposure chamber (PM) or a filtered air chamber (FA) for 12 weeks using the real-ambient exposure system. The CYP2E1 expression trends were opposite between the WT and KO mice following PM_2.5 exposure. After exposure to PM_2.5, CYP2E1 mRNA and protein levels were increased in WT mice but decreased in KO mice, and CYP1A1 expression was increased after exposure to PM_2.5 in both WT and KO mice. CYP2S1 expression decreased after exposure to PM_2.5 in both the WT and KO groups. We studied the effect of PM_2.5 exposure on CYP450 promoter methylation and global methylation levels in WT and KO mice. In WT and KO mice in the PM_2.5 exposure chamber, among the methylation sites examined in the CYP2E1 promoter, the CpG2 methylation level showed an opposite trend with CYP2E1 mRNA expression. The same relationship was evident between CpG3 unit methylation in the CYP1A1 promoter and CYP1A1 mRNA expression, and between CpG1 unit methylation in the CYP2S1 promoter and CYP2S1 mRNA expression. This data suggests that methylation of these CpG units regulates the expression of the corresponding gene. After exposure to PM_2.5, the expression of the DNA methylation markers ten-eleven translocation 3 (TET3) and 5-hydroxymethylcytosine (5hmC) was decreased in the WT group but significantly increased in the KO group. In summary, the changes in CYP2E1, CYP1A1, and CYP2S1 expression in the PM_2.5 exposure chamber of WT and Nrf2^-/- mice might be related to the specific methylation patterns in their promoter CpG units. After exposure to PM_2.5, Nrf2 might regulate CYP2E1 expression by affecting CpG2 unit methylation and induce DNA demethylation via TET3 expression. Our study revealed the underlying mechanism for Nrf2 to regulate epigenetics after lung exposure to PM_2.5.

Air pollution: A culprit of lung cancer

Air pollution is a global health problem, especially in the context of rapid economic development and the expansion of urbanization. Herein, we discuss the harmful effects of outdoor and indoor pollution on the lungs. Ambient particulate matters (PMs) from industrial and vehicle exhausts is associated with lung cancer. Workers exposed to asbestos, polycyclic aromatic hydrocarbons (PAHs), and toxic metals are also likely to develop lung cancer. Indoors, cooking fumes, second-hand smoke, and radioactive products from house decoration materials play roles in the development of lung cancer. Bacteria and viruses can also be detrimental to health and are important risk factors in lung inflammation and cancer. Specific effects of lung cancer caused by air pollution are discussed in detail, including inflammation, DNA damage, and epigenetic regulation. In addition, advanced materials for personal protection, as well as the current government policies to prevent air pollution, are summarized. This review provides a basis for future research on the relationship between lung cancer and air pollution.

Lung toxicity of particulates and gaseous pollutants using ex-vivo airway epithelial cell culture systems

Air pollution consists of a multi-faceted mix of gases and ambient particulate matter (PM) with diverse organic and non-organic chemical components that contribute to increasing morbidity and mortality worldwide. In particular, epidemiological and clinical studies indicate that respiratory health is adversely affected by exposure to air pollution by both causing and worsening (exacerbating) diseases such as chronic obstructive pulmonary disease (COPD), asthma, interstitial pulmonary fibrosis and lung cancer. The molecular mechanisms of air pollution-induced pulmonary toxicity have been evaluated with regards to different types of PM of various sizes and concentrations with single and multiple exposures over different time periods. These data provide a plausible interrelationship between cellular toxicity and the activation of multiple biological processes including proinflammatory responses, oxidative stress, mitochondrial oxidative damage, autophagy, apoptosis, cell genotoxicity, cellular senescence and epithelial-mesenchymal transition. However, these molecular changes have been studied predominantly in cell lines rather than in primary bronchial or nasal cells from healthy subjects or those isolated from patients with airways disease. In addition, they have been conducted under different cell culture conditions and generally in submerged culture rather than the more relevant air-liquid interface culture and with a variety of air pollutant exposure protocols. Cell types may respond differentially to pollution delivered as an aerosol rather than being bathed in media containing agglomerations of particles. As a result, the actual pathophysiological pathways activated by different PMs in primary cells from the airways of healthy and asthmatic subjects remains unclear. This review summarises the literature on the different methodologies utilised in studying the impact of submicron-sized pollutants on cells derived from the respiratory tract with an emphasis on data obtained from primary human cell. We highlight the critical underlying molecular mechanisms that may be important in driving disease processes in response to air pollution in vivo.

Particulate matter in COPD pathogenesis: an overview

Chronic obstructive pulmonary disease (COPD) is a progressive lung disorder with substantial patient burden and leading cause of death globally. Cigarette smoke remains to be the most recognised causative factor behind COPD pathogenesis. Given the alarming increase in prevalence of COPD amongst non-smokers in recent past, a potential role of air pollution particularly particulate matter (PM) in COPD development has gained much attention of the scientists. Indeed, several epidemiological studies indicate strong correlation between airborne PM and COPD incidence/exacerbations. PM-induced oxidative stress seems to be the major player in orchestrating COPD inflammatory cycle but the exact molecular mechanism(s) behind such a process are still poorly understood. This may be due to the complexity of multiple molecular pathways involved. Oxidative stress-linked mitochondrial dysfunction and autophagy have also gained importance and have been the focus of recent studies regarding COPD pathogenesis. Accordingly, the present review is aimed at understanding the key molecular players behind PM-mediated COPD pathogenesis through analysis of various experimental studies supported by epidemiological data to identify relevant preventive/therapeutic targets in the area.

Preparation of Electrospun Active Molecules Membrane Application to Atmospheric Free Radicals

Atmospheric reactive oxygen species (ROS) play a key role in the process of air pollution and oxidative damage to organisms. The analysis of ROS was carried out by the capture-derivative method. Therefore, it is necessary to prepare an effective molecular membrane to trap and detect ROS. Electrospinning membranes were prepared by combining the electrospinning technique with chrysin, baicalein, scutellarin, genistein, quercetin, and baicalin. By comparing the structures of the membranes before and after the reaction, the fluorescence enhancement characteristics of the reactive molecular membranes and the atmospheric radicals were studied. The ability of the active molecular membranes to trap atmospheric radicals was also studied. It was found that the genistein active molecular membrane had good trapping ability in four environments. The fluorescence enhancement rates in ROS, OH radical and O₃ simulated environments were 39.32%, 7.99% and 11.92%, respectively. The fluorescence enhancement rate in atmospheric environment was 16.16%. Indeed, the sites where the atmospheric radicals react with the active molecular membranes are discussed. It is found that it is mainly related to the 5,7 phenolic hydroxyl of ring A, catechol structure and the coexistence structure of 4′ phenolic hydroxyl of ring B and 7 phenolic hydroxyl of ring A. Therefore, the genistein molecular membrane has shown great potential in its trapping ability and it is also environmentally friendly.

