Concentrated Ambient Particles Exposure Research Articles

Chronic air pollution exposure exaggerates obesity-induced tissue inflammation and insulin resistance by activating inflammasome

Abstract Background: Air pollution has been associated with cardiometabolic diseases such as obesity and insulin resistance. However, the underlying mechanisms were not fully understood. In this study, we examined the role of NLRP3 inflammasome in chronic air pollution-induced tissue inflammation and insulin resistance. Methods: 8 weeks old male WT and NLRP3−/− mice were exposed to filtered air (FA) or concentrated ambient particles (CAPS) in a small animal whole-body exposure system with or without high fat diet for 6 hours/day, 5 days/week, for a total of 12 weeks (n= 5–8 per group). Results: CAPS exposure enhanced insulin resistance in the WT mice but not in the NLRP3−/− mice. Cytokine array and ELISA assays indicated that IL-1β secretion was increased in the culture supernatant of macrophages isolated from CAPS-exposed WT mice, compared to that of FA-exposed mice. Electronic microscopy showed particulate deposites in the peritoneal macrophages isolated from the peritoneal cavity of CAPS-exposed animals. The gene expression of Nlrp3 and Il-1β, the rate-limiting factor of NLRP3 inflammasome activation, were also increased in CAPS-exposed WT mice. Deficiency of NLRP3 blocked CAPS exposure-induced lung inflammation, inflammatory gene expression, and IL-1β secretion in mice. Subsequent ex vivo experiments by culturing macrophages with particulate matters indicate that air pollution particles not only initiate the transcription of Nlrp3 and Il-1β, the first signal for inflammasome activation, but also induce the activation of caspase-1, the second signal for inflammasome activation. Conclusions: Our data suggest that NLRP3 inflammasome activation mediates air pollution-induced tissue inflammation and insulin resistance.

Seasonal effects of ambient PM2.5 on the cardiovascular system of hyperlipidemic mice

ABSTRACTPeople in polluted communities are often exposed to both PM and ozone (O3), albeit not always simultaneously; an important question is whether exposure to particles with seasonal compositional differences can influence biological outcomes. We addressed this question using a mouse model of cardiovascular disease by contrasting the health outcomes of exposures to particles formed or aged during periods of relatively high photochemical activity (i.e. spring/summer), which has increased ambient O3 concentrations, with outcomes of exposures to fall/winter particles which are associated with lower O3 concentrations. Electrocardiographs (ECGs) and blood pressures (BPs) were acquired following exposures to concentrated ambient particles (CAPs). ECGs were analyzed to changes in specific waveform parameters and changes in heart rate variability (HRV). Exposures elicited several types of waveform abnormalities that were associated with seasonal differences in particle constituents. Alterations in R-R interval and P-R interval were seen following exposure to summer CAPs but not fall CAPs and differential responses were seen in the corrected Q-T interval following the two seasonal exposures. Measures of HRV increased after exposure to summer CAPs compared to air-exposed controls but not following the winter CAPs exposure. There were chemical differences with respect to the organic constituents in ambient particles between summer and fall aerosol. The oxygen to carbon ratios (O:C) were generally higher in the spring and summer than in the fall, consistent with seasonal differences in atmospheric photochemical activity. Seasonal differences in atmospheric photochemical activity can modify ambient aerosol composition and can alter biological responses in the cardiovascular system. The results from this study confirm that ambient photochemical activity can alter the toxicity of ambient PM. Regional and seasonal differences in PM2.5 composition should be important considerations when evaluating the effects of PM exposure on cardiovascular health.Implications: Particles formed during periods of high photochemical activity (e.g. spring/summer) elicit more adverse cardiovascular health effects than particles formed during periods of low photochemical activity (e.g. fall/winter). Seasonal differences in atmospheric photochemical activity modified ambient aerosol composition and worsened cardiovascular responses. These results can inform regulatory agencies and may help design air quality regulations for PM2.5 that consider seasonal and regional variations.

