Dietary antioxidants and the biochemical response to oxidant inhalation: I. Influence of dietary vitamin E on the biochemical effects of nitrogen dioxide exposure in rat lung

Sprague-Dawley rats derived from a specific pathogen-free colony were raised from birth on a test diet containing either 0 or 50 IU vitamin E/kg diet for 8 weeks. Rats from each dietary group were exposed to 3 ppm (5640 μg/m³) nitrogen dioxide (NO₂) continuously for 7 days. They were then killed, and the lungs analyzed for changes in weight, DNA and protein contents, tissue oxygen utilization, sulfhydryl metabolism, and the activities of NADP-reducing enzymes. The difference in dietary vitamin E alone did not cause any significant changes in these parameters. However, after NO₂ exposure the changes in these parameters relative to their corresponding unexposed controls were greater for the deficient rats than for the supplemented rats. The biochemical changes observed may be a response of the lung to injury from NO₂ exposure. The larger changes in the lungs of deficient rats may reflect a greater sensitivity of these animals to inhaled NO₂. The vitamin E contents of lung tissue in deficient and supplemented rats reflected the dietary levels. After NO₂ exposure, the vitamin E content in the lung increased significantly in supplemented rats but decreased in the deficient rats relative to their corresponding unexposed controls. The elevation of vitamin E levels in the lungs of supplemented rats with NO₂ exposure suggests its mobilization from other body sites, whereas in deficient rats this process may not have been possible.     

Short-term inhalation toxicity studies with peroxyacetyl nitrate in rats

The inhalation toxicity of peroxyacetyl nitrate (PAN) was examined in acute (single exposure), sub-acute (4-week repeated exposure) and subchronic (13-week repeated exposure) studies in rats. The 4-h LC₅₀ was found to be 95 ppm.In the 4-week study rats were exposed to 0, 0.9, 4.1 or 11.8 ppm PAN vapour for 6 h/day, 5 days/week. Exposure to 11.8 ppm caused abnormal behaviour, growth retardation, mortality, elevated haemoglobin contents, haematocrit values and erythrocyte counts, increased lung weights and severe inflammatory changes and epithelial hyper- and metaplasia in the respiratory tract. At 4.1 ppm minimal behavioral disturbance, transient growth depression, slightly increased lung weights and mild histopathological changes in the respiratory tract were found. At 0.9 ppm no treatment-related alterations were detected.In the 13-week study rats were exposed to 0, 0.2, 1.0 or 4.6 ppm PAN vapour for 6.5 h/day, 5 days.week. Exposure to 4.6 ppm resulted in changes similar to those found at 11.8 ppm in the 4-week experiment, but no mortality occurred. At 1.0 ppm minimal irritation of the mucous membranes in the nasal cavity was the only PAN-related effect observed. No treatment- related changes were seen at 0.2 ppm. It was concluded that the no-toxic- effect level is between 0.2 and 1.0 ppm, and very probably close to the upper value.     

Changes in the Response of Lung Mast Cells Isolated from Rats and Guinea Pigs Exposed to Nitrogen Dioxide

Abstract

To clarify the relationship between exposure to nitrogen dioxide (NO₂) and mast-cell responses, rats and guinea pigs were exposed to 0, 1.0, 2.0, and 4.0 ppm NO₂ for 12 wk. Although lung wet weights were not changed in both rats and guinea pigs, the number of lung cells from 2.0 and 4.0 ppm NO₂-exposed rats were significantly decreased compared to that of control. No difference was observed in the number of lung mast cells from rats and guinea pigs exposed to NO₂. in lung mast cells from rats, immunoglobulin E (IgE) mediated histamine release was slightly decreased, but A23187-induced histamine release was not changed. On the contrary, in lung mast cells from guinea pigs, IgE-mediated histamine release was increased in a dose-dependent fashion, though no changes in A23187-induced histamine release were observed. These results suggest that different sensitivity for NO₂ exposure exists in lung mast cells from rats and guinea pigs.     