Characteristics of a novel photoinitiator aceanthrenequinone-initiated polymerization and cytocompatibility of its triggered polymer

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AATQ is a novel photosensitizer with high-photoinitiating conversion efficiency at a relatively low concentration under 455 nm-blue light.

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Cytotoxicity of AATQ to different tissue types of cells is much lower than widely used-BAPO.

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Cytocompatibility of AATQ-initiated polymer is significantly superior to PANQ, but inferior to CQ.

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AATQ offers an alternative in industrial or biomedical areas, especially in the required low concentration of photoinitiators.

A number of photoinitiators are available in chemical industry, but less of them in biomedicine or clinical therapy due to the limitation of their cytotoxicity and biocompatibility. Thus, it is urgently necessary to find non-toxic or low-toxic photoinitiators to meet clinical demands. Aceanthrenequinone (AATQ) is a novel photosensitizer with high-photoinitiating ability, but no reports contribute, to date, to its cytotoxicity and biocompatibility. Here, primary cells and various cell lines were exposed to different concentrations of AATQ with or without irradiation. AATQ had the similar photoinitiating conversion efficiency to the extensively used bis(2,4,6-trimethylbenzoyl)-phenylphosphine oxide (BAPO) and higher one than 9,10-phenanthrenequinone (PANQ) with the similar extent of polymerization in depth within a certain range, but displayed much lower cytotoxicity than BAPO under non-irradiation or irradiation. The biocompatibility of BisGMA/TEGDMA polymer prepared by AATQ was superior to that of PANQ, but inferior to that of camphorquinone (CQ) although the far lower dose of AATQ is enough to initiate polymerization of monomer than that of CQ. Hence, AATQ offers a valuable alternative in applications of industrial or biomedical areas.

SH-29 and SK-119 Attenuates Air-Pollution Induced Damage by Activating Nrf2 in HaCaT Cells

Air pollution has been repeatedly linked to numerous health-related disorders, including skin sensitization, oxidative imbalance, premature extrinsic aging, skin inflammation, and increased cancer prevalence. Nrf2 is a key player in the endogenous protective mechanism of the skin. We hypothesized that pharmacological activation of Nrf2 might reduce the deleterious action of diesel particulate matter (DPM), evaluated in HaCaT cells. SK-119, a recently synthesized pharmacological agent as well as 2,2′-((1E,1′E)-(1,4-phenylenebis(azaneylylidene))bis(methaneylylidene))bis(benzene-1,3,5-triol) (SH-29) were first evaluated in silico, suggesting a potent Nrf2 activation capacity that was validated in vitro. In addition, both compounds were able to attenuate key pathways underlying DPM damage, including cytosolic and mitochondrial reactive oxygen species (ROS) generation, tested by DC-FDA and MitoSOX fluorescent dye, respectively. This effect was independent of the low direct scavenging ability of the compounds. In addition, both SK-119 and SH-29 were able to reduce DPM-induced IL-8 hypersecretion in pharmacologically relevant concentrations. Lastly, the safety of both compounds was evaluated and demonstrated in the ex vivo human skin organ culture model. Collectively, these results suggest that Nrf2 activation by SK-119 and SH-29 can revert the deleterious action of air pollution.

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.

Cytotoxicity and chemical composition of women's personal PM2.5 exposures from rural China

Personal exposure PM samples aid in determining the sources and chemical composition of real-world exposures, particularly in settings with household air pollution. However, their use in toxicological research is limited, despite uncertainty regarding health effects in these settings and evidence of differential toxicity among PM_2.5 sources and components. This study used women's PM_2.5 exposure samples collected using personal exposure monitoring in rural villages in three Chinese provinces (Beijing, Shanxi, and Sichuan) during summer and winter. Water-soluble organic carbon, ions, elements, and organic tracers (e.g. levoglucosan and polycyclic aromatic hydrocarbons [PAHs]) were quantified in water and organic PM_2.5 extracts. Human lung epithelial cells (A549) were exposed to the extracts. Cell death, reactive oxygen species (ROS), and gene expression were measured. Biomass burning contributions were higher in Sichuan samples than in Beijing or Shanxi. Some PM characteristics (total PAHs and coal combustion source contributions) and biological effects of organic extract exposures (cell death, ROS, and cytokine gene expression) shared a common trend of higher levels and effects in winter than in summer for Shanxi and Beijing but no seasonal differences in Sichuan. Modulation of phase I/AhR-related genes (cyp1a1 and cyp1b1) and phase II/oxidative stress-related genes (HO-1, SOD1/2, NQO-1, and catalase) was either low or insignificant, without clear trends between samples. No significant cell death or ROS production was observed for water extract treatments among all sites and seasons, even at possible higher concentrations tested. These results support organic components, particularly PAHs, as essential drivers of biological effects, which is consistent with some other evidence from ambient PM_2.5.

Direct measurement with personal samplers captures the chemical complexity of PM_2.5 exposures better than fixed monitors. To investigate biological effects, lung cells were exposed to extracts of exposure PM_2.5 samples.

Effects of radiation and role of plants in radioprotection: A critical review

Radiation can be lethal at high doses, whereas controlled doses are useful in medical applications. Other applications include power generation, agriculture sterilization, nuclear weapons, and archeology. Radiation damages genetic material, which is reflected in genotoxicity and can cause hereditary damage. In the medical field, it is essential to avoid the harmful effects of radiation. Radiation countermeasures and the need for radioprotective agents have been explored in recent years. Considering plants that evolve in radiative conditions, their ability to protect organisms against radiation has been studied and demonstrated. Crude extracts, fractioned extracts, isolated phytocompounds, and plant polysaccharides from various plants have been used in radioprotection studies, and their efficiency has been proven in various in vitro and in vivo experimental models. It is important to identify the mechanism of action to develop a potent plant-based radioprotective agent. To identify this protective mechanism, it is necessary to understand the damage caused by radiation in biological systems. This review intends to discuss the effects of ionizing radiation on biological systems and evaluate plant-based radioprotectants that have tested thus far as well as their mechanism of action in protecting against the toxic effects of radiation. From the review, the mechanism of radioprotection exhibited by the plant-based products could be understood. Meanwhile, we strongly suggest that the potential products identified so far should undergo clinical trials for critically evaluating their effects and for developing an ideal and compatible radioprotectant with no side-effects.

