Free radical activity and pro-inflammatory effects of particulate air pollution (PM10) in vivo and in vitro

Ambient particle inhalation and the cardiovascular system: potential mechanisms

Well-documented air pollution episodes throughout recent history have led to deaths among individuals with cardiovascular and respiratory disease. Although the components of air pollution that cause the adverse health effects in these individuals are unknown, a small proportion by mass but a large proportion by number of the ambient air particles are ultrafine, i.e., less than 100 nm in diameter. This ultrafine component of particulate matter with a mass median aerodynamic diameter less than 10 microm (PM(10) may mediate some of the adverse health effects reported in epidemiologic studies and for which there is toxicologic evidence to support this contention. The exact mechanism by which ultrafine particles have adverse effects is unknown, but these particles have recently been shown to enhance calcium influx on contact with macrophages. Oxidative stress is also to be anticipated at the huge particle surface; this can be augmented by oxidants generated by recruited inflammatory leukocytes. Atheromatous plaques form in the coronary arteries and are major causes of morbidity and death associated epidemiologically with particulate air pollution. In populations exposed to air pollution episodes, blood viscosity, fibrinogen, and C-reactive protein (CRP) were higher. More recently, increases in heart rate in response to rising air pollution have been described and are most marked in individuals who have high blood viscosity. In our study of elderly individuals, there were significant rises in CRP, an index of inflammation. In this present review, we consider the likely interactions between the ultrafine particles the acute phase response and cardiovascular disease.

Interaction of alveolar macrophages with inhaled mineral particulates

Pulmonary disorders triggered by inhalation of occupational and environmental mineral particulates can be endpoints of a chronic inflammatory process in which alveolar macrophages (AMs), as a first line of defense, play a crucial role. The biological processes involved in particulate-induced activation of AMs include indirect or direct interactions of particulates with the cell membrane, subsequent stimulation of signal transduction pathways, and activation of gene transcription. Depending on the nature of particulate involved, particulate-induced activation of AMs has been shown to result in the release of potent mediators, such as reactive oxygen and nitrogen species, cytokines, eicosanoids, and growth factors. The prolonged and enhanced production of such effector molecules may result in a complex cascade of events that can contribute to the development of pulmonary disorders. This paper will give a short review of the present knowledge of AM interaction with inhaled mineral particulates and of the possible implications these interactions may have in the development of pulmonary disorders.

Impairment of alveolar macrophage phagocytosis by ultrafine particles

We investigated whether slowed clearance after exposure to ultrafine particles was due to a failure in alveolar macrophage phagocytosis. This was achieved by measuring the ability of a macrophage cell line (J774.2 MPhi) to phagocytose 2-microg indicator latex beads following 8-h exposures to a number of test particles. Particles utilized were fine titanium dioxide (TiO2), ultrafine titanium dioxide (UTiO2), carbon black (CB), or ultrafine carbon black (UCB). Cytotoxicity of particles was measured by means of MTT activity. In a preliminary study, we assessed the effects of conditioned medium from particle-treated macrophages on the phagocytic ability of naive macrophages. Ultrafine and fine particles had no significant cytotoxic effects on J774.2 MPhi. A significant reduction in the ability of macrophages to phagocytose the indicator beads occurred after exposure to 0.39 microg/mm(2) (p < 0.001) of UCB and 0.78 microg/mm(2) (p < 0.001) of all particle types compared to the control. Furthermore, ultrafine particles were shown to significantly (p < 0.001) impair macrophage phagocytosis at a lower dose than their fine counterparts (0.39 and 0.78 microg/mm(2), respectively). At all doses, UCB resulted in a greater number (p < 0.001) of nonphagocytic macrophages compared to the other test particles. We tested whether a diffusable mediator being released from particle-exposed cells inhibited the phagocytic activity of adjacent macrophages. The conditioned medium from particle-exposed macrophages had no significant effect on the phagocytic ability of macrophages, suggesting that cell-cell contact is responsible for the pattern of failed phagocytosis (data not shown). We have demonstrated that ultrafine particles impair macrophage phagocytosis to a greater extent than fine particles compared on a mass basis. Therefore, we conclude that slowed clearance of particles, specifically the ultrafines, can in part be attributed to a particle-mediated impairment of macrophage phagocytosis.

Antioxidants and protein carbonyls in bronchoalveolar lavage fluid of children: normal data

Antioxidant-oxidant imbalances in bronchoalveolar lavage fluid (BAL) are thought to contribute to oxidative stress in respiratory disease. However, normal reference ranges for BAL antioxidants and oxidized proteins in children are not available. In this study, we recruited 124 children attending for elective surgery for a noninflammatory condition; 83 were nonasthmatic, nonatopic (N) and 41 were nonasthmatic, atopic (NA). A nonbronchoscopic lavage was performed and ascorbate, uric acid, alpha-tocopherol, and protein carbonyl (as a measure of oxidative damage) concentrations were determined in BAL fluid. The 95% reference range was 0.112-1.897 micromol/L for ascorbate, 0.149-2.163 micromol/L for urate, 0.0029-0.066 micromol/L for alpha-tocopherol, and 0.280-4.529 nmol/mg for protein carbonyls in BAL fluid. Age, gender, and exposure to environmental tobacco smoke did not affect the concentration of ascorbate, urate, alpha-tocopherol, or protein carbonyls. However, in multiple linear regression analyses, the type of home heating (glass-fronted fires or oil-fired central heating) was found to influence ascorbate and urate concentrations in the BAL fluid (ss-coefficient for ascorbate: 0.445, p = 0.031; for urate: 0.114, p = 0.001). There was no significant difference between the N and NA group in BAL fluid concentrations of ascorbate, urate, or protein carbonyls. The alpha-tocopherol concentration was significantly increased in the NA group (p = 0.037). Uric acid and alpha-tocopherol concentrations in BAL fluid and serum were not correlated. Intriguingly, serum and BAL ascorbate concentrations were significantly correlated (r = 0.297, p = 0.018, n = 63), which may offer an explanation for why supplementing the diet with vitamin C can improve asthma symptoms. Further studies will investigate the role of BAL antioxidant concentrations in children with inflammatory respiratory diseases.

