Ascorbic acid in bronchoalveolar wash

Crystalline silica incubated in ascorbic acid acquires a higher cytotoxic potential

Quartz incubated in an aqueous solution of ascorbic acid is partially dissolved and the potential to generate hydroxyl radicals from hydrogen peroxide is enhanced. In order to investigate whether the surface activation triggered by the treatment with ascorbic acid would also involve an enhancement in cell toxicity, a murine macrophage cell line (RAW 264.7) was exposed to untreated and ascorbic acid-treated quartz. Ascorbic acid pretreated quartz was more toxic than untreated quartz and all cells died within 24 hours after exposure. Tetrandrine (a Chinese drug employed to retard or reverse fibrotic lesions of silicosis in humans) partially reduced cell toxicity generated by ascorbic acid pretreated quartz.

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.

Ascorbic acid pre-treated quartz stimulates TNF-alpha release in RAW 264.7 murine macrophages through ROS production and membrane lipid peroxidation

Background

Inhalation of crystalline silica induces a pulmonary fibrotic degeneration called silicosis caused by the inability of alveolar macrophages to dissolve the crystalline structure of phagocytosed quartz particles. Ascorbic acid is capable of partially dissolving quartz crystals, leading to an increase of soluble silica concentration and to the generation of new radical sites on the quartz surface. The reaction is specific for the crystalline forms of silica. It has been already demonstrated an increased cytotoxicity and stronger induction of pro-inflammatory cyclooxygenase-2 (COX-2) by ascorbic acid pre-treated quartz (QA) compared to untreated quartz (Q) in the murine macrophage cell line RAW 264.7.

Methods

Taking advantage of the enhanced macrophage response to QA as compared to Q particles, we investigated the first steps of cell activation and the contribution of early signals generated directly from the plasma membrane to the production of TNF-α, a cytokine that activates both inflammatory and fibrogenic pathways.

Results

Here we demonstrate that TNF-α mRNA synthesis and protein secretion are significantly increased in RAW 264.7 macrophages challenged with QA as compared to Q particles, and that the enhanced response is due to an increase of intracellular ROS. Plasma membrane-particle contact, in the absence of phagocytosis, is sufficient to trigger TNF-α production through a mechanism involving membrane lipid peroxidation and this appears to be even more detrimental to macrophage survival than particle phagocytosis itself.

Conclusion

Taken together these data suggest that an impairment of pulmonary macrophage phagocytosis, i.e. in the case of alcoholic subjects, could potentiate lung disease in silica-exposed individuals.

Ascorbic acid-pretreated quartz enhances cyclo-oxygenase-2 expression in RAW 264.7 murine macrophages

Exposure to quartz particles induces a pathological process named silicosis. Alveolar macrophages initiate the disease through their activation, which is the origin of the later dysfunctions. Ascorbic acid is known to selectively dissolve the quartz surface. During the reaction, ascorbic acid progressively disappears and hydroxyl radicals are generated from the quartz surface. These observations may be relevant to mammalian quartz toxicity, as substantial amounts of ascorbic acid are present in the lung epithelium. We studied the inflammatory response of the murine macrophage cell line RAW 264.7 incubated with ascorbic acid-treated quartz, through the expression and activity of the enzyme cyclo-oxygenase-2 (COX-2). COX-2 expression and prostaglandin secretion were enhanced in cells incubated with ascorbic acid-treated quartz. In contrast, no changes were observed in cells incubated with Aerosil OX50, an amorphous form of silica. Quantification of COX-2 mRNA showed a threefold increase in cells incubated with ascorbic acid-treated quartz compared with controls. The transcription factors, NF-kappaB, pCREB and AP-1, were all implicated in the increased inflammatory response. Reactive oxygen species (H(2)O(2) and OH(*)) were involved in COX-2 expression in this experimental model. Parallel experiments performed on rat alveolar macrophages from bronchoalveolar lavage confirmed the enhanced COX-2 expression and activity in the cells incubated with ascorbic acid-treated quartz compared with untreated quartz. In conclusion, the selective interaction with, and modification of, quartz particles by ascorbic acid may be a crucial event determining the inflammatory response of macrophages, which may subsequently develop into acute inflammation, eventually leading to the chronic pulmonary disease silicosis.