Air pollution and children's health-a review of adverse effects associated with prenatal exposure from fine to ultrafine particulate matter

BACKGROUND

Particulate matter (PM), a major component of ambient air pollution, accounts for a substantial burden of diseases and fatality worldwide. Maternal exposure to PM during pregnancy is particularly harmful to children's health since this is a phase of rapid human growth and development.

METHOD

In this review, we synthesize the scientific evidence on adverse health outcomes in children following prenatal exposure to the smallest toxic components, fine (PM_2.5) and ultrafine (PM_0.1) PM. We highlight the established and emerging findings from epidemiologic studies and experimental models.

RESULTS

Maternal exposure to fine and ultrafine PM directly and indirectly yields numerous adverse birth outcomes and impacts on children's respiratory systems, immune status, brain development, and cardiometabolic health. The biological mechanisms underlying adverse effects include direct placental translocation of ultrafine particles, placental and systemic maternal oxidative stress and inflammation elicited by both fine and ultrafine PM, epigenetic changes, and potential endocrine effects that influence long-term health.

CONCLUSION

Policies to reduce maternal exposure and health consequences in children should be a high priority. PM_2.5 levels are regulated, yet it is recognized that minority and low socioeconomic status groups experience disproportionate exposures. Moreover, PM_0.1 levels are not routinely measured or currently regulated. Consequently, preventive strategies that inform neighborhood/regional planning and clinical/nutritional recommendations are needed to mitigate maternal exposure and ultimately protect children's health.

Role of atmospheric particulate matter exposure in COVID-19 and other health risks in human: A review

Due to intense industrialization and urbanization, air pollution has become a serious global concern as a hazard to human health. Epidemiological studies found that exposure to atmospheric particulate matter (PM) causes severe health problems in human and significant damage to the physiological systems. In recent days, PM exposure could be related as a carrier for severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) virus transmission and Coronavirus disease 2019 (COVID-19) infection. Hence, it is important to understand the adverse effects of PM in human health. This review aims to provide insights on the detrimental effects of PM in various human health problems including respiratory, circulatory, nervous, and immune system along with their possible toxicity mechanisms. Overall, this review highlights the potential relationship of PM with several life-limiting human diseases and their significance for better management strategies.

Toxicity of Water- and Organic-Soluble Wood Tar Fractions from Biomass Burning in Lung Epithelial Cells

Widespread smoke from wildfires and biomass burning contributes to air pollution and the deterioration of air quality and human health. A common and major emission of biomass burning, often found in collected smoke particles, is spherical wood tar particles, also known as "tar balls". However, the toxicity of wood tar particles and the mechanisms that govern their health impacts and the impact of their complicated chemical matrix are not fully elucidated. To address these questions, we generated wood tar material from wood pyrolysis and isolated two main subfractions: water-soluble and organic-soluble fractions. The chemical characteristics as well as the cytotoxicity, oxidative damage, and DNA damage mechanisms were investigated after exposure of A549 and BEAS-2B lung epithelial cells to wood tar. Our results suggest that both wood tar subfractions reduce cell viability in exposed lung cells; however, these fractions have different modes of action that are related to their physicochemical properties. Exposure to the water-soluble wood tar fraction increased total reactive oxygen species production in the cells, decreased mitochondrial membrane potential (MMP), and induced oxidative damage and cell death, probably through apoptosis. Exposure to the organic-soluble fraction increased superoxide anion production, with a sharp decrease in MMP. DNA damage is a significant process that may explain the course of toxicity of the organic-soluble fraction. For both subfractions, exposure caused cell cycle alterations in the G2/M phase that were induced by upregulation of p21 and p16. Collectively, both subfractions of wood tar are toxic. The water-soluble fraction contains chemicals (such as phenolic compounds) that induce a strong oxidative stress response and penetrate living cells more easily. The organic-soluble fraction contained more polycyclic aromatic hydrocarbons (PAHs) and oxygenated PAHs and induced genotoxic processes, such as DNA damage.

Dexmedetomidine ameliorates endotoxin-induced acute lung injury in vivo and in vitro by preserving mitochondrial dynamic equilibrium through the HIF-1a/HO-1 signaling pathway

Increasing lines of evidence identified that dexmedetomidine (DEX) exerted protective effects against sepsis-stimulated acute lung injury via anti-inflammation, anti-oxidation and anti-apoptosis. However, the mechanisms remain unclear. Herein, we investigated whether DEX afforded lung protection by regulating the process of mitochondrial dynamics through the HIF-1a/HO-1 pathway in vivo and in vitro. Using C57BL/6J mice exposed to lipopolysaccharide, it was initially observed that preemptive administration of DEX (50μg/kg) alleviated lung pathologic injury, reduced oxidative stress indices (OSI), improved mitochondrial dysfunction, upregulated the expression of HIF-1α and HO-1, accompanied by shifting the dynamic course of mitochondria into fusion. Moreover, HO-1-knockout mice or HO-1 siRNA transfected NR8383 cells were pretreated with HIF-1α stabilizer DMOG and DEX to validate the effect of HIF-1a/HO-1 pathway on DEX-mediated mitochondrial dynamics in a model of endotoxin-induced lung injury. We found that pretreatment with DEX and DMOG distinctly relieved lung injury, decreased the levels of mitochondrial ROS and mtDNA, reduced OSI, increased nuclear accumulation of HIF-1a and HO-1 protein in wild type mice but not HO-1 KO mice. Similar observations were recapitulated in NC siRNA transfected NR8383 cells after LPS stimulation but not HO-1 siRNA transfected cells. Concertedly, DEX reversed the impaired mitochondrial morphology in LPS stimulated-wild type mice or NC siRNA transfected NR8383 cells, upregulated the expression of mitochondrial fusion protein, while downregulated the expression of fission protein in HIF-1a/HO-1 dependent pathway. Altogether, our data both in vivo and in vitro certified that DEX treatment ameliorated endotoxin-induced acute lung injury by preserving the dynamic equilibrium of mitochondrial fusion/fission through the regulation of HIF-1a/HO-1 signaling pathway.