Effect of acute nitrogen dioxide exposure on the prostacyclin synthesis in lung

The effect of acute nitrogen dioxide (NO₂) exposure on prostacyclin synthesis in the rat lung was studied. Male Wistar rats were exposed to 5, 10, 15, 20 and 25 ppm NO₂ for 24 h. Dose-dependent decrease in prostacyclin-synthesizing activities of both homogenized and intact lung was observed. This decrease in prostacyclin synthesis following NO₂ exposure may be related to formation of lipid peroxides due to NO₂ exposure and to damage of pulmonary epithelial cells and endothelial cells by NO₂ exposure.     

Effect of exposure to carbon disulfide on tryptophan metabolism and the tissue vitamin B6 contents of rats

Female Wistar rats were exposed to 100 ppm or 600 ppm carbon disulfide for 6 hours a day, 5 days a week for 12 weeks. During the exposure period, their urinary excretion of 4-pyridoxic acid was determined. The urinary excretions of xanthurenic acid and kynurenic acid after tryptophan loading were also determined. At the end of the exposure period, the rats were sacrificed and the levels of the five major forms of vitamin B₆, pyridoxine, pyridoxal, pyridoxamine, pyridoxal phosphate and pyridoxamine phosphate, in the liver, kidneys and brain were determined by HPLC fluorometry. During the exposure the urinary excretions of xanthurenic acid and kynurenic acid after i. p. administration of tryptophan increased significantly in both experimental groups. However, urinary excretion of 4-pyridoxic acid decreased only slightly in the group exposed to carbon disulfide at 600 ppm and did not decrease in the group exposed to 100 ppm carbon disulfide. Furthermore, no significant changes were observed in the contents of vitamins B₆ in any tissues examined. These results indicate that carbon disulfide does not cause vitamin B₆ deficiency and thus that the disorders of tryptophan metabolism induced by carbon disulfide intoxication are not due to vitamin B₆ deficiency.     

Effects of nitrous acid exposure on baseline pulmonary resistance and Muc5ac in rats

We examined the baseline pulmonary resistance (RLung), baseline dynamic lung compliance (Cdyn), cytokine inductions, and histological alterations in rats exposed to nitrous acid (HONO) with secondary products of nitrogen dioxide (NO₂) and nitric oxide (NO) to assess its biological effects. We exposed three groups of nine male F344 rats to different doses of HONO for six weeks (24?h/day). The cumulative values of HONO concentration were measured twice. The average concentrations of nitrogen oxide for each group were 5.8 parts per million (ppm) HONO with secondary products of 0.7?ppm NO₂ and 2.3?ppm NO, 4.1?ppm HONO with 0.1?ppm NO₂ and 0.6?ppm NO, and a clean air control. We measured baseline RLung and baseline Cdyn using tracheal cannulation. A tracheal tube was inserted into the trachea by tracheostomy, and lung function measurements (baseline RLung and baseline Cdyn) were conducted in mechanically ventilated rats. We measured mRNA levels of Cxcl-1, TNF-α, and Muc5ac in the right lung using quantitative RT-PCR, and observed histological alterations and the alveolar mean linear intercept (Lm) on the left lung. Our results demonstrated that HONO exposure significantly increased baseline RLung, Lm and Muc5ac expression, but did not affect baseline Cdyn or expression of Cxcl-1 and TNF-α. Further, we identified bronchial smooth muscle hypertrophy, pulmonary emphysema-like alterations in the alveolar duct centriacinar regions, and increased goblet cells in HONO-exposed rats. The present results suggest that HONO (with secondary products) adversely affects respiratory function, but that these pathologies may be unrelated to inflammation.     

