TRPV4-mediated calcium influx into human bronchial epithelia upon exposure to diesel exhaust particles

Background

Human respiratory epithelia function in airway mucociliary clearance and barrier function and have recently been implicated in sensory functions.

Objective

We investigated a link between chronic obstructive pulmonary disease (COPD) pathogenesis and molecular mechanisms underlying Ca²⁺ influx into human airway epithelia elicited by diesel exhaust particles (DEP).

Methods and Results

Using primary cultures of human respiratory epithelial (HRE) cells, we determined that these cells possess proteolytic signaling machinery, whereby proteinase-activated receptor-2 (PAR-2) activates Ca²⁺-permeable TRPV4, which leads to activation of human respiratory disease–enhancing matrix metalloproteinase-1 (MMP-1), a signaling cascade initiated by diesel exhaust particles (DEP), a globally relevant air pollutant. Moreover, we observed ciliary expression of PAR-2, TRPV4, and phospholipase-Cβ3 in human airway epithelia and their DEP-enhanced protein–protein complex formation. We also found that the chronic obstructive pulmonary disease (COPD)–predisposing TRPV4_P19S variant enhances Ca²⁺ influx and MMP 1 activation, providing mechanistic linkage between man-made air pollution and human airway disease.

Conclusion

DEP evoked protracted Ca²⁺ influx via TRPV4, enhanced by the COPD-predisposing human genetic polymorphism TRPV4_P19S. This mechanism reprograms maladaptive inflammatory and extracellular-matrix–remodeling responses in human airways. The novel concept of air pollution–responsive ciliary signal transduction from PAR-2 to TRPV4 in human respiratory epithelia will accelerate rationally targeted therapies, possibly via the inhalatory route.     

Murine Lung Responses to Ambient Particulate Matter: Genomic Analysis and Influence on Airway Hyperresponsiveness

Background

Asthma is a complex disease characterized by airway hyperresponsiveness (AHR) and chronic airway inflammation. Epidemiologic studies have demonstrated that exposures to environmental factors such as ambient particulate matter (PM), a major air pollutant, contribute to increased asthma prevalence and exacerbations.

Objective

We investigated pathophysiologic responses to Baltimore, Maryland, ambient PM (median diameter, 1.78 μm) in a murine model of asthma and attempted to identify PM-specific genomic/molecular signatures.

Methods

We exposed ovalbumin (OVA)-sensitized A/J mice intratracheally to PM (20 mg/kg), and assayed both AHR and bronchoalveolar lavage (BAL) on days 1, 4, and 7 after PM exposure. Lung gene expression profiling was analyzed in OVA- and PM-challenged mice.

Results

Consistent with this murine model of asthma, we observed significant increases in airway responsiveness in OVA-treated mice, with PM exposure inducing significant changes in AHR in both naive mice and OVA-induced asthmatic mice. PM evoked eosinophil and neutrophil infiltration into airways, elevated BAL protein content, and stimulated secretion of type 1 T helper (T_H1) cytokines [interferon-γ, interleukin-6 (IL-6), tumor necrosis factor-α] and T_H2 cytokines (IL-4, IL-5, eotaxin) into murine airways. Furthermore, PM consistently induced expression of genes involved in innate immune responses, chemotaxis, and complement system pathways.

Conclusion

This study is consistent with emerging epidemiologic evidence and indicates that PM exposure evokes proinflammatory and allergic molecular signatures that may directly contribute to the asthma susceptibility in naive subjects and increased severity in affected asthmatics.     

First-Trimester Urine Concentrations of Phthalate Metabolites and Phenols and Placenta miRNA Expression in a Cohort of U.S. Women

Background

There is increasing concern that early-life exposure to endocrine-disrupting chemicals (EDCs) can influence the risk of disease development. Phthalates and phenols are two classes of suspected EDCs that are used in a variety of everyday consumer products, including plastics, epoxy resins, and cosmetics. In utero exposure to EDCs may affect disease propensity through epigenetic mechanisms.