Ascorbic acid modifies the surface of asbestos: possible implications in the molecular mechanisms of toxicity

Ascorbic acid is one of the major components of the antioxidants defenses of the lung lining layer where inhaled asbestos fibers are deposited. Crocidolite fibers were incubated at 37 degrees C in a 0.01 M aqueous solution of ascorbic acid for 25 days in order to investigate modifications in surface reactivity. Iron (820 nmol/mg) and monomeric silica (470 nmol/mg) were released in the supernatant, while ascorbic acid was consumed. The amount of iron and silicon released, respectively, 17 and 6% (in atoms) of the total fiber content, exceeded what was expected at the surface, suggesting a partial disgregation of crocidolite promoted by ascorbic acid. In the absence of ascorbic acid but at the same pH, the release of iron and monomeric silica was minimal. At time intervals, aliquots of fibers were withdrawn to evidence chemical modifications progressively taking place. Three families of Fe(II) centers, differing in coordinative unsaturation and progressively removed during incubation, have been evidenced from the FTIR spectra of NO adsorbed onto the fibers. The most uncoordinated ones are removed first. New highly uncoordinated iron sites are exposed at the fiber surface as a consequence of the erosion of the outmost layers while hydration of silica tetrahedra yields new silanol groups. The activity in the Fenton-like reaction (*OH from H(2)O(2)) decreases following surface iron depauperation. Conversely, the homolytic cleavage of the C-H bond (CO(2)*-) from the formate ion) appears related to the small fraction of iron ions always present but easily quenched by the adsorption of ascorbic acid or its oxidation products.

Possible role of ascorbic acid in the oxidative damage induced by inhaled crystalline silica particles

The selective interaction of ascorbic acid with crystalline silica (quartz) has been studied by measuring the ascorbic acid consumption (by means of UV/vis and IR spectroscopy) and the release of silicon when quartz particles or amorphous silica (Aerosil 50) is incubated in ascorbic acid solution. At a physiological ascorbic acid concentration, quartz, and not amorphous silica, reacts, suggesting the formation of a 1:1 silicon-ascorbate complex, while at higher concentrations, the reacting amount of ascorbic acid exceeds the amount of silicon that is released. Silicon tetrahedra bearing free silanols at the quartz surface are selectively attached by ascorbic acid. The particle-derived hydroxyl radical yield in the presence of hydrogen peroxide is increased on ascorbic acid-treated quartz in comparison with the original sample. The results presented herein are relevant because the depletion of ascorbic acid from the lung lining layer and the increased potential in particle-derived free radical generation may both contribute to the oxidative damage following inhalation of crystalline silica.

Chrysotile-mediated imbalance in the glutathione redox system in the development of pulmonary injury

A significant depletion in the content of glutathione (GSH) and alteration in GSH redox system enzymes were observed in the lung of chrysotile-exposed animals (5 mg) during different developmental stages of asbestosis. In the alveolar macrophages (AM) of exposed animals, the depletion in GSH started from day 1 and reached a maximum at day 16, whereas in lung tissue the maximum depletion was observed when fibrosis has matured. It appears that cellular GSH depletion triggers oxidative stress in the system as observed from increased thiobarbituric acid reactive substance (TBARS) production and alteration in the activities of glutathione peroxidase (GPx), glutathione reductase (GR), glucose 6-phosphate dehydrogenase (G6PD) and glutathione S-transferase (GST), the enzymes regulating oxidative tone. The depletion in GSH was also observed in red blood cells (RBC) of the exposed animals reaching a maximum when fibrosis matured. Thus the observed depletion in GSH, ascorbic acid and alteration in GSH redox system enzymes may be involved in fibrosis and carcinogenesis induced by chrysotile.