Effect of acute nitrogen dioxide exposure on the composition of fatty acids in lung and liver phospholipids

In order to examine the effects of NO₂ on the fatty acid content of the lung and liver phospholipids, the phospholipid fractions of rats exposed to 20 ppm NO₂ for 20 and 40 h were extracted and analyzed using gas chromatography. Among the fatty acid species in the lung, the relative amount of palmitic acid, palmitoleic acid and linoleic acid increased significantly, whereas myristic acid, stearic acid and oleic acid decreased significantly after exposure to NO₂. These changes in the composition of fatty acids are discussed in comparison with the results of acute, subacute and chronic exposure to NO₂ reported by other workers. In the case of the fatty acid species in the liver, a significant increase for stearic acid and arachidonic acid and a decrease in oleic acid were observed.     

DETECTION OF POLY(ADP-RIBOSE) SYNTHETASE ACTIVITY IN ALVEOLAR MACROPHAGES OF RATS EXPOSED TO NITROGEN DIOXIDE AND OZONE

The toxic effects of nitrogen dioxide (NO₂) and ozone (O₃) are mediated through the formation of free radicals, which can cause DNA strand breaks. The present study demonstrates that exposure to NO₂ and O₃ causes a stimulation of poly (ADP-ribose) (poly ADPR) synthetase in alveolar macrophages of rats. Three-month-old male Sprague-Dawley rats, specific pathogen free, were exposed to either 1.2 ppm NO₂ or 0.3 ppm O₃ alone or a combination of these 2 oxidants continuously for 3 days. The control group was exposed to filtered room air. To evaluate whether exposure to these two oxidants (NO₂ and O₃) caused DNA damage to lung cells, the activity of poly ADPR synthetase was measured. Cellular DNA repair is dependent upon the formation of poly (ADP-ribose) polymerase, which is catalyzed by poly ADPR synthetase. Poly ADPR synthetase is known to be activated in response of DNA damage. The results showed that the enzyme activity was stimulated after exposure to O₃ or exposure to NO₂ + O₃. Ozone exposure caused a 25% increase in the enzyme activity as compared to the control. Combined exposure to NO₂ + O₃ showed a 53% increase in the enzyme activity. These results were statistically significant as compared to the control and NO₂ exposure groups. Other parameters such as total cell count, cell viability, and differential cell count were also determined. The stimulation of poly ADPR synthetase activity after O₃ exposure or NO₂ + O₃ exposure reflects a response to lung cellular DNA repair, which may be used as an indicator for assessing DNA damage caused by oxidant injury.     

Effect of variable versus fixed exposure levels on the toxicity of acetaldehyde in rats

The effects of exposure pattern on the toxicity of acetaldehyde vapour were investigated in 4-week inhalation studies. Male rats were exposed to 500 or 150 and 110 ppm for 6 h per day/5 days per week. One group of animals was exposed without interruption, the exposure of a second group was interrupted for 1.5 h between the first and second 3-h periods, the exposure of a third group was similarly interrupted and for six 5 min periods exposure was increased sixfold. Peak exposures of up to 3000 ppm superimposed on 500 ppm acetaldehyde caused irritation and excitation, and reduced body weight gain. No such effects occurred after interrupted or uninterrupted exposure to 500 ppm acetaldehyde without peak loads. A reduced phagocytotic index of lung macrophages was found in each of the groups exposed to 500 ppm acetaldehyde, the effect being most marked in the group with superimposed peaks of 3000 ppm. Degeneration of the nasal olfactory epithelium was observed in rats uninterruptedly exposed to 500 ppm acetaldehyde. Interruption of the exposure or interruption combined with peak exposure did not visibly influence this adverse effect on the nose. No compound-related effects were seen in rats interruptedly or uninterruptedly exposed to 150 ppm acetaldehyde or interruptedly exposed to 110 ppm with peak loads of 660 ppm. As a consequence 150 ppm acetaldehyde can be considered a 'no-toxic-effect level' in male rats exposed for 6 h/day, 5 days/week, during a 4-week period.(ABSTRACT TRUNCATED AT 250 WORDS)     