Hydrogen ameliorates lung injury in a rat model of subacute exposure to concentrated ambient PM2.5 via Aryl hydrocarbon receptor

BackgroundAmbient fine particulate matter (PM2.5) could induce lung injury. Aryl hydrocarbon receptor (AhR) is involved in the molecular mechanisms of prooxidative and pro-inflammatory effect of PM2.5. Molecular hydrogen has antioxidant properties. The protective effect and mechanism of hydrogen on PM2.5-induced lung injury remain unclear. ObjectivesThis study aimed to determine whether hydrogen could alleviate lung injury in a rat model of subacute exposure to concentrated ambient PM2.5, and explore the mechanism related to AhR. MethodsMale Wastar rats were exposed to either concentrated ambient particles (CAPs) (diameter: ≤2.5 μm, average concentration: 1328 ± 730 μg/m3) or filtered air (FA) by nose-only inhalation (5 h/day, 5 days/week for 4 weeks). Hydrogen-treated rats inhaled 66.7% hydrogen from water electrolysis for 2 h after each exposure to CAPs or FA. ResultsCAPs inhalation induced lung injury, as demonstrated by pulmonary function decrease, histopathological damage, mucus hypersecretion [Periodic acid-Schiff (PAS) staining for mucins, immunohistochemistry and quantitative real-time PCR (RT-qPCR) for mucin 5AC (MUC5AC) expression], increased pro-inflammatory cytokines (TNF-α, IL-8 and IL-1β) and oxidative damage indexes [malondialdehyde (MDA) and 8-isoprostane F2α (8-iso-PG)]. While, hydrogen inhalation significantly alleviated the damages mentioned above. In addition, low expression of AhR in lung tissues determined by Western Blot was found after CAPs exposure, whereas hydrogen inhibited AhR decline induced by CAPs. ConclusionsHigh concentrations of hydrogen could ameliorate pulmonary dysfunction, airway mucus hypersecretion, oxidation damage, and inflammation response in rats exposed to concentrated ambient PM2.5. Additionally, hydrogen alleviates lung injury induced by PM2.5 possibly through AhR-dependent mechanisms.

Enhanced cerebellar myelination with concomitant iron elevation and ultrastructural irregularities following prenatal exposure to ambient particulate matter in the mouse

Accumulating evidence indicates the developing central nervous system (CNS) is a target of air pollution toxicity. Epidemiological reports increasingly demonstrate that exposure to the particulate matter (PM) fraction of air pollution during neurodevelopment is associated with an increased risk of neurodevelopmental disorders (NDDs) such as autism spectrum disorder (ASD). These observations are supported by animal studies demonstrating prenatal exposure to concentrated ambient PM induces neuropathologies characteristic of ASD, including ventriculomegaly and aberrant corpus callosum (CC) myelination. Given the role of the CC and cerebellum in ASD etiology, this study tested whether prenatal exposure to concentrated ambient particles (CAPs) produced pathological features in offspring CC and cerebella consistent with ASD. Analysis of cerebellar myelin density revealed male-specific hypermyelination in CAPs-exposed offspring at postnatal days (PNDs) 11–15 without alteration of cerebellar area. Atomic absorption spectroscopy (AAS) revealed elevated iron (Fe) in the cerebellum of CAPs-exposed female offspring at PNDs 11–15, which connects with previously observed elevated Fe in the female CC. The presence of Fe inclusions, along with aluminum (Al) and silicon (Si) inclusions, were confirmed at nanoscale resolution in the CC along with ultrastructural myelin sheath damage. Furthermore, RNAseq and gene ontology (GO) enrichment analyses revealed cerebellar gene expression was significantly affected by sex and prenatal CAPs exposure with significant enrichment in inflammation and transmembrane transport processes that could underlie observed myelin and metal pathologies. Overall, this study highlights the ability of PM exposure to disrupt myelinogenesis and elucidates novel molecular targets of PM-induced developmental neurotoxicity.

The effects of particulate matter on inflammation of respiratory system: Differences between male and female.

Air pollution is known to exacerbate respiratory diseases and epidemiological studies have shown that women present more chronic respiratory symptoms than man exposed to traffic pollution, however, the reason why is unclear. This study evaluated the inflammatory differences in BALB/c mouse males (n=34) and females (n=111) in three phases of the estrous cycle that were exposed to ambient air (AA) or concentrated ambient particles (CAPs). Tracheal hyperreactivity to methacholine, bronchoalveolar lavage fluid (BALF) and immunohistochemical of airways and lung parenchyma were studied. Hyperreactivity increased in CAPs-exposed female mice compared with AA-exposed mice in estrus (p<0.05) and proestrus phases (p<0.05) and decreased in CAPs-exposed males compared with those exposed to AA (p<0.05). Males had increased numbers of total cells (p=0.037) and macrophages (p=0.028) compared to females. BALF levels of cyclooxygenase-2(COX-2) (p=0.000), transforming growth factor alpha (TGF-α) (p=0.001) and IL-8 receptor alpha (IL-8Rα) (p=0.014) were increased in males compared with proestrus, estrus and diestrus females, independent of exposure. Proestrus females exhibited significantly higher cadherin expression in lung parenchyma than did males (p=0.005). CAPs exposure increased matrix metalloproteinase-9 (MMP-9) (p=0.024) and isoprostane (p=0.003) expression in the airways of both, males and females. The level of substance P (SP) (p=0.001) increased in lung parenchyma in males compared with females, while IL-17 levels in airways (p=0.042) and in lung parenchyma (p=0.008) increased in females. MMP-9 levels (p=0.024) were significantly lower in the lung parenchyma of CAPs-exposed females. TGF-α (p=0.007) levels increased in the lung parenchyma of CAPs-exposed females compared to AA-exposed females. These results suggest that inflammatory markers differentially expressed in male mice were mostly linked to acute inflammation (IL-1β, IL-8Rα, COX-2), whereas in females, markers that may lead to a chronic inflammatory process such as IL-17 and remodeling (MMP-9) were increased.

