Biochemical changes in rat lungs after exposure to nitrogen dioxide

Effects of short-term, single and combined exposure to low-level NO2 and O3 on lung tissue enzyme activities in rats

To examine the pulmonary effects of relatively low levels of NO2 and O3, and test for any possible interaction in their effects, we exposed 3-mo-old male Sprague-Dawley rats, free of specific pathogens, to either filtered room air (control) or 1.20 ppm (2256 micrograms/m3) NO2, 0.30 ppm (588 micrograms/m3) O3, or a combination of the two oxidants continuously for 3 d. We studied a series of parameters in the lung, including lung weight, and enzyme activities related to NADPH generation, sulfhydryl metabolism, and cellular detoxification. The results showed that relative to control, exposure to NO2 caused small but nonsignificant changes in all the parameters; O3 caused significant increases in all the parameters except for superoxide dismutase; and a combination of NO2 and O3 caused increases in all the parameters, and the increases were greater than those caused by NO2 or O3 alone. Statistical analysis of the data showed that the effects of combined exposure were synergistic for 6-phosphogluconate dehydrogenase, isocitrate dehydrogenase, glutathione reductase, and superoxide dismutase activities, and additive for glutathione peroxidase and disulfide reductase activities, but indifferent from those of O3 exposure for other enzyme activities.

Pulmonary disposition of inhaled NO2-nitrogen in isolated rat lungs

Nitrogen dioxide (NO2) is a relatively insoluble, reactive gas that, on inhalation, generates a diverse array of pulmonary toxic effects. Its uptake and transformation in isolated lungs have been shown to be proportional to inspired dose and associated with significant accumulations of the nitrite ion. However, not all absorbed NO2 is directly detectable as soluble nitrite. To further characterize its uptake and chemical disposition, we determined the chemical fate of 15NO2-nitrogen in isolated perfused (red cell-free) rat lungs that were exposed to 20 ppm 15NO2 for 60 min. Total excess 15N (relative to unexposed controls) was determined by isotope ratio mass spectrometry and total nitrogen analysis. Excess 15N was detected in whole lungs and in soluble and insoluble fractions but not in the total lipid pool. Perfusate excess 15N and nitrate correlated and accounted for all absorbed NO2 not detectable in tissue fractions. Exogenously instilled [15N]nitrite distributed within lung tissue, bound to insoluble elements, and diffused to the vascular space similar to NO2-nitrogen. Instilled [15N]nitrate did not distribute or bind like NO2-nitrogen or nitrite. Dialysis (1000 molecular weight cutoff) of cytosol, membranes, and perfusate removed excess 15N and nitrite derived from NO2, nitrite, or nitrate sources. We conclude that in isolated lungs, inhaled NO2 (1) undergoes rapid uptake and transformation in sites accessible to the pulmonary circulation; (2) does not form stable addition products with lipids; and (3) forms small-molecular-weight soluble reaction product(s) that behave similarly to nitrite, most likely indicating predominant univalent reduction of NO2 via initial hydrogen abstraction and subsequent HNO2 dissociation.

Effect of altered dose rate on NO2 uptake and transformation in isolated lungs

While the pulmonary toxicity of NO2 is clearly established, the mechanism by which it is removed from inspired air is poorly understood. Uptake is most likely dependent on chemical reaction since, despite limited per se gaseous NO2 aqueous solubility, uptake proceeds rapidly without ready saturation. We utilized an isolated perfused rat lung model to characterize the effect of dose rate on uptake and transformation. Dose rate was varied via alterations in inspired concentration, tidal volume, and ventilation frequency. Dose equaled the total amount inhaled, uptake the amount removed from inspired air, and transformation the amount of NO2- that accumulated in the perfusate. We found a linear proportionality between both inspired concentration (4-20 ppm) and minute ventilation (45-130 ml/min) and uptake. Fractional uptakes (65%) were similar for all groups. Regression of combined concentration and minute ventilation data yielded a linear relationship between total inspired dose (25-330 micrograms NO2) and both uptake (r2 = 0.99) and transformation (r2 = 0.98). Testing of the functional descriptions resulted in measured uptakes and transformation that fell within a few percentage points of those predicted. We conclude that in acutely exposed isolated lungs (1) NO2 uptake is dependent on total inhaled dose rather than on the variables which serve to affect dose rate, (2) transformation is related to both total inspired dose and uptake, and (3) uptake is more accurately described using a regression equation rather than by use of fractional uptakes.