Inhalation toxicity of acetaldehyde in rats. I. Acute and subacute studies

The 4-h LC₅ of acetaldehyde in rats was determined and found to be 13 300 ppm (24.0 g/m³ air). In a 4-week study groups of 10 male and 10 female rats were exposed to 0, 400, 1000, 2200 or 5000 ppm acetaldehyde for 6 h/day, 5 days/week. Treatment-related changes observed at the 5000 ppm level included dyspnoea and excitation during the first 30 min of each exposure, yellow-brown fur, severe growth retardation, more neutrophils and less lymphocytes in the blood, a reduced productioon of urine with a high density, increased lung weights, and severe degenerative, hyperplastic and metaplastic changes of the nasal, laryngeal and tracheal epithelium. Major lesions seen at 1000 and 2200 ppm comprised growth retardation and an increased production of urine in males, slight to moderate degeneration with or without hyper- and metaplasia of the nasal epithelium, and only at 2200 ppm, minimal epithelial changes in the larynx and trachea. The only change observed at the 400 ppm level that could be attributed to acetaldehyde was slight degeneration of the nasal olfactory epithelium seen as loss of microvilli and thinning and disarrangement of the layer of epithelial cells.     

Alterations in the ontogeny of rat pup ultrasonic vocalization produced by prenatal exposure to nitrogen dioxide

Wistar female rats were exposed to low concentrations of nitrogen dioxide, NO₂ (1.5 and 3 ppm) from day 0 to day 20 of pregnancy. The results show that prenatal exposure to this oxidant gas produced significant changes in the duration pattern of ultrasonic vocalizations emitted by male pups removed from their nest. In particular, a significant decrease in the length of ultrasonic calls was found in both 10- and 15-day-old rats exposed to NO₂ (3 ppm) during gestation. These alterations were found at dose levels which did not significantly affect reproduction parameters, body weight gain and motor activity development. These findings suggest that gestational exposure to NO₂, at concentrations below those associated with overt signs of toxicity, induces in rat offspring subtle behavioral changes characterized by altered ontogeny of ultrasonic emission.     

A comparison of biochemical effects of nitrogen dioxide,ozone, and their combination in mouse lung: I. Intermittent exposures

Swiss Webster mice were exposed to either 4.8 ppm (9024 μg/m³) nitrogen dioxide (NO₂), 0.45 ppm (882 μg/m³) ozone (O₃), or their combination intermittently (8 hr daily) for 7 days, and the effects were studied in the lung by a series of physical and biochemical parameters, including lung weight, DNA and protein contents, oxygen consumption, sulfhydryl metabolism, and activities of NADPH generating enzymes. The results show that exposure to NO₂ caused relatively smaller changes than O₃, and that the effect of each gas alone under the conditions of exposure was not significant for most of the parameters tested. However, when the two gases were combined, the exposure caused changes that were greater and significant. Statistical analysis of the data shows that the effects of combined exposure were more than additive, i.e., they might be synergistic. The observations suggest that intermittent exposure to NO₂ or O₃ alone at the concentration used may not cause significant alterations in lung metabolism, but when the two gases are combined the alterations may become significant.     

