Elevation of glutathione levels in bovine pulmonary artery endothelial cells by N-acetylcysteine

How to Increase Cellular Glutathione

Glutathione (GSH) has special antioxidant properties due to its high intracellular concentration, ubiquity, and high reactivity towards electrophiles of the sulfhydryl group of its cysteine moiety. In most diseases where oxidative stress is thought to play a pathogenic role, GSH concentration is significantly reduced, making cells more susceptible to oxidative damage. Therefore, there is a growing interest in determining the best method(s) to increase cellular glutathione for both disease prevention and treatment. This review summarizes the major strategies for successfully increasing cellular GSH stores. These include GSH itself, its derivatives, NRf-2 activators, cysteine prodrugs, foods, and special diets. The possible mechanisms by which these molecules can act as GSH boosters, their related pharmacokinetic issues, and their advantages and disadvantages are discussed.

Direct Interaction between N-Acetylcysteine and Cytotoxic Electrophile—An Overlooked In Vitro Mechanism of Protection

In laboratory experiments, many electrophilic cytotoxic agents induce cell death accompanied by reactive oxygen species (ROS) production and/or by glutathione (GSH) depletion. Not surprisingly, millimolar concentrations of N-acetylcysteine (NAC), which is used as a universal ROS scavenger and precursor of GSH biosynthesis, inhibit ROS production, restore GSH levels, and prevent cell death. The protective effect of NAC is generally used as corroborative evidence that cell death induced by a studied cytotoxic agent is mediated by an oxidative stress-related mechanism. However, any simple interpretation of the results of the protective effects of NAC may be misleading because it is unable to interact with superoxide (O₂•⁻), the most important biologically relevant ROS, and is a very weak scavenger of H₂O₂. In addition, NAC is used in concentrations that are unnecessarily high to stimulate GSH synthesis. Unfortunately, the possibility that NAC as a nucleophile can directly interact with cytotoxic electrophiles to form non-cytotoxic NAC–electrophile adduct is rarely considered, although it is a well-known protective mechanism that is much more common than expected. Overall, apropos the possible mechanism of the cytoprotective effect of NAC in vitro, it is appropriate to investigate whether there is a direct interaction between NAC and the cytotoxic electrophile to form a non-cytotoxic NAC–electrophilic adduct(s).

Fumarate and oxidative stress synergize to promote stability of C/EBP homologous protein in the adipocyte

C/EBP homologous protein (CHOP) is a transcription factor that is elevated in adipose tissue across many models of diabetes and metabolic stress. Although increased CHOP levels are associated with the terminal response to endoplasmic reticulum stress and apoptosis, there is no evidence for CHOP mediated apoptosis in the adipose tissue during diabetes. CHOP protein levels increase in parallel with protein succination, a fumarate derived cysteine modification, in the adipocyte during metabolic stress. We investigated the factors contributing to sustained CHOP proteins levels in the adipocyte, with an emphasis on the regulation of CHOP protein turnover by metabolite-driven modification of Keap1 cysteines. CHOP protein stability was investigated in conditions of nutrient stress due to high glucose or elevated fumarate (fumarase knockdown model); where cysteine succination is specifically elevated. CHOP protein turnover is significantly reduced in models of elevated glucose and fumarate with a ~30% increase in CHOP stability (p > 0.01), in part due to decreased CHOP phosphorylation. Sustained CHOP levels occur in parallel with elevated heme-oxygenase-1, a production of increased Nrf2 transcriptional activity and Keap1 modification. While Keap1 is directly succinated in the presence of excess fumarate derived from genetic knockdown of fumarase (fumarate levels are elevated >20-fold), it is the oxidative modification of Keap1 that predominates in adipocytes matured in high glucose (fumarate increases 4-5 fold). Elevated fumarate indirectly regulates CHOP stability through the induction of oxidative stress. The antioxidant N-acetylcysteine (NAC) reduces fumarate levels, protein succination and CHOP levels in adipocytes matured in high glucose. Elevated CHOP does not contribute elevated apoptosis in adipocytes, but plays a redox-dependent role in decreasing the adipocyte secretion of interleukin-13, an anti-inflammatory chemokine. NAC treatment restores adipocyte IL-13 secretion, confirming the redox-dependent regulation of a potent anti-inflammatory eotaxin. This study demonstrates that physiological increases in the metabolite fumarate during high glucose exposure contributes to the presence of oxidative stress and sustained CHOP levels in the adipocyte during diabetes. The results reveal a novel metabolic link between mitochondrial metabolic stress and reduced anti-inflammatory adipocyte signaling as a consequence of reduced CHOP protein turnover.

N-acetylcysteine as a potential strategy to attenuate the oxidative stress induced by uremic serum in the vascular system

AIMS

Chronic kidney disease (CKD) progression is accompanied by systemic oxidative stress, which contributes to an increase in the risk of cardiovascular diseases (CVDs). N-acetylcysteine (NAC) is among the most studied antioxidants, but its therapeutic benefits in CKD-associated CVDs remain controversial. Here, we investigated whether NAC could inhibit the oxidative stress induced by uremia in vitro and in vivo.

MAIN METHODS

Endothelial and smooth muscle cells were challenged with human uremic or non-uremic sera, and the effects of a pre-treatment with 2mM NAC were evaluated. Reactive oxygen species (ROS) production, protein oxidation and total glutathione/glutathione disulfide (tGSH/GSSG) ratios were measured. Five-sixths nephrectomized or sham-operated rats were orally treated (in the drinking water) with 60 mg/kg/day NAC or not treated for 53 days. Plasma cysteine/cystine reduction potential Eh(Cyss/2Cys) was determined as a novel marker of the systemic oxidative stress.

KEY FINDINGS

NAC inhibited all the determined oxidative stress parameters, likely by increasing the tGSH/GSSG ratio, in both cell lines exposed to uremic serum. Orally administered NAC attenuated the systemic oxidative stress in uremic rats.

SIGNIFICANCE

The present results indicate that NAC, by preventing GSH depletion in vascular cells exposed to uremic serum and by attenuating the systemic oxidative stress during CKD progression, emerges as a potential strategy to prevent the oxidative stress induced by uremic toxicity in the vascular system.