Objective

The objective of this study was to determine whether prenatal exposure to multiple EDCs is associated with changes in miRNA expression of human placenta, and whether miRNA alterations are associated with birth outcomes.

Methods

Our study was restricted to a total of 179 women co-enrolled in the Harvard Epigenetic Birth Cohort and the Predictors of Preeclampsia Study. We analyzed associations between first-trimester urine concentrations of 8 phenols and 11 phthalate metabolites and expression of 29 candidate miRNAs in placenta by qRT-PCR.

Results

For three miRNAs—miR-142-3p, miR15a-5p, and miR-185—we detected associations between Σphthalates or Σphenols on expression levels (p < 0.05). By assessing gene ontology enrichment, we determined the potential mRNA targets of these microRNAs predicted in silico were associated with several biological pathways, including the regulation of protein serine/threonine kinase activity. Four gene ontology biological processes were enriched among genes significantly correlated with the expression of miRNAs associated with EDC burden.

Conclusions

Overall, these results suggest that prenatal phenol and phthalate exposure is associated with altered miRNA expression in placenta, suggesting a potential mechanism of EDC toxicity in humans.

Citation

LaRocca J, Binder AM, McElrath TF, Michels KB. 2016. First-trimester urine concentrations of phthalate metabolites and phenols and placenta miRNA expression in a cohort of U.S. women. Environ Health Perspect 124:380–387; http://dx.doi.org/10.1289/ehp.1408409     

The Adjuvant Effect of Ambient Particulate Matter Is Closely Reflected by the Particulate Oxidant Potential

Background

It has been demonstrated that ambient particulate matter (PM) can act as an adjuvant for allergic sensitization. Redox-active organic chemicals on the particle surface play an important role in PM adverse health effects and may determine the adjuvant effect of different particle types according to their potential to perturb redox equilibrium in the immune system.

Objectives

We determined whether the adjuvant effect of ambient fine particles versus ultrafine particles (UFPs) is correlated to their prooxidant potential.

Methods

We have established an intranasal sensitization model that uses ambient PM as a potential adjuvant for sensitization to ovalbumin (OVA), which enhances the capacity for secondary OVA challenge to induce allergic airway inflammation.

Results

UFPs with a greater polycyclic aromatic hydrocarbon (PAH) content and higher oxidant potential enhanced OVA sensitization more readily than did fine particles. This manifests as enhanced allergic inflammation upon secondary OVA challenge, leading to eosinophilic inflammation and mucoid hyperplasia starting at the nasal turbinates all the way down to the small pulmonary airways. The thiol antioxidant N-acetyl cysteine was able to suppress some of these sensitization events.

Conclusions

The adjuvant effects of ambient UFP is determined by their oxidant potential, which likely plays a role in changing the redox equilibrium in the mucosal immune system.     

Polychlorinated Biphenyls Disrupt Intestinal Integrity via NADPH Oxidase-Induced Alterations of Tight Junction Protein Expression

Background

Polychlorinated biphenyls (PCBs) are widely distributed environmental toxicants that contribute to numerous disease states. The main route of exposure to PCBs is through the gastrointestinal tract; however, little is known about the effects of PCBs on intestinal epithelial barrier functions.

Objective

The aim of the present study was to address the hypothesis that highly chlorinated PCBs can disrupt gut integrity at the level of tight junction (TJ) proteins.

Methods

Caco-2 human colon adenocarcinoma cells were exposed to one of the following PCB congeners: PCB153, PCB118, PCB104, and PCB126. We then assessed NAD(P)H oxidase (NOX) activity and expression and the barrier function of Caco-2 cells. In addition, the integrity of intestinal barrier function and expression of TJ proteins were evaluated in C57BL/6 mice exposed to individual PCBs by oral gavage.