ANTIOXIDANT AND INFLAMMATORY RESPONSE AFTER ACUTE NITROGEN DIOXIDE AND OZONE EXPOSURES IN C57Bl/6 MICE

Ozone (O₃) and nitrogen dioxide (NO₂) are highly reactive and toxic oxidant pollutants. The objective of this study is to compare chemokine, cytokine, and antioxidant changes elicited by acute exposures of O₃ and NO₂ in a genetically sensitive mouse. Eight-weekold C57Bl/6J mice were exposed to 1 or 2.5 ppm ozone or 15 or 30 ppm NO₂ for 4 or 24 h. Changes in mRNA abundance in lung were assayed by slot blot and ribonuclease protection assay (RPA). Messages encoding metallothionein (Mt), heme oxygenase I (HO-I), and inducible nitric oxide synthase (iNOS) demonstrated increased message abundance after 4 and 24 h of exposure to either O₃ or NO₂. Furthermore, increases in message abundance were of a similar magnitude for O₃ and NO₂. Messages encoding eotaxin, macrophage inflammatory protein (MIP)-1 a, and MIP-2 were elevated after 4 and 24 h of exposure to 1 ppm ozone. Interleukin-6 was elevated after 4 h of exposure to ozone. After 4 h of 2.5 ppm ozone exposure, increased mRNAs of eotaxin, MIP-1 a, MIP-2, Mt, HO-I, and iNOS were elevated to a higher magnitude than were detected after 1 ppm ozone. Monocyte chemoattractant protein (MCP-1) was elevated following 15 ppm NO₂ exposure. After 4 h of 30 ppm NO₂ exposure, messages encoding eotaxin, MIP-1 a, MIP-2, and MCP-1 were elevated to levels similar to those detected after ozone exposure. Our results demonstrate a similar antioxidant and chemokine response during both O₃ and NO₂ exposure. Induction of these messages is associated with the duration and concentration of exposure. These studies suggest that these gases exert toxic action through a similar mechanism.     

Inhalation Toxicity of Phosphine for Fischer 344 Rats and B6C3F1 Mice

Abstract

Because of the potential increased use of phosphine (PH₃) as a fumigant and the lack of adequate toxicity data, short-term inhalation studies were conducted to characterize the toxicity of PH₃ for Fischer 344 (F344) rats and B6C3F1 mice. Male rats and mice were exposed to 0, 1, 5, or 10 ppm PH₃ for up to 4 days, and males and females to 0, 1.25, 2.5, or 5 ppm for 2 wk. In the 4-day study, all rats died by the end of the third exposure to 10 ppm, and all mice were euthanized in moribund condition after the fourth exposure to 10 ppm. Clinical pathology data were obtained only for mice, due to early mortality of rats. There were no significant treatment-related effects in hematological indices in mice exposed to 1 or 5 ppm; at 10 ppm there was a moderate anemia, and leukocyte counts were significantly decreased. There were significant biologically relevant increases in serum activity of alanine aminotransferase (ALT) and sorbitol dehydrogenase (SDH) and in the concentration of urine nitrogen (UN) at 10 ppm. Flectrophoretic evaluation of hemoglobin from mice exposed to 10 ppm did not reveal any differences in banding patterns from controls. Moribund mice euthanized after 4 exposures to 10 ppm had minimal to mild degeneration and necrosis of the renal tubule epithelium, minimal myocardial degeneration, and minimal to mild subcapsular foci of hemorrhage and necrosis in the liver. Bound PH₃ could not be detected in blood, lung, liver, or kidney of mice or lungs of rats exposed to 10 ppm for 3–4 days. There were no treatment-related mortalities in rats or mice exposed for 2 weeks. Lung weights of male rats and mice were significantly decreased and heart weights of female rats and mice were significantly increased after 2 wk of exposure to 5 ppm. Slight but statistically significant increases were observed in serum UN in male mice exposed to 5 ppm. There was no microscopic evidence of treatment-related effects in any of the tissues examined from rats or mice exposed to 5 ppm for 2 wk. Bound PH₃ could not be detected in blood, lung, liver, or kidney of mice or rats exposed to 5 ppm for 2 wk. These studies demonstrated that PH₃ inhalation does not cause a specific target organ toxicity in the B6C3F1 mouse or F344 rat, and that the primary hazard of subchronic inhalation in these species is lethality.     

