Effects of inhaled acids on lung biochemistry

Effects of respirable aerosols of sulfuric acid, ammonium sulfate, sodium sulfite, and ammonium persulfate on lungs of rats are reviewed. The literature regarding interactions between ozone or nitrogen dioxide and acidic aerosols (ammonium sulfate, sulfuric acid) is discussed. An unexpected interaction between nitrogen dioxide and sodium chloride aerosol is also discussed. An attempt is made to identify bases for prediction of how and when acid aerosols might potentiate effects of inhaled gases.

Changes in pulmonary lavage fluid of guinea pigs exposed to ultrafine zinc oxide with adsorbed sulfuric acid

Ultrafine metal oxide particles (diameters less than 0.1 microns) and sulfur dioxide are important products of coal combustion. Interaction of these products in the effluent stream results in formation of ultrafine particles with adsorbed sulfur compounds, including sulfuric acid. The toxicity of ultrafine zinc oxide particles with adsorbed sulfuric acid was evaluated by comparing pulmonary lavage fluid from guinea pigs exposed for 1, 2, 3, 4, or 5 consecutive daily 3-h periods to ultrafine zinc oxide generated in the presence of sulfur dioxide (ZnO + SO2) to pulmonary lavage fluid from guinea pigs exposed to an equivalent concentration of ultrafine ZnO. Two groups of guinea pigs exposed either to SO2 or to particle-free furnace gas served as additional controls. Cells, protein, and activities of lactate dehydrogenase, acid phosphatase, and alkaline phosphatase were increased in lavage fluid obtained from guinea pigs exposed to ZnO + SO2 as compared to guinea pigs exposed to ZnO. These results demonstrate the potential importance of ultrafine metal oxides as carries of sulfuric acid derived from fossil fuel combustion.

Health effects of acid aerosols formed by atmospheric mixtures

Under ambient conditions, sulfur and nitrogen oxides can react with photochemical products and airborne particles to form acidic vapors and aerosols. Inhalation toxicological studies were conducted, exposing laboratory animals, at rest and during exercise, to multicomponent atmospheric mixtures under conditions favorable to the formation of acidic reaction products. Effects of acid and ozone mixtures on early and late clearance of insoluble radioactive particles in the lungs of rats appeared to be dominated by the oxidant component (i.e., the mixture did cause effects that were significantly different from those of ozone alone). Histopathological evaluations showed that sulfuric acid particles alone did not cause inflammatory responses in centriacinar units of rat lung parenchyma (expressed in terms of percent lesion area) but did cause significant damage (cell killing followed by a wave of cell replication) in nasal respiratory epithelium, as measured by uptake of tritiated thymidine in the DNA of replicating cells. Mixtures of ozone and nitrogen dioxide, which form nitric acid, caused significant inflammatory responses in lung parenchyma (in excess of effects seen in rats exposed to ozone alone), but did not damage nasal epithelium. Mixtures containing acidic sulfate particles, ozone, and nitrogen dioxide damaged both lung parenchyma and nasal epithelia. In rats exposed at rest, the response of the lung appeared to be dominated by the oxidant gas-phase components, while responses in the nose were dominated by the acidic particles. In rats exposed at exercise, however, mixtures of ozone and sulfuric acid particles significantly (2.5-fold) elevated the degree of lung lesion formation over that seen in rats exposed to ozone alone under an identical exercise protocol.

Synergistic interaction of ozone and respirable aerosols on rat lungs. IV. Protection by quenchers of reactive oxygen species

In previous studies we have shown interactions between ozone and acidic respirable aerosols as evaluated by sensitive biochemical and quantitative morphological endpoints. In the present paper we have attempted to test the hypothesis that active oxygen species might play a role in lung damage caused by ozone +/- sulfuric acid aerosol. Rats were administered various scavengers of active oxygen species via the intraperitoneal (i.p.) route before and during exposure to 0.12, 0.20, or 0.64 ppm of ozone +/- 0.04, 0.1, 0.2, 0.5, or 1.0 mg/m3 of sulfuric acid aerosol. Vitamin E, a lipid-soluble free radical scavenger, beta-carotene (the precursor of vitamin A), a singlet oxygen scavenger, and dimethylthiourea, a hydrogen peroxide scavenger, were tested. Dimethylthiourea at doses of 50-500 mg/kg per day was able to protect rats from the effects of ozone, suggesting a role for hydrogen peroxide in ozone-induced lung damage in vivo. Neither vitamin E nor beta-carotene at 100 mg/kg doses had any protective activity in our experiments, despite documentation of increased lung content of the scavengers in animals receiving these agents. These results suggest that water solubility may play a role in the efficacy of the scavenging agents under our exposure protocols. We conclude that: (1) hydrogen peroxide may be involved in ozone-induced lung damage; and (2) that lung injury by ozone and by ozone + sulfuric acid aerosol may share common pathways.