Results

Exposure of Caco-2 cells to individual PCB congeners resulted in activation of NOX and increased permeability of fluorescein isothiocyanate (FITC)-labeled dextran (4 kDa). Treatment with PCB congeners also disrupted expression of TJ proteins zonula occludens-1 (ZO-1) and occludin in Caco-2 cells. Importantly, inhibition of NOX by apocynin significantly protected against PCB-mediated increase in epithelial permeability and alterations of ZO-1 protein expression. Exposure to PCBs also resulted in alterations of gut permeability via decreased expression of TJ proteins in an intact physiological animal model.

Conclusions

These results suggest that oral exposure to highly chlorinated PCBs disrupts intestinal epithelial integrity and may directly contribute to the systemic effects of these toxicants.     

Traffic-Related Particulate Matter and Acute Respiratory Symptoms among New York City Area Adolescents

Background

Exposure to traffic-related particulate matter (PM) has been associated with adverse respiratory health outcomes in children. Diesel exhaust particles (DEPs) are a local driver of urban fine PM [aerodynamic diameter ≤ 2.5 μm (PM_2.5)]; however, evidence linking ambient DEP exposure to acute respiratory symptoms is relatively sparse, and susceptibilities of urban and asthmatic children are inadequately characterized.

Objectives

We examined associations of daily ambient black carbon (BC) concentrations, a DEP indicator, with daily respiratory symptoms among asthmatic and nonasthmatic adolescents in New York City (NYC) and a nearby suburban community.

Methods

BC and PM_2.5 were monitored continuously outside three NYC high schools and one suburban high school for 4–6 weeks, and daily symptom data were obtained from 249 subjects (57 asthmatics, 192 nonasthmatics) using diaries. Associations between pollutants and symptoms were characterized using multilevel generalized linear mixed models, and modification by urban residence and asthma status were examined.

Results

Increases in BC were associated with increased wheeze, shortness of breath, and chest tightness. Multiple lags of nitrogen dioxide (NO₂) exposure were associated with symptoms. For several symptoms, associations with BC and NO₂ were significantly larger in magnitude among urban subjects and asthmatics compared with suburban subjects and nonasthmatics, respectively. PM_2.5 was not consistently associated with increases in symptoms.

Conclusions

Acute exposures to traffic-related pollutants such as DEPs and/or NO₂ may contribute to increased respiratory morbidity among adolescents, and urban residents and asthmatics may be at increased risk. The findings provide support for developing additional strategies to reduce diesel emissions further, especially in populations susceptible because of environment or underlying respiratory disease.     

Src-Mediated EGF Receptor Activation Regulates Ozone-Induced Interleukin 8 Expression in Human Bronchial Epithelial Cells

Background:

Human exposure to ozone (O₃) results in pulmonary function decrements and airway inflammation. The mechanisms underlying these adverse effects remain unclear. Epidermal growth factor receptor (EGFR) plays an important role in the pathogenesis of lung inflammation.

Objective

We examined the role of EGFR activation in O₃-induced expression of the chemokine interleukin 8 (IL-8) in human bronchial epithelial cells (HBEC).

Methods

We detected phosphorylated EGFR using immunoblotting. EGFR dimerization was examined through cross-linking reaction and immunoblotting, and levels of IL-8 protein were measured using ELISA.

Results

Exposure to O₃ (0.25–1.0 ppm) induced rapid and marked increase in EGFR phosphorylation at the autophosphorylation site Y1068 and the transphosphorylation site Y845, implicating the involvement of Src kinase. Further investigation showed that O₃ stimulation induced phosphorylation of Src at Y416, indicative of Src activation. Pharmacological inhibition of Src kinase activity abrogated O₃-induced EGFR phosphorylation at tyrosines 1068 and 845. Moreover, pretreatment of BEAS-2B cells with inhibitor of either EGFR or Src kinase activities significantly blocked O₃-induced IL-8 expression.

Conclusion

Conclusion: O₃ exposure increased IL-8 expression through Src-mediated EGFR transactivation in HBEC.

