Attenuation of ozone-induced airway permeability in rats by pretreatment with cyclophosphamide, FPL 55712, and indomethacin

Role of Macrophages in Acute Lung Injury and Chronic Fibrosis Induced by Pulmonary Toxicants

A diverse group of toxicants has been identified that cause injury to the lung including gases (eg, ozone, chlorine), particulates/aerosols (eg, diesel exhaust, fly ash, other combustion products, mustards, nanomaterials, silica, asbestos), chemotherapeutics (eg, bleomycin), and radiation. The pathologic response to these toxicants depends on the dose and duration of exposure and their physical/chemical properties. A common response to pulmonary toxicant exposure is an accumulation of proinflammatory/cytotoxic M1 macrophages at sites of tissue injury, followed by the appearance of anti-inflammatory/wound repair M2 macrophages. It is thought that the outcome of the pathogenic responses to toxicants depends on the balance in the activity of these macrophage subpopulations. Overactivation of either M1 or M2 macrophages leads to injury and disease pathogenesis. Thus, the very same macrophage-derived mediators, released in controlled amounts to destroy injurious materials and pathogens (eg, reactive oxygen species, reactive nitrogen species, proteases, tumor necrosis factor α) and initiate wound repair (eg, transforming growth factor β, connective tissue growth factor, vascular endothelial growth factor), can exacerbate acute lung injury and/or induce chronic disease such as fibrosis, chronic obstructive pulmonary disease, and asthma, when released in excess. This review focuses on the role of macrophage subsets in acute lung injury and chronic fibrosis. Understanding how these pathologies develop following exposure to toxicants, and the contribution of resident and inflammatory macrophages to disease pathogenesis may lead to the development of novel approaches for treating lung diseases.

Noncardiogenic pulmonary edema associated with ozone exposure in three kittens

CASE DESCRIPTION Three 21-week-old sexually intact female sibling domestic shorthair cats were brought to an emergency clinic because of signs of sudden respiratory distress that were noted by the owner after the cats had been confined for approximately 10 hours in a room with an operating ozone-generating air purifier. No other potential toxicant exposures were reported. CLINICAL FINDINGS On initial examination, the 3 cats were severely dyspneic and tachypneic. Pulmonary crackles were audible on thoracic auscultation. Thoracic radiography revealed a marked peribronchial, unstructured interstitial pulmonary pattern that coalesced to a patchy alveolar pattern, consistent with noncardiogenic pulmonary edema. TREATMENT AND OUTCOME A diuretic (furosemide, 2 mg/kg [0.9 mg/lb], IV) and bronchodilator (terbutaline sulfate, 0.01 mg/kg [0.005 mg/lb], IM) were administered, and supplemental oxygen was provided by placing the cats in an oxygen cage at 80% oxygen saturation. By 24 hours after placement in the oxygen cage, all cats had unremarkable respiratory rates and thoracic auscultation findings. Complete resolution of the respiratory signs and radiographic pulmonary lesions was achieved within 48 to 72 hours after initial evaluation. At a recheck examination performed 3 months after initial evaluation, the cats remained free of respiratory signs, and no radiographic pulmonary lesions were detected. CLINICAL RELEVANCE To the authors' knowledge, this was the first reported case of pulmonary toxicosis believed to have been caused by ozone exposure in cats. Associated respiratory signs were successfully and rapidly reversed following oxygen supplementation and medical treatment.

Environmental risk factors for acute respiratory distress syndrome

Acute respiratory distress syndrome (ARDS) remains a major cause of morbidity and mortality in critically ill patients. Over the past several decades, alcohol abuse and cigarette smoke exposure have been identified as risk factors for the development of ARDS. The mechanisms underlying these relationships are complex and remain under investigation but are thought to involve pulmonary immune impairment and alveolar epithelial and endothelial dysfunction. This review summarizes the epidemiologic data supporting links between these exposures and ARDS susceptibility and outcomes and highlights key mechanistic investigations that provide insight into the pathways by which each exposure is linked to ARDS.