Glutathione redox status of control and cadmium oxide-exposed rat lungs during oxidant stress

Activities of enzymes responsible for the maintenance of reduced glutathione (GSH) levels have been shown in a previous study to be increased in rat lungs following a 3-h exposure to cadmium oxide aerosols at 5.0 mg/m3. In this study, the ability of the lung to maintain levels of GSH during challenge with tert-butyl hydroperoxide (tBuOOH) was evaluated in isolated perfused lungs from control and cadmium oxide-exposed rats. Changes in glutathione redox status were indicated by measurements of nonprotein sulfhydryls (NPSH), total glutathione (1/2 GSH + GSSG), and glutathione disulfide (GSSG) in liquid nitrogen freeze-clamped lungs after 3-min infusions with 0-0.6 mM tBuOOH. In control and cadmium oxide-exposed lungs, levels of 1/2 GSH + GSSG remained constant over the range of 0-0.6 mM tBuOOH, indicating that no loss of glutathione from the system had occurred. In experiments with control lungs, levels of NPSH fell from 8.04 +/- 0.22 to 3.09 +/- 0.40 mumol/g dry weight when tBuOOH concentrations were increased from 0 to 0.6 mM (n = 20-23). In cadmium oxide-exposed lungs, NPSH levels also decreased proportionally to increases in GSSG. However, at concentrations of 0.075 and 0.15 mM tBuOOH, significantly smaller decreases in NPSH levels were observed in cadmium oxide-exposed lungs compared with controls. This protection against the GSH-depleting effects of tBuOOH might be explained by increased tissue levels of GSH-related enzymes.

Pulmonary biochemical effects of inhaled phosgene in rats

Three exposure regimens were used to study the time course of indicators of lung damage and recovery response to single or repeated exposures to phosgene (COCl2). Rats were sacrificed immediately or throughout a 38-d recovery period after inhalation of 1 ppm COCl2 for 4 h, at intervals during a 7-h exposure to 1 ppm phosgene, or at several time points throughout a 17-d exposure to 0.125 and 0.25 ppm COCl2 (4 h/d, 5 d/wk) and during a 21-d recovery period. Regimen 1 revealed significantly elevated lung wet weight, lung nonprotein sulfhydryl (NPSH) content, and glucose-6-phosphate dehydrogenase (G6PD) activity that stayed elevated for up to 14 d. A significant decrease in body weight and food intake was observed 1 d after exposure. Regimen 2 caused a slight depression in NPSH content but did not affect G6PD activity. Regimen 3 animals showed sustained elevations in lung wet weight, NPSH content, and G6PD activity after 7 d of exposure. No significant changes in these endpoints were observed for the 0.125 ppm COCl2 group. No consistent elevation in hydroxyproline content was seen at either exposure concentration. Light microscopic examination of lung tissue exposed to 0.25 ppm COCl2 for 17 d revealed moderate multifocal accumulation of mononuclear cells in the centriacinar region. In summary, exposure to COCl2 caused changes similar in most ways to those observed for other lower-respiratory-tract irritants.

Nitrogen dioxide exposure and lung antioxidants in ascorbic acid-deficient guinea pigs

We have previously found that ascorbic acid (AA) deficiency in guinea pigs enhances the pulmonary toxicity of nitrogen dioxide (NO2). The present study showed that exposure to NO2 (4.8 ppm, 3 hr) significantly increased lung lavage fluid protein (a sensitive indicator of pulmonary edema) only in guinea pigs fed rabbit chow (a diet not supplemented with vitamin C) for at least 7 days, at which time lung AA was about 50% of normal. The rabbit chow diet did not cause reduced body weight as did commercial synthetic scorbutic diets, even when they were supplemented with AA. After 14 days of feeding rabbit chow, lung AA was reduced to 15% of control. At this time, alpha-tocopherol (AT) in the same lungs was reduced to 85% of control, and lung nonprotein sulfhydryls (NPSH) were increased to 114% of control. Exposure of the guinea pigs to NO2 (4.5 ppm, 16 hr) increased wet lung weight and further altered the antioxidants in deficient (but not normally fed) animals in the following manner: NPSH content was increased to 130% of control, AT was decreased to 74% of control, and AA was increased from 15 to 50% of control. These findings suggest that depletion of AA in guinea pigs removes an important defense against NO2. The lung appears to be able to partially compensate for the dietary lack of antioxidant by accumulating AA from other tissues and by increasing NPSH concentrations. However, sufficient exposure to NO2 leads to oxidation of AT and pulmonary edema. Conditions in which NO2 produced edema were accompanied by only a slight consumption of AT, and no detectable oxidation of lung AA or NPSH.