Nitrate formation in rats exposed to nitrogen dioxide

Sprague-Dawley rats exposed to atmospheres containing low levels of nitrogen dioxide (NO₂) for 24 hr had increased levels of nitrate in their urine on the day of exposure and on the 3 subsequent days. The total increase in urinary nitrate was linearly related to the nitrogen dioxide concentration administered. We recovered in urine 8.4 ± 1.1 μmol nitrate/ppm $\text{NO}{}_2\text{24}\text{-hr}$ exposure (slope ± 95% confidence limits) for 185-g rats. Both the linearity and magnitude of this effect imply that reaction with respiratory tract water is not a major pathway of NO₂ absorption in the lung. Instead, our observations support the hypothesis that the major interaction of NO₂ in the lung is with readily oxidizable tissue components to form nitrite. We estimate that 9.6 μmol of nitrite is formed in the respiratory tract of the rat per ppm NO₂ per 24-hr exposure. We also estimate that humans breathing air containing 0.1 ppm NO₂ have about 3.6 mg of nitrite formed in their respiratory tract per day.     

Vitamin E Protects Against Lipid Peroxidation Due to Cold-SO2 Coexposure in Mouse Lung

Exposure to sulfur dioxide (SO₂) and cold increases especially in the winter. SO₂ or cold exposure destroys the oxidant/antioxidant balance and increases lipid peroxidation. However, the effect of coexistence of both factors has not been studied yet. Therefore, we investigated the effect of SO₂ and/or repeated short-term cold exposure on the oxidant–antioxidant status and the possible protective role of vitamin E in the cardiopulmonary tissues of mice. Swiss albino mice of both sexes were assigned to eight groups. Four groups were kept at room temperature, injected either with saline or vitamin E (100 mg/kg) in the presence or absence of SO₂ exposure (10 ppm, 1 h/day, 30 days). The remaining four groups received the same protocol but were exposed to cold (4 ± 1°C, 1 h/days, 30 days) instead of room temperature. On day 30, the lung and heart tissues were removed for biochemical analysis. SO₂ and cold coexposure increased lactate level in the lung, and elevated thiobarbituric acid-reactive substance (TBARS) and reduced glutathione levels in both tissues, while vitamin E treatment reversed TBARS increment predominantly in the lung. In conclusion, cold and SO₂ coexposure exerts more deleterious effects in the cardiopulmonary tissues, while vitamin E treatment seems to be protective, particularly in the lung.     

Effect of NO2 and SO2 inhalation on benzo(a)pyrene metabolism in rat lung

Male Wistar rats were continuously exposed to NO₂ (14.4 ppm), SO₂ (46.5 ppm) and to a mixture of both gases and their effect on lung microsomal aryl hydrocarbon (benzo(a)pyrene) hydroxylase (AHH) activity was determined. The pre-exposed animals were administered methylcholanthrene (MC) to investigate the exposure effect on enzyme inducibility and pattern of B(a)P metabolites. NO₂ significantly increased AHH activity but no marked change was noted with SO₂. Induction of AHH by MC was markedly inhibited by SO₂, only slightly by mixture of NO₂-SO₂ but not with NO₂ alone.     

Critical review of the human data on short-term nitrogen dioxide (NO2) exposures: Evidence for NO2 no-effect levels

Nitrogen dioxide (NO₂) is a ubiquitous atmospheric pollutant due to the widespread prevalence of both natural and anthropogenic sources, and it can be a respiratory irritant when inhaled at elevated concentrations. Evidence for health effects of ambient NO₂ derives from three types of studies: observational epidemiology, human clinical exposures, and animal toxicology. Our review focuses on the human clinical studies of adverse health effects of short-term NO₂ exposures, given the substantial uncertainties and limitations in interpretation of the other lines of evidence. We examined more than 50 experimental studies of humans inhaling NO₂, finding notably that the reporting of statistically significant changes in lung function and bronchial sensitivity did not show a consistent trend with increasing NO₂ concentrations. Functional changes were generally mild and transient, the reported effects were not uniformly adverse, and they were not usually accompanied by NO₂-dependent increases in symptoms. The available human clinical results do not establish a mechanistic pathway leading to adverse health impacts for short-term NO₂ exposures at levels typical of maximum 1-h concentrations in the present-day ambient environment (i.e., below 0.2 ppm). Our review of these data indicates that a health-protective, short-term NO₂ guideline level for susceptible (and healthy) populations would reflect a policy choice between 0.2 and 0.6 ppm.