Macrophages and tissue injury: agents of defense or destruction?

The past several years have seen the accumulation of evidence demonstrating that tissue injury induced by diverse toxicants is due not only to their direct effects on target tissues but also indirectly to the actions of resident and infiltrating macrophages. These cells release an array of mediators with cytotoxic, pro- and anti-inflammatory, angiogenic, fibrogenic, and mitogenic activity, which function to fight infections, limit tissue injury, and promote wound healing. However, following exposure to toxicants, macrophages can become hyperresponsive, resulting in uncontrolled or dysregulated release of mediators that exacerbate acute tissue injury and/or promote the development of chronic diseases such as fibrosis and cancer. Evidence suggests that the diverse activity of macrophages is mediated by distinct subpopulations that develop in response to signals within their microenvironment. Understanding the precise roles of these different macrophage populations in the pathogenic response to toxicants is key to designing effective treatments for minimizing tissue damage and chronic disease and for facilitating wound repair.

Permeability, inflammation and oxidant status in airspace epithelium exposed to ozone

The aim of the study was to investigate possible mechanisms of epithelial injury in normal subjects exposed to environmentally relevant concentrations of ozone. Fifteen healthy non-smoking subjects (M:F 12:3) were studied. Five of the 15 subjects were exposed to filtered air, six were exposed to ozone 100 parts per billion (ppb) and seven were exposed to ozone 400 ppb with 99mtechnetium labelled diethylene-triamine-penta-acetate (99mTc-DTPA) or bronchoalveolar lavage (BAL) performed 1 or 6 h after exposure as indicated above. All the above studies were performed on different occasions at least 5 days apart. The subjects were exposed on each occasion for 1h during intermittent exercise at a ventilation of 40l min-1. 99mTc-DTPA lung clearance did not change after either level of ozone exposure, but neutrophils increased in BAL 6 h after exposure to 400 ppb. Superoxide anion release from mixed BAL leucocytes decreased 1 h after 100 ppb and 6 h after 400 ppb. Products of lipid peroxidation in epithelial lining fluid decreased both 1 and 6 h after 400 ppb. There was no change in anti-oxidant capacity or glutathione concentrations. Ozone exposure did not increase epithelial permeability, but was associated with neutrophil influx into the airspaces, without evidence of increased oxidative stress.

Inflammatory cell availability affects ozone-induced lung damage

Identifying whether or not neutrophils have a role to play in the early stages of acute lung epithelial injury brought about by inhalation of reactive substances continues to be a major area of investigation. In this study, the availability of circulating neutrophils was manipulated by treatment with either cyclophosphamide or rabbit antiserum against rat neutrophils, prior to exposures to air, a single high ozone exposure of 1 or 2 ppm for 3 h, or a continuous exposure to 0.8-1.0 ppm for up to 48 h. Although cyclophosphamide treatment resulted in undetectable levels of neutrophils in the blood, the recovery of tissue marginated-interstitial neutrophils of 1 x 10(6) cells by collagenase tissue digestion was not significantly diminished at the onset of air and ozone exposures. Cyclophosphamide treatment alone did not cause any permeability damage to air-exposed rat lungs, but did ameliorate ozone-induced increases in bronchoalveolar lavage (BAL) neutrophil and albumin recoveries after both short-term and 1 d of continuous ozone exposure. In contrast to cyclophosphamide, antiserum treatment resulted in greater than a 90% decrease in neutrophil recoveries from both blood and lung tissue at the onset of air and ozone exposures. Antiserum treatment also abrogated ozone-induced neutrophil accumulations in lung lavageable spaces following both single and continuous ozone exposures, but did not significantly affect ozone-associated lung permeability damage indicated by unaltered BAL fluid albumin recoveries. These data demonstrated that under experimental conditions when neutrophils remain within lung tissue marginated and interstitial pools, reduction in circulating blood neutrophil availability is associated with a concomitant decrease in ozone-induced lung damage.