Determination of low-molecular-mass antioxidant concentrations in human respiratory tract lining fluids

Antioxidants present within lung epithelial lining fluids (ELFs) constitute an initial line of defense against inhaled environmental oxidants such as ozone, nitrogen oxides, and tobacco smoke, but the antioxidant composition of human ELFs is still incompletely characterized. We analyzed ELF concentrations of the low-molecular-mass antioxidants ascorbate, urate, glutathione (GSH), and alpha-tocopherol by obtaining bronchoalveolar lavage (BAL) and nasal lavage fluids from healthy nonsmoking volunteers and compared two different BAL procedures. ELF dilution by the lavage procedures was estimated by measurement of urea in recovered BAL fluids in comparison with those in blood plasma from the same subjects. The results indicated that a recently developed single-cycle BAL procedure minimizes influx of non-ELF urea into the instilled fluid and thus allows for a more accurate determination of ELF antioxidant concentrations. Using this procedure, we determined that bronchoalveolar ELF contains 40 +/- 18 (SD) microM ascorbate, 207 +/- 167 microM urate, 109 +/- 64 microM GSH, and 0.7 +/- 0.3 microM alpha-tocopherol (n = 12 subjects). Similar analysis of nasal lavage fluid yielded nasal ELF levels of 28 +/- 19 microM ascorbate and 225 +/- 105 microM urate (n = 12 subjects), whereas GSH was undetectable (<0.5 microM). Our results demonstrate that ascorbate and urate are major low-molecular-mass ELF antioxidants in both the upper and lower respiratory tract, whereas GSH is present at significant concentrations only in bronchoalveolar ELF.

Lung lining fluid antioxidants in male broilers: age-related changes under thermoneutral and cold temperature conditions

The purpose of this study was to determine age-related changes in lung lining fluid antioxidants in broilers reared under thermoneutral or cold temperature conditions. Male broilers (Cobb 500) were placed in floor pens within environmental chambers and fed a standard commercial starter diet. The thermoneutral Control chamber was maintained at 32, 30, 27, and 22 to 25 C for Weeks 1, 2, 3, and 4 to 7, respectively, whereas temperature in the Cold chamber was lowered to 18 C during Week 3 and maintained between 15 and 18 C for the rest of the study. At 2, 4, and 7 wk, four to six birds per chamber were selected randomly. The lungs were lavaged with heparinized saline (2 mL/g lung) to obtain lung lining fluid. Antioxidants [reduced (GSH), oxidized (GSSG), and total (TGSH) glutathione, uric acid, ascorbic acid, and alpha- and gamma-tocopherol] in lung lining fluid were determined by HPLC; protein was determined colorimetrically. In Controls, levels of alpha- and -gamma-tocopherol, uric acid, and GSH in lung lining fluid decreased between 2 and 7 wk of age. Birds in the Cold chamber exhibited higher protein, a higher GSSG:TGSH ratio, and a decrease in ascorbic acid (7 wk) in lung lining fluid relative to Controls. Lung lining fluid antioxidants were not correlated with antioxidants in plasma. To determine the effect of vitamin E supplementation on lung lining fluid antioxidants, birds were given a supplement of 200 IU alpha-tocopherol per day for 7 d. Alpha-tocopherol supplementation elevated alpha-tocopherol levels in lung lining fluid, but lowered ascorbic acid, GSH, and GSSG and had no effect on uric acid in lung lining fluid. The results of this study suggest that antioxidant protection in lung lining fluid may diminish with age, that cold conditions in this study produced an oxidative stress in lung lining fluid in broilers, and that oral supplementation of alpha-tocopherol elevated lung lining fluid alpha-tocopherol.