Extended abstract

Nitrogen dioxide (NO₂) is a ubiquitous atmospheric pollutant due to the widespread prevalence of both natural and anthropogenic sources, and it can be a respiratory irritant when inhaled at elevated concentrations. Natural NO₂ sources include volcanic action, forest fires, lightning, and the stratosphere; man-made NO₂ emissions derive from fossil fuel combustion and incineration.

The current National Ambient Air Quality Standard (NAAQS) for NO₂, initially established in 1971, is 0.053 ppm (annual average). Ambient concentrations monitored in urban areas in the United States are ~0.015 ppm, as an annual mean, i.e., below the current NAAQS. Short-term (1-h peak) NO₂ concentrations outdoors are not likely to exceed 0.2 ppm, and even 1-h periods exceeding 0.1 ppm are infrequent. Inside homes, 1-h NO₂ peaks, typically arising from gas cooking, can range between 0.4 and 1.5 ppm.

The health effects evidence of relevance to ambient NO₂ derives from three lines of investigation: epidemiology studies, human clinical studies, and animal toxicology studies. The NO₂ epidemiology remains inconsistent and uncertain due to the potential for exposure misclassification, residual confounding, and co-pollutant effects, whereas animal toxicology findings using high levels of NO₂ exposure require extrapolation to humans exposed at low ambient NO₂ levels. Given the limitations and uncertainties in the other lines of health effects evidence, our review thus focused on clinical studies where human volunteers (including asthmatics, children, and elderly) inhaled NO₂ at levels from 0.1 to 3.5 ppm during short-term (½–6-h) exposures, often combined with exercise, and occasionally combined with co-pollutants. We examined the reported biological effects and classified them into (a) lung immune responses and inflammation, (b) lung function changes and airway hyperresponsiveness (AHR), and (c) health effects outside the lungs (extrapulmonary).

We examined more than 50 experimental studies of humans inhaling NO₂, finding that such clinical data on short-term exposure allowed discrimination of NO₂ no-effect levels versus lowest-adverse-effects levels. Our conclusions are summarized by these six points: For lung immune responses and inflammation: (1) healthy subjects exposed to NO₂ below 1 ppm do not show pulmonary inflammation; (2) at 2 ppm for 4?h, neutrophils and cytokines in lung-lavage fluid can increase, but these changes do not necessarily correlate with significant or sustained changes in lung function; (3) there is no consistent evidence that NO₂ concentrations below 2 ppm increase susceptibility to viral infection; (4) for asthmatics and individuals having chronic obstructive pulmonary disease (COPD), NO₂-induced lung inflammation is not expected below 0.6 ppm, although one research group reported enhancement of proinflammatory processes at 0.26 ppm. With regard to NO₂-induced AHR: (5) studies of responses to specific or nonspecific airway challenges (e.g., ragweed, methacholine) suggest that asthmatic individuals were not affected by NO₂ up to about 0.6 ppm, although some sensitive subsets may respond to levels as low as 0.2 ppm. And finally, for extra-pulmonary effects: (6) such effects (e.g., changes in blood chemistry) generally required NO₂ concentrations above 1–2 ppm.

Overall, our review of data from experiments with humans indicates that a health-protective, short-term-average NO₂ guideline level for susceptible populations (and healthy populations) would reflect a policy choice between 0.2 and 0.6 ppm. The available human clinical results do not establish a mechanistic pathway leading to adverse health impacts for short-term NO₂ exposures at levels typical of maximum 1-h concentrations in the present-day ambient environment (i.e., below 0.2 ppm).     