Skin Damage Mechanisms Related to Airborne Particulate Matter Exposure.

Epidemiological studies suggest a correlation between increased airborne particulate matter (PM) and adverse health effects. The mechanisms of PM-health effects are believed to involve oxidative stress and inflammation. To evaluate the ability of PM promoting skin tissue damage, one of the main organs exposed to outdoor pollutants, we analyzed the effect of concentrated ambient particles (CAPs) in a reconstructed human epidermis (RHE) model. RHE tissues were exposed to 25 or 100 µg/ml CAPs for 24 or 48 h. Data showed that RHE seems to be more susceptible to CAPs-induced toxicity after 48 h exposure than after 24 h. We found a local reactive O(2) species (ROS) production increase generated from metals present on the particle, which contributes to lipids oxidation. Furthermore, as a consequence of altered redox status, NFkB nucleus translocation was increase upon CAPs exposure, as well as cyclooxygenase 2 and cytochrome P450 levels, which may be involved in the inflammatory response initiated by PM. CAPs also triggered an apoptotic process in skin. Surprisingly, by transition electron microscopy analysis we showed that CAPs were able to penetrate skin tissues. These findings contribute to the understanding of the cutaneous pathophysiological mechanisms initiated by CAPs exposure, where oxidative stress and inflammation may play predominant roles.

Differential gene expression associated with inflammation and blood pressure regulation induced by concentrated ambient particle exposure

Epidemiological studies have indicated that exposure to particle matter (PM) increased the risk of respiratory and cardiovascular morbidity and mortality. It is suggested that PM smaller than 2.5 μm in aerodynamic diameter (PM2.5) may contribute to these responses. However, the molecular mechanism is still unknown. To elucidate the changes in molecular level, we investigated the gene expression profile of concentrated ambient particles (CAPs)-exposed rats. Aged F344 rats were exposed with CAPs (594 μg/m3) or clean air 4 h per day for 3 days, and lung and heart tissues were then excised for DNA microarray analysis. Expression profiles related to inflammation and blood pressure regulation revealed differential expression of 7 genes in the lung and that of 3 genes in the heart ventricle. According to the complement activation-associated genes, complement factor B (Bf), complement component 2 and 4a (C4a), and C1 inhibitor genes were up-regulated in CAPs-exposed rat lung. Bf and C4a genes were also up-regulated in the heart. These suggest the treated animal ready for production of these proteins when activation of complement cascade is required. Pro-inflammatory cytokine, interleukin-1β, was also up-regulated in CAPs-exposed rat lung. Gene related with blood pressure regulation (angiotensin I converting enzyme) was also up-regulated in CAPs-exposed rat lung. Negative regulator of blood pressure (neuropeptide Y) was down-regulated in CAPs-exposed rat heart. These results indicate that CAPs may affect respiratory and cardiovascular organs by activation of inflammatory responses and disintegration of blood pressure regulation in early stage of CAPs exposure.

Cardiopulmonary responses in spontaneously hypertensive and Wistar-Kyoto rats exposed to concentrated ambient particles from Detroit, Michigan