Activation of alveolar macrophages and peripheral red blood cells in rats exposed to fibers/particles

The cytotoxic and oxidative responses of crocidolite and chrysotile asbestos fibers and ultrafine titanium dioxide (UF-TiO2) particles were measured in alveolar macrophages (AM) and peripheral red blood cells (RBC) of rat after 30 days with a single intratracheal exposure (5 mg). The following responses were observed one month after fiber/particle instillation: (1) AM population increased; (2) lactate dehydrogenase and acid phosphatase activities in cell free lung lavage fluid increased; (3) substances that react with hydrogen peroxide or thiobarbituric acid were elevated in both AM and peripheral RBC; (4) glutathione peroxidase, glutathione reductase, and catalase were altered in both AM and peripheral RBC; (5) glutathione and ascorbic acid decreased in both AM and peripheral RBC. A significant difference from negative controls was noted in all responses of the two fiber-exposed groups, and in most responses of the UF-TiO2-exposed group. The level of responses to the three test substances suggested a decreasing order of toxicity, with crocidolite > chrysotile > UF-TiO2.

Antioxidant defenses in lung lining fluid of broilers: impact of poor ventilation conditions

Lung lining fluid antioxidants represent a potentially important protective barrier of lung epithelial cells to damaging effects of air pollutants, yet no information is apparently available concerning lung lining fluid antioxidants in broilers. Therefore, goals of this study were to establish uric acid, ascorbic acid, reduced (GSH) and oxidized (GSSG) glutathione, and protein concentrations in lung lining fluid obtained from male broiler chickens maintained for 6 to 7 wk within environmentally controlled rooms (Control) or chronically exposed to high levels of dust and ammonia within a broiler rearing house (House). The entire respiratory tract was carefully removed following an overdose of anesthetic and lavage fluid was collected after flushing the lungs with heparin-saline (10 mL per lung). There was no difference in GSH, but GSSG, uric acid, and protein concentrations were higher in House birds than in Controls. An increase in the GSSG to total glutathione (GSx) ratio, an indicator of oxidative stress, was also observed in birds maintained in the House environment. Ascorbic acid was not detected in House-reared birds and detected in only 4 of 12 Controls. Regression analysis revealed positive correlations between lung lining fluid protein and uric acid (r = 0.71; P < 0.01), protein and GSSG (r = 0.73; P < 0.01), and uric acid and GSSG concentrations (r = 0.69, P < 0.01). Additionally, GSSG was positively correlated (r = 0.66; P < 0.01) with the right ventricular weight ratio, an index commonly used in identifying the development of pulmonary hypertension syndrome in broilers. These data, the first to document lung lining fluid antioxidants in avian species, indicate an oxidative stress can be detected in fluid of broilers exposed to high levels of dust and ammonia in a simulated poultry house environment.

Modeling the interactions of ozone with pulmonary epithelial lining fluid antioxidants

Water soluble antioxidant--ascorbate (AA), urate (UA), and reduced glutathione (GSH)--consumption by ozone (O3) was investigated in a range of pulmonary epithelial lining fluid (ELF) models. Antioxidants were exposed individually and as a composite mixture, with and without human albumin to a range of ambient O3 concentrations: 0-1500 ppb using a continually mixed, interfacial exposure setup. We observed the following: (1) UA constituted the most o3-reactive substrate in each of the models examined. Reactivity hierarchies in each were as follows: UA > AA >> GSH (individual antioxidant), UA > AA > GSH (composite antioxidant), and UA >> AA approximately equal to GSH (composite antioxidant + albumin). Consumption of GSH as a pure antioxidant solution was associated with a 2:1 stoichiometric conversion of GSH to GSSG. This simplistic relationship was lost in the more complex models. (3) Consumption of antioxidants by O3 occurred without alteration of sample pH. (4) Protein carbonyl formation was observed when albumin alone was exposed to O3. However, in the presence of the composite antioxidant solution no evidence of this oxidative modification was apparent. These data indicate that GSH does not represent an important substrate for O3. In contrast, UA displays high reactivity consistent with its acting as a sacrificial substrate in the ELF. As UA concentrations are highest in the ELF of the proximal airways, its localization, allied to its reactivity, suggesting that it plays important roles, both in conferring protection locally and also by "scrubbing" O3, from inhaled air, limiting its penetration to the more sensitive distal lung.

