Menadione-resistant Chinese hamster ovary cells have an increased capacity for glutathione synthesis

A cell line (MRc40) resistant to the model quinone compound, menadione, has been isolated from a parental Chinese hamster ovary cell line (CHO-K1). The known relationship between menadione toxicity and glutathione (GSH) depletion led us to investigate whether the mechanism of resistance of MRc40 was related to alteration in GSH homeostasis. Intracellular concentrations of GSH and cysteine (CySH) were twofold and 3.2-fold greater in MRc40 than in CHO-K1. Following exposure to menadione, GSH and CySH were depleted, but subsequent recovery of thiols was more rapid and of greater magnitude in MRc40 than in CHO-K1. Twelve hours after exposure to menadione, the concentrations of GSH and CySH were 9.7- and 4.2-fold greater in MRc40 than in CHO-K1. Using nuclear magnetic resonance (NMR) spectroscopy, we observed the in situ removal of menadione from cell suspensions of CHO-K1 and MRc40. However, only in CHO-K1 did we observe concomitant depletion of NMR-visible GSH. We conclude that the perturbation of GSH metabolism contributes to the resistant phenotype and is an important characteristic of menadione-resistant CHO cells.

Effect of N-acetyl cysteine on the concentrations of thiols in plasma, bronchoalveolar lavage fluid, and lung tissue

BACKGROUND

Oxidant/antioxidant imbalance may occur in the lungs of patients with chronic obstructive pulmonary disease (COPD). Glutathione is an important extracellular and intracellular thiol oxidant in the lungs. These studies were carried out to determine the effect of N-acetyl cysteine on thiol concentrations in plasma, bronchoalveolar lavage fluid, and lung tissue.

METHODS

Studies were carried out on normal subjects, patients with COPD, and those undergoing lung resection. In the first study N-acetyl cysteine was given to three groups; healthy subjects (600 mg once daily by mouth) and two groups of patients with COPD. In the first group of patients with COPD the dose was 600 mg once daily and in the second 600 mg thrice daily, all for five days. The latter dosage regimen was also given to six patients before bronchoscopy and to 11 patients before lung resection. Lung glutathione (GSH) levels in bronchoalveolar lavage fluid or lung tissue were compared with the same numbers of patients who did not receive N-acetyl cysteine.

RESULTS

N-acetyl cysteine was detected in plasma after a single 600 mg dose in normal subjects and patients with COPD up to 1.5 hours after the drug was given. Plasma cysteine concentrations increased in normal subjects on both days 1 and 5, and in patients with COPD on day 5. Glutathione concentrations in plasma increased on day 1 in normal subjects but not in patients with COPD given 600 mg N-acetyl cysteine daily. With the higher dose of 600 mg thrice daily, however, there was a sustained elevation of GSH concentrations in plasma in patients with COPD. In patients undergoing routine diagnostic bronchoscopy and bronchoalveolar lavage those who were given N-acetyl cysteine (600 mg) thrice daily for five days had higher concentrations of cysteine in the plasma, but no significant differences in cysteine concentrations in bronchoalveolar lavage or epithelial lining fluid compared with a control group; nor were there any differences in reduced glutathione concentrations in plasma, bronchoalveolar lavage or epithelial lining fluids between the control and treated groups. Moreover, in patients undergoing lung resection those treated with N-acetyl cysteine (600 mg thrice daily for five days) had similar concentrations of cysteine and glutathione in both plasma and lung tissue when compared with a control untreated group.

CONCLUSIONS

These data suggest that, even when given in high oral doses, N-acetyl cysteine does not produce a sustained increase in glutathione levels sufficient to increase the antioxidant capacity of the lungs.

Decreased leukocyte deformability after acute cigarette smoking in humans

Acute cigarette smoking increases the sequestration of neutrophils in the lungs of humans. This may be due to the delayed transit of cells in the pulmonary microcirculation, which may result from a reduction in cell deformability as suggested by in vitro studies of smoke-exposed neutrophils. In order to support this hypothesis we wished to determine if a reduction in leukocyte deformability could be measured in whole blood exposed to smoke in vitro or in vivo. Whole blood filterability, which largely reflects leukocyte deformability, was measured as the pressure developed by filtration of diluted whole blood through a micropore membrane. Whole blood filtration pressures did not change when blood was exposed to smoke in vitro or in venous blood after acute smoking in vivo. However, arterial blood sampled from chronic smokers during acute smoking showed a consistent reduction in leukocyte deformability associated with a small increase in plasma elastase. To assess whether these changes were induced by oxidants in cigarette smoke, we measured the levels of the antioxidant glutathione (GSH), erythrocyte (RBC) membrane fragility, and products of lipid peroxidation in plasma and RBC in blood exposed to smoke in vivo and in vitro. No change in RBC lipid peroxidation or membrane fragility could be detected after in vitro smoke exposure, possibly because of the high antioxidant capacity of the RBC. However, reduced blood GSH levels and increased levels of lipid peroxidation products were detected in plasma, reflecting oxidant stress. In contrast, we were unable to detect evidence of an increased oxidant burden in blood after acute smoking in vivo, in either arterial or venous blood samples.(ABSTRACT TRUNCATED AT 250 WORDS)