Toxicological effects have been observed in rats exposed to concentrated ambient particles (CAPs) from different regions of the United States. The objective of this study was to evaluate the cardiopulmonary and systemic effects of CAPs in Detroit. The authors stationed a mobile concentrator at a location near major traffic and industrial sources. Spontaneously hypertensive (SH) and Wistar-Kyoto (WKY) rats were exposed to fine CAPs (diameter < 0.1–2.5 μm) 8 h/day for 13 consecutive days. Animals were implanted with telemeters, and electrocardiogram data were recorded continuously. Bronchoalveolar lavage (BAL) fluid and plasma were analyzed. Comprehensive exposure monitoring was conducted, including CAPs components. CAPs exposure concentrations were 103–918 μg/m3 (mean = 502 μg/m3). The authors found no statistically significant differences in heart rate or SDNN (standard deviation of the normal-to-normal intervals), a measure of heart rate variability, between CAPs-exposed and control rats. The authors found significantly higher levels of C-reactive protein in the serum of CAPs-exposed SH rats compared with air-exposed animals. Protein in BAL fluid was elevated in WKY rats exposed to CAPs. Measurement of trace metals in lung tissue showed elevated concentrations of V, Sb, La, and Ce in CAPs-exposed SH animals versus controls. These elements are generally associated with oil combustion, oil refining, waste incineration, and traffic. Examination of wind rose data from the exposure period confirmed that the predominant wind direction was SSW, the direction of many of the aforementioned sources. These results indicate that ambient particles in Detroit can cause mild pulmonary and systemic changes in rats, and suggest the importance of local PM2.5 sources in these effects.

Cardiac Oxidative Stress and Electrophysiological Changes in Rats Exposed to Concentrated Ambient Particles are Mediated by TRP-Dependent Pulmonary Reflexes

Previous studies suggest that, through the stimulation of pulmonary nervous endings, ambient particles modulate the autonomic tone on the heart leading to cardiac oxidant stress and dysfunction. In this paper we investigated the effect of blockade of vanilloid receptor 1 (Transient Receptor Potential Vanilloid Receptor 1 [TRPV1]) on concentrated ambient particles (CAPs)-induced cardiac oxidative stress and dysfunction in a rat model of inhalation exposure. Capsazepine (CPZ), a selective antagonist of TRPV1, was given ip or as an aerosol immediately before exposure to CAPs. Control and CPZ-treated rats were exposed to filtered air or CAPs aerosols for 5 h using the Harvard Ambient Particle Concentrator (mean PM(2.5) mass concentration: 218 +/- 23 mug/m(3)). At the end of the exposure we measured cardiac oxidative stress (in situ chemiluminescence [CL]), lipid peroxidation (thiobarbituric acid reactive substances [TBARS]), and tissue edema. Cardiac function was monitored throughout the exposure. CPZ (ip or aerosol) decreased CAPs-induced CL, lipid TBARS, and edema in the heart, indicating that blocking TRP receptors, systemically or locally, decreases heart CL. CAPs exposure led to significant decreases in heart rate (CAPs 350 +/- 32 bpm, control: 370 +/- 29), and in the length of the QT, RT, Pdur and Tpe intervals. These changes were observable immediately upon exposure and were maintained throughout the 5 h of CAPs inhalation. Changes in cardiac rhythm and electrocardiogram morphology were prevented by CPZ. These data suggest that current abnormalities in CAPs-exposed rats alter the action potentials leading to changes in conduction velocity and ventricular repolarization, and that triggering of TRPV1-mediated autonomic reflexes in the lung is essential for the observed changes in cardiac rhythms.

Air pollution particles diminish bacterial clearance in the primed lungs of mice

Epidemiological studies reveal increased incidence of lung infection when air pollution particle levels are increased. We postulate that one risk factor for bacterial pneumonia, prior viral infection, can prime the lung for greater deleterious effects of particles via the interferon-gamma (IFN-γ) characteristic of successful host anti-viral responses. To test this postulate, we developed a mouse model in which mice were treated with γ-interferon aerosol, followed by exposure to concentrated ambient particles (CAPs) collected from urban air. The mice were then infected with Streptococcus pneumoniae and the effect of these treatments on the lung's innate immune response was evaluated. The combination of IFN-γ priming and CAPs exposure enhanced lung inflammation, manifest as increased polymorphonuclear granulocyte (PMN) recruitment to the lung, and elevated expression of pro-inflammatory cytokine mRNAs. Combined priming and CAPs exposure resulted in impaired pulmonary bacterial clearance, as well as increased oxidant production and diminished bacterial uptake by alveolar macrophages (AMs) and PMNs. The data suggest that priming and CAPs exposure lead to an inflamed alveolar milieu where oxidant stress causes loss of antibacterial functions in AMs and recruited PMNs. The model reported here will allow further analysis of priming and CAPs exposure on lung sensitivity to infection.