Clara cell specific protein (CC16) expression after acute lung inflammation induced by intratracheal lipopolysaccharide administration

Clara cell secretory protein (CC16, CC10, or CCSP), the major secretory protein of the Clara cell, presents several biologic properties, suggesting that it may play a protective role against intrapulmonary inflammatory processes. The aim of the present study was to investigate the changes of CC16 concentrations in the lung, bronchoalveolar lavage fluid (BALF), and serum of rats with acute lung injury induced by lipopolysaccharide (LPS). These changes were compared with Clara cell density, CC16 mRNA level in the lung and classic indices of inflammation in BALF. Injected at doses of 10, 100, or 200 microgram/100 g body weight, LPS induced an acute lung inflammation as estimated by an increased influx of cells and albumin in the BALF. This inflammatory response was associated with a marked reduction of CC16 concentrations in BALF and lung homogenate as well as of the CC16 mRNA levels in the lung. At the highest dose of LPS, the CC16-positive cell density in the bronchiolar epithelium was also decreased. In serum, by contrast, the concentration of CC16 was elevated as a consequence of increased airway permeability. Pretreating rats intraperitoneally with dexamethasone (2 mg/kg) significantly lowered the leukocyte influx and attenuated the albumin increase in BALF. Dexamethasone, however, failed to prevent the increased airway permeability to CC16, suggesting that during inflammation different mechanisms regulate the leakage of proteins across the alveolocapillary barrier depending on the direction of passage and/or the size of the protein. Our results show a marked decrease of the secretion and synthesis of CC16 during LPS-induced acute lung inflammation.

Attenuation of ozone-induced lung injury by interleukin-10

Ozone (O3), an oxidant air pollutant, is capable of producing pulmonary inflammation and injury. Exposure to O3 results in the release of inflammatory cytokines including tumor necrosis factor-alpha (TNF-alpha) and interleukin-1 (IL-1) by alveolar macrophages. In addition, O3 exposure results in an increased expression of the inducible isoform of nitric oxide synthetase (iNOS). Interleukin-10 (IL-10) is an anti-inflammatory cytokine which inhibits the synthesis of TNF-alpha and IL-1 by macrophages and decreases the expression of iNOS. To test the protective properties of IL-10 in vivo, on the pulmonary injury induced by O3 exposure, we intratracheally instilled rat recombinant IL-10 1 h prior to O3 exposure (0.8 ppm x 3 h). Approximately 10-12 h following exposure, the animals were sacrificed and the bronchoalveolar lavage fluid (BALF) collected. The quantification of albumin, protein and fibronectin in the BALF provided a means of assessing pulmonary injury while the analysis of the BALF cells reflected the inflammatory response. Ozone exposure resulted in a significant (P<0.05) increase in BALF albumin, protein and fibronectin content as compared to air-exposed controls. In addition, significant increases in the percentage of BALF polymorphonuclear leukocytes (PMNs) and tissue expression of fibronectin mRNA were observed. The intratracheal instillation of IL-10 prior to O3 exposure resulted in a significant reduction in BALF albumin, protein and fibronectin content, and lung fibronectin mRNA as compared to O3 exposure alone. The data shows that IL-10, when given intratracheally, significantly reduces the pulmonary injury following O3 exposure in the rat. However, since the PMNs and the levels of albumin, protein and fibronectin in the IL-10 treated group did not reach baseline values, we conclude that other mediators of inflammation and injury not regulated by IL-10 also contribute to the pathophysiology of O3-induced lung injury.