The effects of N-acetylcysteine and glutathione on smoke-induced changes in lung phagocytes and epithelial cells

We studied the mechanism of the delay in neutrophil traffic in pulmonary microvasculature previously observed during cigarette smoking, the effect of cigarette smoke on lung phagocytes and epithelial cell function, and augmentation of the glutathione (GSH) antioxidant system using the thiol drug N-acetylcysteine. Using a micropore membrane system to mimic the dimensions of the average pulmonary capillary, we showed that cigarette smoke reduces cell deformability, increasing the difficulty experienced by the larger neutrophils in negotiating the smaller capillary segments, so delaying their passage during smoking. This effect is both diminished and recoverable by the addition of plasma, and by GSH in concentrations found in plasma. Cigarette smoke induces oxidative changes in both the cell membrane and the cell cytoskeleton, and diminishes the ability of neutrophils to release reactive oxygen intermediates. The injurious effect of oxidants can be measured in vitro by the detachment of 51Cr-radiolabeled alveolar epithelial cells grown in monolayers, an effect also diminished by the addition of GSH. Such epithelial cell detachment in vitro may be reflected as the epithelial permeability that occurs at an early stage in asymptomatic smokers. N-Acetylcysteine given orally (600 mg/day) increases both plasma and bronchoalveolar lavage GSH in normal subjects, but a sustained increase in plasma GSH requires higher dosage regimens in patients with chronic obstructive pulmonary disease (600 mg three times daily). Thus, the potential exists to enhance the antioxidant status of both plasma and the airspaces of the lungs against oxidant-induced injury.

Lack of effect of N-acetylcysteine on the release of oxygen radicals from neutrophils and alveolar macrophages

N-acetylcysteine (NAC) is rapidly de-acetylated in vivo to cysteine (CYSH), a precursor of glutathione (GSH) which is an antioxidant in cells and body fluids. We investigated the effect of oral administration of N-acetyl cysteine for 5 days on the spontaneous and stimulated generation of hydrogen peroxide (H2O2) and superoxide anion (O2-) from human and rat phagocytic leucocytes. Alveolar macrophages (AM) were obtained by bronchoalveolar lavage (BAL) in control rats and rats given NAC in their drinking water. Neutrophils (PMNL) were harvested from whole blood in normal nonsmoking volunteers before and after NAC was given by mouth. The stimulated release of H2O2 and O2 from both rat AM and human PMN was not changed by administration of NAC. However, a small but significant increase was observed in both the spontaneous generation of O2- from rat AM and the spontaneous generation of H2O2 from human PMNL. Administration of NAC significantly increased cysteine levels in human plasma and rat BAL, but the levels in human PMNL and rat AM after NAC did not differ from control levels. GSH levels were not altered significantly by NAC.

Lack of effect of N-acetylcysteine on the release of oxygen radicals from neutrophils and alveolar macrophages

N-acetylcysteine (NAC) is rapidly de-acetylated in vivo to cysteine (CYSH), a precursor of glutathione (GSH) which is an antioxidant in cells and body fluids. We investigated the effect of oral administration of N-acetyl cysteine for 5 days on the spontaneous and stimulated generation of hydrogen peroxide (H2O2) and superoxide anion (O2-) from human and rat phagocytic leucocytes. Alveolar macrophages (AM) were obtained by bronchoalveolar lavage (BAL) in control rats and rats given NAC in their drinking water. Neutrophils (PMNL) were harvested from whole blood in normal nonsmoking volunteers before and after NAC was given by mouth. The stimulated release of H2O2 and O2 from both rat AM and human PMN was not changed by administration of NAC. However, a small but significant increase was observed in both the spontaneous generation of O2- from rat AM and the spontaneous generation of H2O2 from human PMNL. Administration of NAC significantly increased cysteine levels in human plasma and rat BAL, but the levels in human PMNL and rat AM after NAC did not differ from control levels. GSH levels were not altered significantly by NAC.

Cysteine and glutathione concentrations in plasma and bronchoalveolar lavage fluid after treatment with N-acetylcysteine

N-acetylcysteine (600 mg/day) was given to patients by mouth for five days before bronchoscopy and bronchoalveolar lavage to determine whether N-acetylcysteine could increase the concentrations of the antioxidant reduced glutathione in plasma and bronchoalveolar lavage fluid. Bronchoalveolar lavage was performed 1-3 hours (group 2, n = 9) and 16-20 hours (group 3, n = 10) after the last dose of N-acetylcysteine and the values were compared with those in a control group receiving no N-acetylcysteine (group 1, n = 8). N-acetylcysteine was not detected in plasma or lavage fluid. Plasma concentrations of cysteine, the main metabolite of N-acetylcysteine and a precursor of reduced glutathione, were greater in the groups receiving treatment (groups 2 and 3) than in group 1. Cysteine concentrations in lavage fluid were similar in the three groups. Concentrations of reduced glutathione were greater in both plasma and lavage fluid in group 2 than in group 1. These data suggest that N-acetylcysteine given by mouth is rapidly deacetylated to cysteine, with resulting increases in the concentrations of cysteine in plasma and of reduced glutathione in plasma and the airways, which thus temporarily increase the antioxidant capacity of the lung.