Activation of the Stress Axis and Neurochemical Alterations in Specific Brain Areas by Concentrated Ambient Particle Exposure with Concomitant Allergic Airway Disease

ObjectiveExposure to ambient particulate matter (PM) has been linked to respiratory diseases in people living in urban communities. The mechanism by which PM produces these diseases is not clear. We hypothesized that PM could act on the brain directly to stimulate the stress axis and predispose individuals to these diseases. The purpose of this study was to test if exposure to PM can affect brain areas involved in the regulation of neuroendocrine functions, especially the stress axis, and to study whether the presence of preexisting allergic airway disease aggravates the stress response.DesignAdult male rats (n = 8/group) with or without ovalbumin (OVA)-induced allergic airway disease were exposed to concentrated air particles containing PM with an aerodynamic diameter ≤ 2.5 μm (PM2.5) for 8 hr, generated from ambient air in an urban Grand Rapids, Michigan, community using a mobile air research laboratory (AirCARE 1). Control animals were exposed to normal air and were treated with saline.MeasurementsA day after PM2.5 exposure, animals were sacrificed and the brains were removed, frozen, and sectioned. The paraventricular nucleus (PVN) and other brain nuclei were micro-dissected, and the concentrations of aminergic neurotransmitters and their metabolites were measured using high-performance liquid chromatography with electrochemical detection. Serum corticosterone levels were measured using radioimmunoassay.ResultsA significant increase in the concentration (mean ± SE, pg/μg protein) of norepinephrine in the PVN was produced by exposure to concentrated ambient particles (CAPs) or OVA alone (12.45 ± 2.7 and 15.84 ± 2.8, respectively) or after sensitization with OVA (19.06 ± 3.8) compared with controls (7.98 ± 1.3; p < 0.05). Serum corticosterone (mean ± SE, ng/mL) was significantly elevated in the OVA + CAPs group (242.786 ± 33.315) and in the OVA-presensitized group (242.786 ± 33.315) compared with CAP exposure alone (114.55 ± 20.9). Exposure to CAPs (alone or in combination with OVA pretreatment) can activate the stress axis, and this could probably play a role in aggravating allergic airway disease.

Effects of Subchronic Exposures to Concentrated Ambient Particles (CAPs) in Mice: III. Acute and Chronic Effects of CAPs on Heart Rate, Heart-Rate Fluctuation, and Body Temperature

Normal mice (C57) and mice prone to develop atherosclerosis (ApoE−/−) were implanted with electrocardiograph (EKG), core body temperature, and motion transmitters and were exposed daily for 6 h to Tuxedo, NY, concentrated ambient particles (CAPs) for 5 days/wk during the spring and summer of 2003. Time series of 5-min EKG monitoring and body-temperature measurements were obtained for each animal in the CAPs and filtered air sham exposure groups. Our hypothesis was that chronic exposure could cause cumulative health effects. We used our recently developed nonparametric method to estimate the daily time periods that mean heart rates (HR), body temperature, and physical activity differed significantly between the CAPs and sham exposed groups. CAPs exposure most affected heart rate between 1:30 a.m. and 4:30 a.m. With the response variables being the average heart rate, body temperature, and physical activity, we adopted a two-stage modeling approach to obtain the estimates of chronic and acute effects on the changes of these three response variables. In the first stage, a time-varying model estimated daily crude effects. In the second stage, the true means of the estimated crude effects were modeled with a polynomial function of time for chronic effects, a linear term of daily CAPs exposure concentrations for acute effects, and a random component for unknown noise. A Bayesian framework combined these two stages. There were significant decreasing patterns of HR, body temperature, and physical activity for the ApoE−/− mice over the 5 mo of CAPs exposure, with smaller and nonsignificant changes for the C57 mice. The chronic effect changes of the three response variables for ApoE−/− mice were maximal in the last few weeks. There was also a significant relationship between CAPs exposure concentration and short-term change of heart rate in ApoE−/− mice during exposure. Response variables were also defined for examining fluctuations of 5-min heart rates within long (i.e., 3–6 h) and short time periods (i.e., ∼ 15 min). The results for the ApoE−/− mice showed that heart- rate fluctuation within the longer periods increased to 1.35-fold by the end of exposure experiment, while the heart-rate fluctuation within 15 min decreased to 0.7-fold.