Nrf2 modulated the restriction of lung function via impairment of intrinsic autophagy upon real-ambient PM2.5 exposure

Compelling studies approve that fine particle matter (PM_2.5) exposure was associated with high risk of respiratory disorders. However, the available data assessing the detailed influence of PM_2.5 on lung was limited. To overcome the difficulty of inhalational PM_2.5 exposure, the real-ambient PM_2.5 exposure system was constructed. The mice were exposed to filtered air (FA) or real-ambient PM_2.5 (PM_2.5), and the adverse effect on lung was determined. Nuclear factor E2-related factor 2 (Nrf2) as a transcription factor, was reported to affect autophagy. Autophagy was proposed as a two-edge sword in respiratory disorders. Here, our data presented that PM_2.5 exposure dramatically reduced the lung function of WT mice rather than Nrf2^-/- mice. Consistently, thickened alveolar walls was observed in WT mice in PM_2.5 exposure group, whereas the histological phenotype of Nrf2^-/- mice exhibited no obvious alteration. Furthermore, PM_2.5 exposure triggered low-grade production of inflammatory profile in WT and Nrf2^-/- mice. Moreover, the protein levels of p62, Beclin1 and LC3B of WT mice rather than Nrf2^-/- mice were also altered in PM_2.5 exposure group. Taken together, the present study applied the real-ambient exposure system, revealed the adverse effect of air pollution on lung, and proposed the underlying mechanism.

The Role of Nrf2 in the PM-Induced Vascular Injury Under Real Ambient Particulate Matter Exposure in C57/B6 Mice

Short-and long-term exposure to particulate matter (PM) has been associated with cardiovascular disease (CVD). It is well recognized that oxidative stress is a potential major mechanism in PM-induced vascular injuries, in which the nuclear factor E2-related factor 2 (Nrf2) signaling pathway plays a critical role. In the current study, a Nrf2 knockout mouse model was used in combination with an individual ventilated cage (IVC)-based real-ambient PM exposure system to assess the potential vascular injury and the potential role of Nrf2 in the angiotensin II (Ang II)-associated vascular injury. After 6-or 11-week exposure to PM, the histopathology assay revealed that PM exposure resulted in the thickening of the walls of vascular. After 6 weeks exposure to PM, the ELISA assay revealed that PM exposure resulted in the elevated plasma concentration of Ang II. The expression levels of genes of interest were then further investigated with quantitative real-time PCR. Notably, the results showed that Angiotensinogen (AGT), Angiotensin converting enzyme (ACE) and Angiotensin type I receptor (AT1R) were involved in PM-induced pathological changes. Western blotting for ACE showed similar results. Moreover, the extent of vascular thickening and the Ang II elevation was most prominent in the Nrf2 gene knockout PM exposure group (KOE). Furthermore, the expression of Nrf2 downstream relevant genes (HO1, Nqo1, Gclc, Gsta4) were significantly enhanced in the wildtype PM exposure group (WTE), while those were remarkably suppressed in the Nrf2 gene knockout groups. The ELISA result of monocyte chemoattractant protein-1 (MCP-1) serum levels in the KOE group was significantly higher in relation to that in the Nrf2 knockout control group (KOC). In summary, PM exposure is associated with thickening of vascular wall, while Nrf2 knockout may further enhance this effect. A potential mechanistic contributor of such effects is the activation of ACE/ANGII/AT1R axis, in which Nrf2 played a regulatory role.

Emerging role of mitochondria in airborne particulate matter-induced immunotoxicity

The immune system is one of the primary targets of airborne particulate matter. Recent evidence suggests that mitochondria lie at the center of particulate matter-induced immunotoxicity. Particulate matter can directly interact with mitochondrial components (proteins, lipids, and nucleic acids) and impairs the vital mitochondrial processes including redox mechanisms, fusion-fission, autophagy, and metabolic pathways. These disturbances impede different mitochondrial functions including ATP production, which acts as an important platform to regulate immunity and inflammatory responses. Moreover, the mitochondrial DNA released into the cytosol or in the extracellular milieu acts as a danger-associated molecular pattern and triggers the signaling pathways, involving cGAS-STING, TLR9, and NLRP3. In the present review, we discuss the emerging role of mitochondria in airborne particulate matter-induced immunotoxicity and its myriad biological consequences in health and disease.

Mechanistic Implications of Biomass-Derived Particulate Matter for Immunity and Immune Disorders

Particulate matter (PM) is a major and the most harmful component of urban air pollution, which may adversely affect human health. PM exposure has been associated with several human diseases, notably respiratory and cardiovascular diseases. In particular, recent evidence suggests that exposure to biomass-derived PM associates with airway inflammation and can aggravate asthma and other allergic diseases. Defective or excess responsiveness in the immune system regulates distinct pathologies, such as infections, hypersensitivity, and malignancies. Therefore, PM-induced modulation of the immune system is crucial for understanding how it causes these diseases and highlighting key molecular mechanisms that can mitigate the underlying pathologies. Emerging evidence has revealed that immune responses to biomass-derived PM exposure are closely associated with the risk of diverse hypersensitivity disorders, including asthma, allergic rhinitis, atopic dermatitis, and allergen sensitization. Moreover, immunological alteration by PM accounts for increased susceptibility to infectious diseases, such as tuberculosis and coronavirus disease-2019 (COVID-19). Evidence-based understanding of the immunological effects of PM and the molecular machinery would provide novel insights into clinical interventions or prevention against acute and chronic environmental disorders induced by biomass-derived PM.