The role of particulate pollutants in pulmonary inflammation and asthma: evidence for the involvement of organic chemicals and oxidative stress

We review the literature indicating that the adverse health effects of ambient particulate matter involve the generation of oxidative stress and inflammation, as well as immunomodulating effects by particle-associated chemicals. We discuss evidence that diesel exhaust particle organic extracts induce reactive oxygen species in macrophages and bronchial epithelial cells, two key cell types targeted by particulate matter in the lung. Reactive oxygen species activate the promoters of cytokines and chemokines involved in allergic inflammation through activator protein-1 and nuclear factor- kappaB signaling pathways, which may explain exacerbation of allergic inflammation. Organic diesel exhaust particle chemicals also induce apoptosis and necrosis in bronchial epithelial cells via a mitochondrial pathway. This may be responsible for epithelial shedding and bronchial hyperreactivity in asthma.

Suspended particulate matter in indoor air: adjuvants and allergen carriers

The overall purpose of this study was to investigate how airborne house dust particles may contribute to an allergic immune response, and thereby also to asthma and other respiratory symptoms. The following aims were set: first, to quantify and characterize indoor suspended particulate matter (SPM) with regard to amount, as well as elemental and size distribution, second, to identify possible mechanisms by which SPM may affect the allergic immune response. A vast majority of the particles in SPM samples from homes in Oslo were found to be less than 2.5 microm in diameter. This PM(2.5) fraction contained, in addition to a large amount of sulfur aerosols and silicates, a lot of soot particles. Most of these were less than 1 microm in diameter. Using an immunogold labeling technique, we found that these soot particles carried cat, dog and birch allergens on their surface. These results show that indoor SPM contains a lot of potential allergen carriers, i.e. soot particles (carbon aggregates), most of them less that 1 microm in diameter and therefore able to transport allergens deep into the respiratory tree. We further found that diesel exhaust particles (DEP), which is likely the main soot component of SPM, adsorbed several well-known allergens in vitro. Furthermore, SPM was found to elicit a local lymph node inflammatory response, and to have an adjuvant activity on the production of IgE antibodies to ovalbumin (OA).

Airborne particles are a risk factor for hospital admissions for heart and lung disease

We examined the association between particulate matter [less than/equal to] 10 microm; (PM(10)) and hospital admission for heart and lung disease in ten U.S. cities. Our three goals were to determine whether there was an association, to estimate how the association was distributed across various lags between exposure and response, and to examine socioeconomic factors and copollutants as effect modifiers and confounders. We fit a Poisson regression model in each city to allow for city-specific differences and then combined the city-specific results. We examined potential confounding by a meta-regression of the city-specific results. Using a model that considered simultaneously the effects of PM(10) up to lags of 5 days, we found a 2.5% [95% confidence interval (CI), 1.8-3. 3] increase in chronic obstructive pulmonary disease, a 1.95% (CI, 1. 5-2.4) increase in pneumonia, and a 1.27% increase (CI, 1-1.5) in CVD for a 10 microg/m(3) increase in PM(10). We found similar effect estimates using the mean of PM(10) on the same and previous day, but lower estimates using only PM(10) for a single day. When using only days with PM(10) < 50 mg/m(3), the effect size increased by [greater/equal to] 20% for all three outcomes. These effects are not modified by poverty rates or minority status. The results were stable when controlling for confounding by sulfur dioxide, ozone, and carbon monoxide. These results are consistent with previous epidemiology and recent mechanistic studies in animals and humans.

Respiratory tract pathology and cytokine imbalance in clinically healthy children chronically and sequentially exposed to air pollutants

Chronic exposure of children to a complex mixture of air pollutants leads to recurrent episodes of upper and lower respiratory tract injury. An altered nasal mucociliary apparatus leaves the distal acinar airways more vulnerable to reactive gases and particulate matter (PM). The heterogeneity of structure in the human lung can impart significant variability in the distribution of ozone dose and particle deposition; this, in turn, influences the extent of epithelial injury and repair in chronically exposed children. Cytokines are low-molecular-weight proteins that act as intercellular mediators of inflammatory reactions, including lung injury of various etiologies. Cytokines are involved in generating inflammatory responses that contribute to injury at the lung epithelial and endothelial barriers. Mexico City is a 20-million-person megacity with severe air pollution problems. Southwest Metropolitan Mexico City (SWMMC) atmosphere is characterized by a complex mixture of air pollutants, including ozone, PM, and aldehydes. There is radiological evidence that significant lower respiratory tract damage is taking place in clinically healthy children chronically and sequentially exposed to air pollutants while growing up in SWMMC. We hypothesize that there is an imbalanced and dysregulated cytokine network in SWMMC children with overproduction of proinflammatory cytokines and cytokines involved in lung tissue repair and fibrosis. The nature of the sustained imbalance among the different cytokines ultimately determines the final lung histopathology, which would include subchronic inflammation, emphysema, and fibrosis. Cytokines likely would reach the systemic circulation and produce systemic effects. Individuals with an underlying respiratory or cardiovascular disease are less able to maintain equilibrium of the precarious cytokine networks.