Effects of N-acetyl-L-cysteine on bleomycin induced oxidative stress in malignant testicular germ cell tumors

Testicular cancer is a very common cancer in males aged 15-44 years. Bleomycin is used in chemotherapy regimens in the treatment of patients having testicular germ-cell tumor. Bleomycin generates oxygen radicals, induces oxidative cleavage of DNA strand and induces apoptosis in cancer cells. There is no study in the literature investigating effects of N-Acetyl-L-Cysteine (NAC) on bleomycin-induced oxidative stress in testicular germ cell tumors. For this reason, we studied effects of NAC on oxidative stress produced in wild-type NTera-2 and p53-mutant NCCIT testis cancer cells incubated with bleomycin and compared the results with H(2)O(2) which directly produces oxidative stress. We determined protein carbonyl content, thiobarbituric acid reactive substances (TBARS), glutathione (GSH), 8-isoprostane, lipid hydroperoxide levels and total antioxidant capacity in both testicular cancer cells. Bleomycin and H(2)O(2) significantly increased 8-isoprostane, TBARS, protein carbonyl and lipid hydroperoxide levels in NTera-2 and NCCIT cells. Bleomycin and H(2)O(2) significantly decreased antioxidant capacity and GSH levels in both cell lines. Co-incubation with NAC significantly decreased lipid hydroperoxide, 8-isoprostane, protein carbonyl content and TBARS levels increased by bleomycin and H(2)O(2). NAC enhanced GSH levels and antioxidant capacity in the NTera-2 and NCCIT cells. It can be concluded that NAC diminishes oxidative stress in human testicular cancer cells induced by bleomycin and H(2)O(2).

Novel therapeutic approaches for pulmonary fibrosis

Pulmonary fibrosis represents the end stage of a number of heterogeneous conditions and is, to a greater or lesser degree, the hallmark of the interstitial lung diseases. It is characterized by the excessive deposition of extracellular matrix proteins within the pulmonary interstitium leading to the obliteration of functional alveolar units and in many cases, respiratory failure. While a small number of interstitial lung diseases have known aetiologies, most are idiopathic in nature, and of these, idiopathic pulmonary fibrosis is the most common and carries with it an appalling prognosis - median survival from the time of diagnosis is less than 3 years. This reflects the lack of any effective therapy to modify the course of the disease, which in turn is indicative of our incomplete understanding of the pathogenesis of this condition. Current prevailing hypotheses focus on dysregulated epithelial-mesenchymal interactions promoting a cycle of continued epithelial cell injury and fibroblast activation leading to progressive fibrosis. However, it is likely that multiple abnormalities in a myriad of biological pathways affecting inflammation and wound repair - including matrix regulation, epithelial reconstitution, the coagulation cascade, neovascularization and antioxidant pathways - modulate this defective crosstalk and promote fibrogenesis. This review aims to offer a pathogenetic rationale behind current therapies, briefly outlining previous and ongoing clinical trials, but will focus on recent and exciting advancements in our understanding of the pathogenesis of idiopathic pulmonary fibrosis, which may ultimately lead to the development of novel and effective therapeutic interventions for this devastating condition.

Glutathione synthesis and turnover in the human erythrocyte: alignment of a model based on detailed enzyme kinetics with experimental data

The erythrocyte is exposed to reactive oxygen species in the circulation and also to those produced by autoxidation of hemoglobin. Consequently, erythrocytes depend on protection by the antioxidant glutathione. Mathematical models based on realistic kinetic data have provided valuable insights into the regulation of biochemical pathways within the erythrocyte but none have satisfactorily accounted for glutathione metabolism. In the current model, rate equations were derived for the enzyme-catalyzed reactions, and for each equation the nonlinear algebraic relationship between the steady-state kinetic parameters and the unitary rate constants was derived. The model also includes the transport processes that supply the amino acid constituents of glutathione and the export of oxidized glutathione. Values of the kinetic parameters for the individual reactions were measured predominately using isolated enzymes under conditions that differed from the intracellular environment. By comparing the experimental and simulated results, the values of the enzyme-kinetic parameters of the model were refined to yield conformity between model simulations and experimental data. Model output accurately represented the steady-state concentrations of metabolites in erythrocytes suspended in plasma and the changing glutathione concentrations in whole and hemolyzed erythrocytes under specific experimental conditions. Analysis indicated that feedback inhibition of gamma-glutamate-cysteine ligase by glutathione had a limited effect on steady-state glutathione concentrations and was not sufficiently potent to return glutathione concentrations to normal levels in erythrocytes exposed to sustained increases in oxidative load.

N-acetylcysteine impairs survival of luteal cells through mitochondrial dysfunction

N-acetylcysteine (NAC) is known as an antioxidant and used for mucus viscosity reduction. However, this drug prevents or induces cell death depending on the cell type. The response of steroidogenic luteal cells to NAC is unknown. Our data shows that NAC can behave as an antioxidant or prooxidant in dependency on the concentration and mitochondrial energization. NAC elevated the flowcytometric-measured portion of hypodiploid (dying) cells. This rise was completely abolished by aurintricarboxylic acid, an inhibitor of topoisomerase II. NAC increased the secretion of nitric oxide and cellular nitrotyrosine. An image analysis indicated that cells pretreated with NAC and loaded with DHR showed a fluorescent structure probably elicited by the oxidative product of DHR, rhodamine 123 that sequesters mitochondrially. Pretreating luteal cells with NAC or adding NAC directly to mitochondrial fractions followed by assessing the mitochondrial transmembrane potential difference (Deltapsi) by the JC-1 technique demonstrated a marked decrease in Deltapsi. A protonophore restored Deltapsi and rotenone (an inhibitor of respiratory chain complex I) inhibited mitochondrial recovering. Thus, in steroidogenic luteal cells from healthy mature corpus luteum, NAC impairs cellular survival by interfering with mitochondrial metabolism. The protonophore-induced recovering of NAC-provoked decrease in Deltapsi indicates that an ATP synthase-favored route of H(+) re-entry to the matrix is essentially switched off by NAC while other respiratory chain complexes remain intact. These data may be important for therapeutic timing of treatments with NAC. (c) 2010 International Society for Advancement of Cytometry.

Protective effect of N-acetyl-L-cysteine (L-NAC) against styrene-induced cochlear injuries

CONCLUSION

Styrene exposure causes hair cell death through both apoptotic and necrotic pathways and treatment with N-acetyl-L-cysteine (L-NAC) reduces styrene ototoxicity.

OBJECTIVE

Exposure to styrene causes hearing loss and hair cell death in the middle frequency region in the cochlea. The current study was designed to examine the cell death pathways and the protective effect of L-NAC against styrene-induced cochlear injuries.

MATERIALS AND METHODS

Seventeen rats were exposed to styrene by gavage at 400 mg/kg 5 days per week for 3 weeks. Nine of the styrene-treated rats received L-NAC by intraperitoneal injection (325 mg/kg), and the remaining eight rats received saline injections as controls. The styrene-induced hearing loss was assessed by auditory brainstem responses (ABRs). Apoptotic, necrotic, and missing hair cells were quantified using combined methods, including nuclear staining with propidium iodide, F-actin staining with FITC-phalloidin, and the TUNEL assay.