Mechanism of pyocyanin- and 1-hydroxyphenazine-induced lung neutrophilia in sheep airways

Pyocyanin (Pyo) and 1-hydroxyphenazine (1-HP) are extracellular products of Pseudomonas aeruginosa. To test whether these products were capable of producing an inflammatory response in the airways, combinations of Pyo and 1-HP at concentrations of 10(-4) and 10(-5) M were instilled into sheep airways, and indexes of inflammation were assessed by bronchoalveolar lavage (BAL) 24 h later. Challenge with the phenazines caused a significant dose-dependent increase in the number of cells and neutrophils recovered by BAL. Control challenges produced no such changes. The lung neutrophilia was accompanied by an increased concentration of albumin in BAL. The increases in BAL neutrophils and albumin could be blocked by treating the sheep with the 5-lipoxygenase inhibitor zileuton. Neither 1-HP nor Pyo was chemotactic to neutrophils when tested in vitro, but when alveolar macrophages (AM) were cultured in vitro in the presence of both Pyo and 1-HP (1 microM), the supernatants caused neutrophil chemotaxis. Analysis of AM culture supernatants incubated with the combination of pigments showed significant increases in leukotriene B4 and interleukin-8, and blocking these mediators separately or together reduced AM supernatant-induced neutrophil chemotaxis. We conclude that local instillation of Pyo and 1-HP can initiate an inflammatory response in the airways of sheep in vivo. This effect can be explained, in part, by the release of chemotactic factors produced by AM.

The influence of polymorphonuclear leukocytes on altered pulmonary epithelial permeability during ozone exposure

Ozone (O3), a pulmonary irritant, and a major toxic component of photochemical smog, is capable of inducing pulmonary inflammation characterized by recruitment of polymorphonuclear leukocytes (PMNs) into the lung. The recruited PMNs, in turn, can release toxic mediators and produce lung injury. The mechanism of ozone-induced changes in lung permeability remains unknown. It is our hypothesis that PMNs migrating into the lung play a significant role in the pathophysiology following O3 exposure and that increasing the number of PMNs coming into the lung will exaggerate the changes in lung permeability. To test this hypothesis, we induced an influx of PMNs into the lungs of Sprague-Dawley rats by intratracheal instillation of 1% rabbit serum and then exposed the animals to either 0.8 ppm O3 or filtered air for 3 h. Control animals were intratracheally instilled with phosphate-buffered saline (PBS) and simultaneously exposed to O3 or filtered air in the same manner as the serum-treated animals. The animals were sacrificed and the lungs lavaged 10-12 h after exposure. The bronchoalveolar lavage fluid (BALF) was analyzed for albumin and protein, as indicators of permeability. In addition, BALF from the various groups was tested for its ability to alter epithelial resistance of pulmonary type II cells in culture. O3 exposure resulted in a significant increase in albumin and protein levels in the BALF as compared to air-exposed controls. The instillation of serum resulted in a significant increase in airway PMNs, but no significant elevations in albumin levels in both the O3 and air-exposed groups, as compared to PBS instillation. In vitro studies did not reveal a differential BALF effect on epithelial resistance. The data demonstrate that an excessive neutrophilia in the lung is not matched by a comparable amplification of epithelial injury. It is therefore suggested that a simple elevation in PMN number in the air spaces, as that induced by serum instillation, does not necessarily augment the lung pathophysiology, but that a more complex interaction with O3 may be required for cellular activation and release of toxic products.

Lipopolysaccharide-induced alveolar epithelial permeability: the role of nitric oxide

Intratracheal instillation of lipopolysaccharide (LPS) in the rat has been used as a model of acute lung inflammation. Among the early events in this process is a transient increase in airspace epithelial permeability which peaks 4 h after intratracheal instillation of LPS. The increased epithelial permeability is concomitant with the influx of neutrophils into the airspaces, peaking 8 h postinstillation. We have investigated the mechanism of this LPS-induced increase in epithelial permeability. The role of the neutrophil in LPS-induced epithelial permeability was assessed by pretreatment with neutrophil antibody to abolish neutrophil influx, which did not affect the increase in epithelial permeability. Because LPS instillation also induced increased tumor necrosis factor alpha (TNF-alpha) activity in bronchoalveolar lavage (BAL) fluid, and its release by cultured BAL leukocytes from treated animals, TNF-alpha antibody was coinstilled intratracheally with LPS in rats. TNF-alpha antibody eliminated TNF-alpha activity in BAL fluid, but had no effect on LPS-induced increased epithelial permeability. Increased levels of nitric oxide (NO), measured as nitrite, were also present in BAL fluid from LPS-treated rat lungs and LPS-elicited BAL leukocytes produced increased NO in culture. Treatment of rats with the specific NO synthase inhibitor L-NMMA significantly diminished the LPS-induced increased epithelial permeability. These data suggest that NO is involved in LPS-induced changes in epithelial integrity. However, other mechanisms should be evoked in addition to NO to explain completely the increased epithelial permeability produced by LPS.