Pulmonary effects induced by ultrafine PTFE particles

PTFE (polytetrafluoroethylene) fumes consisting of large numbers of ultrafine (uf) particles and low concentrations of gas-phase compounds can cause severe acute lung injury. Our studies were designed to test three hypotheses: (i) uf PTFE fume particles are causally involved in the induction of acute lung injury, (ii) uf PTFE elicit greater pulmonary effects than larger sized PTFE accumulation mode particles, and (iii) preexposure to the uf PTFE fume particles will induce tolerance. We used uf Teflon (PTFE) fumes (count median particle size approximately 16 nm) generated by heating PTFE in a tube furnace to 486 degrees C to evaluate principles of ultrafine particle toxicity. Teflon fumes at ultrafine particle concentrations of 50 microg/m(3) were extremely toxic to rats when inhaled for only 15 min. We found that when generated in argon, the ultrafine Teflon particles alone are not toxic at these exposure conditions; neither were Teflon fume gas-phase constituents when generated in air. Only the combination of both phases when generated in air caused high toxicity, suggesting either the existence of radicals on the surface or a carrier mechanism of the ultrafine particles for adsorbed gas compounds. Aging of the fresh Teflon fumes for 3.5 min led to a predicted coagulation to >100 nm particles which no longer caused toxicity in exposed animals. This result is consistent with a greater toxicity of ultrafine particles compared to accumulation mode particles, although changes in particle surface chemistry during the aging process may have contributed to the diminished toxicity. Furthermore, the pulmonary toxicity of the ultrafine Teflon fumes could be prevented by adapting the animals with short 5-min exposures on 3 days prior to a 15-min exposure. Messages encoding antioxidants and chemokines were increased substantially in nonadapted animals, yet were unaltered in adapted animals. This study shows the importance of preexposure history for the susceptibility to acute ultrafine particle effects.

Expression of heme oxygenase isoenzymes 1 and 2 in normal and asthmatic airways: effect of inhaled corticosteroids

Heme oxygenase (HO) is considered to be an antioxidant enzyme that catabolizes heme to produce carbon monoxide (CO) and biliverdin. We determined the expression and distribution of HO-1 and HO-2, two isoenzymes of HO, in the airways of patients with asthma, and determined the effect of inhaled corticosteroid therapy. Immunostaining for both enzymes was widely distributed in the airways' submucosa, particularly in airway epithelium and submucosal macrophages (CD68(+)) as determined by double immunostaining. There was no difference in intensity and extent of staining in biopsies from normal subjects (n = 10) and subjects with asthma (n = 10). Following 1 mo of treatment with inhaled corticosteroids (budesonide 1,600 microg/d), there was no significant change in the expression and distribution of either HO-1 or HO-2 in the airways' submucosa in eight subjects with mild asthma, despite a significant reduction in airway eosinophils and a reduction in bronchial responsiveness to methacholine. Levels of exhaled nitric oxide were significantly reduced, but exhaled CO levels remained unchanged by the treatment. Treatment with a placebo inhaler (n = 8) had no effects on these parameters. Thus, both HO-1 and HO-2 are extensively distributed equally in normal subjects and subjects with asthma, and are not modulated by inhaled corticosteroid therapy in subjects with asthma. HO may be an important endogenous antioxidant enzyme.

Airborne particles are a risk factor for hospital admissions for heart and lung disease

We examined the association between particulate matter [less than/equal to] 10 microm; (PM(10)) and hospital admission for heart and lung disease in ten U.S. cities. Our three goals were to determine whether there was an association, to estimate how the association was distributed across various lags between exposure and response, and to examine socioeconomic factors and copollutants as effect modifiers and confounders. We fit a Poisson regression model in each city to allow for city-specific differences and then combined the city-specific results. We examined potential confounding by a meta-regression of the city-specific results. Using a model that considered simultaneously the effects of PM(10) up to lags of 5 days, we found a 2.5% [95% confidence interval (CI), 1.8-3. 3] increase in chronic obstructive pulmonary disease, a 1.95% (CI, 1. 5-2.4) increase in pneumonia, and a 1.27% increase (CI, 1-1.5) in CVD for a 10 microg/m(3) increase in PM(10). We found similar effect estimates using the mean of PM(10) on the same and previous day, but lower estimates using only PM(10) for a single day. When using only days with PM(10) < 50 mg/m(3), the effect size increased by [greater/equal to] 20% for all three outcomes. These effects are not modified by poverty rates or minority status. The results were stable when controlling for confounding by sulfur dioxide, ozone, and carbon monoxide. These results are consistent with previous epidemiology and recent mechanistic studies in animals and humans.

Increased inflammation and intracellular calcium caused by ultrafine carbon black is independent of transition metals or other soluble components

OBJECTIVES

Particulate air pollution has been shown to cause adverse health effects, and the ultrafine particle component has been implicated. The aim of the present study was to investigate whether an ultrafine particle exerted its effects through transition metals or other soluble factors released from the surface of the particles.

METHODS

Both in vitro and in vivo models were used to test the imflammogenicity of carbon black (CB) and ultrafine carbon black (UfCB) and the role of transition metals was investigated by treating the particles with desferrioxamine mesylate (desferal), a transition metal chelator. Rats were instilled with particles and the cell population assessed by bronchoalveolar lavage (BAL). Calcium homeostasis in macrophages was assessed with a fluorimetric technique.

RESULTS

UfCB was inflammogenic compared with CB when instilled into Wistar rat lungs, an effect which could not be ameliorated by desferal treatment of the particles. Particle leachates produced no significant inflammation in vivo. In vitro experiments showed that the cytosolic calcium ion concentration in Mono Mac 6 cells was increased significantly after UfCB treatment and treatment of particles with desferal did not alter these effects. Particle leachates had no effect on cytosolic calcium ion concentration. Iron was not detected in leachates of the particles with the desferal assay, however, ng/mg of particles were detectable in citrate leachates with inductively coupled plasma-mass spectrometry (ICP-MS).

CONCLUSIONS

The increased inflammogenicity of UfCB compared with CB cannot be explained by soluble transition metals released from or by accumulation of iron at the particle surface. Differences may be accounted for by increased surface area or particle number.

