Effect of vitamin C and hydrocortisone on the pulmonary edema produced by ozone in mice

The effect of vitamin C on bronchoconstriction and respiratory symptoms caused by exercise: a review and statistical analysis

Physical activity increases oxidative stress and therefore the antioxidant effects of vitamin C administration might become evident in people undertaking vigorous exercise. Vitamin C is involved in the metabolism of histamine, prostaglandins, and cysteinyl leukotrienes, all of which appear to be mediators in the pathogenesis of exercise-induced bronchoconstriction (EIB). Three studies assessing the effect of vitamin C on patients with EIB were subjected to a meta-analysis and revealed that vitamin C reduced postexercise FEV1 decline by 48% (95% CI: 33% to 64%). The correlation between postexercise FEV1 decline and respiratory symptoms associated with exercise is poor, yet symptoms are the most relevant to patients. Five other studies examined subjects who were under short-term, heavy physical stress and revealed that vitamin C reduced the incidence of respiratory symptoms by 52% (95% CI: 36% to 65%). Another trial reported that vitamin C halved the duration of the respiratory symptoms in male adolescent competitive swimmers. Although FEV1 is the standard outcome for assessing EIB, other outcomes may provide additional information. In particular, the mean postexercise decline of FEF50 is twice the decline of FEV1. Schachter and Schlesinger (1982) reported the effect of vitamin C on exercise-induced FEF60 levels in 12 patients suffering from EIB and their data are analyzed in this paper. The postexercise FEF60 decline was greater than 60% for five participants and such a dramatic decline indicates that the absolute postexercise FEF60 level becomes an important outcome in its own right. Vitamin C increased postexercise FEF60 levels by 50% to 150% in those five participants, but had no significant effect in the other seven participants. Thus, future research on the effects of vitamin C on EIB should not be restricted to measuring only FEV1. Vitamin C is inexpensive and safe, and further study on those people who have EIB or respiratory symptoms associated with exercise is warranted.

Oxalate deposition on asbestos bodies

We report on a deposition of oxalate crystals on ferruginous bodies after occupational exposure to asbestos demonstrated in 3 patients. We investigated the mechanism and possible significance of this deposition by testing the hypothesis that oxalate generated through nonenzymatic oxidation of ascorbate by asbestos-associated iron accounts for the deposition of the crystal on a ferruginous body. Crocidolite asbestos (1000 microg/mL) was incubated with 500 micromol H(2)O(2) and 500 micromol ascorbate for 24 hours at 22 degrees C. The dependence of oxalate generation on iron-catalyzed oxidant production was tested with the both the metal chelator deferoxamine and the radical scavenger dimethylthiourea. Incubation of crocidolite, H(2)O(2), and ascorbate in vitro generated approximately 42 nmol of oxalate in 24 hours. Oxalate generation was diminished significantly by the inclusion of either deferoxamine or dimethylthiourea in the reaction mixture. Incubation of asbestos bodies and uncoated fibers isolated from human lung with 500 micromol H(2)O(2) and 500 micromol ascorbate for 24 hours at 22 degrees C resulted in the generation of numerous oxalate crystals. We conclude that iron-catalyzed production of oxalate from ascorbate can account for the deposition of this crystal on ferruginous bodies.

Ozone adaptation in mice and its association with ascorbic acid in the lung

We have previously shown that ozone (O(3)) adaptation occurred in rats after daily exposure to an "urban-type" concentration. The adaptation was positively associated with an excess of ascorbic acid (AA) in bronchoalveolar lavage fluid (BALF), suggesting that AA may play a role in the adaptation mechanism. This relationship was not seen at higher and more toxic exposures. The present work exposed mice to low and high levels of O(3) to see if the adaptation-AA relationship is common among rodent species. Male CD-1 mice were studied during repeated 6-h/day exposures to 0.0 or 0.25 ppm O(3) for 10 days and 10 days of recovery in air (experiment 1) and to 0.0, 0.5, or 1.0 ppm O(3) for 5 days (experiment 2). Approximately 20 h after each daily exposure, groups of mice were randomly selected from each concentration type and examined for patterns of response. They were anesthetized (urethane, ip), intubated, and the lungs were lavaged with 37 degrees C saline. BALF was assayed for cells, cell differential, protein, albumin, lactate dehydrogenase, lysozymes, N-acetyl-beta-D-glucosaminidase, gamma-glutamyl transferase, uric acid, glutathione, and AA. Body weight and total lung capacity were also measured. Mice from experiment 1 (10/exposure) were tested for adaptation on day 12 by challenging them with 1.0 ppm O(3) for 6 h and collecting BALF 20 h later. In experiment 2, adaptation was assessed by evaluating the attenuation in response to continued exposure. There was only minimal response to the daily O(3) exposures in experiment 1 except for AA, which was significantly increased in BALF by day 3 and remained elevated well into the recovery period. The O(3)-preexposed mice demonstrated adaptation when compared to their O(3)-naive counterparts. Daily exposure to 1. 0 ppm O(3) in experiment 2 caused weight loss and changes in BALF consistent with toxicity, and neither adaptation nor an excess quantity of AA was seen. The findings in mice were in agreement with those seen in rats and suggest that there may be a common O(3) adaptation mechanism among rodents that involves the regulation of AA in lung lining fluid.