Effect of beta 2-agonists on histamine-induced airway microvascular leakage in ozone-exposed guinea pigs

beta 2-adrenergic agonists exhibit antipermeability effects in the airways. However, it is not known whether beta 2-agonists have this beneficial effect in airway mucosa that is already inflamed. We evaluated the effects of two inhaled beta 2-agonists, salbutamol and formoterol, on the histamine-induced bronchoconstriction and plasma extravasation in the airways of guinea pigs with or without ozone exposure. Total pulmonary resistance (RL) was measured before and after histamine inhalation in anesthetized animals that were pretreated with inhaled salbutamol, formoterol, or saline. Plasma extravasation in the airways was measured using Evans blue dye. In the control animals not exposed to ozone, salbutamol and formoterol each significantly reduced both the histamine-induced bronchoconstriction and the plasma extravasation in the trachea and main bronchi. In the ozone-exposed animals, the increase in RL after histamine was greater than that in control animals. Salbutamol and formoterol each significantly reduced histamine-induced bronchoconstriction, even in the ozone-exposed animals. Salbutamol did not affect the histamine-induced plasma extravasation, whereas formoterol reduced the plasma extravasation in the main bronchi, but not in the trachea, of the animals exposed to ozone. These results suggest that the anti-inflammatory properties of formoterol in inflamed airways may contribute to the beneficial effects in the treatment of airway inflammation.

Rat lung phospholipid fatty acid composition in prepregnant, pregnant, and lactating rats: relationship to ozone-induced pulmonary toxicity

Our laboratory has demonstrated recently that pulmonary inflammation induced by acute ozone exposure is much more severe in late stage pregnant and lactating rats than in postlactating rats or age-matched virgin females. It is currently widely believed that such pulmonary damage results, at least in part, from the reaction of ozone at sites of unsaturation in phospholipid fatty acid (PLFA) molecules located in the epithelial fluid layer lining the lung surfaces and/or the plasma membranes of epithelial cells underlying this fluid layer. The objective of this study was to compare the PLFA composition of lung tissue and surfactant from ozone-sensitive late stage pregnant and lactating rats with comparable tissue from relatively ozone-insensitive age-matched prepregnant (virgin female) rats to explore the possibility that changes in lung PLFA composition during pregnancy and/or lactation contribute to the enhanced sensitivity of these physiologic states to ozone. In addition, the correlation of changes in plasma PLFA composition with those in lung was investigated. There were minor differences in the composition of lung tissue and surfactant PLFAs between prepregnant rats and pregnant rats at day 17 of gestation and only slightly greater differences between prepregnant and lactating rats. Changes from the prepregnant state in the PLFA composition of lung tissue, but not surfactant, correlated with changes in the plasma only in lactating rats and not in pregnant rats. Overall, the double bond index of PLFAs in surfactant and lung tissue was decreased in pregnant and lactating rats compared with prepregnant rats. Thus, the increased sensitivity of pregnant and lactating rats to ozone-induced lung injury cannot be attributed to an increased availability of unsaturated fatty acids. In addition, the arachidonic acid composition of phospholipids did not appear to explain differences between prepregnant rats and pregnant or lactating rats in their inflammatory response to ozone. In conclusion, there is no evidence that the relatively minor changes in lung tissue PLFA composition which occur during pregnancy and lactation predispose rats in these physiologic states to ozone-induced pulmonary toxicity.