RESULTS

The styrene exposure caused a threshold shift of 15±4.3 dB. Both apoptosis and necrosis were involved in the pathogenesis of the cochlear lesion, but apoptosis appeared to be the major cell death pathway leading to the styrene ototoxicity. Treatment with L-NAC reduced the number of missing and dying outer hair cells (OHCs) and reduced the styrene-induced hearing loss.

A novel approach to enhancing cellular glutathione levels

GSH and GSH-associated metabolism provide the major line of defense for the protection of cells from oxidative and other forms of toxic stress. Of the three amino acids that comprise GSH, cysteine is limiting for GSH synthesis. As extracellularly cysteine is readily oxidized to form cystine, cystine transport mechanisms are essential to provide cells with cysteine. Cystine uptake is mediated by system x(c)(-), a Na(+)-independent cystine/glutamate antiporter. Inhibition of system x(c)(-) by millimolar concentrations of glutamate, a pathway termed oxidative glutamate toxicity, results in GSH depletion and nerve cell death. Recently, we described a series of compounds derived from the conjugation of epicatechin (EC) with cysteine and cysteine derivatives that protected nerve cells in culture from oxidative glutamate toxicity by maintaining GSH levels. In this study, we characterize an additional EC conjugate, cysteamine-EC, that is 5- to 10-fold more potent than the earlier conjugates. In addition, we show that these EC conjugates maintain GSH levels by enhancing the uptake of cystine into cells through induction of a disulfide exchange reaction, thereby uncoupling the uptake from system x(c)(-). Thus, these novel EC conjugates have the potential to enhance GSH synthesis under a wide variety of forms of toxic stress.

Modulation of cell growth and cisplatin sensitivity by membrane γ-glutamyltransferase in melanoma cells

The plasma membrane enzyme gamma-glutamyltransferase (GGT) is regarded as critical for the maintenance of intracellular levels of glutathione (GSH). GGT expression has been implicated in drug resistance through elevation of intracellular GSH. The dependence of intracellular GSH on GGT expression was not conclusively ascertained. The present study was designed to investigate the role of GGT and of intracellular GSH levels in modulating proliferation and sensitivity to cisplatin of melanoma cells. GGT transfection resulted in increased growth, both in vitro and in tumour xenografts. In addition, GGT-transfected cells exhibited reduced sensitivity to cisplatin associated with lower DNA platination. A decrease in intracellular GSH levels, rather than an increase, was observed in GGT-transfected cells; moreover, in cysteine-deficient conditions, the expression of GGT did not provide transfected cells with the ability of utilising extracellular GSH. In conclusion, these results indicate that GGT activity confers a growth advantage unrelated with intracellular glutathione supply, and are consistent with the interpretation that cisplatin resistance is the consequence of modifications of cellular pharmacokinetics as a result of extracellular drug inactivation by thiol metabolites originated by GGT-mediated GSH cleavage.

Emerging drugs for idiopathic pulmonary fibrosis

Pulmonary fibrosis is often the end stage of chronic, persistent, low-level lung injury, either of known or unknown cause. The most severe form of pulmonary fibrosis is idiopathic pulmonary fibrosis (IPF), a disease process of unknown aetiology and one that often leads to respiratory failure and death. At present there are no proven or effective drug therapies for IPF. Recent advances in understanding of disease pathogenesis have focused attention on drug targeting of fibrogenic pathways, as opposed to traditional anti-inflammatory approaches. In this report, the present status of drug development of a number of emerging antifibrotic strategies and agents that may prove more effective in the therapy of this progressive, debilitating and fatal disease are reviewed.

Idiopathic pulmonary fibrosis: emerging concepts on pharmacotherapy

Idiopathic pulmonary fibrosis (IPF) is a progressive, fibrosing disease of the distal air spaces of the lung of unknown aetiology. IPF is usually fatal with a median survival of < 3 years. There are currently no effective pharmacotherapeutic agents for the treatment of IPF. In this review, unifying concepts on the pathogenesis of IPF based on understanding of host responses to tissue injury are presented. These host responses involve tightly regulated and contextually orchestrated inflammatory and repair processes. Dysregulation of either of these processes can lead to pathological outcomes. Fibrosis results from an exaggerated or dysregulated repair process that proceeds 'uncontrolled' even after inflammatory responses have subsided. Disease heterogeneity may arise when inflammation and repair are in different (dys)regulatory phases, thus accounting for regional disparity. Usual interstitial pneumonia (UIP), the histopathological correlate of clinical IPF, represents a more fibrotic tissue reaction pattern and for which anti-inflammatory agents are ineffective. Emerging 'antifibrotic' drugs and strategies for UIP/IPF are discussed. The importance of accurately phenotyping a highly heterogeneous disease process that may require individualised and 'combined' therapies is emphasised.

Nitric oxide attenuates insulin- or IGF-I-stimulated aortic smooth muscle cell motility by decreasing H2O2 levels: essential role of cGMP

Insulin and insulin-like growth factor I (IGF-I) both play important roles in vascular remodeling. Moreover, nitric oxide (NO) is well established as a counterregulatory agent that opposes the actions of several vascular agonists, in part by decreasing smooth muscle motility. We tested the hypothesis that NO blocks insulin or IGF-I-induced rat aortic smooth muscle cell motility via a mechanism involving the attenuation of agonist-induced elevation of hydrogen peroxide levels and cGMP as mediator. Insulin or IGF-I induced an increase of hydrogen peroxide levels and cell motility. Both effects were blocked by catalase or diphenyleneiodonium, indicating that hydrogen peroxide elevation is necessary for induction of cell motility. Two NO donors mimicked the effects of catalase, indicating that NO decreases cell motility by suppressing agonist-induced elevation of hydrogen peroxide. A cGMP analogue mimicked the effect of NO, whereas a guanyl cyclase inhibitor blocked the effect of NO on hydrogen peroxide levels, indicating that elevation of cGMP is both necessary and sufficient to account for the reduction of hydrogen peroxide levels. A NO donor as well as a cGMP analogue attenuated insulin-stimulated NADPH activity, indicating that NO decreases hydrogen peroxide levels by inhibiting the generation of superoxide, via a cGMP-mediated mechanism. Finally, exogenous hydrogen peroxide increased cell motility and reversed the inhibitory effect of cGMP. These results support the view that NO plays an antioxidant role via reduction of hydrogen peroxide in cultured rat aortic smooth muscle cells and that this effect is both necessary and sufficient to account for its capacity to decrease cell motility.

