Effects of Ozone Combined with Components of Acid Fogs on Breathing Pattern, Metabolic Rate, Pulmonary Surfactant Composition, and Lung Injury in Rats

Structure and stability studies of mixed monolayers of saturated and unsaturated phospholipids under low-level ozone

In the present study, stability and structure of single and binary mixed monolayers of an unsaturated phospholipid, DOPC, and a saturated phospholipid, DPPC-d75, on the water surface, were explored using the π-A isotherm, atomic force microscopy (AFM) and sum frequency generation (SFG) vibrational spectroscopy in various environments. Our results demonstrated that DOPC in the monolayers becomes unstable after the exposure to a low concentration of ozone (20 ± 10 ppb) or even to ambient laboratory air, which has a similar ozone level, but is stable in nitrogen or oxygen. DOPC can be selectively oxidized by a trace amount of ozone in the ambient environment but can be partially inhibited by the presence of DPPC in the monolayer. The present study provides useful information for understanding the physicochemical properties of the cell membranes.

Toxicity of chemical components of ambient fine particulate matter (PM 2.5) inhaled by aged rats

The toxicity of two important chemical components of fine ambient particulate matter (PM 2.5)-ammonium bisulfate (ABS) and elemental carbon (C)-was studied using aged (senescent) rats. The study tested the hypotheses that fine particle exposure can damage lungs and impair host defenses in aged rats and that ozone would potentiate the toxicity of these particles. Ammonium bisulfate aerosols were generated by nebulization of dilute aqueous solutions. Elemental carbon was generated from an aqueous suspension of carbon black. Carbon and ABS mixtures were generated by nebulization of a suspension of carbon black in a dilute aqueous solution of ABS. Rats were exposed, nose-only, for 4 h a day, three consecutive days a week, for 4 weeks. The rats were exposed to one of six atmospheres: (1) purified air; (2) C, 50 microg m(-3), 0.3 microm mass median aerodynamic diameter (MMAD); (3) ABS, 70 microg m(-3), 0.3 microm MMAD; (4) O3, 0.2 ppm; (5) ABS + C, 0.46 microm MMAD; and (6) ABS + C + O3, 0.45 microm MMAD. Data were analyzed using ANOVA and Tukey multiple comparison tests; a two-tailed significance level of 0.05 was used. The nuclei of lung epithelial and interstitial cells were examined to determine the labeling of the DNA of dividing cells by 5-bromo-2-deoxyuridine and to identify the location of injury-repair-related cell replication. Increased labeling of both epithelial and interstitial lung cells occurred following all pollutant exposures. Although epithelial cells are most likely impacted by inhaled particles first, the adjacent interstitial cells were the cells that showed the greatest degree of response. Exposure to the ABS + C + O3 mixture resulted in losses of lung collagen and increases in macrophage respiratory burst and phagocytic activities that were statistically significant. Our results demonstrate that ozone can increase the toxicity of inhaled particles (or vice versa), and suggest that detailed study of mixtures could provide a more comprehensive understanding of the mechanisms by which inhaled pollutants adversely affect human health.

Effect of air pollutants on the pulmonary surfactant system

Air pollutants have been recognized to influence the structure and function of the surfactant system. Agents that have received the most attention include ozone, nitrogen dioxide, hyperoxia, diesel exhaust, tobacco smoke, silica and fibrous materials such as asbestos. The deleterious effects of air pollutants on the surfactant system depend on the size of the agent, on its solubility in aqueous solutions and chemical reactivity and on its concentration and the duration of exposure. Hereby the following general rules apply: the smaller the agent's size and the less water soluble the pollutant is, the greater the tendency to reach the alveoli during breathing. In addition, the reactivity also determines the depth of penetration into alveoli. Compounds with high reactivity such as O3, which also fulfil the earlier rules, will react with the upper respiratory tract compared with compounds with slightly reduced reactivity, such as NO2, which will penetrate the alveoli. The common consequence of exposure to air pollutants is an accumulation of surfactant phospholipids and surfactant-specific proteins in the bronchoalveolar lavage fluid. These components also are structurally altered, mainly by oxidant gases, resulting in impairment of their biological activity. Thus, for surfactant phospholipids, there is impaired adsorption to the air-liquid interface due to oxidation of their fatty acids. Also, surfactant protein A, regarded as a modulator of the surfactant system, shows impaired functions after exposure to oxidants. It is likely that in addition to the effects described in this review not all effects are known because the molecular effects of several key components (e.g. SP-B and C) have not been well studied.