NO2-induced generation of extracellular reactive oxygen is mediated by epithelial lining layer antioxidants

Nitrogen dioxide (NO2) is an environmental oxidant that causes acute lung injury. Absorption of this aqueous insoluble gas into the epithelial lining fluid (ELF) that covers air space surfaces is, in part, governed by reactions with ELF constituents. Consequently, NO2 absorption is coupled to its chemical elimination and the formation of ELF-derived products. To investigate mechanisms of acute epithelial injury, we developed a model encompassing the spatial arrangements of the lung surface wherein oxidation of cell membranes immobilized below a chemically defined aqueous compartment was assessed after NO2 exposures. Because aqueous-phase unsaturated fatty acids displayed minimal NO2 absorptive activity, these studies focused on glutathione (GSH) and ascorbic acid (AH2) as the primary NO2 absorption substrates. Results demonstrated that membrane oxidation required both gasphase NO2 and aqueous-phase GSH and/or AH2. Membrane oxidation was antioxidant concentration and exposure duration dependent. Furthermore, studies indicated that GSH- and AH2-mediated NO2 absorption lead to the production of the reactive oxygen species (ROS) O-2. and H2O2 but not to .OH and that Fe-O2 complexes likely served as the initiating oxidant. Similar results were also observed in combined systems (GSH + AH2) and in isolated rat ELF. These results suggest that the exposure-induced prooxidant activities of ELF antioxidants generate extracellular ROS that likely contribute to NO2-induced cellular injury.

Nitrogen dioxide depletes uric acid and ascorbic acid but not glutathione from lung lining fluid

The aim of this study was to determine the kinetics of the reactions between the gaseous free-radical pollutant, nitrogen dioxide (NO2), and the water-soluble antioxidants present in respiratory tract lining fluid (RTLF). Samples of RTLF, recovered from 12 subjects (mean age 54.1+/-16.3 years; eight male, four female) as bronchoalveolar lavage (BAL) fluid were exposed ex vivo to NO2 [50-1000 parts per billion (ppb)] for 4 h. For comparison, similar exposures were carried out with single and composite solutions with relevant RTLF antioxidant concentrations. Ascorbic acid (AA), uric acid (UA), GSH depletion, and GSSG and malondialdehyde (MDA) formation were determined with time. In the three models, UA and AA were consumed in a time- and NO2-concentration-related fashion. In addition, their rate of depletion correlated positively with their initial concentration (UA, r=0.92, P<0.05; AA, r=0.94, P<0.05). Little difference was found between the rate of loss of AA (2.2+/-0. 2; 1.9+/-0.5; 1.4+/-0.3 nmol.l-1.h-1.ppb-1), and that of UA (2.4+/-0. 2; 2.1+/-0.6; 1.3+/-0.2 nmol.l-1.h-1.ppb-1) in the three RTLF models examined (single, composite, BAL fluid respectively). GSH loss from BAL fluid (0.2+/-0.1) was significantly less than that seen in either single (1.4+/-0.3) or composite (1.2+/-0.5 nmol.l-1.h-1. ppb-1) antioxidant solutions. In all cases, GSH consumption was significantly less than AA or UA. As model complexity increased, the rate of individual antioxidant loss decreased, such that in BAL fluid, AA, UA and GSH consumption rates were significantly less (P<0. 05) than in the pure or composite antioxidant mixtures. In BAL fluid, little GSSG production was observed at any NO2 concentration. MDA concentration, determined as a measure of lipid peroxidation, did not change following exposure to 50, 150 or 400 ppb NO2, but increased MDA was seen in BAL fluid from 8/12 subjects following exposure to 1000 ppb NO2 for 1 h or more. In conclusion, NO2, at environmentally relevant concentrations, depletes BAL fluid of the antioxidant defences, UA and AA, but not GSH.