N-acetylcysteine effect on the luminol-dependent chemiluminescence pattern of reactive oxygen species generation by human polymorphonuclear leukocytes

The evidence of the effect of N-acetylcysteine on reactive oxygen species produced by human polymorphonuclear leukocytes (PMNs) is often contradictory, as thiol compounds may react with not only reactive oxygen and nitrogen species but also they may influence intracellular glutathione levels. The effect of 20, 100 and 200 microM N-aceylcysteine (NAC) on luminol dependent chemiluminescence (LDCL) of human PMNs (10(6) cells/ml phospate buffered saline (PBS)) and whole blood to N-formyl-methionyl-leucyl-phenylalanine (fMLP) and phorbol-12-myristate-13-acetate (PMA) was studied. Further, the ability of NAC to increase PMNs intracellular thiols and affect subsequent PMNs, stimulation was assessed. NAC 100 and 200 microM, but not 20 microM, was found to attenuate the kinetic parameters of initial phase of fMLP-stimulated PMNs oxidative burst. NAC at the concentration of 100 and 200 microM decreased the rate, maximum and integrated value of PMNs response to fMLP. The integrated value of PMA-induced PMNs and fMLP-induced whole blood LDCL response was also decreased by 100 and 200 microM NAC. Furthermore, all tested NAC concentrations decreased LDCL of resting PMNs suspension. The chemiluminescence pattern of reactive oxygen species (ROS) generation by PMNs stimulated with fMLP or PMA did not differ significantly from those preincubated with either 20, 100, or 200 microM NAC. Similarly, NAC did not increase the concentration of intracellular thiols in resting PMNs. However, addition of 200 microM NAC to PMA-stimulated PMNs prevented the decline in intracellular thiols pool. Both PMA- and fMLP-activated PMNs oxidized extracellular NAC. These results indicate that NAC decreases the intensity of PMNs oxidative burst by direct scavenger activity.

L-cysteine prevents oxidation-induced block of the cardiac Na+ channel via interaction with heart-specific cysteinyl residues in the P-loop region

The present study investigated the protective effects of L-cysteine on the oxidation-induced blockade of Na+ channel a-subunits, hH1 (cardiac) and hSkM1 (skeletal), expressed in COS7 cells. Na+ currents were recorded by the whole-cell patch clamp technique (n = 3-7). L-cysteine alone blocked hH1 and hSkM1 in a dose-dependent manner, with saturating L-cysteine block at 3,000 micromol/L. Hg2+, a potent sulfhydryl oxidizing agent, blocked hH1 with a time to 50% inhibition (Time50%) of 20s. Preperfusion of COS7 cells with 100 micromol/L L-cysteine significantly slowed the Hg2+ block of hH1 (Time50% = 179 s). L-cysteine did not prevent Hg2+ block of hSkM1 (Time50% = 37s) or the C373Y hH1 mutant (Time50% = 43s). As for other sulfo-amino acids, homocysteine prevented the Hg2+ block of hH1, with the Time50% (70s) being significantly smaller than that of L-cysteine, whereas methionine did not prevent the Hg2+ block of hH1. L-cysteine did not prevent the Cd2+ block of hH1. These results indicate that L-cysteine selectively acts on heart-specific Cys373 in the P-loop region of hH1 to prevent Cys373 from the oxidation-induced sulfur-Hg-sulfur bridge formation.

Increased sensitivity of homozygous Sod2 mutant mice to oxygen toxicity

Induction or overexpression of pulmonary manganese superoxide dismutase (MnSOD) has been shown to protect against oxygen (O2) toxicity. Genetic inactivation of MnSOD (Sod2) results in multiple organ failure and early neonatal death. However, lungs or O2-tolerance of Sod2 knockout mice have not been investigated. We evaluated survival, lung histopathology, and other pulmonary antioxidants (glutathione cycle) of homozygous (-/-) and heterozygous (+/-) Sod2 mutant mice compared with wild-type controls (Sod2+/+) following 48 h exposure to either room air or to O2. The ability of antioxidant N-acetylcysteine to compensate for the loss of MnSOD was explored. Mortality of Sod2-/- mice increased from 0% in room air to 18 and 83% in 50 and 80% O2, respectively. N-acetylcysteine did not alter mortality of Sod2-/- mice. Histopathological analysis revealed abnormalities in saccules of Sod2-/- mice exposed either to room air or to 50% O2 suggestive of delayed postnatal lung development. In 50% O2, activities of glutamate-cysteine ligase (GCL) (previously known as gamma-glutamylcysteine synthetase, gamma-GCS) and glutathione peroxidase increased in Sod2-/- (35 and 70%, respectively) and Sod2+/- (12 and 70%, respectively) mice, but glutathione levels remained unaltered. We conclude that MnSOD is required for normal O2 tolerance and that in the absence of MnSOD there is a compensatory increase in pulmonary glutathione-dependent antioxidant defense in hyperoxia.

Ceramide-mediated apoptosis in lung epithelial cells is regulated by glutathione

Reactive oxygen species (ROS) are mediators of lung injury, and glutathione (GSH) is the major nonprotein antioxidant that protects the cell from oxidative stress. We have recently shown that H(2)O(2) induces ceramide-mediated apoptosis in human lung epithelial cells. We hypothesized that ROS-mediated depletion of GSH plays a regulatory role in ceramide generation, and thus in the induction of apoptosis. Our present studies demonstrate that GSH at physiologic concentrations (1 to 10 mM) inhibits ceramide production in a time- and dose-dependent manner in A549 human alveolar epithelial cells. On the other hand, buthionine-sulfoximine-mediated depletion of intracellular GSH induces elevation of ceramide levels and apoptosis. In addition, GSH blocks H(2)O(2)-mediated induction of intracellular ceramide generation and apoptosis. These effects were not mimicked by oxidized GSH (GSSG) or other thiol antioxidants, such as dithiothreitol and 2-mercaptoethanol. Moreover, increase of intracellular H(2)O(2), mediated by inhibition of catalase by aminotriazole, also induces ceramide generation and apoptosis. These effects were blocked by N-acetylcysteine. Our results suggest that GSH depletion may be the link between oxidative stress and ceramide-mediated apoptosis in the lung.