Activation of NF-kappaB by PM(10) occurs via an iron-mediated mechanism in the absence of IkappaB degradation

Exposure to particulate air pollution (PM(10)) is associated with exacerbations of respiratory diseases and increased cardiopulmonary mortality. PM(10) induces lung inflammation in rats, which has been attributed to many factors, including the ultrafine components of PM(10), endotoxins, and transition metals. In this study, we investigated in alveolar epithelial (A549) cells whether PM(10) could activate nuclear factor-kappa B (NF-kappaB), a transcription factor stimulated in response to many proinflammatory agents. Our results show that PM(10) samples from various sites within the United Kingdom cause nuclear translocation, DNA-binding, and transcriptional activation of NF-kappaB in A549 cells. Furthermore, increased NF-kappaB activity was observed in the absence of IkappaB degradation. To evaluate the role of iron, A549 cells were exposed to PM(10) previously treated with phosphate-buffered saline (PBS), deferoxamine mesylate, or deferoxamine plus ferrozine. PBS-treated and, to a lesser extent, deferoxamine-treated PM(10) were able to activate NF-kappaB, whereas this response was completely abrogated in cells exposed to PM(10) treated with both deferoxamine and ferrozine. Moreover, we studied the effects of soluble components of PM(10) on NF-kappaB activation by exposing alveolar epithelial cells to soluble fractions from PM(10) treated with PBS or the metal chelators. We found that, compared with fractions from PBS-treated PM(10) which activated NF-kappaB, fractions from PM(10) treated with deferoxamine and ferrozine did not stimulate NF-kappaB activity above background levels. Coincubation of polymixin B, an endotoxin-binding compound, and PM(10) did not inhibit NF-kappaB. In summary, PM(10) activates NF-kappaB in A549 cells by an iron-mediated mechanism in the absence of IkappaB degradation.

Airway inflammation after controlled exposure to diesel exhaust particulates

Epidemiologic evidence suggests a link between morbidity and mortality and levels of particulate matter in the atmosphere. We studied the inflammatory response to inhalation of diesel exhaust particulates (DEP) in normal volunteers. DEP were collected from the exhaust of a stationary diesel engine and were resuspended in an exposure chamber. Ten nonsmoking healthy volunteers were exposed for 2 h at rest to a controlled concentration of DEP (monitored at 200 microg/m(3) particulate matter of less than 10 microm aerodynamic diameter [PM(10)]) or air in a double-blind, randomized, crossover study. Exposures were followed by serial spirometry and measurement of pulse, blood pressure, exhaled carbon monoxide (CO), and methacholine reactivity, as well as sputum induction and venesection for up to 4 h after exposure, and a repeat of all these procedures at 24 h after exposure. There were no changes in cardiovascular parameters or lung function following exposure to DEP. Levels of exhaled CO were increased ater exposure to DEP, and were maximal at 1 h (air: 2.9 +/- 0.2 ppm [mean +/- SEM]; DEP: 4.4 +/- 0.3 ppm; p < 0.001). There was an increase in sputum neutrophils and myeloperoxidase (MPO) at 4 h after DEP exposure as compared with 4 h after air exposure (neutrophils: 41 +/- 4% versus 32 +/- 4%; MPO: 151 ng/ml versus 115 ng/ml, p < 0.01), but no change in concentrations of inflammatory markers in peripheral blood. Exposure to DEPs at high ambient concentrations leads to an airway inflammatory response in normal volunteers.

Exacerbations of COPD: environmental mechanisms

Air pollution as a trigger for exacerbations of COPD has been recognized for > 50 years, and has led to the development of air quality standards in many countries that substantially decreased the levels of air pollutants derived from the burning of fossil fuels, such as black smoke and sulfur dioxide. However, the recent dramatic increase in motor vehicle traffic has produced a relative increase in the levels of newer pollutants, such as ozone and fine-particulate air pollution < 10 microm in diameter. Numerous epidemiologic studies have shown associations between the levels of these air pollutants and adverse health effects, such as exacerbations of airways diseases and even deaths from respiratory and cardiovascular causes. Elucidation of the mechanism of the harmful effects of these pollutants should allow improved risk assessment for patients with airways diseases who are be susceptible to the effects of these air pollutants.

Effects of short-term exposure to 0.2 ppm ozone on biomarkers of inflammation in sputum, exhaled nitric oxide, and lung function in subjects with mild atopic asthma

To gain further insight into the kinetics of airway inflammatory response and explore the possibility of nitric oxide as a surrogate marker of the lower airway inflammatory response to ozone, nine subjects with mild atopic asthma were exposed to filtered air or 0.2 ppm ozone for 2 hours with intermittent exercise. Lung function was measured at baseline and immediately after exposures. Sputum induction was performed at 6 hours and at 24 hours after exposures, and exhaled nitric oxide levels were measured at baseline, immediately, 6, and 24 hours after both exposures. A significant decline in forced expiratory volume in one second and inspiratory capacity was detectable following exposure to ozone. In addition, a 2-fold increase was observed in the percentage of polymorphonuclear leukocytes 6 hours after exposure to ozone, with no changes in other biomarkers at this time point. By 24 hours after ozone exposure, the neutrophilia had subsided but there was an increase in albumin, total protein, myeloperoxidase, and eosinophil cationic protein. Exhaled nitric oxide levels, histamine, interleukin-8, and growth-related oncogene-alpha in sputum did not change significantly following ozone exposure. It was concluded that short-term ozone exposure induces an acute inflammatory response in asthmatic airways, characterized by early polymorphonuclear leukocyte influx followed by plasma extravasation and activation of eosinophils and neutrophils. Exhaled nitric oxide is not a useful marker for detecting inflammatory response to ozone in persons with mild asthma.