Influence of age on the biochemical response of rat lung to ozone exposure

We have previously examined the influence of animal age on the pulmonary response to ozone (O3) in rats between 7 and 90 days of age (Elsayed et al., 1982a). In the present study, we expanded the age groups of rats, and examined in greater detail the relationship between animal age and pulmonary response to inhaled O3. We exposed 7 groups of specific pathogen free, male Sprague-Dawley rats, aged 24, 30, 45, 60, 90, 180, and 365 days, to 0.8 ppm (1568 micrograms/m3) O3 continuously for 3 days. After O3 exposure, we sacrificed the exposed rats and a matched number of controls from each age group, and analyzed their lungs for a series of physical and biochemical parameters, including glutathione metabolizing and NADPH producing enzyme activities. We observed that in control rats all the parameters increased as a function of age. However, the rate of increase was generally slower after age 60 days. After O3 exposure there was an increase in all the parameters for all age groups relative to their corresponding controls, but the extent of increase was significantly larger in rats 60 days and older than in younger rats. A regression of the difference in mean values between control and exposed animals for each parameter against age showed a linear correlation, indicating that the response was age-dependent. Since the magnitude of such increases is thought to reflect the degree of lung injury, the results suggest that O3 exposure causes greater lung injury in older rats than in younger rats. We tested this assumption by exposing rats from four different age groups (24, 45, 60 and 90 days) to a lethal dose of O3 (4 ppm or 7840 micrograms/m3 for 8 hours). The mortality rates were 50% and 83% for 24 and 45 day old rats, respectively, and 100% for 60 and 90 day old rats. The results of these studies further demonstrate that older rats are more susceptible to lung injury from O3 than younger rats.

Dietary antioxidants and the biochemical response to oxidant inhalation : III. Selenium influence on mouse lung response and tolerance to ozone

We fed female strain A/St mice selenium (Se) test diets containing either no Se (-Se) or 1 ppm Se (+Se) for 11 wk. Both diets contained 55 ppm vitamin E. We then exposed three groups of mice from each dietary regimen to either 0.8 ppm (1568 μg/m(3)) O3 (low-level) continuously for 5 d, 10.0 ppm (19,600 μg/m(3)) O3 (high-level) for 12 h, or filtered room air, where the latter served as a control for both O3 exposures. After O3 exposures we analyzed the lungs for various physical and biochemical parameters, and compared the results to those obtained from the air controls. The results showed that the difference in dietary Se intake produced an eightfold difference in Se content and a three-fold difference in glutathione peroxidase (GP) activity in the lung, but few changes in other lung parameters. With low-level O3 exposure, NADPH production increased significantly in +Se mice, but did not change in -Se mice. With high-level O3 exposure we observed comparable effects for both dietary regimens, including animal mortality, which was 24% for -Se and 14% for +Se mice. Thus, it seems that diminished GP activity resulting from Se deficiency and the ensuing lack of increase in NADPH production were poorly correlated with mouse tolerance to O3. The lung Se content increased in both dietary regimens after O3 exposure, but the increase was greater after high-level O3 exposure. This suggests a "mobilization" of Se to the lung under O3 stress. It is possible that such a mobilization contributes to the lung reserve of antioxidants, and hence the comparable mortality in both dietary Se regimens.