Thiol-based antioxidants

The thiol redox status of intracellular and extracellular compartments is critical in the determination of protein structure, regulation of enzyme activity, and control of transcription factor activity and binding. Thiol antioxidants act through a variety of mechanisms, including (1) as components of the general thiol/disulfide redox buffer, (2) as metal chelators, (3) as radical quenchers, (4) as substrates for specific redox reactions (GSH), and (5) as specific reductants of individual protein disulfate bonds (thioredoxin). The composition and redox status of the available thiols in a given compartment is highly variable and must play a part in determining the metabolic activity of each compartment. It is generally beneficial to increase the availability of specific antioxidants under conditions of oxidant stress. Cells have devised a number of mechanisms to promote increased intracellular levels of thiols such as GSH and thioredoxin in response to a wide variety of stresses. Exogenous thiols have been used successfully to increase cell and tissue thiol levels in cell cultures, in animal models, and in humans. Increased levels of GSH and other thiols have been associated with increased tolerance to oxidant stresses in all of these systems and in some cases, with disease prevention or treatment in humans. A wide variety of thiol-related compounds have been used for these purposes. These include thiols such as GSH and its derivatives, cysteine and NAC, dithiols such as lipoic acid, which is reduced to the thiol form intracellularly, and "prothiol" compounds such as OTC, which are enzymatically converted to free thiols within the cell. In choosing a thiol for a specific function (e.g., protection of lung from oxidant exposure or protection of organs from ischemia reperfusion injury), the global effects must also be considered. For example, large increases in free thiols in the circulation are associated with toxic effects. These effects may be the result of thiyl radical-mediated reactions but could also be due to destabilizing effects of increases in thiol/disulfide ratios in the plasma, which normally is in a more oxidized state than intracellular compartments. Changes in the thiol redox gradient across cells could also adversely affect any transport or cell signaling processes, which are dependent on formation and rupture of disulfide linkages in membrane proteins. Therapeutic thiol administration has been shown to have great potential, and its efficacy should be increased by selecting compounds and methods of delivery that will minimize perturbations in the thiol status of regions external to the targeted areas.

Regulation of iNOS expression and glutathione levels in rat liver by oxygen tension

Molecular oxygen (O(2)) regulates the expression of a variety of genes. We hypothesized that O(2) tension may regulate iNOS expression in rat liver through the production of reactive oxygen species (ROS) and the reduction of intracellular glutathione (GSH) levels. To investigate this hypothesis, we determined the effects of hyperoxia upon iNOS induction (both at the protein and mRNA level) and the intracellular concentration of GSH in an isolated in vitro perfused rat liver preparation. To study the potential involvement of ROS in the intracellular signaling pathway linking changes in oxygen tension to gene expression, we repeated these determinations in the presence of the thiol antioxidant N-acetyl-L-cysteine (NAC). We found that 95% O(2) tension caused a significant induction of the iNOS protein and mRNA levels paralleled by a significant fall in intracellular GSH concentration. The addition of NAC (1 mM) to the perfusate during hyperoxia blocked the induction of iNOS and restored GSH levels. These results indicate that molecular O(2) regulates the expression of iNOS in rat liver at the transcriptional level, most likely through the production of ROS and the reduction of intracellular GSH levels.

Human thioredoxin attenuates hypoxia-reoxygenation injury of murine endothelial cells in a thiol-free condition

The adult T cell leukemia-derived factor (ADF), or human thioredoxin (hTRX), has a radical scavenging effect similar to that of N-acetyl cysteine (NAC). We have recently shown that ADF/hTRX protects the lung and the heart from ischemia-reperfusion induced injury. To elucidate mechanisms of the protective effect, a hypoxia-reoxygenation (H-R) injury model was developed using a murine endothelial cell line, cultured in a thiol-free medium. In this condition, cells became much more vulnerable to H-R injury. The viability of cells decreased significantly after 1 h of hypoxic incubation followed by 1 h of reoxygenation. The injury was reduced by ADF/hTRX (100 microM) or NAC (10 mM). These two agents also demonstrated an additive protective effect. When cells were cultured in thiol-free medium for 2 h in a normoxic condition, intracellular hydrogen peroxide production was increased, which was associated with a decrease in glutathione level. NAC (10 mM) attenuated these changes whereas ADF/hTRX (100 microM) did not. These results suggest that although both ADF/hTRX and NAC protected cells from H-R injury, the underlying mechanisms are different. Because the cytoprotective effect of ADF/hTRX occurs in the thiol-free condition, it must be mediated via a novel mechanism other than enhancing thiol uptake. The additive cytoprotective effect between ADF/hTRX and NAC suggests that we should combine these two agents clinically.

Lung glutathione and oxidative stress: implications in cigarette smoke-induced airway disease

Glutathione (GSH), a ubiquitous tripeptide thiol, is a vital intra- and extracellular protective antioxidant in the lungs. The rate-limiting enzyme in GSH synthesis is gamma-glutamylcysteine synthetase (gamma-GCS). The promoter (5'-flanking) region of the human gamma-GCS heavy and light subunits are regulated by activator protein-1 and antioxidant response elements. Both GSH and gamma-GCS expression are modulated by oxidants, phenolic antioxidants, and inflammatory and anti-inflammatory agents in lung cells. gamma-GCS is regulated at both the transcriptional and posttranscriptional levels. GSH plays a key role in maintaining oxidant-induced lung epithelial cell function and also in the control of proinflammatory processes. Alterations in alveolar and lung GSH metabolism are widely recognized as a central feature of many inflammatory lung diseases including chronic obstructive pulmonary disease (COPD). Cigarette smoking, the major factor in the pathogenesis of COPD, increases GSH in the lung epithelial lining fluid of chronic smokers, whereas in acute smoking, the levels are depleted. These changes in GSH may result from altered gene expression of gamma-GCS in the lungs. The mechanism of regulation of GSH in the epithelial lining fluid in the lungs of smokers and patients with COPD is not known. Knowledge of the mechanisms of GSH regulation in the lungs could lead to the development of novel therapies based on the pharmacological or genetic manipulation of the production of this important antioxidant in lung inflammation and injury. This review outlines 1) the regulation of cellular GSH levels and gamma-GCS expression under oxidative stress and 2) the evidence for lung oxidant stress and the potential role of GSH in the pathogenesis of COPD.

Endothelial permeability and IL-6 production during hypoxia: role of ROS in signal transduction

Prolonged hypoxia produces reversible changes in endothelial permeability, but the mechanisms involved are not fully known. Previous studies have implicated reactive oxygen species (ROS) and cytokines in the regulation of permeability. We tested whether prolonged hypoxia alters permeability to increasing ROS generation, which amplifies cytokine production. Human umbilical vein endothelial cell (HUVEC) monolayers were exposed to hypoxia while secretion of tumor necrosis factor-alpha (TNF-alpha), interleukin (IL)-1alpha, IL-6, and IL-8 was measured. IL-6 and IL-8 secretion increased fourfold over 24 h in a pattern corresponding to changes in HUVEC permeability measured by transendothelial electrical resistance (TEER). Addition of exogenous IL-6 to normoxic HUVEC monolayers caused time-dependent changes in TEER that mimicked the hypoxic response. An antibody to IL-6 significantly attenuated the hypoxia-induced changes in TEER (86 +/- 4 vs. 63 +/- 3% with hypoxia alone at 18 h), whereas treatment with anti-IL-8 had no effect. To determine the role of hypoxia-induced ROS on this response, HUVEC monolayers were incubated with the antioxidants ebselen (50 microM) and N-acetyl-L-cysteine (NAC, 1 mM) before hypoxia. Antioxidants attenuated hypoxia-induced IL-6 secretion (13 +/- 2 pg/ml with ebselen and 19 +/- 3 pg/ml with NAC vs. 140 +/- 15 pg/ml with hypoxia). Ebselen and NAC prevented changes in TEER during hypoxia (94 +/- 2% with ebselen and 90 +/- 6% with NAC vs. 63 +/- 3% with hypoxia at 18 h). N-nitro-L-arginine (500 microM) did not decrease hypoxia-induced changes in dichlorofluorescin fluorescence, IL-6 secretion, or TEER. Thus ROS generated during hypoxia act as signaling elements, regulating secretion of the proinflammatory cytokines that lead to alterations of endothelial permeability.