Fine particles are more strongly associated than coarse particles with acute respiratory health effects in schoolchildren

Numerous studies have reported associations between airborne particles and a range of respiratory outcomes from symptoms to mortality. Current attention has been focused on the characteristics of these particles responsible for the adverse health effects. We have reanalyzed three recent longitudinal diary studies to examine the relative contributions of fine and coarse particles on respiratory symptoms and peak expiratory flow in schoolchildren. In the Harvard Six Cities Diary Study, lower respiratory symptoms in a two-pollutant model were associated with an interquartile range increment in fine particles [(for 15 microg/m3 particulate matter (PM) <2.5 microm in aerodynamic diameter (PM2.5), odds ratio = 1.29, 95% confidence limits (CL) = 1.06, 1.57] but not coarse particles (for 8 microg/m3 PM2.5-10, odds ratio = 1.05, 95% CL = 0.90, 1.23). In Uniontown, PA, we found that peak flow was associated with fine particles (for 15 microg/m3 PM2.1, peak flow = -0.91 liters/minute, 95% CL = -0.14, -1.68), especially fine sulfate particles, but not with coarse particles (for 15 microg/m3 PM2.1-10, +1.04 liters/minute, 95% CL = -1.32, +3.40). We found similar results for an equivalent children's cohort in State College, PA. We conclude that fine particles, especially fine sulfate particles, have much stronger acute respiratory effects than coarse particles.

Lung glutathione and oxidative stress: implications in cigarette smoke-induced airway disease

Glutathione (GSH), a ubiquitous tripeptide thiol, is a vital intra- and extracellular protective antioxidant in the lungs. The rate-limiting enzyme in GSH synthesis is gamma-glutamylcysteine synthetase (gamma-GCS). The promoter (5'-flanking) region of the human gamma-GCS heavy and light subunits are regulated by activator protein-1 and antioxidant response elements. Both GSH and gamma-GCS expression are modulated by oxidants, phenolic antioxidants, and inflammatory and anti-inflammatory agents in lung cells. gamma-GCS is regulated at both the transcriptional and posttranscriptional levels. GSH plays a key role in maintaining oxidant-induced lung epithelial cell function and also in the control of proinflammatory processes. Alterations in alveolar and lung GSH metabolism are widely recognized as a central feature of many inflammatory lung diseases including chronic obstructive pulmonary disease (COPD). Cigarette smoking, the major factor in the pathogenesis of COPD, increases GSH in the lung epithelial lining fluid of chronic smokers, whereas in acute smoking, the levels are depleted. These changes in GSH may result from altered gene expression of gamma-GCS in the lungs. The mechanism of regulation of GSH in the epithelial lining fluid in the lungs of smokers and patients with COPD is not known. Knowledge of the mechanisms of GSH regulation in the lungs could lead to the development of novel therapies based on the pharmacological or genetic manipulation of the production of this important antioxidant in lung inflammation and injury. This review outlines 1) the regulation of cellular GSH levels and gamma-GCS expression under oxidative stress and 2) the evidence for lung oxidant stress and the potential role of GSH in the pathogenesis of COPD.

The effect of air pollution on exhaled nitric oxide of atopic and nonatopic subjects

Levels of exhaled nitric oxide (NO) were determined in well-characterized atopic and nonatopic subjects on 4 days with a different level of outdoor air pollution. The two groups matched well regarding spirometric values, i.e., no difference with regard to FEV(1), FVC, and peak flow. On the 4 test days asymptomatic atopic subjects exhaled 1.5- to 2.4-fold higher levels of NO compared with nonatopic subjects. In both groups the increase in exhaled NO in response to air pollution was similar (2.5 times maximal increase, P < 0.01). In conclusion, atopic subjects exhale higher levels of NO compared with nonatopic subjects, but respond to a similar degree to increased levels of air pollution.

Chemicals in Diesel Exhaust Particles Generate Reactive Oxygen Radicals and Induce Apoptosis in Macrophages

There is increasing evidence that particulate air pollutants, such as diesel exhaust particles (DEP), potentiate chronic inflammatory processes as well as acute symptomatic responses in the respiratory tract. The mechanisms of action as well as the cellular targets for DEP remain to be elucidated. We show in this paper that the phagocytosis of DEP by primary alveolar macrophages or macrophage cell lines, RAW 264.7 and THP-1, leads to the induction of apoptosis through generation of reactive oxygen radicals (ROR). This oxidative stress initiates two caspase cascades and a series of cellular events, including loss of surface membrane asymmetry and DNA damage. The apoptotic effect on macrophages is cell specific, because DEP did not induce similar effects in nonphagocytic cells. DEP that had their organic constituents extracted were no longer able to induce apoptosis or generate ROR. The organic extracts were, however, able to induce apoptosis. DEP chemicals also induced the activation of stress-activated protein kinases, which play a role in cellular apoptotic pathways. The injurious effects of native particles or DEP extracts on macrophages could be reversed by the antioxidant, N-acetyl-cysteine. Taken together, these data suggest that organic compounds contained in DEP may exert acute toxic effects via the generation of ROR in macrophages.

Particulate air pollution and the blood

BACKGROUND

Particulate air pollution has been associated with excess deaths from, and increases in hospital admissions for, cardiovascular disease among older people. A study was undertaken to determine whether this may be a consequence of alterations in the blood, secondary to pulmonary inflammation caused by the action of fine particles on alveolar cells, by repeatedly measuring haematological factors in older people and relating them to measurements of exposure to airborne particles.

METHODS

One hundred and twelve individuals aged 60+ years in two UK cities provided repeated blood samples over 18 months, 108 providing the maximum of 12 samples. Estimates of individual exposure to particles of less than 10 microm diameter (PM(10)), derived from a mathematical model based on activity diaries and comparative measurements of PM(10) at multiple sites and during a variety of activities, were made for each three day period prior to blood sampling. The relationships between blood values and estimates of both personal exposure and city centre measurements of PM(10) were investigated by analysis of covariance, adjusting for city, season, temperature, and repeated individual measurements.