Depletion of urate in human nasal lavage following in vitro ozone exposure

Ozone, a strong oxidant present in summer smog, is thought to primarily react with antioxidant molecules found in the epithelial lining fluid of the respiratory tract. In humans, as much as 40% of inhaled ozone can be removed in the nasal cavity where the major extracellular antioxidant has been identified as uric acid. The present study was undertaken to examine urate/oxidant interactions in human nasal lavage fluid following in vitro exposure to ozone at concentrations relevant to the U.K. Lavage fluid was collected from 8 volunteers using a modified Foley catheter which permits prolonged contact of isotonic saline with the anterior nasal cavity. Nasal lavage samples in multiwell plates were exposed to ozone at concentrations of 50, 100 and 250 ppb. Samples were removed at intervals from 15 to 240 min following exposure and assayed for uric acid depletion. Uric acid concentrations in the nasal lavage were found to fall from 8.52 (time zero) to 3.99 microM, 0.05 and 0.07 microM after 240 min at 50, 100 and 250 ppb ozone respectively. At a non-environmentally relevant ozone concentration of 1000 ppb, uric acid was completely depleted after 60 min. Regression analysis showed a linear correlation between rate of loss of urate and ozone concentration (R2 = 0.97). A novel, non-invasive technique is described to investigate antioxidant compromise and its importance in individual subjects. We conclude that uric acid in nasal lavage samples is scavenged by ozone in a dose and time dependent manner.

Effect of ascorbic acid supplementation during the inhalation exposure of guinea-pigs to industrial dust on bronchoalveolar lavage and pulmonary enzymes

The aim of this study was to investigate the interaction between ascorbic acid (AA) and inhaled particles separated from the dumped waste of a nickel smelter and refinery. Tricoloured male guinea pigs were exposed in an inhalation chamber to 50 mg kg-1 of < 5 microns particles that mainly consisted of metal oxides. Exposure lasted for 4 weeks (5 days per week and 5 h per day). The drinking water of half of the exposed and half of the control groups was supplemented with 1 g l-1 AA. Each group received 0.4 mmol kg-1 AA in their food. Ascorbic acid supplementation increased the pulmonary AA concentration in both exposed and control groups to the same extent, but in bronchoalveolar lavage fluid the increase was higher in control than in exposed guinea pigs. The number of alveolar macrophages was increased by exposure and AA increased the number only in the exposed group; the acid phosphatase activity of the alveolar macrophages was increased only by AA, and more in the exposed than in the control group. Alkaline phosphatase activity in bronchoalveolar lavage fluid was the same in both supplemented groups, but it was enhanced in the exposed group with a low intake of AA. Effects on lactate dehydrogenase were not consistent. Neither exposure nor AA influenced significantly this enzyme in bronchoalveolar lavage fluid, but in the lung both AA and exposure caused an increase in the activity. The levels were similar in the AA-treated control and exposed guinea pigs.

Inhalation exposure of rats to metal aerosol. I. Effects on pulmonary surfactant and ascorbic acid

Female albino Wistar rats were exposed to less than 5 microns particles separated from nickel refinery waste. The generated aerosol of 50 mg m-3 mainly consisted of metal oxides, the most toxic being NiO and Cr2O3. The exposure of 5 h per day, 5 days per week, lasted for 4 weeks or 4 months. At the end of the exposure period the amounts of pulmonary surfactant and ascorbic acid were estimated in both exposed and control rats. The amount of pulmonary surfactant was elevated after both exposure times, while ascorbic acid increased significantly (P less than 0.02) only after 4 weeks of exposure.