Effect of N-acetylcysteine on mitochondrial function following traumatic brain injury in rats

Efficacy of N-acetylcysteine (NAC) in traumatic brain injury (TBI)-induced mitochondrial dysfunction was evaluated following controlled cortical impact injury in rats. Respiratory function and calcium transport of rat forebrain mitochondria from injured and uninjured hemispheres were examined. NAC significantly restored mitochondrial electron transfer, energy coupling capacity, calcium uptake activity and reduced calcium content absorbed to brain mitochondrial membranes when examined 12 h post-TBI if NAC was administered i.p. 5 min before injury or 30 min or 1 h postinjury. Glutathione (reduced form, GSH) levels in brain tissues were decreased at all time points examined over a 14-day observation period, while mitochondrial GSH levels significantly decreased only at 3 days and 14 days following TBI. NAC treatment given within 1 h greatly restored brain GSH levels from 1 h to 14 days and mitochondrial GSH levels from 12 h to 14 days post-TBI. NAC did not show protective effects when given 2 h postinjury. Our data indicate that NAC administered postinjury at an early stage can effectively restore TBI-induced mitochondrial dysfunction and the protective effect of NAC may be related to its restoration of GSH levels in the brain.

Shear-induced tyrosine phosphorylation in endothelial cells requires Rac1-dependent production of ROS

The shear-induced intracellular signal transduction pathway in vascular endothelial cells involves tyrosine phosphorylation and activation of mitogen-activated protein (MAP) kinase, which may be responsible for the sustained release of nitric oxide. MAP kinase is known to be activated by reactive oxygen species (ROS), such as H2O2, in several cell types. ROS production in ligand-stimulated nonphagocytic cells appears to require the participation of a Ras-related small GTP-binding protein, Rac1. We hypothesized that Rac1 might serve as a mediator for the effect of shear stress on MAP kinase activation. Exposure of bovine aortic endothelial cells to laminar shear stress of 20 dyn/cm2 for 5-30 min stimulated total cellular and cytosolic tyrosine phosphorylation as well as tyrosine phosphorylation of MAP kinase. Treating endothelial cells with the antioxidants N-acetylcysteine and pyrrolidine dithiocarbamate inhibited in a dose-dependent manner the shear-stimulated increase in total cytosolic and, specifically, MAP kinase tyrosine phosphorylation. Hence, the onset of shear stress caused an enhanced generation of intracellular ROS, as evidenced by an oxidized protein detection kit, which were required for the shear-induced total cellular and MAP kinase tyrosine phosphorylation. Total cellular and MAP kinase tyrosine phosphorylation was completely blocked in sheared bovine aortic endothelial cells expressing a dominant negative Rac1 gene product (N17rac1). We concluded that the GTPase Rac1 mediates the shear-induced tyrosine phosphorylation of MAP kinase via regulation of the flow-dependent redox changes in endothelial cells in physiological and pathological circumstances.

Phospholipase D activation in endothelial cells is redox sensitive

Reactive oxygen species (ROS) are implicated in the pathophysiology of a number of vascular disorders, including atherosclerosis. Recent studies indicate that ROS modulate signal transduction in mammalian cells. Previously, we have shown that ROS (hydrogen peroxide, fatty acid hydroperoxide, diperoxovanadate, and 4-hydroxynonenal) enhance protein tyrosine phosphorylation and activate phospholipase D (PLD) in bovine pulmonary artery endothelial cells (BPAECs). In the present study, our aim was to investigate the role of exogenous thiol agents on ROS-induced PLD activation in conjunction with the role of cellular thiols--glutathione (GSH) and protein thiols--on PLD activation and protein tyrosine phosphorylation. Pretreatment of BPAECs with N-acetyl-L-cysteine (NAC) or 2-mercaptopropionylglycine (MPG) blocked ROS-induced changes in intracellular GSH and PLD activation. Also, pretreatment with NAC attenuated diperoxovanadate-induced protein tyrosine phosphorylation. Pretreatment of BPAECs with diamide or L-buthionine-(S,R)-sulfoximine (BSO), agents that lower intracellular GSH and thiols, enhanced PLD activity. Furthermore, NAC blocked diamide- or BSO-mediated changes in GSH levels, PLD activity, and protein tyrosine phosphorylation. NAC also attenuated diamide-induced tyrosine phosphorylation of proteins between 69 and 118 KDa. These results support the hypothesis that modulation of thiol-redox status (cellular nonprotein and protein thiols) may contribute to the regulation of ROS-induced protein tyrosine phosphorylation and PLD activation in vascular endothelium.

Receptor-activated Ca2+ increases in vibrodissociated cortical astrocytes: a nonenzymatic method for acute isolation of astrocytes

A new nonenzymatic method for the acute isolation of astrocytes from rat cerebral cortex is described. A vibratory device was used to dissociate the cells from thin brain slices, and the method yielded fresh and relatively well-preserved astrocytes without previous enzyme incubation. These cells were examined in a microspectrofluorometric system for measurement of changes in intracellular free calcium concentrations ([Ca2+]i), and their expression of various neurotransmitter receptors was determined. Acutely isolated glial fibrillary acidic protein (GFAP)-positive astrocytes (p7-p18) were seen to respond to the metabotropic glutamate receptor agonist (1S,3R)-1-aminocyclopentane-1,3-dicarboxylic acid (ACPD, 10(-4) M) with increases in [Ca2+]i, and this response was blocked by (RS)-1-aminoindan-1,5 dicarboxylic acid (AIDA, 10(-3) M), an antagonist to group 1 metabotropic glutamate receptors. The delta-opioid receptor agonist D-Pen2, D-Pen5-enkephalin (DPDPE, 10(-6) M) evoked [Ca2+]i increases that were blocked by the delta-opioid antagonist ICI 174.388 (10(-5) M). The astrocytes failed to respond to 5-hydroxytryptamine (5-HT, 10(-5) M), although the same cells subsequently were found to respond to other agonists. Furthermore, [Ca2+]i responses evoked by phenylephrine (10(-5) M) were blocked by prazosin (0.2x10(-6) M), suggesting the expression of alpha1-adrenergic receptors on the acutely isolated astrocytes. The cells were also shown to react with [Ca2+]i increases in response to depolarization with high extracellular potassium concentrations (50x10(-3) M). The signals induced by depolarization were not seen in Ca2+-free buffer, indicating the presence of voltage-activated calcium channels in these cells. Thus, the present study confirms some of the results earlier obtained in cell cultures, suggesting that cortical astrocytes in vivo express glutamate, opiate, and adrenergic receptors, coupled to increases in [Ca2+]i, whereas no receptors for 5-HT could be detected.