Respiratory Responses to Exposures With Fine Particulates and Nitrogen Dioxide in the Elderly With and Without COPD

Elderly people, with and without chronic obstructive pulmonary disease (COPD), may be susceptible to particulate matter (PM) air pollution. However, the respiratory impacts of inhaled PM combined with copollutant(s) in controlled exposure studies are unclear and warrant investigation since exposures to PM–gas mixtures constitute realistic scenarios. Thus, we exposed 6 healthy subjects and 18 volunteers with COPD (mean age 71 yr) on separate days to (a) filtered air (FA); (b) 0.4 ppm NO2; (c) concentrated ambient particles (CAP), predominantly in the fine (PM2.5) size range, at concentrations near 200 μg/m3; and (d) CAP and NO2 together. Each 2-h exposure included exercise for 15 min every half hour. Most respiratory responses, including symptoms, spirometry, and total and differential counts of induced sputum cells, showed no statistically significant responses attributable to separate or combined effects of CAP and NO2. However, maximal mid-expiratory flow and arterial O2 saturation (measured by pulse oximetry) showed small but statistically significant decrements associated with CAP, greater in healthy than COPD subjects. CAP exposure was also associated with decreased percentages of columnar epithelial cells in sputum. The results suggest that the respiratory effect of the PM–NO2 mixture may be primarily PM driven since coexposure to NO2 did not significantly enhance the responses. In conclusion, older adults exposed to urban fine particles may experience acute small-airways dysfunction with impaired gas exchange. Healthy subjects appear more susceptible, suggesting that the respiratory effect may be related to efficient penetration and deposition of inhaled toxic particles in distal small airways. More clinical investigation of the elderly population is warranted.

Effects of Subchronic Exposures to Concentrated Ambient Particles (CAPs) in Mice: IV. Characterization of Acute and Chronic Effects of Ambient Air Fine Particulate Matter Exposures on Heart-Rate Variability

Long-term exposure to fine particulate air pollution (PM2.5) has been associated with increased risk of death from cardiopulmonary diseases. Cardiac function parameters have also been affected by ambient particulate matter (PM) exposure, including heart-rate variability (HRV), a measure of autonomic function that has been recognized as a well-defined, quantitative indicator of autonomic dysfunction. However, the role of HRV in ambient PM-induced cardiovascular effects is not fully understood. In an accompanying article, we report significant decreasing patterns of heart rate (HR), body temperature, and physical activity for mice lacking apoliproprotein (ApoE−/−) over 5 mo of exposure to concentrated ambient PM (CAPs), with smaller and nonsignificant changes for C57 mice. In this article, we report the effects of subchronic CAPs exposure on HRV parameters that are sensitive to cardiac sympathetic and parasympathetic nerve activity. The standard deviation of normal to normal beat intervals (SDNN) and the square root of the mean squared differences of successive RR intervals (RMSSD) in the late afternoon and overnight for the ApoE−/− mice showed a gradual increase for the first 6 wk, a decline for about 12 more wk, and a slight turn upward at the end of the study period. For C57 mice, there were no chronic effect changes of SDNN or RMSSD in the late afternoon, and a slight increase after 6 wk for the overnight period. The response patterns of ApoE−/− mice indicated a perturbation of the homeostatic function in the cardiovascular system (initial enhancement and later depression of the HRV parameters). Our results complement the findings in human panel and controlled CAPs exposure studies in demonstrating that increased levels of particle pollution are able to perturb cardiac autonomic function, which may lead to adverse cardiovascular outcomes.

Effects of Subchronic Exposures to Concentrated Ambient Particles (CAPs) in Mice: V. CAPs Exacerbate Aortic Plaque Development in Hyperlipidemic Mice

Recent epidemiological studies suggest that long-term exposure to particulate matter (PM) causes chronic effects on the cardiovascular system that result in cumulative increases cardiovascular morbidity and mortality. Since atherosclerosis is a progressive irreversible condition and an underlying cause of many cardiovascular diseases, we hypothesized that long-term exposure to PM causes adverse cardiovascular effects by exacerbating atherosclerosis. In this study, we exposed C57- and ApoE-deficient (ApoE−/−) and ApoE, LDLr (DK)-deficient mice to concentrated ambient PM2.5 for 6 h/day, 5 days/wk, for up to 5 mo. The overall mean exposure concentration for these groups of animals was 110 μ g/m3. The cross-sectional area of the aorta root of DK mice was examined morphologically using confocal microscopy for the severity of lesion, extent of cellularity, and lipid contents. Aortas from the arch to the iliac bifurcations were also sectioned longitudinally and lesion areas were stained with Sudan IV. All DK mice regardless of exposure had developed extensive lesions in the aortic sinus regions, with lesion areas that covered more than 79% of the total area. In male DK mice, the lesion areas in the aortic sinus regions appeared to be enhanced by concentrated ambient particles (CAPs), with changes approaching statistical significance (p = .06). In addition, plaque cellularity was increased by 28% (p = .014, combined), whereas there were no CAPs-associated changes in the lipid content in these mice. When examining the entire aorta opened longitudinally, both the ApoE−/− and DK mice had prominent areas of severe atherosclerosis covering 40% or more of the lumenal surface. Visual examination of all images suggested that plaques tend to form in clusters concentrating near the aortic arch and the iliac bifurcations. Quantitative measurements showed that CAPs exposure increased the percentage of aortic intimal surface covered by grossly discernible atherosclerotic lesion by 57% in the ApoE−/− mice (p = .03). Changes produced by CAPs in male (10% increase) or female DK mice (8% decrease) were not statistically significant. In this study, we have demonstrated that subchronic exposure to CAPs in mice prone to develop atherosclerotic lesions had a significant impact on the size, severity, and composition of aortic plaque.