Respiratory dose-response study of normal and asthmatic volunteers exposed to sulfuric acid aerosol in the sub-micrometer size range

Twenty-one healthy and 21 asthmatic volunteers were exposed to respirable sulfuric acid aerosol (mass median particle diameter approximately 0.9 micron, geometric standard deviation 2.5) in a chamber at 21 degrees and 50% relative humidity. Measured sulfuric acid concentrations averaged 0, 380, 1060, and 1520 micrograms/m3 (in the occupational range, higher than concentrations observed in ambient air pollution). Exposures to different concentrations occurred in randomized order 1 week apart. They lasted 1 hr and included three 10-min periods of heavy exercise. Healthy volunteers showed no statistically significant changes in pulmonary function, airway reactivity to inhaled methacholine, or overall reporting of irritant symptoms which could be attributed to acid exposure. They did show a slight statistically significant (P less than .01) increase in cough with increasing acid concentration. At the two highest acid concentrations, asthmatics showed significant increases in irritant symptoms and decrements in pulmonary function, without significant changes in airway reactivity. Their function decrements appeared to increase with time during exposure. Previous studies in fog (10 degrees, median particle diameter approximately 10 micron) with similar concentrations of sulfuric acid showed more symptoms but less pulmonary function change, perhaps reflecting different sites of particle deposition in airways and/or different degrees of neutralization by airway ammonia. This and earlier evidence predicts little, if any, acute irritant response in short-term (1 hr or less) exposures to sulfuric acid at concentrations found in ambient air pollution.

The induction of numerical chromosome aberrations in human lymphocyte cultures and V79 Chinese hamster cells by diethyl sulfate

Human lymphocyte cultures were treated with increasing concentrations of diethyl sulfate (DES) at different times after stimulation with phytohemagglutinin (0, 24 and 45 h) and were scored for numerical chromosomal aberrations at different culture times (52, 72 and 96 h). A total of 3500 metaphases were analyzed. A statistically significant (p less than 0.01) increase in hypodiploid and hyperdiploid metaphases was found throughout the tested dose range (0.1-3 mM DES); the increase in polyploid metaphases was statistically significant at 1 mM (p less than 0.05) and 3 mM (p less than 0.01) DES. In human lymphocytes treated in Go, DES also induced chromatid breaks as well as micronuclei. In V79 Chinese hamster cells, DES induced micronuclei and polyploidy.

Response of the tracheobronchial mucociliary clearance system to repeated irritant exposure: effect of sulfuric acid mist on function and structure

This study was designed to determine quantitative and temporal alterations in tracheobronchial mucociliary clearance function and structure due to repeated inhalation exposures to a common irritant, sulfuric acid mist. Rabbits were exposed to 250 micrograms/m3 sulfuric acid (0.3 micron) for 1 h/day, 5 days/week, for up to 1 year, with some animals allowed a 3-month recovery period following the end of the acid exposures. Control animals received temperature- and humidity-conditioned water vapor. At intervals of 2 to 4 weeks, animals inhaled a radioactively tagged tracer aerosol (ferric oxide microspheres, 4.5 micron), and its clearance via mucociliary transport from the thorax was monitored by external serial counting. Clearance became slower during the first month of acid exposure, and this slowing became progressive with time through the end of the 12-month exposure period. After cessation of acid exposure, clearance became extremely slow and did not return to normal by the end of the follow-up period. To assess specific histological changes in the tracheobronchial tree, groups of rabbits were killed after 4, 8, or 12 months of exposure and after the follow-up period. Tissue samples from each lung were embedded in plastic, sectioned at 3 micron, and stained with hematoxylin and eosin or alcian blue/periodic acid-Schiff (AB/PAS). Acid exposure changed the airway diameter distribution compared to the control; except for the follow-up group, all acid-exposed animals had a shift to smaller airways. Acid inhalation also caused an increase in epithelial secretory cell density and a shift from PAS to AB staining of glycoprotein within secretory cells, both of which were unresolved by 3 months after the exposures ceased. No evidence of inflammation was found in any of the animals. Thus, repeated exposures to H2SO4 resulted in a slowing of mucociliary clearance that was associated with alterations in airway morphometry and morphology. Such changes may be involved in the early pathogenesis of chronic airway disease.