Alteration of alveolar macrophage chemotaxis, cell adhesion, and cell adhesion molecules following ozone exposure of rats

Ozone (O3) exposure of humans and animals induces an inflammatory response in the lung, which is associated with macrophage stimulation, release of chemotactic agents, and recruitment of polymorphonuclear leukocytes (PMNs). This study was designed to investigate the functional aspects of the macrophages that impact inflammatory processes in the lung. Macrophages recovered by bronchoalveolar lavage (BAL) from rats exposed to purified air or 0.8 ppm O3 were studied for their chemotactic activity, adhesive interactions with alveolar epithelial cells in culture, surface morphology, and surface expression of cell adhesion molecules. The macrophages isolated from O3-exposed rats exhibited a greater motility in response to a chemotactic stimulus than the macrophages isolated from rats exposed to purified air. The macrophages from O3-exposed animals also displayed greater adhesion when placed in culture with epithelial cells isolated from adult rat lung (ARL-14) than the macrophages from control rats. Both chemotactic motility and cell adhesion stimulated by O3 exposure were attenuated when the macrophages were incubated in the presence of monoclonal antibodies to leukocyte adhesion molecules, CD11b, or epithelial cell adhesion molecules, ICAM-1. Flow cytometry revealed a modest increase in the surface expression of CD11b but no change in ICAM-1 expression in macrophages from O3-exposed rats when compared to those from the air-exposed controls. The results demonstrate an alteration of macrophage functions following O3 exposure and suggest the dependence of these functions on the biologic characteristics, rather than the absolute expression, of the cell adhesion molecules.

Modification of macrophage adhesion by ozone: role of cytokines and cell adhesion molecules

The inflammatory response in the lungs following an inhalation exposure of animals and humans to ozone (O3) is associated with macrophage stimulation, release of chemotactic agents, and neutrophilia. This study investigated the adhesive behavior of the alveolar macrophages and its relevance to the inflammatory processes in the lung. Macrophages recovered by BAL from rats exposed to purified air or 0.8 ppm O3 were studied in vitro for their adhesion to epithelial cells derived from ARL-14. The macrophages from O3-exposed animals displayed greater adhesion to the epithelial cells than the macrophages from control rats exposed to purified air. The O3-induced adhesion was attenuated in the macrophages treated with a combination of interleukin-1 alpha and tumor necrosis factor-alpha antibodies (anti-IL-1+anti-TNF). The cell adhesion stimulated by O3 exposure was also attenuated when the macrophages were incubated in the presence of antibodies to leukocyte adhesion molecules, CD11b, or epithelial cell adhesion molecules, ICAM-1. A marginal increase in the surface expression of CD11b was noticed in macrophages from the rats exposed to O3. A similar change in the ICAM-1 expression was, however, not observed. The results suggest that the O3-induced modifications of macrophages are mediated by IL-1 and TNF, and that these modifications are accompanied by a minimal change in the expression of the cell-adhesion molecules.

Mechanisms of cigarette smoke induced increased airspace permeability

BACKGROUND

Increased epithelial permeability of the airspaces occurs commonly in the lungs of cigarette smokers. It is likely to be important in augmenting the inflammatory response in the airspaces and hence may have a role in the pathogenesis of emphysema. It has previously been shown that intratracheal instillation of cigarette smoke condensate induces increased epithelial permeability in vivo in rats and in vitro in epithelial cell monolayers, associated with a disturbance in the lung antioxidant, glutathione (GSH). The aim of this study was to assess the role of neutrophils, GSH, and tumour necrosis factor (TNF) in the increased epithelial permeability following intratracheal instillation of cigarette smoke condensate.

METHODS

Epithelial permeability of the airspaces was measured in rat lungs as the passage of intratracheally instilled 125-iodine labelled bovine serum albumin (BSA) into the blood. The permeability of a monolayer of human type II alveolar epithelial cells to 125I-BSA was also measured.