Effects of Subchronic Exposures to Concentrated Ambient Particles (CAPs) in Mice: II. The Design of a CAPs Exposure System for Biometric Telemetry Monitoring

We modified, assembled, tested, and validated the versatile aerosol concentration enrichment system (VACES) developed by for use in a subchronic experiment that involved exposures of mice in vivo and of respiratory epithelial cells in vitro to concentrated ambient particles (CAPs). Since the labor-intensive nose-only exposure regimen is not an option in a long-term experiment, a whole-body exposure mouse chamber was designed specifically for use with the VACES. The exposure system consists of a stainless-steel (SS) tub with 32 cubicles (1 mouse per cubicle) separated by perforated SS sheets. The tops of these cubicles are covered with perforated plastic sheets to allow telemetry monitoring during the exposure. In each exposure chamber, perforated aluminum tubes are used to distribute CAPs evenly (within 2% difference) throughout the exposure chamber. The exhaust consists of perforated aluminum tubes covered with a urine shield. The modification to the original design of the VACES facilitated the operation of the system in a subchronic study. Mass flow controllers maintain a constant flow rate into the exposure chambers. For a sham control exposure, the identical system is used, except that a HEPA filter at the inlet to the VACES removes 98% of ambient particles. The entire system allows for simultaneous exposure of 64 mice to CAPs, with an equal number of sham-exposed mice as controls. Telemetry receivers have been modified so that 16 mice per group with electrocardiograph (EKG) transmitters can be monitored during exposure. Furthermore, a BioSampler is used to collect CAPs (one sample per day) for the in vitro exposures. In this article, the assessments of flow and particle distribution of the exposure chamber as well as the performance of the system during the subchronic exposure experiment are described.

Effects of Concentrated Ambient Particles on Airway Responsiveness and Pulmonary Inflammation in Pulmonary Hypertensive Rats

Epidemiological studies have associated particulate air pollution with exacerbation of lung function in human populations. However, the relationship between ambient particles and lung function in animal studies has been inconsistent. In order to investigate the effects of concentrated ambient particles (CAPs) on airway responsiveness, we exposed pulmonary hypertensive rats to CAPs using particle concentrator at an EPA of Taiwan supersite, located at a traffic busy urban area nearing Taipei city. The exposure group (n = 5) was exposed to CAPs for 6 h each day for 3 consecutive days (mean mass concentration = 371.7 μ g/m3), while a control group (n = 6) was exposed to HEPA-filtered air. Whole-body barometric plethysmography was used to measure respiratory frequency, tidal volume, and airway responsiveness before and after exposure. Enhanced pause (Penh) was used as an indicator of airway responsiveness. To improve the accuracy of airway responsiveness measurement, we controlled temperature and humidity. Further, airway responsiveness was determined 5 h after particle exposure to overcome the stress effect in nose-only exposure chambers. After CAPs exposure, we found decreased respiratory frequency and increased tidal volume (p <. 05). Using the methacholine challenge test, a significant difference of Penh measured before and after experiment was observed in the CAPs group (p <. 05), but not in the filtered air group. Further analysis showed that the Penh difference before and after exposure in the CAPs group was significantly greater than that in the filtered air group (p <. 05). We conclude that CAPs could induce airway hyperresponsiveness in pulmonary hypertensive rats.