Ozone does not react with human erythrocyte membrane lipids

Ozone was applied to sealed red cell ghost membranes at the rate of 95 nmol/min for periods up to 20 min. Acetylcholine esterase, on the outer face of the membrane, was inhibited up to 20%. Glyceraldehyde-3-phosphate dehydrogenase, on the inner surface of the membrane, was inhibited up to 87%. These differences reflected the inherent susceptibilities of the two enzymes and the presence or absence of the membrane barrier. Analysis of the total lipids of the ozone-treated ghosts showed no significant change in the distribution of lipid classes and no significant change in the fatty acid composition. There was no significant change in the fatty acid composition of the phosphatidylcholine fraction. There was a slight increase in 18:0 and 20:2 + 20:3 in the phosphatidylethanolamine fraction. There was no change in the molecular species distribution of the phosphatidylcholine or the phosphatidylethanolamine fraction. There was no evidence for the formation of the phospholipid ozonolysis product, 1-acyl-2-(9-oxo-nonanyl) derivatives of glyceryl-phosphoryl choline. There was no decline in the amount of cholesterol in the lipids derived from ozone-treated red cell membranes. Treatment of red cell ghost membranes and, by implication, the plasma membrane of cells by ozone therefore oxidizes peripheral proteins before it oxidizes lipids.

Toxic oxidant species and their impact on the pulmonary surfactant system

In this review the effects of oxidant inhalation on the pulmonary surfactant system of laboratory animals are discussed. Oxidant lung injury is a complex phenomenon with many aspects. Inhaled oxidants interact primarily with the epithelial lining fluid (ELF), a thin layer covering the epithelial cells of the lung which contains surfactant and antioxidants. In the upper airways this layer is thick and contains high levels of antioxidants. Therefore oxidant injury in this area is rare and is more common in the lower airways where the ELF is thin and contains fewer antioxidants. In the ELF oxidants can react with antioxidants or biomolecules, resulting in inactivation of the biomolecules or in the formation of even more reactive agents. Oxidation of extracellular surfactant constituents may impair its function and affect breathing. Oxidized ELF constituents may promote inflammation and edema, which will impair the surfactant system further. Animal species differences in respiratory tract anatomy, ventilatory rate, and antioxidant levels influence susceptibility to oxidants. The oxidant exposure dose dictates injury, subsequent repair processes, and tolerance induction.

Assessment of toxicologic interactions resulting from acute inhalation exposure to sulfuric acid and ozone mixtures