Depletion of iron and ascorbate in rodents diminishes lung injury after silica

Exposures of the lung to iron chelates can be associated with an injury. The catalysis of oxygen-based free radicals is postulated to participate in this injury. Such oxidant generation by mineral oxide particles can be dependent on availability of both iron and a reductant. We tested the study hypothesis that lung injury after silica is associated with the availability of both iron and ascorbate in the host by depleting this metal and reductant in the lungs of rats and guinea pigs, respectively. Rats were fed either a normal diet or a diet deficient of iron. After 30 days, animals were instilled with either saline or 1.0 mg Minusil-5 silica. Relative to saline, silica significantly increased neutrophils and lavage protein. Iron depletion significantly diminished both the cellular influx and injury but only at 1 week after silica exposure. Guinea pigs were provided either a normal diet supplemented with 1,000 ppm vitamin C or a diet deficient in ascorbate. After 14 days, the guinea pigs were instilled with either saline or 1.0 mg silica. Silica exposure significantly increased neutrophils and lavage protein. Ascorbate depletion significantly diminished the influx of inflammatory cells and injury at both 1 day and 1 week after silica exposure. We conclude that host concentrations of both iron and ascorbate can affect lung injury after silica exposure.

Ozone-induced tissue injury and changes in antioxidant homeostasis in normal and ascorbate-deficient guinea pigs

It has been reported previously that ozone (O3) toxicity from acute (4 hr) exposure is enhanced by ascorbate (AH2) deficiency in guinea pigs. We hypothesized that lung injury from continuous 1-week O3 exposure would also be increased under conditions of AH2 deficiency because of (1) a diminished antioxidant pool to counteract the oxidant challenge, (2) impaired reparation of tissue injury, and/or (3) altered antioxidant redox homeostasis. Female Hartley guinea pigs (260-330 g) were made AH2 deficient by providing a diet similar to guinea pig chow, but having no AH2. The dietary regimen was started 1 week prior to exposure and was continued during exposure to O3 (0, 0.2, 0.4, or 0.8 ppm, 23 hr/day, 7 days) as well as 1 week post-exposure. Bronchoalveolar lavage (BAL) and tissue AH2 were measured in subgroups at the beginning of exposure (1 week on the AH2-deficient diet), at its termination and 1 week post-exposure. AH2 measured in ear tissue punches proved to be an easy and effective monitor for AH2 deficiency. One week on the AH2-deficient diet caused a 70-80% drop in ear, lung and liver AH2, while AH2 in BAL was decreased by 90%. Immediately after the exposure, total BAL protein and albumin (markers of lung permeability) were increased (approximately 50%) at 0.8 ppm with no difference between the dietary groups. O3 caused an increase in total BAL cells and neutrophils in a concentration-dependent manner with only a slight augmentation due to diet. Exposure to O3 caused an increase in lung and BAL AH2 in normal guinea pigs. Glutathione and uric acid were also increased in the lung and BAL after O3 exposure (40-570%) in both dietary groups, and the levels remained elevated during the recovery period. Lung alpha-tocopherol was not changed due to O3. A significant overall diet-related decrease was seen in AH2-deficient guinea pigs, immediately after the exposure and recovery. In summary, lung injury/inflammation following 1 week O3 exposure and recovery were minimally affected by AH2 deficiency. Antioxidants also appeared to increase in response to O3 exposure despite the deficiency in AH2.