Studies on the biochemical effects of nitrogen dioxide. IV. Relation between the change of lipid peroxidation and the antioxidative protective system in rat lungs upon life span exposure to low levels of NO2

This study examined the relation between lipid peroxidation and the antioxidative protective system in lungs of rats exposed to low levels of nitrogen dioxide (NO2). JCL:male Wistar rats were exposed to 0, 0.04, 0.4, and 4 ppm NO2 for 9, 18, and 27 months. Lipid peroxidation measured by TBA method, increased significantly in the 4 ppm NO2 group of the 9-month exposure and in the 0.4 and 4 ppm NO2 groups of the 18-month exposure. The activity of glutathione peroxidase measured with hydrogen peroxide as substrate decreased significantly in the 4 ppm NO2 group of the 9-month exposure and in the 0.4 and 4 ppm NO2 groups of the 18-month exposure. Furthermore, the activities of two glutathione S-transferases, aryl and aralkyl S-transferase, also decreased in the 0.4 and 4 ppm NO2 groups of the 18-month exposure, but not in any groups of the 9-month exposure. The activity of glutathione peroxidase measured with cumene hydroperoxide as substrate did not show any significant changes in any NO2 group. The activities of glucose-6-phosphate dehydrogenase and glutathione reductase were significantly higher than those in the control group for the 9-month exposure. In the 18-month exposure, however, they showed a tendency to return to control level. The activities of superoxide dismutase and disulfide reductase upon NO2 exposure for 9 and 18 months were not different from control values. To confirm that lipid peroxidation was increased with greater NO2 concentrations and exposure times, ethane and pentane exhalation in breath as an index of lipid peroxidation was examined. Ethane exhalation increased significantly following 0.04, 0.4, and 4 ppm NO2 exposure for 9 and 18 months. Furthermore, ethane formation of rats exposed to 0.04 and 0.4 ppm NO2 for 27 months also increased to twice the control level. On the other hand, after exposure to 4 ppm NO2 for 27 months, ethane levels returned to control level. Pentane formation increased significantly only in the 0.04 and 0.4 ppm groups in the 18-month exposure. Ethane exhalation in rats exposed to 0.04, 0.12, and 0.4 ppm NO2 for 9 and 18 months was similar. These results suggested that the antioxidative protective ability was decreased with prolonged exposure, while formation of cytotoxic lipid peroxides was increased.(ABSTRACT TRUNCATED AT 400 WORDS)

A comparison of biochemical effects of nitrogen dioxide, ozone, and their combination in mouse lung

Swiss Webster mice were exposed to either 4.8 ppm (9024 microgram/m3) nitrogen dioxide (NO2), 0.45 ppm (882 microgram/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.

Pulmonary NO2 toxicity in neonate and adult guinea pigs and rats

The pulmonary effects of NO2 were investigated in two animal species. Rats and guinea pigs aged from 5 to 60 days or more were exposed for 3 days either to 2 ppm or to 10 ppm NO2. Lung histology or superoxide dismutase (SOD) determination in alveolar macrophages was assessed in air and NO2-exposed animals. Results demonstrated that the lung histological alterations are different for both NO2-exposed species. Rats were more tolerant than guinea pigs, but rat and guinea pig newborns were less affected than adults. The enzyme response to NO2 exposure was similar in both species and a decrease in SOD activity was noted in animals of all ages. These observations support the conclusion that NO2 exposure leads to increased lung damage during the life span, but on the contrary, exposure to oxygen does not involve SOD induction. This suggests that the defense mechanisms against NO2 are different from those of O2.

Comparison of pulmonary biochemical effects of low-level ozone exposure on mice and rats

The biochemical effects of a 5-d continuous exposure to 0.45 ppm (882 microgram/m3) O3, were studied in the lungs of 2-mo-old male, specific-pathogen-free mice (Swiss Webster) and three strains of rats (Long-Evans, Wistar, and Sprague-Dawley). The results, expressed per lung, indicated a general increase in lung weight, DNA and protein contents, oxygen consumption, sulfhydryl metabolism, and the activities of several NADP+-reducing enzymes for all exposed animals relative to their controls. When the increases in the two species (mice versus three strains of rats) were compared, the mice showed significantly higher increases than the rats in several parameters. The responses among the three strains of rats were variable, but the differences were not significant. These observations suggest that Swiss Webster mice may offer a more sensitive animal model than rats for studying the pulmonary effects of a given low-level O3 exposure.