Acid rain: effects on arachidonic acid metabolism in perfused and ventilated guinea-pig lung

Isolated, perfused and ventilated guinea-pig lungs were exposed for 10 min to acid (sulphuric + nitric acid) aerosol mimicking acid rain at pH 4.5 or 2.5, as well as to a control distilled water aerosol (pH 6.0-6.5). Lung perfusing solution was recovered and thromboxane (TX) B2 and leukotriene (LT) B4 were measured by radioimmunoassay (RIA) techniques. In a series of experiments TXB2 release averaged 0.43 +/- 0.18 (+/- SD) ng/min during exposure to distilled water aerosol and increased to 0.70 +/- 0.30 ng/min during exposure to acid aerosol at pH 4.5 (P less than 0.05). In a second series of experiments TXB2 release was 0.46 +/- 0.18 ng/min and increased to 1.07 +/- 0.51 ng/min (P less than 0.01) after acid aerosol at pH 2.5. In both cases LTB4 release, reflecting lipoxygenase activity, was unchanged. LTC4 levels were not measurable under basal conditions as well as after exposure to acid aerosol. A pneumoconstriction was also observed, being more pronounced after acid aerosol at pH 2.5. Individual sulphuric and nitric acid aerosol component solutions at pH 2.5 evoked TXB2 and airway resistance changes corresponding to those observed with the mixed acid aerosol. LTB4 was not modified. Acid rain inhalation may directly stimulate pathways leading to the bronchoconstrictor and pro-aggregating TXA2 synthesis in isolated guinea-pig lung, without affecting the lipoxygenase pathway of arachidonic acid metabolism.

Long-term consequences of exposure to ozone. II. Structural alterations in lung collagen of monkeys

The effects of chronic exposure to ozone on lung collagen crosslinking were investigated in two groups of juvenile cynomolgus monkeys exposed to 0.61 ppm of ozone 8 hrs per day for 1 year. One group was killed immediately after the exposure period; the second exposed group breathed filtered air for 6 months after the ozone exposure before being killed. Previous studies of these monkeys had revealed that lung collagen content was increased in both exposed groups (J.A. Last et al., (1984). Toxicol. Appl. Pharmacol. 72, 111-118). In the present study specific collagen crosslinks were quantified in order to determine whether the excess collagen in the lungs of these animals was structurally normal or abnormal. In the group killed immediately after exposure, the difunctional crosslink dehydrodihydroxylysinonorleucine (DHLNL) was elevated, as was the ratio of DHLNL to dehydrohydroxylysinonorleucine (HLNL). Lung content of the mature nonreducible crosslink hydroxypyridinium was also increased in this group. In the group killed after a 6-month postexposure period, lung content of the difunctional crosslinks DHLNL and HLNL was indistinguishable from control values. However, lung hydroxypyridinium content was significantly increased. The changes in collagen crosslinking observed in the group killed at the termination of exposure are characteristic of those seen in lung tissue in the acute stage of experimental pulmonary fibrosis. The changes seen in the postexposure group suggest that while the lung collagen being synthesized at the time the animals were killed was apparently normal, "abnormal" collagen synthesized during the period of ozone exposure was irreversibly deposited in the lungs. This study suggests that long-term exposure to relatively low levels of ozone may cause irreversible changes in lung collagen structure.

Intermittent exposures to mixed atmospheres of nitrogen dioxide and sulfuric acid: effect on particle clearance from the respiratory region of rabbit lungs

Nitrogen dioxide (NO2) and sulfuric acid (H2SO4) are important constituents of the gas-particle complex in ambient air. The purpose of this study was to examine the effects of combined exposures upon the clearance of insoluble tracer particles from the respiratory region of the lungs. Rabbits were the animal model, and were exposed for 2 h/day for 14 days to either 0.3 ppm NO2, 1 ppm NO2, or 500 microgram/m3 H2SO4 alone, or to mixtures of the low and high NO2 concentrations with acid. Inhaled singly, both concentrations of NO2 accelerated clearance while H2SO4 retarded it, compared to control. Exposure to the combination of 0.3 ppm NO2 plus H2SO4 resulted in a response which was not different from that due to the acid alone. However, exposure to 1 ppm NO2 plus H2SO4 resulted in a clearance pattern which differed from that of both NO2 and H2SO4, but was more similar to that of the latter.