Mechanisms of radical formation from reactions of ozone with target molecules in the lung

Ozone is known to cause radicals to be formed in biological systems: for example, it initiates lipid peroxidation and vitamin E protects in vitro model systems, cells, and animals against the effects of ozone. Ozone is not itself a radical, and we have asked: With what molecules does ozone react in the lung and how are radicals produced? Ozone reacts by two quite different mechanisms to produce radicals; one involves an ozone-olefin reaction and the other a reaction with electron donors such as glutathione (GSH). The first mechanism splits an R radical out of an olefin with the structure R-CH = CH2. The R then reacts with dioxygen to become a peroxyl radical (ROO), and both carbon- and oxygen-centered radicals can be detected by the electron spin resonance spin trap method. From the effects of temperature, metal chelators, and water, it is concluded that ozone reacts by the Criegee ozonation pathway to give the classical 1,2,3-trioxolane, which then undergoes O--O bond homolysis to form a diradical. This diradical then either undergoes beta-scission to split out the R radical or forms the more usual carbonyl oxide and a carbonyl compound. (See Figure 3 in the text). The low yield of Criegee ozonide that is generally obtained probably is due in part to the reactions forming radicals from the 1,2,3-trioxolane that compete with production of the Criegee ozonide. The second mechanism for radical production involves the reaction of ozone with electron donors. If the electron donor is, for example, GSH or its ion (GS-), this reaction produces the thiyl radical GS. and 0.3-. The ozone radical anion then reacts with a proton to form the hydroxyl radical and dioxygen: O3.- + H+-->HO. and O2. Using 5,5-dimethyl-1-pyrroline-N-oxide, the spin adduct of the hydroxyl radical is detected. Similar reactions are observed with catechol.

Mechanisms contributing to ozone-induced bronchial hyperreactivity in guinea-pigs

The effect of ozone (3 ppm, 15-120 min) on bronchial reactivity in the guinea-pig was studied. Ozone induced marked (6-250-fold) bronchial hyperreactivity (BHR) to a range of inhaled, but not intravenous bronchoconstrictors. The degree of BHR was related to the duration of prior ozone exposure. The glutathione redox status was shifted to a more oxidized state in lung after 120 min ozone treatment, although no changes were found in the energy status of lung tissue, as judged by the concentrations of adenosine phosphates. Ascorbic acid pretreatment prevented BHR induced by 30 min ozone exposure. Neutral endopeptidase inhibitors elicited BHR to both substance P and histamine, but did not further enhance bronchoconstriction to substance P after ozone exposure for 120 min. Neither mepyramine, fentanyl, indomethacin nor a 5-lipoxygenase inhibitor (BW B70C), given prior to ozone exposure prevented the induction of BHR to histamine. Atropine or bilateral vagotomy reduced BHR after a 120-min, but not 30-min exposure to ozone. We conclude that in the guinea-pig, ozone induces non-specific, route-dependent BHR by oxidative injury, reducing airway NEP activity and enhancing the cholinergic and peptidergic component to bronchoconstriction. Neither cyclooxygenase nor 5-lipoxygenase products appear to play a role in ozone-induced BHR in this animal model.

Biochemical basis of ozone toxicity

Ozone (O3) is the major oxidant of photochemical smog. Its biological effect is attributed to its ability to cause oxidation or peroxidation of biomolecules directly and/or via free radical reactions. A sequence of events may include lipid peroxidation and loss of functional groups of enzymes, alteration of membrane permeability, and cell injury or death. An acute exposure to O3 causes lung injury involving the ciliated cell in the airways and the type 1 epithelial cell in the alveolar region. The effects are particularly localized at the junction of terminal bronchioles and alveolar ducts, as evident from a loss of cells and accumulation of inflammatory cells. In a typical short-term exposure the lung tissue response is biphasic: an initial injury-phase characterized by cell damage and loss of enzyme activities, followed by a repair-phase associated with increased metabolic activities, which coincide with a proliferation of metabolically active cells, for example, the alveolar type 2 cells and the bronchiolar Clara cells. A chronic exposure to O3 can cause or exacerbate lung diseases, including perhaps an increased lung tumor incidence in susceptible animal models. Ozone exposure also causes extrapulmonary effects involving the blood, spleen, central nervous system, and other organs. A combination of O3 and NO2, both of which occur in photochemical smog, can produce effects which may be additive or synergistic. A synergistic lung injury occurs possibly due to a formation of more powerful radicals and chemical intermediates. Dietary antioxidants, for example, vitamin E, vitamin C, and selenium, can offer a protection against O3 effects.