RESULTS

Estimated personal exposure to PM(10) over the previous three days showed negative correlations with haemoglobin concentration, packed cell volume (PCV), and red blood cell count (p<0.001), and with platelets and factor VII levels (p<0.05). The changes in red cell indices persisted after adjustment for plasma albumin in a sample of 60 of the subjects. City centre PM(10) measurements over three days also showed negative correlations with haemoglobin and red cell count (p<0.001) and with PCV and fibrinogen (p<0.05), the relationship with haemoglobin persisting after adjustment for albumin. C reactive protein levels showed a positive association with city centre measurements of PM(10) (p<0.01). Based on a linear relationship, the estimated change in haemoglobin associated with an alteration in particle concentration of 100 microg/m(3) is estimated to have been 0.44 g/dl (95% CI 0.62 to 0.26) for personal PM(10) and 0.73 g/dl (95% CI 1.11 to 0.36) for city centre PM(10) measurements.

CONCLUSIONS

This investigation is the first to estimate personal exposures to PM(10) and to demonstrate associations between haematological indices and air pollution. The changes in haemoglobin adjusted for albumin suggest that inhalation of some component of PM(10) may cause sequestration of red cells in the circulation. We propose that an action of such particles either on lung endothelial cells or on erythrocytes themselves may be responsible for changing red cell adhesiveness. Peripheral sequestration of red cells offers an explanation for the observed cardiovascular effects of particulate air pollution.

Induction of fibrogenic mediators by fine and ultrafine titanium dioxide in rat tracheal explants

Respirable ambient particles [particulate matter <10 micrometer (PM(10))] are associated with both acute and chronic adverse health effects including chronic airflow obstruction. PM(10) can induce expression of inflammatory and fibrogenic mediators, but there is controversy about the types and/or sizes of particles involved and, in particular, whether ultrafine particles are the major toxic agents. To examine whether particle size affects mediator generation, we exposed rat tracheal explants, an inflammatory cell-free model of the airway wall, to various concentrations up to 500 microgram/cm(2) of fine (0.12 micrometer) or ultrafine (0.021 micrometer) titanium dioxide (anatase), maintained the explants in an organ culture in air for 1-7 days, and used RT-PCR to examine the expression of fibrogenic mediators and procollagen. No increase in gene expression was seen at 1 or 3 days, but at 5 days, ultrafine dust induced a small increase in procollagen. At 7 days, fine titanium dioxide produced significantly greater increases for platelet-derived growth factor (PDGF)-B, transforming growth factor-alpha, and transforming growth factor-beta compared with those by ultrafine dust; both dusts produced similar increases for PDGF-A; and ultrafine dust produced increases in procollagen expression, whereas fine dust had no effect. Expression levels were dose related. Both dusts produced a similar decrease in expression of PDGF receptor-alpha and a similar increase in PDGF receptor-beta. These observations suggest that ultrafine particles are intrinsically able to induce procollagen expression even in the absence of inflammatory cells; that chronic exposure to PM(10) may result in chronic airflow obstruction, in part because of ultrafine particle-mediated increases in airway wall fibrosis; and that chemically identical dusts of differing size can produce quite different patterns of gene expression in the airway wall. Differential upregulation of PDGF receptors does not appear to explain dust-induced fibrosis in this model.

Asthma, oxidant stress, and diet

It has been suggested that the increased prevalence of atopy and asthma observed in many developed countries over the past 30 y is in part the result of a decrease in the incidence and severity of early childhood infections. The immunologic consequence of this phenomenon has been the expansion of T-lymphocyte populations away from the T-helper 1 (Th1) subset and in the direction of the Th2 subset. This leads to the creation of a cytokine-mediated propensity for the development of an intense inflammatory response in the airways, resulting in oxidative stress, airway tissue injury, and the development of atopy and asthmatic symptomatology. Over this same period, there has been a decreased intake of dietary substances that contribute to antioxidant defense, and this appears to have contributed to the rise of atopy and asthma. Studies evaluating the efficacy of these antioxidant substances in the prevention of asthma and as adjuvants in the treatment of asthma are reviewed, and suggestions are made for the direction of future studies.

Modeling the interactions of particulates with epithelial lining fluid antioxidants

Oxidative stress may be a fundamental mode of injury associated with inspired particles. To examine this, we determined the ability of three carbon black particles (CBPs; M120, M880, and R250) and two forms of silicon dioxide, amorphous (Cabosil) and crystalline (DQ12) quartz, to deplete epithelium lining fluid antioxidant defenses. Single and composite antioxidant solutions of uric acid, ascorbic acid (AA), and reduced glutathione (GSH) were examined in the presence of particle concentrations of 150 microgram/ml. Uric acid was not depleted by any particle considered. AA was depleted in a near-linear fashion with time by the three different CBPs; however, AA depletion rates varied markedly with CBP type and decreased in the presence of metal chelators. An initially high GSH depletion rate was noted with all CBPs, and this was always accompanied by the appearance of oxidized glutathione. Exposure to Cabosil or DQ12 did not result in the loss of GSH. Together, these data demonstrate that particle type, size, and surface area are all important factors when considering particle-antioxidant interactions in the airways.