The role of titratable acidity in acid aerosol-induced bronchoconstriction

We evaluated the importance of pH, titratable acidity, and specific chemical composition in acid aerosol-induced bronchoconstriction in 8 asthmatic subjects. We administered aerosols of HCl and H2SO4 at pH 2.0 in an unbuffered state and buffered with glycine. The buffered acids were given in order of increasing titratable acidity (defined as the number of ml of 1 N NaOH required to neutralize 100 ml of acid solution to pH 7.0). Each set of buffered or unbuffered acid aerosols was given on a separate day and each aerosol was inhaled through a mouthpiece during 3 min of tidal breathing. Bronchoconstriction was assessed by measurement of specific airway resistance (SRaw) before and after inhalation of each aerosol. SRaw increased by more than 50% above baseline in 1 of 8 subjects after inhalation of unbuffered HCl and in no subjects after inhalation of unbuffered H2SO4, even at pH 2.0. In contrast, SRaw increased by greater than 50% in all 8 subjects after inhalation of HCl and glycine at pH 2.0 and 7 of 8 subjects after inhalation of H2SO4 and glycine at pH 2.0. The mean titratable acidity required to increase SRaw by 50% above baseline was calculated for each challenge by linear interpolation; these values for H2SO4 and glycine (5.1 ml of 1 N NaOH) and HCl and glycine (2.2 ml of 1 N NaOH) were slightly, but significantly, different (p = 0.01) and were considerably higher than the titratable acidity of the unbuffered acids at pH 2 (1.0 ml of 1 N NaOH).(ABSTRACT TRUNCATED AT 250 WORDS)

Functional assessment of rabbit alveolar macrophages following intermittent inhalation exposures to sulfuric acid mist

Sulfuric acid (H2SO4) aerosols are common in both ambient and occupational environments. This study examined the numbers and selected in vitro functional properties of alveolar macrophages recovered from rabbits undergoing inhalation exposure to 0.5 mg/m3 submicrometer (0.3 micron) H2SO4 for 2 hr/day. Bronchoalveolar lavage was performed on Days 3, 7, and 14 during the exposure period (specifically, 24 hr after either 2, 6, or 13 exposures). Total cell numbers and macrophage counts were increased on Day 3, but returned to control levels by Day 7; no change in polymorphonuclear leukocytes was observed at any time point. Macrophage substrate attachment was not affected by exposures to H2SO4, but random mobility was severely depressed at Days 7 and 14. The numbers of phagocytically active macrophages and the level of such activity were increased on Day 3, but became depressed by Day 14. These results demonstrate significant alterations in important functional properties of alveolar macrophages due to short-term intermittent exposures to H2SO4 aerosols; these changes have implications for the ability of the lungs to maintain adequate defense against deposited viable and nonviable particles.

Sulfuric acid-induced airway hyperresponsiveness

Rabbits were exposed to submicrometer sulfuric acid (H2SO4) mist at 250 micrograms/m3 for 1 hr/day, 5 days/week for 4, 8, or 12 months in order to examine the effects on bronchial responsiveness, which was assessed at the end of each exposure series by administration (iv) of doubling doses of acetylcholine and measurement of pulmonary resistance (RL). Dynamic compliance (Cdyn) and respiratory rate (f) were also measured following agonist challenge. Animals exposed for 4 months showed increased sensitivity to acetylcholine (dose required to produce a 150% increase in RL), and there was an increase in reactivity (slope of dose vs change in RL) by 8 months, with a leveling off of the response after this time. No changes in Cdyn or f were noted at any time. Thus, repeated exposures to H2SO4 resulted in the production of hyperresponsive airways in previously healthy animals. This has implications for the role of nonspecific irritants in the pathogenesis of airway disease.

A mammalian cell variant in which 3-aminobenzamide does not potentiate the cytotoxicity of dimethyl sulphate

Variants of mouse leukaemia L1210 cells have been isolated in which cytotoxicity to dimethyl sulphate is not fully potentiated by ADP-ribosyl transferase inhibitor 3-aminobenzamide, as occurs in normal L1210 cells. These variants were selected after mutagenesis by growing the cells in dimethyl sulphate and 3-aminobenzamide. The characterisation of one of these variants is described. Variant 3 cells repair low doses of DNA damage in the presence of ADP-ribosyl transferase inhibitors. The Vmax of the ADP-ribosyl transferase enzyme in these cells is only increased 35% compared to normal wild-type L1210 cells. The basal DNA ligase I activity is increased 66% above wild-type whereas DNA ligase II activity appears to be unchanged. The most striking observation, however, is that the DNA ligase II activity is not increased after dimethyl sulphate treatment as occurs in wild-type L1210 cells. It seems that by increasing DNA ligase I levels these cells can survive DNA damage in the presence of 3-aminobenzamide. This variant (mutant) provides genetic evidence for our previously published hypothesis that (ADP-ribose)n biosynthesis is required for efficient DNA repair after DNA damage by monofunctional alkylating agents, because ADP-ribosyl transferase activity regulates DNA ligase activity. This variant is the first mammalian cell reported in which DNA ligase activity is altered, as far as we are aware. In yeast, a DNA ligase mutant has a cell division cycle (cdc) phenotype. Presumably, DNA ligase is essential for DNA synthesis, repair and recombination. The present variant provides further evidence that in mammalian cells, DNA ligase II activity is related to ADP-ribosyl transferase activity.