Characterization of N-acetylcysteine and ambroxol in anti-oxidant therapy

Reactive free oxygen radicals are known to play an important role in the pathogenesis of various lung diseases such as idiopathic pulmonary fibrosis (IPF), adult respiratory distress syndrome (ARDS) or cystic fibrosis (CF). They can originate from endogenous processes or can be part of exogenous exposures (e.g. ozone, cigarette smoke, asbestos fibres). Consequently, therapeutic enhancement of anti-oxidant defence mechanisms in these lung disorders seems a rational approach. In this regard, N-acetyl-L-cysteine (NAC) and ambroxol have both been frequently investigated. Because of its SH group, NAC scavenges H2O2 (hydrogen peroxide), .OH (hydroxol radical), and HOCl (hypochlorous acid). Furthermore, NAC can easily be deacetylated to cysteine, an important precursor of cellular glutathione synthesis, and thus stimulate the cellular glutathione system. This is most evident in pulmonary diseases characterized by low glutathione levels and high oxidant production by inflammatory cells (e.g. in IPF and ARDS). NAC is an effective drug in the treatment of paracetamol intoxication and may even be protective against side-effects of mutagenic agents. In addition NAC reduces cellular production of pro-inflammatory mediators (e.g. TNF-alpha, IL-1). Also, ambroxol [trans-4-(2-amino-3,5-dibromobenzylamino)-cyclohexane hydrochloride] scavenges oxidants (e.g. .OH, HOCl). Moreover, ambroxol reduces bronchial hyperreactivity, and it is known to stimulate cellular surfactant production. In addition, ambroxol has anti-inflammatory properties owing to its inhibitory effect on the production of cellular cytokines and arachidonic acid metabolites. For both substances effective anti-oxidant and anti-inflammatory function has been validated when used in micromolar concentrations. These levels are attainable in vivo in humans. This paper gives an up-to-date overview about the current knowledge of the hypothesis that oxidant-induced cellular damage underlies the pathogenesis of many human pulmonary diseases, and it discusses the feasibility of anti-oxidant augmentation therapy to the lung by using NAC or ambroxol.

N-acetylcysteine inhibits IL-1 alpha-induced IL-8 secretion by bronchial epithelial cells

The protective effects of N-acetylcysteine (NAC) have been documented in experimental and clinical acute lung injury. However, the effect of NAC on the secretion of interleukin-8-(IL-8), which is an important mediator of the pathogenesis of acute lung injury through the recruitment of neutrophils, has not been determined. In the present study, therefore, we examined the effect of NAC on IL-8 secretion by IL-1 alpha-stimulated bronchial epithelial cells. NAC inhibited IL-8 secretion by bronchial epithelial cells in a dose-dependent manner. In addition, the structurally unrelated antioxidants, butylated hydroxyanisole (BHA) and pyrrolidine dithiocarbamate (PDTC) also effectively inhibited secretion. These results indicated that an antioxidant-sensitive mechanism might be involved in inhibition of IL-8 secretion by IL-1 alpha-stimulated bronchial epithelial cells. The protective effects of NAC on acute lung injury have been suggested to be due to scavenging reactive oxygen intermediates (ROIs) and stimulation of glutathione synthesis. In addition to this, our results may provide an alternative explanation for the efficacy of NAC on acute lung injury.

Characterization of multiple cysteine and cystine transporters in rat alveolar type II cells

Cysteine availability is rate limiting for the synthesis of glutathione, an important antioxidant in the lung. We used rat alveolar epithelial type II cells to study the mechanism of cysteine and cystine uptake. Consistent with carrier-mediated transport, each uptake process was saturable with Michaelis-Menten kinetics and was inhibited at 4 degrees C and by micromolar levels of amino acids or analogs known to be substrates for a specific transporter. A unique system XAG was found that transports cysteine and cystine (as well as glutamate and aspartate, the only substrates previously described for system XAG). We also identified a second Na(+)-dependent cysteine transporter system, system ASC, and two Na(+)-independent transporter systems, system xc for cystine and system L for cysteine. In the presence of glutathione at levels measured in rat plasma and alveolar lining fluid, cystine was reduced to cysteine and was transported on systems ASC and XAG, doubling the transport rate. Cysteinylglycine, released from glutathione at the cell surface by gamma-glutamyl transpeptidase, also stimulated uptake after reduction of cystine. These findings suggest that, under physiological conditions, cysteine and cystine transport is influenced by the extracellular redox state.

Protection against glutamate-induced cytotoxicity in C6 glial cells by thiol antioxidants

In many cell lines, glutamate cytotoxicity is known to be medicated by an inhibition of cystine transport. Because glutamate and cystine share the same transporter, elevated levels of extracellular glutamate competitively inhibit cystine transport leading to depletion of intracellular glutathione. A glutathione-depleted state impairs cellular antioxidant defenses resulting in oxidative stress. It was therefore of interest to investigate whether proglutathione agents, e.g., N-acetylcysteine and lipoic acid, are able to protect against glutamate cytotoxicity. Both lipoic acid (100 microM-1 mM) and N-acetylcysteine (100 microM-1 mM) completely protected C6 cells from the glutamate-induced cell death. Both agents facilitate extracellular supply of cysteine, the reduced form of cystine, that is transported into the cell by a glutamate-insensitive transport mechanism. Protection by lipoic acid and N-acetylcysteine corresponded with a sparing effect on cellular glutathione, which is usually depleted after glutamate treatment. In the presence of L-buthionine-(S,R)-sulfoximine, a gamma-glutamylcysteine synthetase inhibitor, low doses (< 100 microM) of lipoic acid and N-acetylcysteine did not protect cells against glutamate-induced cytotoxicity. At higher concentrations (> 500 microM), however, both lipoic acid and N-acetylcysteine provided partial protection against glutamate cytotoxicity even in glutathione synthesis-arrested cells. These results indicate that at low concentrations the primary mechanism of protection by the thiol antioxidants was mediated by their proglutathione property rather than direct scavenging of reactive oxygen. At higher concentrations (> 500 microM), a GSH-independent direct antioxidant effect of lipoic and N-acetylcysteine was observed. Dichlorofluorescin fluorescence, a measure of intracellular peroxides, increased sixfold after glutamate treatment of C6 cells. Lipoic acid and N-acetylcysteine treatment significantly lowered glutamate-induced dichlorofluorescin fluorescence compared with that of controls. Interestingly, alpha-tocopherol (50 microM) also suppressed glutamate-induced dichlorofluorescin fluorescence, indicating the peroxides detected by dichlorofluorescin were likely lipid hydroperoxides. Both thiol antioxidants, particularly lipoic acid, appear to have remarkable therapeutic potential in protecting against neurological injuries involving glutamate and oxidative stress.