RESULTS

Cigarette smoke condensate produced a 59.7% increase in epithelial permeability over control values peaking six hours after instillation and returning to control values by 24 hours. Depletion of neutrophils and, to a lesser extent, macrophages by an intraperitoneal injection of antineutrophil antibody did not influence the increased epithelial permeability induced by cigarette smoke condensate. Although instillation of human recombinant TNF alpha produced an increase in epithelial permeability in the rat lung from 0.62 (0.61)% to 1.27 (0.08)%, only a trivial amount of TNF alpha was detected in bronchoalveolar lavage (BAL) fluid in vivo or in culture medium from BAL leucocytes obtained from animals treated with cigarette smoke condensate (94.9 (28.8) units/ml). Furthermore, antiTNF antibody did not abolish the increased epithelial permeability produced by cigarette smoke condensate. The role of GSH was assessed by measuring the changes in both the reduced (GSH) and oxidised form (GSSG) in lung tissue and in BAL fluid. One hour after instillation of cigarette smoke condensate there was a marked fall in the GSH content in the lung (from 809.8 (31.8) to 501.7 (40.5) nmol/g) in association with increased GSSG levels (from 89.8 (2.7) to 148.7 (48.8) nmol/g). This was followed by a return of GSH levels to control values, with a concomitant decrease in GSSG levels six hours after instillation. GSH levels in BAL fluid fell dramatically following cigarette smoke condensate (from 2.56 (0.30) to 0.31 (0.21) nmol/ml) and this fall was sustained up to six hours after instillation of cigarette smoke condensate.

CONCLUSIONS

These studies suggest that neutrophils and TNF do not have a major role in the increased epithelial permeability induced by cigarette smoke condensate. However, the data support a role for the depletion of the antioxidant glutathione in the increased epithelial permeability caused by cigarette smoke condensate.

Ozone-induced human respiratory dysfunction and disease

Exercising volunteers exposed in chambers to as little as 80 ppb O3 for several hours exhibit impaired lung function and irritative lower airway symptoms. Comparable changes occur among children and young adults exposed to summer smog containing O3. Intensity of the response is reproducible but varies widely among individuals. The (reversible) decrements in vital capacity are due to involuntary inhibition of deep inspiration probably mediated by nociceptive bronchial C-fibers that may be stimulated by local prostaglandin release, and can be modulated by appropriate pharmacologic agents. A second characteristic response to low O3 levels is mucosal neutrophilic inflammation probably mediated by phospholipid-derived products and by epithelial cell-derived chemokines and cytokines, but poorly correlated with lung function changes. Fluctuations in ambient O3 levels are associated with acute respiratory health effects in exposed populations but concomitant acid aerosol pollution is an important confounder. Whether irreversible impairment of lung function occurs among residents of chronically high ozone-pollution areas is debated.

The toxicity of air pollution in experimental animals and humans: the role of oxidative stress

Nitrogen dioxide (NO2) and ozone (O3) occur throughout the world as the primary pollutants of urban air. NO2 and O3 oxidize cell membrane lipids and proteins. Inflammatory agents are elaborated from the lung either as a direct result of oxidation or as a consequence of leukocytes recruited into the lung by injury. My hypothesis is that NO2 and O3 initiate or exacerbate chronic lung disease through an inflammatory mechanism which can be reduced by supplementation with greater amounts than those required to alleviate vitamin deficiency symptoms of vitamins C (ascorbic acid) and E (alpha-tocopherol). Children, whose lungs are developing, are the most likely group to benefit from supplementation with vitamins C and E because the adverse effects of inflammation on the developing lung are likely to be greater and the time of exposure is longer than in adults. This hypothesis is in accord with current human and experimental animal data and the chemistry of O3 and NO2 toxicity, and is supported by recent ecological epidemiological studies of persons supplementing their intake of vitamins C and E.