Citation>

Wu W, Wages PA, Devlin RB, Diaz-Sanchez D, Peden DB, Samet JM. 2015. Src-mediated EGF receptor activation regulates ozone-induced interleukin 8 expression in human bronchial epithelial cells. Environ Health Perspect 123:231–236; http://dx.doi.org/10.1289/ehp.1307379     

Air Pollution–Related Prothrombotic Changes in Persons with Diabetes

Background

Population studies suggest that persons with diabetes are more sensitive to the effects of particulate matter (PM) air pollution. However, the biological mechanisms of a possible prothrombotic effect underlying this enhanced susceptibility remain largely unknown.

Objective

We hypothesized that exposure to PM causes prothrombotic changes in persons with diabetes, possibly via systemic inflammation.

Methods

Our study included 137 nonsmoking adults with diabetes who were outpatients at the University Hospital Leuven. Recent exposure (2 hr before examination) to ambient PM was measured at the entrance of the hospital. Individual chronic exposure to PM was assessed by measuring the area occupied by carbon in airway macrophages obtained by sputum induction. Platelet function was measured ex vivo with the PFA-100 platelet function analyzer, which simulates a damaged blood vessel; we analyzed the function of platelets in primary hemostasis under high shear conditions. Total and differential blood leukocytes were counted.

Results

Independent of antiplatelet medication, an interquartile range (IQR) increase of 39.2 μg/m³ in PM₁₀ (PM with aerodynamic diameter ≤ 10 μm) concentration measured 2 hr before the clinical examination (recent exposure) was associated with a decrease of 21.1 sec [95% confidence interval (CI), − 35.3 to − 6.8] in the PFA-100 closure time (i.e., increased platelet activation) and an increase in blood leukocytes of 512 per microliter of blood (95% CI, 45.2–979). Each area increase of 0.25 μm² (IQR) in carbon load of airway macrophages (chronic exposure) was associated with an increase of 687 leukocytes per microliter of blood (95% CI, 224–1,150).

Conclusions

A relevant increase in recent PM exposure was associated with a change in platelet function toward a greater prothrombotic tendency. The magnitude of the change was about two-thirds (in the opposite direction) of the average effect of antiplatelet medication. Diabetic patients showed evidence of proinflammatory response to both recent and chronic exposure to PM air pollution.     

Black Carbon Exposures,Blood Pressure,and Interactions with Single Nucleotide Polymorphisms in MicroRNA Processing Genes

Background

Black carbon (BC) is a marker of traffic pollution that has been associated with blood pressure (BP), but findings have been inconsistent. MicroRNAs (miRNAs) are emerging as key regulators of gene expression, but whether polymorphisms in genes involved in processing of miRNAs to maturity influence susceptibility to BC has not been elucidated.

Objectives

We investigated the association between BC and BP, as well as potential effect modification by single nucleotide polymorphisms (SNPs) in miRNA processing genes.

Methods

Repeated measures analyses were performed using data from the VA Normative Aging Study. Complete covariate data were available for 789 participants with one to six study visits between 1995 and 2008. In models of systolic and diastolic BP, we examined SNP-by-BC interactions with 19 miRNA-related variants under recessive models of inheritance. Mixed-effects models were adjusted for potential confounders including clinical characteristics, lifestyle, and meteorologic factors.

Results

A 1-SD increase in BC (0.415 μg/m³) was associated with 3.04 mmHg higher systolic (95% confidence interval (CI), 2.29–3.79) and 2.28 mmHg higher diastolic BP (95% CI, 1.88–2.67). Interactions modifying BC associations were observed with SNPs in the DICER, GEMIN4, and DiGeorge critical region-8 (DGCR8) genes, and in GEMIN3 and GEMIN4, predicting diastolic and systolic BP, respectively.

Conclusions

We observed evidence of effect modification of the association between BP and 7-day BC moving averages by SNPs associated with miRNA processing. Although the mechanisms underlying these associations are not well understood, they suggest a role for miRNA genesis and processing in influencing BC effects.     