Nitrogen dioxide: no influence on allergic sensitization in an intranasal mouse model with ovalbumin and diesel exhaust particles

The role of traffic-related air pollution in the development of allergic diseases is still unclear. We therefore investigated if NO₂, an important constituent of traffic-related air pollution, promotes allergic sensitization to the allergen ovalbumin (OVA). We also examined if NO₂ influenced the allergy adjuvant activity of diesel exhaust particles (DEP). For this purpose, mice were exposed intranasally to OVA with or without DEP present, immediately followed by exposure to NO₂ (5 or 25 parts per million [ppm]) or room air for 4?h in whole body exposure chambers. Eighteen hours after the last of three exposures, the lungs of half of the animals were lavaged with saline and markers of lung damage and lung inflammation in the bronchoalveolar lavage fluid (BALF) were measured. Three weeks later, after intranasal booster immunizations with OVA, the levels of OVA-specific IgE and IgG2a antibodies in serum were determined. Both NO₂ (25?ppm) and DEP gave lung damage, measured as increased total protein concentration in BALF, whereas only NO₂ seemed to stimulate release of the proinflammatory cytokine tumor necrosis factor alpha (TNF-α). In contrast, only DEP significantly increased the number of neutrophils. Furthermore, DEP in combination with OVA stimulated the production of serum allergen-specific IgE antibodies. NO₂, however, neither increased the production of allergen-specific IgE antibodies, nor influenced the IgE adjuvant activity of DEP. Thus, based on our findings, NO₂ seems to be of less importance than combustion particles in the development of allergic diseases after exposure to traffic-related air pollution.     

Toxicity Sudies of Acetone Administered in the Drinking Water of Rodents

Toxicity Studies of Acetone Administered in the Drinking Waterof Rodents. DIETZ, D. D., LEININGER, J. R., RAUCKMAN, E. J.,THOMPSON, M. B., CHAPIN, R. E., MORRISSEY, R. L., AND LEVINE,B. S. (1991). Fundam Appl. Toxicol 17, 347–360. Two- andthirteen-week toxicity studies were conducted using male andfemale F344/N rats and B6C3F1 mice. Animals were exposed tothe following concentrations of acetone in their drinking water:two-week studm 0; 5000; 10,000; 20,000; 50,000; or 100,000 ppmacetone. Thirteen-week rat and female mouse studies 0; 2500;5000; 10,000; 20,000; or 50,000 ppm acetone. Thirteen week malemice were exposed to 0; 1250; 2500; 5000; 10,000; or 20,000ppm acetone. Depressed body weight gain was restricted to the50,000 and 100,000 ppm exposure groups. Male and female miceexposed respectively to 20,000 or 50,000 ppm acetone for 2 weeksdeveloped hepatocellular hypertrophy. This change was not apparentafter 13 weeks of exposure although relative and alsolute liverweight was increased in high dose female mice. Bone marrow hypoplasiawas observed In 5/5 high dose (100,000 ppm) male rats duringthe 2-week studies. Treatment of male rats for 13 weeks resultedin a variety of mild and subtle hematological changes that oftenoccurred at relatively low levels of exposure (5000 ppm) andresembled those seen during the clinical condition of megaloblasticanemia Changes characteristic of hypogonadism (depressed spermmotility and cauda epididymal and epididymal weight and elevatedincidence of abnormal sperm) were observed in male rats raceiving50,000 ppm acetone for 13 weeks. The incidence and severityof a kidney laion that is morphologically similar to the spontaneouslyoccurring nephropathy among aging F-344 rats were increasedat 20,000 and 50,000 ppm acetone, respectively, in 13-week malerats. In summary, the effects of acetone were either subtlein nature or occurred during very high levels of exposure confirmingacetone's low level of toxicity. The daily levels of acetoneexposure were often several-fold greater than possibly encounteredby humans during the accidental consumption of contaminatedgroundwater (250 ppm; 5 mg/day) and frequently exceeded maximumlevels reported following acute toxic exposures (2,500 mg/kg).