Exposures of Elderly Volunteers with and without Chronic Obstructive Pulmonary Disease (COPD) to Concentrated Ambient Fine Particulate Pollution

The elderly and individuals who have chronic obstructive pulmonary disease (COPD) may be sensitive to particulate matter (PM) air pollution. We evaluated short-term health responses of 13 elderly volunteers with COPD and 6 age-matched healthy adults to controlled exposures of ambient PM pollution in suburban Los Angeles. Using a Harvard particle concentrator and a whole-body chamber, we exposed each person on separate occasions to approximately 200 μg/m3 concentrated ambient particles (CAP) less than 2.5 μm in diameter and to filtered air (FA). Each exposure lasted 2 h with intermittent mild exercise. We found no significant effects of CAP on symptoms, spirometry, or induced sputum. A significant negative effect of CAP on arterial oxygenation (measured by pulse oximetry) immediately postexposure was more pronounced in healthy subjects. Peripheral blood basophils increased after CAP in healthy but not in COPD subjects. In both groups, red cell counts increased slightly 1 day after exposure to FA but not to CAP. Preexposure ectopic heartbeats were infrequent in healthy subjects, but increased modestly during/after CAP exposure relative to FA. Ectopic beats were more frequent in COPD subjects, but decreased modestly during/after CAP relative to FA. Heart-rate variability over multihour intervals was lower after CAP than after FA in healthy elderly subjects but not in COPD subjects. Thus, in this initial small-scale study of older volunteers experimentally exposed to ambient PM, some acute cardiopulmonary responses were consistent with effects reported from epidemiologic studies. Unexpectedly, individuals with COPD appeared less susceptible than healthy elderly individuals. Further investigation of older adults is warranted to understand the pathophysiology and public health significance of these findings.

Effects of Asian dust event particles on inflammation markers in peripheral blood and bronchoalveolar lavage in pulmonary hypertensive rats

The health impact of dust events from China has become a concern within China and in its neighboring countries. Previous epidemiological studies have demonstrated an association between particulate matter exposure and cardiopulmonary mortality. Here, we use pulmonary hypertensive rat models to examine inflammation markers in the lung and in peripheral blood after exposure to Asian dust storm particles. Using a nose-only inhalation system, eight pulmonary hypertensive rats were exposed to concentrated ambient particles (CAPs) from an actual Asian dust storm that took place between March 18 and 19, 2002; four control rats were also exposed to room air. Four rats exposed to CAPs of 315.6μg/m3 for 6h were classified as the low-exposure group, and another four rats exposed to CAPs of 684.5μg/m3 for 4.5h were classified as the high-exposure group. The animals were sacrificed 36h after exposure. Inflammation markers in the peripheral blood and in the bronchoalveolar lavage (BAL) were analyzed, and IL-6 in BAL was also determined using ELISA. White blood cell counts in peripheral blood increased with increased CAP exposure levels (P<0.001, test for trend). In BAL analysis, total cell numbers and the proportion of neutrophil also increased with increased CAP levels (P<0.001, test for trend for both markers). Positive dose–response relationships between CAP exposure and total protein (P<0.05) and between CAPs and LDH activity (P<0.05) were also observed. Moreover, IL-6 protein in BAL increasing with CAP levels (P<0.05, test for trend) was demonstrated. Our results revealed that exposure to particulate matters during an Asian dust storm could increase lung inflammation and injury in pulmonary hypertensive rats. Further studies are needed to determine the components of dust storm particles that may contribute to the particle toxicity.

Inhalation of concentrated ambient air particles exacerbates myocardial ischemia in conscious dogs.

Short-term increases in ambient air pollution have been associated with an increased incidence of acute cardiac events. We assessed the effect of inhalation exposure to concentrated ambient particles (CAPs) on myocardial ischemia in a canine model of coronary artery occlusion. Six mongrel dogs underwent thoracotomy for implantation of a vascular occluder around the left anterior descending coronary artery and tracheostomy to facilitate particulate exposure. After recovery (5-13 weeks), pairs of subjects were exposed for 6 hr/day on 3 or 4 consecutive days. Within each pair, one subject was randomly assigned to breathe CAPs on the second exposure day and filtered air at other times. The second subject breathed CAPs on the third exposure day and filtered air at other times. Immediately after each exposure, subjects underwent 5-min coronary artery occlusion. We determined ST-segment elevation, a measure of myocardial ischemia heart rate, and arrhythmia incidence during occlusion from continuous electrocardiograms. Exposure to CAPs (median, 285.7; range, 161.3-957.3 microg/m3) significantly (p = 0.007) enhanced occlusion-induced peak ST-segment elevation in precordial leads V4 (9.4 +/- 1.7 vs. 6.2 +/- 0.9 mm, CAPs vs. filtered air, respectively) and V5 (9.2 +/- 1.3 vs. 7.5 +/- 0.9 mm). ST-segment elevation was significantly correlated with the silicon concentration of the particles and other crustal elements possibly associated with urban street dust (p = 0.003 for Si). No associations were found with CAPs mass or number concentrations. Heart rate was not affected by CAPs exposure. These results suggest that exacerbation of myocardial ischemia during coronary artery occlusion may be an important mechanism of environmentally related acute cardiac events.