Black Carbon Exposure,Oxidative Stress Genes,and Blood Pressure in a Repeated-Measures Study

Background

Particulate matter (PM) air pollution has been associated with cardiovascular morbidity and mortality, and elevated blood pressure (BP) is a known risk factor for cardiovascular disease. A small number of studies have investigated the relationship between PM and BP and found mixed results. Evidence suggests that traffic-related air pollution contributes significantly to PM-related cardiovascular effects.

Objectives

We hypothesized that black carbon (BC), a traffic-related combustion by-product, would be more strongly associated with BP than would fine PM [aerodynamic diameter ≤ 2.5 μm (PM_2.5)], a heterogeneous PM mixture, and that these effects would be larger among participants with genetic variants associated with impaired antioxidative defense.

Methods

We performed a repeated-measures analysis in elderly men to analyze associations between PM_2.5 and BC exposure and BP using mixed-effects models with random intercepts, adjusting for potential confounders. We also examined statistical interaction between BC and genetic variants related to oxidative stress defense: GSTM1, GSTP1, GSTT1, NQO1, catalase, and HMOX-1.

Results

A 1-SD increase in BC concentration was associated with a 1.5-mmHg increase in systolic BP [95% confidence interval (CI), 0.1–2.8] and a 0.9-mmHg increase in diastolic BP (95% CI, 0.2–1.6). We observed no evidence of statistical interaction between BC and any of the genetic variants examined and found no association between PM_2.5 and BP.

Conclusions

We observed positive associations between BP and BC, but not between BP and PM_2.5, and found no evidence of effect modification of the association between BC and BP by gene variants related to antioxidative defense.     

Personal exposures to traffic-related air pollution and acute respiratory health among Bronx schoolchildren with asthma

Background

Previous studies have reported relationships between adverse respiratory health outcomes and residential proximity to traffic pollution, but have not shown this at a personal exposure level.

Objective

We compared, among inner-city children with asthma, the associations of adverse asthma outcome incidences with increased personal exposure to particulate matter mass ≤ 2.5 μm in aerodynamic diameter (PM_2.5) air pollution versus the diesel-related carbonaceous fraction of PM_2.5.

Methods

Daily 24-hr personal samples of PM_2.5, including the elemental carbon (EC) fraction, were collected for 40 fifth-grade children with asthma at four South Bronx schools (10 children per school) during approximately 1 month each. Spirometry and symptom scores were recorded several times daily during weekdays.

Results

We found elevated same-day relative risks of wheeze [1.45; 95% confidence interval (CI), 1.03–2.04)], shortness of breath (1.41; 95% CI, 1.01–1.99), and total symptoms (1.30; 95% CI, 1.04–1.62) with an increase in personal EC, but not with personal PM_2.5 mass. We found increased risk of cough, wheeze, and total symptoms with increased 1-day lag and 2-day average personal and school-site EC. We found no significant associations with school-site PM_2.5 mass or sulfur. The EC effect estimate was robust to addition of gaseous pollutants.

Conclusion

Adverse health associations were strongest with personal measures of EC exposure, suggesting that the diesel “soot” fraction of PM_2.5 is most responsible for pollution-related asthma exacerbations among children living near roadways. Studies that rely on exposure to PM mass may underestimate PM health impacts.     

Ambient particulate matter air pollution and venous thromboembolism in the Women's Health Initiative Hormone Therapy trials

Background

The putative effects of postmenopausal hormone therapy on the association between particulate matter (PM) air pollution and venous thromboembolism (VTE) have not been assessed in a randomized trial of hormone therapy, despite its widespread use among postmenopausal women.

Objective

In this study, we examined whether hormone therapy modifies the association of PM with VTE risk.

Methods

Postmenopausal women 50–79 years of age (n = 26,450) who did not have a history of VTE and who were not taking anticoagulants were enrolled in the Women’s Health Initiative Hormone Therapy trials at 40 geographically diverse U.S. clinical centers. The women were randomized to treatment with estrogen versus placebo (E trial) or to estrogen plus progestin versus placebo (E + P trial). We used age-stratified Cox proportional hazard models to examine the association between time to incident, centrally adjudicated VTE, and daily mean PM concentrations spatially interpolated at geocoded addresses of the participants and averaged over 1, 7, 30, and 365 days.