Early alveolar clearance in rabbits intermittently exposed to sulfuric acid mist

During the course of 1-h/d, 5-d/wk exposure to submicrometer sulfuric acid mist at 250 micrograms/m3, rabbits were exposed to a radioactively tagged polystyrene latex tracer aerosol to assess clearance from the alveolar region during the period 2-14 d after tracer exposure. The latex was administered on d 1, 57, and 240 following the start of the H2SO4 exposures. Early alveolar clearance was found to be accelerated during the first test, and this acceleration was maintained throughout the 8-mo monitoring period.

Effects of ozone and sulfuric acid aerosol on gas trapping in the guinea pig lung

Four groups of 20 guinea pigs were sequentially exposed by inhalation to either air followed by sulfuric acid aerosol, ozone followed by sulfuric acid aerosol, ozone followed by air, or air followed by air to determine whether ozone preexposure sensitizes guinea pigs to the airway constrictive effects of sulfuric acid aerosol. All first exposures to ozone or air were 2 h in duration; all second exposures to sulfuric acid or air were for 1 h. All ozone and sulfuric acid exposures were 0.8 ppm and 12 mg/m3, respectively. Animals were observed for respiratory distress during exposure, and excised lungs were quantitated for trapped gas and wet/dry ratios. None of the guinea pigs developed dyspnea, and wet/dry ratios were not altered. Ozone significantly (p less than 0.05) increased trapped gas volumes, which were 44% (ozone-acid) to 68% (ozone-air) greater than in the air-air group. Trapped gas volume was 23% greater in the ozone-acid group than in the air-acid group, but the difference was not statistically significant (p less than 0.20). Thus, ozone increased gas trapping but did not significantly sensitize guinea pigs to the bronchoconstrictive action of sulfuric acid.

Potential risks to human respiratory health from "acid fog": evidence from experimental studies of volunteers

Observations of high acidity (pH as low as 1.7) in fogwater collected in polluted areas have provoked concern for public health. Effects of exposure to acidic pollutants have not been studied under foggy conditions; thus there is no directly relevant information from which to estimate the health risk. Indirectly relevant information is available from numerous studies of volunteers exposed to "acid fog precursors" under controlled conditions at less than 100% relative humidity. The effect of fog in modifying responses to inhaled acidic pollutants is difficult to predict: depending on circumstances, fog droplets might either increase or decrease the effective dose of pollutants to the lower respiratory tract. Fog inhalation per se may have unfavorable effects in some individuals. Sulfur dioxide is known to exacerbate airway constriction in exercising asthmatics, at exposure concentrations attainable in ambient air. Nitrogen dioxide has shown little untoward respiratory effect at ambient concentrations in most studies, although it has been suggested to increase bronchial reactivity. Sulfuric acid aerosol has shown no clear effects at concentrations within the ambient range. At somewhat higher levels, increased bronchial reactivity and change in mucociliary clearance have been suggested. Almost no information is available concerning nitric acid.

Effects of inhaled acid aerosols on lung mechanics: an analysis of human exposure studies

There exist significant gaps in our understanding of human health effects from inhalation of pollutants associated with acid precipitation. Controlled clinical studies examine effects of criteria pollutants almost exclusively by assessing changes in lung mechanics. One constituent of acid precipitation, sulfuric acid aerosols, has been shown to induce bronchoconstriction in exercising extrinsic asthmatics at near ambient levels. These asthmatics may be an order of magnitude more sensitive to sulfuric acid aerosols than normal adults. More recently, a second component nitrogen dioxide has been observed to provoke changes in lung mechanics at progressively lower concentrations. To date, virtually no data exist from clinical exposures to acidic aerosols for subjects with chronic obstructive pulmonary disease.

Mutagenesis of anaerobic cultures of Salmonella typhimurium by nitrosoguanidine, diethyl sulfate and 9-aminoacridine

Despite a previous report to the contrary, anaerobic cultures of Salmonella typhimurium strain LT2 hisG46 are revertible (although to a slightly reduced extent) by both N-methyl-N'-nitro-N-nitrosoguanidine and diethyl sulfate, while anaerobic cultures of a strain carrying the frameshift hisC3076 marker are fully revertible by 9-aminoacridine.