Keap1-Nrf2 pathway up-regulation via hydrogen sulfide mitigates polystyrene microplastics induced-hepatotoxic effects

Microplastics, which are new types of environmental pollutants, are recently receiving widespread attention worldwide. Hydrogen sulfide (H₂S) as the third endogenous gaseous mediator had protective effects in multiple physiological and pathological conditions. However, the protective role of H₂S in microplastics-induced hepatotoxocity remain unclear. In this study, our data showed that H₂S significantly suppressed inflammation, apoptosis and oxidative stress induced by polystyrene microplastics (mic-PS) (20 mg/kg b.w.) in the liver. Strikingly, although mic-PS exposure increased the expression of nuclear factor-E2-related factor (Nrf2), it did not influence the levels of heme oxygenase-1 (HO-1) and NAD(P)H: quinone oxidoreductase 1 (NQOl) in the L02 hepatocytes. Immunofluorescence assay showed that sodium hydrosulfide (NaHS) reduced micro-Ps-induced hepatic apoptosis by facilitating nuclear accumulation of Nrf2. Simultaneously, flow cytometry also showed that NaHS could prevent mic-PS-induced accumulation of reactive oxygen species (ROS) by increasing the expression of HO-1 and NQO1. Furthermore, inhibition of HO-1 could reverse the hepatic protective effects of NaHS during mic-PS exposure. Mechanistically, H₂S elevating the HO-1 and NQO1 expression by facilitating nuclear accumulation of Nrf2, and consequently reducing mic-PS-induced hepatic apoptosis and inflammation. This study unveils the hepatotoxic effects of MPs and suggest NaHS have protective effects on mic-PS-induced liver damage.

Transcriptomic analysis identifies dysregulated genes and functional networks in human small airway epithelial cells exposed to ambient PM2.5

Cellular models exhibiting human physiological features of pseudostratified columnar epithelia, provide a more realistic approach for elucidating detailed mechanisms underlying PM_2.5-induced pulmonary toxicity. In this study, we characterized the barrier and mucociliary functions of differentiated human small airway epithelial cells (SAECs), cultured at the air-liquid interface (ALI). Due to the presence of mucociliary protection, particle internalization was reduced, with a concomitant decrease in cytotoxicity in differentiated S-ALI cells, as compared to conventional submerged SAEC cultures. After 24-hour exposure to PM_2.5 surrogates, 117 up-regulated genes and 156 down-regulated genes were detected in S-ALI cells, through transcriptomic analysis using the Affymetrix Clariom™ S Human Array. Transcription-level changes in >60 signaling pathways, were revealed by functional annotation of the 273 differentially expressed genes, using the PANTHER Gene List Analysis. These pathways are involved in multiple cellular processes, that include inflammation and apoptosis. Exposure to urban PM_2.5 led to complex responses in airway epithelia, including a net induction of downstream pro-inflammatory and pro-apoptotic responses. Collectively, this study highlights the importance of using the more advanced ALI model rather than the undifferentiated submerged model, to avoid over-assessment of inhaled particle toxicity in human. The results of our study also suggest that reduction of ambient PM_2.5 concentrations would have a protective effect on respiratory health in humans.

Analysis by Metabolomics and Transcriptomics for the Energy Metabolism Disorder and the Aryl Hydrocarbon Receptor Activation in Male Reproduction of Mice and GC-2spd Cells Exposed to PM2.5

Fine particulate matter (PM_2.5)-induced male reproductive toxicity arouses global public health concerns. However, the mechanisms of toxicity remain unclear. This study aimed to further investigate toxicity pathways by exposure to PM_2.5in vitro and in vivo through the application of metabolomics and transcriptomics. In vitro, spermatocyte-derived GC-2spd cells were treated with 0, 25, 50, 100 μg/mL PM_2.5 for 48 h. In vivo, the real-world exposure of PM_2.5 for mouse was established. Forty-five male C57BL/6 mice were exposed to filtered air, unfiltered air, and concentrated ambient PM_2.5 in Tangshan of China for 8 weeks, respectively. The results in vitro and in vivo showed that PM_2.5 exposure inhibited GC-2spd cell proliferation and reduced sperm motility. Mitochondrial damage was observed after PM_2.5 treatment. Increased Humanin and MOTS-c levels and decreased mitochondrial respiratory indicated that mitochondrial function was disturbed. Furthermore, nontargeted metabolomics analysis revealed that PM_2.5 exposure could disturb the citrate cycle (TCA cycle) and reduce amino acids and nucleotide synthesis. Mechanically, the aryl hydrocarbon receptor (AhR) pathway was activated after exposure to PM_2.5, with a significant increase in CYP1A1 expression. Further studies showed that PM_2.5 exposure significantly increased both intracellular and mitochondrial reactive oxygen species (ROS) and activated NRF2 antioxidative pathway. With the RNA-sequencing technique, the differentially expressed genes induced by PM_2.5 exposure were mainly enriched in the metabolism of xenobiotics by the cytochrome P450 pathway, of which Cyp1a1 was the most significantly changed gene. Our findings demonstrated that PM_2.5 exposure could induce spermatocyte damage and energy metabolism disorder. The activation of the aryl hydrocarbon receptor might be involved in the mechanism of male reproductive toxicity.

Time-Resolved Single-Cell Assay for Measuring Intracellular Reactive Oxygen Species upon Exposure to Ambient Particulate Matter

Health risks associated with exposure to ambient particulate matter (PM) are a major concern around the world. Adverse PM health effects have been proposed to be linked to oxidative stress through the generation of reactive oxygen species (ROS). In vitro cellular assays can provide insights into components or characteristics of PM that best account for its toxicity at a cellular level. However, most current assays report cell population averages and are mostly time endpoint measurements and thus provide no temporal information. This poses limitations on our understanding of PM health effects. In this study, we developed a microfluidic assay that can measure cellular ROS responses at the single-cell level and evaluate temporal dynamic behavior of single cells. We first established a protocol that enables culturing cells in our microfluidic platform and that can provide reproducible ROS readouts. We further examined the heterogeneous ROS responses of cell populations and tracked the dynamics of individual cellular responses upon exposure to different concentrations of PM extracts. Our results show that in an alveolar macrophage cell line, cellular ROS responses are highly heterogeneous. ROS responses from different cells can vary over an order of magnitude, and large coefficients of variation at each timepoint measurement indicate a high variability. The dynamic behavior of single-cell responses is strongly dependent on PM concentrations. Our work serves as a proof-of-principle demonstration of the capability of our microfluidic technology to study time-resolved single-cell responses upon PM exposure. We envision applying this high-resolution, high-content assay to investigate a wide array of single-cell responses (beyond ROS) upon exposure to different types of PM in the future.