Results

During the follow-up period (mean, 7.7 years), 508 participants (2.0%) had VTEs at a rate of 2.6 events per 1,000 person-years. Unadjusted and covariate-adjusted VTE risk was not associated with concentrations of PM < 2.5 μm (PM_2.5) or < 10 μm (PM₁₀)] in aerodynamic diameter and PM × active treatment interactions were not statistically significant (p > 0.05) regardless of PM averaging period, either before or after combining data from both trials [e.g., combined trial-adjusted hazard ratios (95% confidence intervals) per 10 μg/m³ increase in annual mean PM_2.5 and PM₁₀, were 0.93 (0.54–1.60) and 1.05 (0.72–1.53), respectively]. Findings were insensitive to alternative exposure metrics, outcome definitions, time scales, analytic methods, and censoring dates.

Conclusions

In contrast to prior research, our findings provide little evidence of an association between short-term or long-term PM exposure and VTE, or clinically important modification by randomized exposure to exogenous estrogens among postmenopausal women.     

California Wildfires of 2008: Coarse and Fine Particulate Matter Toxicity

Background

During the last week of June 2008, central and northern California experienced thousands of forest and brush fires, giving rise to a week of severe fire-related particulate air pollution throughout the region. California experienced PM_10–2.5 (particulate matter with mass median aerodynamic diameter > 2.5 μm to < 10 μm; coarse ) and PM_2.5 (particulate matter with mass median aerodynamic diameter < 2.5 μm; fine) concentrations greatly in excess of the air quality standards and among the highest values reported at these stations since data have been collected.

Objectives

These observations prompt a number of questions about the health impact of exposure to elevated levels of PM_10–2.5 and PM_2.5 and about the specific toxicity of PM arising from wildfires in this region.

Methods

Toxicity of PM_10–2.5 and PM_2.5 obtained during the time of peak concentrations of smoke in the air was determined with a mouse bioassay and compared with PM samples collected under normal conditions from the region during the month of June 2007.

Results

Concentrations of PM were not only higher during the wildfire episodes, but the PM was much more toxic to the lung on an equal weight basis than was PM collected from normal ambient air in the region. Toxicity was manifested as increased neutrophils and protein in lung lavage and by histologic indicators of increased cell influx and edema in the lung.

Conclusions

We conclude that the wildfire PM contains chemical components toxic to the lung, especially to alveolar macrophages, and they are more toxic to the lung than equal doses of PM collected from ambient air from the same region during a comparable season.     

Time-series analysis of mortality effects of fine particulate matter components in Detroit and Seattle

Background

Recent toxicological and epidemiological studies have shown associations between particulate matter (PM) and adverse health effects, but which PM components are most influential is less well known.

Objectives

In this study, we used time-series analyses to determine the associations between daily fine PM [PM ≤ 2.5 μm in aerodynamic diameter (PM_2.5)] concentrations and daily mortality in two U.S. cities—Seattle, Washington, and Detroit, Michigan.

Methods

We obtained daily PM_2.5 filters for the years of 2002–2004 and analyzed trace elements using X-ray fluorescence and black carbon using light reflectance as a surrogate measure of elemental carbon. We used Poisson regression and distributed lag models to estimate excess deaths for all causes and for cardiovascular and respiratory diseases adjusting for time-varying covariates. We computed the excess risks for interquartile range increases of each pollutant at lags of 0 through 3 days for both warm and cold seasons.

Results

The cardiovascular and respiratory mortality series exhibited different source and seasonal patterns in each city. The PM_2.5 components and gaseous pollutants associated with mortality in Detroit were most associated with warm season secondary aerosols and traffic markers. In Seattle, the component species most closely associated with mortality included those for cold season traffic and other combustion sources, such as residual oil and wood burning.

Conclusions

The effects of PM_2.5 on daily mortality vary with source, season, and locale, consistent with the hypothesis that PM composition has an appreciable influence on the health effects attributable to PM.