Relationships between ascorbic acid and alpha-tocopherol during diquat-induced redox cycling in isolated rat hepatocytes

The effects of diquat-induced redox cycling on the levels of cellular ascorbic acid and alpha-tocopherol were investigated in isolated rat hepatocytes. In untreated hepatocytes, the metabolism of 1 or 2 mM diquat resulted in the depletion of cellular ascorbic acid and glutathione, but not of alpha-tocopherol, in association with the induction of cell death during the experimental period. In 1,3-bis(2-chloroethyl)-1-nitrosourea (BCNU) pretreated cells, 1 mM diquat induced cell death accompanied by glutathione was rapid (to 9% of controls by 15 min) and cell ascorbate was completely consumed by 2 hr of incubation. In contrast, cellular alpha-tocopherol levels were stable for the first 30 min, but were depleted in association with the onset of lipid peroxidation. Supplementation of 0.1 or 1.0 mM ascorbic acid in the incubation medium delayed the onset of diquat-induced alpha-tocopherol loss, lipid peroxidation and cytotoxicity. When the concentration of exogenous cellular ascorbic acid was consumed to below that of endogenous ascorbic acid, alpha-tocopherol loss and lipid peroxidation were initiated. The results indicate that untreated hepatocytes have an effective multicomponent antioxidant system against diquat-induced oxidative stress. However, when glutathione is depleted from hepatocytes by treatment with BCNU and diquat, ascorbic acid plays a vital role in maintaining cellular alpha-tocopherol levels and survival of the cell.

Glutathione and inflammatory disorders of the lung

Glutathione (GSH) is an essential tripeptide present in most eukaryotic cells. Because of its sulfhydryl group, GSH is a versatile molecule capable of protecting cells against oxidants and toxic xenobiotics. However, it also plays key roles in multiple metabolic pathways, such as the synthesis of certain leukotrienes, proteins, and DNA precursors as well as the activation of enzymes, the regulation of immune responses and others. Not only is GSH synthesized by cells for local use but it also participates in an elaborate intercellular exchange process regulated by the gamma-glutamyl cycle. Extracellular GSH in plasma and in alveolar epithelial lining fluid is thus subject to variations according to the degree of expression of gamma-glutamyl cycle enzymes and the rate of consumption of GSH by electrophilic molecules. Bronchoalveolar lavage has allowed us to observe many of these variations of GSH within the extracellular environment of the normal and diseased human lung. Studies of lung GSH have lead to a better understanding of pathogenic processes and have stimulated investigations of novel therapeutic approaches in lung inflammatory disorders.

Antioxidant macromolecules in the epithelial lining fluid of the normal human lower respiratory tract

We hypothesized that the alveolar structures may contain extracellular macromolecules with antioxidant properties to defend against oxidants. To evaluate this 51Cr-labeled human lung fibroblasts (HFL-1) and cat lung epithelial cells (AKD) were exposed to a H2O2-generating system and alveolar epithelial lining fluid (ELF) from healthy nonsmokers was tested for its ability to protect the lung cells from H2O2-mediated injury. The ELF provided marked antioxidant protection, with most from a H2O-soluble fraction in the 100-300-kD range. Plasma proteins with anti-H2O2 properties were in insufficient concentrations to provide the antioxidant protection observed. However, catalase, a normal intracellular antioxidant, was present in sufficient concentration to account for most of the observed anti-H2O2 properties of ELF. Depletion of ELF with an anticatalase antibody abolished the anti-H2O2 macromolecular defenses of ELF. Since catalase is not normally released by cells, a likely explanation for its presence in high concentrations in normal ELF is that it is released by lung inflammatory and parenchymal cells onto the epithelial surface of the lower respiratory tract during their normal turnover and collects there due to the slow turnover of ELF. It is likely that catalase in the ELF of normal individuals plays a role in protecting lung parenchymal cells against oxidants present in the extracellular milieu.

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.

Ascorbic acid in fetal rat brain

Ascorbic acid in fetal rat brain increases from 374 mg/g on the 15th day of gestation to 710 mg/g by the 20th day and remains at that level until birth. There is an 18% drop from this plateau after birth.