PM2.5 triggered apoptosis in lung epithelial cells through the mitochondrial apoptotic way mediated by a ROS-DRP1-mitochondrial fission axis

Epidemiological studies revealed a sharp increase in respiratory diseases attributed to PM_2.5. However, the underlying mechanisms remain unclear. Evidence suggested mitochondrion as a sensitive target upon the stimulus of PM_2.5, and the centrality in the pathological processes and clinical characterization of lung diseases. To investigate cell fate and related mechanisms caused by PM_2.5, we exposed human lung epithelial cells (BEAS-2B) to PM_2.5 (0-100 μg/mL). Consequently, PM_2.5 components were found in cytoplasm, and morphological and functional alterations in mitochondria occurred, as evidenced by loss of cristae, vacuolization and even the outer mitochondrial membrane rupture, mitochondrial membrane potential collapse, enhanced reactive oxygen species (ROS)/mtROS level, calcium overload, suppressed cellular respiration and ATP production in PM_2.5-treated cells. Further, disturbed dynamics toward fission was clearly observed in PM_2.5-treated mitochondria, associated with DRP1 mitochondrial translocation and phosphorylation. Besides, PM_2.5 induced mitochondria-mediated apoptosis. More importantly, mechanistic results revealed ROS- and DRP1-mediated mitochondrial fission in a reciprocal way, and DRP1 inhibitor (Mdivi-1) significantly alleviated the pro-apoptotic effect of PM_2.5 through reversing the activated mitochondrial apoptotic pathway. In summary, our results firstly revealed PM_2.5 induced apoptosis in lung epithelial cells through a ROS-DRP1-mitochodrial fission axis-mediated mitochondrial apoptotic pathway, ultimately contributing to the onset and development of pulmonary diseases.

Mechanism of PM2.5-induced human bronchial epithelial cell toxicity in central China

Exposure to PM_2.5 has been linked to respiratory disorders, yet knowledge of the molecular mechanism is limited. Here, PM_2.5 was monitored and collected in central China, and its cytotoxicity mechanism on human bronchial epithelial cells (BEAS-2B) was investigated. With the average concentration of 109 ± 69 μg/m³, PM_2.5 was rich in heavy metals and organic pollutants. After exposure to PM_2.5, the viability of BEAS-2B cells decreased, where 510 dysregulated genes were predicted to induce necroptosis via inhibiting ATP synthesis through the oxidative phosphorylation signaling pathway. Cellular experiments demonstrated that the content of ATP was downregulated, while the expression of RIP3, a necroptosis indicator, was upregulated. Besides, four enzymes in charge of ATP synthesis were downregulated, including ATP5F, NDUF, COX7A, and UQCR, while two genes of RELA and CAPN1 responsible for necroptosis were upregulated. Furthermore, N-acetylcysteine was applied as an enhancer for ATP synthesis, which reversed the downregulation of ATP5F, NDUF, and COX7A, and consequently alleviated the elevation of RELA, CAPN1, and RIP3. In conclusion, PM_2.5 exposure downregulates ATP5F, NDUF, COX7A, and UQCR, and that inhibits ATP synthesis via the oxidative phosphorylation signaling pathway, which subsequently upregulates RELA and CAPN1 and ultimately leads to necroptosis of BEAS-2B cells.

Mitochondrial alterations triggered by repeated exposure to fine (PM2.5-0.18) and quasi-ultrafine (PM0.18) fractions of ambient particulate matter

Nowadays ambient particulate matter (PM) levels still regularly exceed the guideline values established by World Health Organization in most urban areas. Numerous experimental studies have already demonstrated the airway toxicity of the fine fraction of PM (FP), mainly triggered by oxidative stress-induced airway inflammation. However, only few studies have actually paid close attention to the ultrafine fraction of PM (UFP), which is likely to be more easily internalized in cells and more biologically reactive. Mitochondria are major endogenous sources of reactive oxygen species (ROS) through oxidative metabolism, and coordinate many critical cellular signaling processes. Mitochondria have been often studied in the context of PM toxicity and generally associated with apoptosis activation. However, little is known about the underlying adaptation mechanisms that could occur following exposure at sub-apoptotic doses of ambient PM. Here, normal human bronchial epithelial BEAS-2B cells were acutely or repeatedly exposed to relatively low doses (5 µg.cm^-2) of FP (PM_2.5-0.18) or quasi-UFP (Q-UFP; PM_0.18) to better access the critical changes in mitochondrial morphology, functions, and dynamics. No significant cytotoxicity nor increase of apoptotic events were reported for any exposure. Mitochondrial membrane potential (ΔΨm) and intracellular ATP content were also not significantly impaired. After cell exposure to sub-apoptotic doses of FP and notably Q-UFP, oxidative phosphorylation was increased as well as mitochondrial mass, resulting in increased production of mitochondrial superoxide anion. Given this oxidative boost, the NRF2-ARE signaling pathway was significantly activated. However, mitochondrial dynamic alterations in favor of accentuated fission process were observed, in particular after Q-UFP vs FP, and repeated vs acute exposure. Taken together, these results supported mitochondrial quality control and metabolism dysfunction as an early lung underlying mechanism of toxicity, thereby leading to accumulation of defective mitochondria and enhanced endogenous ROS generation. Therefore, these features might play a key role in maintaining PM-induced oxidative stress and inflammation within lung cells, which could dramatically contribute to the exacerbation of inflammatory chronic lung diseases. The prospective findings of this work could also offer new insights into the physiopathology of lung toxicity, arguably initiate and/or exacerbate by acutely and rather repeated exposure to ambient FP and mostly Q-UFP.