Role of soluble metals in oil fly ash-induced airway epithelial injury and cytokine gene expression

Particulate matter (PM) metal content and bioavailability have been hypothesized to play a role in the health effects epidemiologically associated with PM exposure, in particular that associated with emission source PM. Using rat tracheal epithelial cells in primary culture, the present study compared and contrasted the acute airway epithelial effects of an emission source particle, residual oil fly ash (ROFA), with that of its principal constitutive transition metals, namely iron, nickel, and vanadium. Over a 24-h period, exposure to ROFA, vanadium, or nickel plus vanadium, but not to iron or nickel, resulted in increased epithelial permeability, decreased cellular glutathione, cell detachment, and lytic cell injury. Treatment of vanadium-exposed cells with buthionine sulfoximine further increased cytotoxicity. Conversely, treatment with the radical scavenger dimethylthiourea inhibited the effects in a dose-dependent manner. RT-PCR analysis of RNA isolated from ROFA-exposed rat tracheal epithelial cells demonstrated significant macrophage inflammatory protein-2 and interleukin-6 gene expression as early as 6 h after exposure, whereas gene expression of inducible nitric oxide synthase was maximally increased 24 h postexposure. Again, vanadium (not nickel) appeared to be mediating the effects of ROFA on gene expression. Treatment with dimethylthiourea inhibited both ROFA- and vanadium-induced gene expression in a dose-dependent manner. Corresponding effects were observed in interleukin-6 and macrophage inflammatory protein-2 synthesis. In summary, generation of an oxidative stress was critical to induction of the ROFA- or vanadium-induced effects on airway epithelial gene expression, cytokine production, and cytotoxicity.

Air pollution is associated with increased level of exhaled nitric oxide in nonsmoking healthy subjects

The authors sought to determine which air pollutant is responsible for the increase in exhaled nitric oxide observed in healthy subjects. Exhaled nitric oxide was measured in 16 nonsmoking healthy subjects on 14 workdays, during which there were varying air-pollution levels. Contamination of samples by ambient nitric oxide was excluded. The baseline value of exhaled nitric oxide, determined at times when outdoor air pollution was low, ranged from 7 to 43 ppb (mean = 28+/-5 ppb). The daily value of exhaled nitric oxide (range = 5-60 ppb) was associated positively with ambient carbon monoxide (r = .85) and nitric oxide (r = .81). Exposure during the morning hours to high levels of outdoor pollution was associated with increased exhaled nitric oxide (i.e., 50% above baseline), which persisted for up to 5 h (i.e., 32% above baseline). These results indicated that exhaled nitric oxide levels represent a useful biomonitor of individual exposure to air pollutants.

Episodes of high coarse particle concentrations are not associated with increased mortality

Fine particle concentration (i.e., particles <2.5 microm in aerodynamic diameter; PM2.5), but not coarse particle concentration, was associated with increased mortality in six U.S. cities. Others criticized this result, arguing that it could result from differences in measurement error between the two size ranges. Fine particles are primarily from combustion of fossil fuel, whereras coarse particles (i.e., particles between 2.5 and 10 microm in aerodynamic diameter) are all crustal material, i.e., dust. One way to determine if coarse particles are a risk for mortality is to identify episodes of high concentrations of coarse, but not fine, particles. Spokane, Washington, is located in an arid area and is subject to occasional dust storms after crops have been harvested. Between 1989 and 1995, we identified 17 dust storms in Spokane. The 24-hr mean PM10 concentration during those storms was 263 microg/m3. Using control dates that were the same day of the year in other years (but with no dust storm on that day) and that had a mean PM10 concentration of 42 microg/m3, we compared the rate of nonaccidental deaths on the episode versus nonepisode days. There was little evidence of any risk [relative risk (RR) = 1.00; 95% confidence interval (CI), 0.81-1.22] on the episode days. Defining episode deaths as those occurring on the same or following day as the dust storm produced similar results (RR = 1.01; CI, 0.87-1.17). Sensitivity analyses, which tested more extensive seasonal control, produced smaller estimates. We conclude that coarse particles from windblown dust are not associated with mortality risk.

Inflammation and the regulation of glutathione level in lung epithelial cells

Inflammation is a highly complex biochemical protective response to cellular injury. If this process is continuously unchecked, it leads to chronic inflammation, a hallmark of various inflammatory lung diseases. Reactive oxygen intermediates generated by immune cells recruited to the sites of inflammation are a major cause of cell damage. Glutathione (GSH), is a vital intra- and extracellular protective antioxidant in the lungs. The rate-limiting enzyme in GSH synthesis is gamma-glutamylcysteine synthetase (gamma-GCS). Both GSH and gamma-GCS expression are modulated by oxidants, phenolic antioxidants, inflammatory, and anti-inflammatory agents in lung cells. GSH plays a key role in regulating oxidant-induced lung epithelial cell function and also in the control of pro-inflammatory processes. Alterations in the alveolar and lung GSH metabolism are widely recognized as a central feature of many inflammatory lung diseases. Oxidative processes have a fundamental role in lung inflammation through redox-sensitive transcription factors such as NF-kappaB and AP-1, which regulated the genes for pro-inflammatory mediators and protective antioxidant genes such as gamma-GCS. The critical balance between the induction of pro-inflammatory mediators and antioxidant genes in response to oxidative stress at the site of inflammation is not known. Knowledge of the mechanisms of GSH regulation in lung inflammation could lead to the development of novel therapies based on the pharmacological manipulation of the production of this important antioxidant in lung inflammation and injury. This review describes the potential role of GSH for lung oxidant stress, inflammation and injury.

Particulate matter initiates inflammatory cytokine release by activation of capsaicin and acid receptors in a human bronchial epithelial cell line