Studies examining effects of air pollutants often use single compounds, while "real world" exposures are to more than one chemical. Thus, it is necessary to assess responses following inhalation of chemical mixtures. Rabbits were exposed for 3 hr to sulfuric acid aerosol at 0, 50, 75, or 125 micrograms/m3 in conjunction with ozone at 0, 0.1, 0.3, or 0.6 ppm, following which broncho-pulmonary lavage was performed. Various pulmonary response endpoints related to general cytotoxicity and macrophage function were examined. In addition, a goal of the study was to define an improved approach to the analysis of data sets involving binary pollutant mixtures. Results were evaluated using analysis of variance with multiple linear contrasts to determine the significance of any effect in the pollutant-exposed groups compared to sham control animals and to assess the type, and extent, of any toxicological interaction between acid and ozone. Interaction was considered to occur when the effects of combined exposure were either significantly greater or less than additive. Pollutant exposures had no effect on lavage fluid levels of lactate dehydrogenase, prostaglandins E2 and F2 alpha, nor on the numbers, viability, or types of immune cells recovered by lavage. Phagocytic activity of macrophages was depressed at the two highest acid levels and at all levels of ozone. Exposure to all mixtures showed significant antagonism. Superoxide production by stimulated macrophages was depressed by acid exposure at the two highest concentrations, while ozone alone had no effect. Significant antagonistic interaction was observed following exposure to mixtures of 75 or 125 micrograms/m3 acid with 0.1 or 0.3 ppm ozone. The activity of tumor necrosis factor elicited from stimulated macrophages was depressed by acid at 75 and 125 micrograms/m3 while ozone had no effect. Exposure to mixtures of 125 micrograms/m3 acid with 0.3 or 0.6 ppm ozone resulted in synergistic interaction. This study provided additional evidence for antagonism between two common air pollutants and demonstrated that the type of interaction between sulfuric acid and ozone depended upon the endpoint but that the magnitude of any interaction was not always related to the exposure concentrations of the constituent pollutants.

Long-term intermittent exposure to sulfuric acid aerosol, ozone, and their combination: alterations in tracheobronchial mucociliary clearance and epithelial secretory cells

Understanding the effects from long-term exposure to individual ambient air pollutants and mixtures of pollutants is necessary for adequate assessment of health risk. This study examined quantitative and temporal alterations in tracheobronchial mucociliary clearance function and bronchial epithelial secretory cells in rabbits exposed to sulfuric acid (125 micrograms/m3), ozone (0.1 ppm), and their combination for 2 h/d, 5 d/wk for up to 1 yr; some animals were allowed a 6-month post-exposure period. Clearance times were altered during exposure to sulfuric acid or to the mixture, and became progressively slower following the end of exposures to each of the pollutant atmospheres. There was no indication of any interaction in terms of clearance response between the acid and ozone in the group exposed to the mixture. Histological examination of intrapulmonary conducting airways was performed after 4, 8, or 12 months of exposure, and after the post-exposure period. Sulfuric acid resulted in an increase in the number of secretory cells in small airways by 12 months of exposure. Ozone and the mixture resulted in an increase in secretory cell number by 4 months, but the response became attenuated with continued exposure. There was evidence for synergistic interaction between ozone and acid at 4 months, and antagonistic interaction at subsequent times. No inflammation or other biologically significant histological effects were found in any of the animals.

Reactions of dinitrogen pentoxide and nitrogen dioxide with 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine

The reactions of gaseous dinitrogen pentoxide (N2O5) and nitrogen dioxide (NO2) with 1-palmitoyl-2-oleoyl-sn-glycerol-3-phosphocholine (POPC) coated on the inside surface of a glass reaction cell were studied at 298 K. Unsaturated phosphatidylcholines are significant components of pulmonary surfactant in the alveolar region of the lung and hence serve as a simple model to examine reactions of pulmonary surfactant with these oxidant air pollutants. Using high-performance liquid chromatography (HPLC), Fourier transform infrared and fast atom bombardment mass spectroscopy, the major products of reactions of POPC with N2O5 and NO2 were separated and identified. In the POPC-N2O5 reaction using either air or helium as a buffer gas, the nitronitrate, vinyl nitro and allylic nitro derivatives, as well as a small amount of the trans-isomer of the starting material, were obtained. The nature of the products obtained from the POPC-NO2 reaction depends on the concentration of NO2 as well as whether air is present. At low NO2 concentrations (PNO2/N2O4 less than or equal to 3.8 Torr) in air or in helium, the trans-isomer of POPC was formed almost exclusively. At higher NO2 concentrations (PNO2/N2O4 greater than or equal to 20 Torr) in helium, the dinitro, vinyl nitro and nitro alcohol derivatives were formed. In the presence of air (or 24% 18O2 in helium), a nitronitrate and a dinitronitrate were additional products. Mechanisms for the formation of the observed products and implications for the inhalation of oxides of nitrogen are discussed.