Nrf2 mitigates prolonged PM2.5 exposure-triggered liver inflammation by positively regulating SIKE activity: Protection by Juglanin

Air pollution containing particulate matter (PM) less than 2.5 μm (PM2.5) plays an essential role in regulating hepatic disease. However, its molecular mechanism is not yet clear, lacking effective therapeutic strategies. In this study, we attempted to investigate the effects and mechanisms of PM2.5 exposure on hepatic injury by the in vitro and in vivo experiments. At first, we found that PM2.5 incubation led to a significant reduction of nuclear factor erythroid-derived 2-related factor 2 (Nrf2), along with markedly reduced expression of different anti-oxidants. Notably, suppressor of IKKε (SIKE), known as a negative regulator of the interferon pathway, was decreased in PM2.5-incubated cells, accompanied with increased activation of TANK-binding kinase 1 (TBK1) and nuclear factor-κB (NF-κB). The in vitro studies showed that Nrf2 positively regulated SIKE expression under the conditions with or without PM2.5. After PM2.5 treatment, Nrf2 knockdown further accelerated SIEK decrease and TBK1/NF-κB activation, and opposite results were observed in cells with Nrf2 over-expression. Subsequently, the gene loss- and gain-function analysis demonstrated that SIKE deficiency further aggravated inflammation and TBK1/NF-κB activation caused by PM2.5, which could be abrogated by SIKE over-expression. Importantly, SIKE-alleviated inflammation was mainly dependent on TBK1 activation. The in vivo studies confirmed that SIKE- and Nrf2-knockout mice showed significantly accelerated hepatic injury after long-term PM2.5 exposure through reducing inflammatory response and oxidative stress. Juglanin (Jug), mainly isolated from Polygonum aviculare, exhibits anti-inflammatory and anti-oxidant effects. We found that Jug could increase Nrf2 activation, and then up-regulated SIKE in cells and liver tissues, mitigating PM2.5-induced liver injury. Together, all these data demonstrated that Nrf2 might positively meditate SIKE to inhibit inflammatory and oxidative damage, ameliorating PM2.5-induced liver injury. Jug could be considered as an effective therapeutic strategy against this disease by improving Nrf2/SIKE signaling pathway.

Real-ambient exposure to air pollution exaggerates excessive growth of adipose tissue modulated by Nrf2 signal

Air pollution was becoming a global threat to the public health, which was primarily mediated by PM_2.5 induced cardiovascular diseases and pulmonary diseases. Recently, observational epidemiologic studies proposed the link between PM_2.5 and obesity. Consistently, the link was also supported by limited animal researches. However, the potential mechanism mediating the harmful effects of PM_2.5 was still elusive. In this study, we applied the "real-ambient exposure" system to conduct the experiments, which was closer to the status of ambient air pollution compared with the method of intratracheal instillation and concentrated air particles (CAPs) exposure system. Nuclear factor E2-related factor 2 (Nrf2) was previously reported to protect against inflammation and oxidative stress when exposed to PM_2.5. Here, we reported that Nrf2^-/- mice developed overgrowth of adipose tissue after "real-ambient exposure" to PM_2.5, compared to filtered air (FA) group. Consistently, compared to FA group, adipocytes from subcutaneous (sWAT) and gonadal (gWAT) white adipose tissue of Nrf2^-/- mice exhibited enlarged cell size in PM_2.5 exposure group. Furthermore, the levels of high-density lipoprotein (HDL) and low-density lipoprotein (LDL) in serum and liver of Nrf2^-/- mice were also altered statistically in PM_2.5 exposure group. Importantly, when the expression of lipogenic enzymes was analyzed, the levels of the related specific genes in adipose tissue and liver of Nrf2^-/- mice were altered in PM_2.5 exposure group. Interestingly, the key transcription factors modulating expression of lipogenic enzymes in liver of Nrf2^-/- mice were also found altered in PM_2.5 exposure group, such as peroxisome proliferator-activated receptor (PPARα, PPARγ). Taken together, our study mimicked the status of ambient air pollution, revealed new insights into the adverse effect of PM_2.5 exposure, provided new link between air pollution and overgrowth of adipose tissue, and supported the vital role of Nrf2 in mediating the side effects of PM_2.5.

Short-term effects of air pollution on daily single- and co-morbidity cardiorespiratory outpatient visits

Several studies have noted that the existence of comorbidities lead to an increase in the risk of premature mortality and morbidity. Most of the studies examining the effects of air pollution on comorbidity visits were from Northern American countries, with scarce literature from Asia. This study contributes to existing, yet limited understanding of air pollution-comorbidity by examining the effects of daily air pollutants on outpatient single morbidity and comorbid cardiorespiratory visits in Japan. A total of 1,452,505 outpatient cardiorespiratory visits were recorded among the 21 Japanese cities from 2013 to 2016. Daily outpatient cardiorespiratory visit data were obtained from a health insurance claims database managed by the Japan Medical Data Center Co., Ltd. (JMDC). A time-stratified case crossover analysis coupled with Generalized Additive Mixed Model was used to analyze the association of daily air pollutants (particulate matter 2.5 μm or less in diameter, ozone and nitrogen dioxide) on daily single (respiratory and cardiovascular) and comorbidity health outcomes. We further examined single and cumulative effects for 0-3 and 0-14 lag periods. Ozone, NO₂, and PM_2.5 were positively associated with cardiorespiratory visits in either shorter or longer lags, with more apparent comorbidity associations with NO₂ exposure. A 10-unit increase in NO₂, after adjusting for ozone, was associated with a 2.24% (95% CI: 1.34-3.15) and 6.49% (95% CI: 5.00-8.01) increase in comorbidity visit at Lag 0 (of Lag 0-3) and cumulative lag 0-3, respectively. Our results contribute to existing evidence suggesting that short-term and extended exposure to air pollution elicit health risks on cardiovascular, respiratory and comorbid clinic visits. Exposure to NO₂, in particular, was associated with increase in the risk of single and comorbidity cardiorespiratory visits. Results can be potentially utilized for both individual health (e.g. risk population health management) and health facility management (e.g. health visit influx determination).

The role of influenza vaccination in mitigating the adverse impact of ambient air pollution on lung function in children: New insights from the Seven Northeastern Cities Study in China

BACKGROUND

Ambient air pollution exposure and influenza virus infection have been documented to be independently associated with reduced lung function previously. Influenza vaccination plays an important role in protecting against influenza-induced severe diseases. However, no study to date has focused on whether influenza vaccination may modify the associations between ambient air pollution exposure and lung function.

METHODS

We undertook a cross-sectional study of 6740 children aged 7-14 years into Seven Northeast Cities (SNEC) Study in China during 2012-2013. We collected information from parents/guardians about sociodemographic factors and influenza vaccination status in the past three years. Lung function was measured using portable electronic spirometers. Machine learning methods were used to predict 4-year average ambient air pollutant exposures to nitrogen dioxide (NO₂) and particulate matter with an aerodynamic diameter <1 μm (PM₁), <2.5 μm (PM_2.5) and <10 μm (PM₁₀). Two-level linear and logistic regression models were used to assess interactions between influenza vaccination and long-term ambient air pollutants exposure on lung function reduction, controlling for potential confounding factors.