Recent experiments have shown that human bronchial epithelial cells (i.e., BEAS-2B) release pro-inflammatory cytokines (i.e., IL-6 and TNFalpha) in a receptor-mediated fashion in response to the neuropeptides, substance P (SP), calcitonin gene-related protein (CGRP), and the prototype botanical irritant capsaicin. In the present experiments, we examined the relevance of these receptors to particulate matter (PM)-associated cellular inflammation. BEAS-2B cells, exposed to residual oil fly ash particles (ROFA), responded with an immediate (<30 s) increase in intracellular calcium levels ([Ca2+]i), increases of key inflammatory cytokine transcripts (i.e., IL-6, IL-8, TNFalpha) within 2 h exposure, and subsequent release of IL-6 and IL-8 cytokine protein after 4 h exposure. Pretreatment of BEAS-2B cells with pharmacological antagonists selective for the SP or CGRP receptors reduced the ROFA-stimulated IL-6 cytokine production by approximately 25 and 50%, respectively. However, pretreatment of these cells with capsazepine (CPZ), an antagonist for capsaicin (i.e., vanilloid) receptors, inhibited the immediate increases in [Ca2+]i, diminished transcript (i.e., IL-6, IL-8, TNFalpha) levels and reduced IL-6 cytokine release to control levels. BEAS-2B cells exposed to ROFA in calcium-free media failed to demonstrate increases of [Ca2+]i and showed reduced levels of cytokine transcript (i.e., IL-6, IL-8, TNFalpha) and IL-6 release, suggesting that ROFA-stimulated cytokine formation was partially dependent on extracellular calcium sources. A final set of experiments compared the inflammatory properties of the soluble and acidic insoluble components of ROFA. BEAS-2B cells, exposed to ROFA or ROFA that had been filtered through a 0.2-micrometer pore filter, produced equivocal IL-6. BEAS-2B cells exposed to pH 5.0 media for 15 min released moderate amounts of IL-6, 4 h later. This cytokine release could be blocked by amiloride, a pH receptor antagonist, but not by CPZ. BEAS-2B cells, pretreated with amiloride before ROFA exposure, showed a partial (approximately 25%) reduction of IL-6. Together, these data indicate that the acidic, soluble components of ROFA initiate cytokine release in BEAS-2B cells through activation of both capsaicin- and pH-sensitive irritant receptors.

Airborne house dust elicits a local lymph node reaction and has an adjuvant effect on specific IgE production in the mouse

Indoor suspended particulate matter (SPM) consists of many different types of particles, the vast majority of which are less than 2.5 microm in diameter. An important question is how these particles, being inhalable, contribute to asthma and respiratory symptoms. One possibility is that these particles have an adjuvant effect on the immune response and increase the IgE production, or cause a non-specific irritation in the airways, contributing to bronchial hyper-responsiveness. In this study, the adjuvant activity of indoor SPM on the response to the model allergen ovalbumin (OA) in BALB/c mice was investigated, using the popliteal lymph node (PLN) assay. The adjuvant activity on the local lymph node response was determined by measuring the PLN weight, cell numbers and cell proliferation, and the adjuvant activity on the IgE production by measuring the levels of serum IgE specific to OA. SPM was found to give a significant PLN response, both when injected alone and together with OA. SPM was also found to enhance the production of specific IgE to OA when injected together with OA, after reinjection with OA, compared with immunisation with OA alone.

Effects of photochemical air pollution and allergen exposure on upper respiratory tract inflammation in asthmatics

Asthma is an inflammatory disease of the airways, and exacerbations of this disease have been associated with high levels of air pollution. The objective of this study was to examine whether ambient air pollution and/or allergen exposure induces inflammatory changes in the upper airways of asthmatics. Sixty patients with intermittent to severe persistent asthma visited the Hospital's Out Patient Clinic every 2 wk for a period of 3 mo, and on each visit a nasal lavage was obtained. Associations between nasal inflammatory parameters and seasonal allergens and/or air pollution exposures were analyzed using linear regression analysis. The study ran from July 3 to October 6, 1995, during which period ozone (8-h mean: 80 micrograms/m3) and PM10 (24-h mean: 40 micrograms/m3) were the major air pollutants; the major aeroallergen was mugwort pollen (24-h mean: 27 pollen grains/m3). Effects on both cellular and soluble markers in nasal lavage were demonstrated for both ozone and mugwort pollen, but not for PM10. Ambient ozone exposure was associated with an increase in neutrophils (112% per 100 micrograms/m3 increase in 8-h average ozone concentration), eosinophils (176%), epithelial cells (55%), IL-8 (22%), and eosinophil cationic protein (ECP) (19%). Increases in environmental mugwort pollen counts were associated with an increase in nasal eosinophils (107% per 100 pollen/m3) and ECP (23%), but not with neutrophils, epithelial cells, or lL-8. This study demonstrated that both ambient ozone and allergen exposure are associated with inflammatory responses in the upper airways of subjects with asthma, although the type of inflammation is qualitatively different.

Inhibition of airway inflammation in rDer f 2-sensitized mice by oral administration of recombinant der f 2

Recombinant Der f 2 (rDer f 2) is a promising new allergen expected to improve the diagnosis and immunotherapy of house dust mite allergy and to further immunological studies. To evaluate the hyposensitizing activity of rDer f 2 to mite allergy, we examined the effect of its oral administration on allergic inflammation in A/J mice immunized with mite allergens. A/J mice immunized with rDer f 2 alone or rDer f 2 + crude mite extract were orally given 0 (control), 0.01, 0.1, or 1 mg/day of rDer f 2 for 4 weeks, followed by an antigen inhalation challenge. Twenty-four hours after rDer f 2 inhalation, control animals experienced severe leukocyte influx into the airway. The infiltrating cells were mainly neutrophils, with some eosinophils and lymphocytes. The concentrations of IL4, IFNgamma, and soluble ICAM-1 in the bronchial alveolar lavage fluid increased twofold compared with values before rDer f 2 inhalation. In contrast, inflammation was significantly suppressed in mice given 1 mg/day of rDer f 2 orally for 4 weeks and partially suppressed in those fed 0.1 mg/day of the antigen. Plasma anti-rDer f 2 antibody levels were unchanged by oral rDer f 2 treatment. Mite extract inhalation challenge provoked neutophilia in rDer f 2 + mite-sensitized control mice, and this allergic reaction tended to decrease in sensitized mice fed 1 mg/day of rDer f 2 orally for 4 weeks. We conclude that rDer f 2 has hyposensitizing activities and may be useful in immunotherapy for house dust mite allergy.