Antioxidant system and ozone tolerance

Rats were initially exposed to 2 ppm ozone for 3 hr in order to induce ozone tolerance. The time course of the content of nonprotein SH as well as the activities of glutathione peroxidase, glutathione reductase, and glucose 6-phosphate dehydrogenase (so-called antioxidant system) in lungs of the animals was compared to the development of tolerance in the animals to a challenge exposure of 5.6 ppm ozone for 3 hr. An enhancement of a part of the antioxidant system was detected on the second day and thereafter following the initial exposure, but the clear and complete tolerance to ozone was demonstrated 1 day before the enhancement of the antioxidant system. Alternatively, the induction of tolerance to ozone was found to be experimentally suppressed by actinomycin D or colchicine, but the levels of the antioxidant system in animals thus treated were not significantly different from the matched controls, or only partly enhanced. These events suggest that the tolerance to ozone is not related to an enhancement of the antioxidant system.

Ascorbic acid turnover in the mouse following acute ozone exposure

Swiss Webster mice were continuously exposed to an atmosphere containing 1.5 ppm ozone (O3) for 5 days. Control mice breathed filtered air. Immediately following the exposure period each mouse was then injected with [1-14C] ascorbic acid. The rate of disappearance of [1-14C] ascorbic acid and the levels of total ascorbic acid were determined in serum, lung, liver, and the remaining carcass over a 9-day period. O3 exposure caused transient decreases in the ascorbic acid levels in liver and serum, whereas lung ascorbic acid levels increased. The apparent biological half-life of ascorbate in carcasses (minus lung and liver) from O3-exposed mice, was significantly prolonged. Significant changes were also observed in the net flux of ascorbic acid in all tissues examined. The results indicated that the change in ascorbic acid levels in a given tissue appeared to reflect changes in the rate of ascorbic acid degradation, its mobilization or tissue compartmentalization, rather than increased synthesis in response to O3 exposure.

Air Pollution: Adverse Effects on Athletic Performance

Airborne pollutants can have significant objective and subjective effects on athletes and can cause substantial decrements in their performance.

Decreased levels of ascorbic acid in lung following exposure to oxone

Mice were exposed to concentrations of 20, 40 and 200 ppm ozone in air for 30 min. Ozone exposure decreased lung ascorbic acid levels and increased lung weight by up to 50% in a dose related manner. On incubation in Krebs-phosphate solution, lung slices from mice exposed to 200 ppm ozone released a smaller fraction of their content of ascorbic acid into the medium than did lung slices from control mice, suggesting that there was a preferential loss of extracellular ascorbic acid during oxone exposure. These results are consistent with the proposed function of ascorbic acid as an extracellular antioxidant in lungs.

Extracellular ascorbic acid in lung

Fifty percent of the ascorbic acid content of sliced rat lung was released from the tissue to the media within a few minutes by either washing or incubating the slices with Krebs-phosphate solution. Measurement of the lactate dehydrogenase and potassium content of the medium after incubating lung slices for 5 min showed that about 20% of the cells were damaged by slicing. Sephadex chromatography of tissue extracts prepared from washed lung slices showed that none of the ascorbic acid in these slices were bound to protein. Also, metabolic poisons were shown to deplete the ascorbic acid content of washed lung slices. Approx. 57% of the lung ascorbic acid of guinea pigs that had been supplemented with ascorbic acid and 78% of the lung ascorbic acid of ascorbic acid-deficient guinea pigs were found in the medium when lung slices from these animals were incubated with Krebs-phosphate solution. These results were taken to indicate the presence of an extracellular pool of ascorbic acid in lung which is maintained even during scurvy.

Protection by Sulfur Compounds against the Air Pollutants Ozone and Nitrogen Dioxide

Two distinct but related pathways of protection against the lethal effects of ozone and nitrogen dioxide are shown by (i) simultaneous inhalation of compounds that furnish -SH or -SS-, or both, and (ii) by injection of thiourea derivatives several days prior to exposure to these oxidant gases. The mechanism of (i) is believed similar to that proposed for the action of radiation-protective compounds; that of (ii) involves the development of a tolerance initiated by the thiourea against the oxidants.