RESULTS

Ambient air pollution were observed significantly associated with reductions in lung function among children. We found significant interactions between influenza vaccination and air pollutants on lung function, suggesting greater vulnerability to air pollution among unvaccinated children. For example, an interaction (p_interaction = 0.002) indicated a -283.44 mL (95% CI: -327.04, -239.83) reduction in forced vital capacity (FVC) per interquartile range (IQR) increase in PM₁ concentrations among unvaccinated children, compared with the -108.24 mL (95%CI: -174.88, -41.60) reduction in FVC observed among vaccinated children. Results from logistic regression models also showed stronger associations between per IQR increase in PM₁ and lung function reduction measured by FVC and peak expiratory flow (PEF) among unvaccinated children than the according ORs among vaccinated children [i.e., Odds Ratio (OR) for PM₁ and impaired FVC: 2.33 (95%CI: 1.79, 3.03) vs 1.65 (95%CI: 1.20, 2.28); OR for PM_2.5 and impaired PEF: 1.45 (95%CI: 1.12,1.87) vs 1.04 (95%CI: 0.76,1.43)]. The heterogeneity of the modification by influenza vaccination of the associations between air pollution exposure and lung function reduction appeared to be more substantial in girls than in boys.

CONCLUSION

Our results suggest that influenza vaccination may moderate the detrimental effects of ambient air pollution on lung function among children. This study provides new insights into the possible co-benefits of strengthening and promoting global influenza vaccination programs among children.

Nrf2/HO-1 partially regulates cytoprotective effects of carbon monoxide against urban particulate matter-induced inflammatory responses in oral keratinocytes

INTRODUCTION

Exposure to airborne particulate matter (PM) increases the proportion of oral inflammatory diseases. During the formation of inflammatory conditions, the nucleotide-binding domain and leucine-rich repeat protein 3 (NLRP3) inflammasome activation plays an important regulator. Carbon monoxide (CO) arising from heme degradation, catalyzed particularly by heme oxygenase-1 (HO-1), has been shown to own cytoprotective effects including anti-inflammation and antioxidant. Here, we determined the novel mechanisms of carbon monoxide releasing molecule-2 (CORM-2) on PM-induced inflammatory responses in human oral keratinocytes (HOKs).

METHODS

The effects of CORM-2 on the expression of various inflammatory proteins induced by PM were determined by Western blot, real-time PCR, promoter assay, and ELISA. The involvement of signaling molecules in these responses was studied by using the selective pharmacological inhibitors and siRNAs.

RESULTS

We proved that PM enhanced C-reactive protein (CRP) levels, NLRP3 inflammasome and caspase-1 activation, and IL-1β release, which were reduced by preincubation with CORM-2. Transfection with PKCα siRNA and preincubation with the ROS scavenger (N-acetyl-cysteine, NAC), an inhibitor of NADPH oxidase (diphenyleneiodonium, DPI), or the mitochondria-specific superoxide scavenger (MitoTEMPO) inhibited PM-mediated inflammatory responses. In addition, PM-regulated PKCα and NADPH oxidase activation as well as NADPH oxidase- and mitochondria-derived ROS generation were inhibited by CORM-2, but not inactivate CORM-2 (iCORM-2) pretreatment. At the end, we confirmed that CORM-2 improved PM-induced inflammatory responses via the induction of Nrf2 activation and HO-1 expression.

CONCLUSION

We suggest that CORM-2 inhibits PM-induced inflammatory responses in HOKs via the inhibition of PKCα/ROS/NLRP3 inflammasome activation combined with the induction of Nrf2/HO-1 expression.

Mapping the Mitochondrial Regulation of Epigenetic Modifications in Association With Carcinogenic and Noncarcinogenic Polycyclic Aromatic Hydrocarbon Exposure

Polycyclic aromatic hydrocarbons (PAHs) refer to a ubiquitous group of anthropogenic air pollutants that are generated through incomplete carbon combustion. Although the immunotoxic nature of PAHs has been previously reported, the underlying molecular mechanisms of this effect are not fully understood. In the present study, we investigated the mitochondrial-mediated epigenetic regulation of 2 PAHs, carcinogenic (benzo[a]pyrene; BaP) and noncarcinogenic (anthracene [ANT]), in peripheral lymphocytes. While ANT exposure triggered mitochondrial oxidative damage, no appreciable epigenetic modifications were observed. On the other hand, exposure to BaP perturbed the mitochondrial redox machinery and initiated cascade of epigenetic modifications. Cells exposed to BaP showed prominent changes in the expression of mitochondrial microRNAs (miR-24, miR-34a, miR-150, and miR-155) and their respective gene targets (NF-κβ, MYC, and p53). The exposure of BaP also caused significant alterations in the expression of epigenetic modifiers (DNMT1, HDAC1, HDAC7, KDM3a, EZH2, and P300) and hypomethylation within nuclear and mitochondrial DNA. This further induced methylation of histone tails, which play a crucial role in the regulation of chromatin structure. Overall, our study provides novel mechanistic insights into the mitochondrial regulation of epigenetic modifications in association with PAH-induced immunotoxicity.

Particulate Matter Toxicity Is Nrf2 and Mitochondria Dependent: The Roles of Metals and Polycyclic Aromatic Hydrocarbons

Particulate matter (PM), an important component of air pollution, induces significant adverse health effects. Many of the observed health effects caused by inhaled PM are associated with oxidative stress and inflammation. This association has been linked in particular to the particles’ chemical components, especially the inorganic/metal and the organic/polycyclic aromatic hydrocarbon (PAH) fractions, and their ability to generate reactive oxygen species in biological systems. The transcription factor NF-E2 nuclear factor erythroid-related factor 2 (Nrf2) is activated by redox imbalance and regulates the expression of phase II detoxifying enzymes. Nrf2 plays a key role in preventing PM-induced toxicity by protecting against oxidative damage and inflammation. This review focuses on specific PM fractions, particularly the dissolved metals and PAH fractions, and their roles in inducing oxidative stress and inflammation in cell and animal models with respect to Nrf2 and mitochondria.