N-acetylcysteine attenuates TNF-alpha-dependent reduction of IL-4-induced Fc epsilon RII expression in human monocytes

We have previously shown that tumor necrosis factor-alpha (TNF-alpha) reduces interleukin-4 (IL-4)-induced Fc epsilon RII expression in human monocytes. It has been shown that TNF-alpha activates nuclear transcriptional factors through the generation of reactive oxygen intermediates (ROIs), and antioxidant N-acetylcysteine (NAC) inhibits TNF-alpha-induced activation of nuclear transcriptional factors. Therefore, we hypothesized that TNF-alpha-dependent reduction of IL-4-induced Fc epsilon RII expression in monocytes might be mediated through the ROIs-activated mechanism. In the present study, to test our hypothesis, we examined the effect of NAC on TNF-alpha-dependent reduction of IL-4-induced Fc epsilon RII expression in human monocytes. NAC attenuated TNF-alpha-dependent reduction of IL-4-induced Fc epsilon RII expression by attenuating TNF-alpha-dependent reduction of Fc epsilon RII mRNA expression. Similarly, the structurally unrelated antioxidant, pyrrolidine dithiocarbamate (PDTC), also effectively attenuated this-reduction. These results indicate that an ROIs-activated and antioxidant-sensitive mechanism might be involved in TNF-alpha-dependent reduction of IL-4-induced Fc epsilon RII expression in monocytes.

Nacystelyn, a novel lysine salt of N-acetylcysteine, to augment cellular antioxidant defence in vitro

Nacystelyn (NAL), a recently-developed lysine salt of N-acetylcysteine (NAC), and NAG, both known to have excellent mucolytic capabilities, were tested for their ability to enhance cellular antioxidant defence mechanisms. To accomplish this, both drugs were tested in vitro for their capacity: (1) to inhibit O2- and H2O2 in cell-free assay systems; (2) to reduce O2- and H2O2 released by polymorphonuclear leukocytes (PMN); and (3) for their cellular glutathione (GSH) precursor effect. In comparison with GSH, NAL and NAC inhibited H2O2, but not O2-, in cell-free, in vitro test systems in a similar manner. The anti-H2O2 effect of these drugs was as potent as that of GSH, an important antioxidant in mammalian cells. To enhance cellular GSH levels, increasing concentrations (0-2 x 10(-4) mol l-1) of both substances were added to a transformed alveolar cell line (A549 cells). After NAC administration (2 x 10(-4) mol l-1), total intracellular GSH (GSH + 2GSSG) levels reached 4.5 +/- 1.1 x 10(-6) mol per 10(6) cells, whereas NAL increased GSH to 8.3 +/- 1.6 x 10(-6) mol per 10(6) cells. NAC and NAL administration also induced extracellular GSH secretion; about two-fold (NAC), and 1.5-fold (NAL), respectively. The GSH precursor potency of cystine was about two-fold higher than that of NAL and NAC, indicating that the deacetylation process of NAL and NAC slows the ability of both drugs to induce cellular glut production and secretion. Buthionine-sulphoximine, which is an inhibitor of GSH synthetase, blocked the cellular GSH precursor effect of all substances. In addition, these data demonstrate that NAC and NAL reduce H2O2 released by freshly-isolated cultured blood PMN from smokers with chronic obstructive pulmonary disease (COPD) (n = 10) in a similar manner (about 45% reduction of H2O2 activity by NAC or NAL at 4 x 10(-6) mol l-1). In accordance with the results obtained from cell-free, in vitro assays, O2- released by PMN was not affected. Ambroxol (concentrations: 10(-9)-10(-3) mol l-1) did not reduce activity levels of H2O2 and O2- in vitro. Due to the basic effect of dissolved lysine, which separates easily in solution from NAL, the acidic function of the remaining NAC molecule is almost completely neutralized [at concentration 2 x 10(-4) M: pH 3.6 (NAC), pH 6.4 (NAL)]. Due to their function as H2O2 scavengers, and due to their ability to enhance cellular glutathione levels, NAL and NAC both have potent antioxidant capabilities in vitro. The advantage of NAL over NAC is two-fold; it enhances intracellular GSH levels twice as effectively, and it forms neutral pH solutions whereas NAC is acidic. Concluding from these in vitro results, NAL could be an interesting alternative to enhance the antioxidant capacity at the epithelial surface of the lung by aerosol administration.

Effect of antioxidants on hyperoxia-induced ICAM-1 expression in human endothelial cells

The regulating mechanism of hyperoxia-induced ICAM-1 expression has not been elucidated. We studied the effect of antioxidants, including superoxide dismutase (SOD), catalase and N-acetylcysteine (NAC), on hyperoxia-induced ICAM-1 expression in human pulmonary artery endothelial cells (HPAEC) and human umbilical vein endothelial cells (HUVEC). Cells were cultured to confluence and exposed to either hyperoxic or normoxic gas with or without various kinds of antioxidants. The levels of ICAM-1 expression in the endothelial cells and the concentrations of reduced (GSH) and oxidized glutathione (GSSG) in the media were examined by flow cytometry and by spectrophotometry, respectively. After 48-hour exposure to hyperoxia, ICAM-1 expression was increased (HPAEC; 161 +/- 21% and HUVEC; 163 +/- 16%) and total glutathione concentration in the media was decreased as compared with normoxia. SOD did not change the GSH and GSSG concentrations in the media. Catalase dose-dependently decreased the supernatant GSSG concentration in both HPAEC and HUVEC, while the GSH concentration was nearly constant. NAC dose-dependently increased the supernatant GSH concentrations in both HPAEC and HUVEC. There was no difference in the supernatant GSSG concentrations between the NAC-treated HPAEC and HUVEC. There was no difference in ICAM-1 expression in either HPAEC or HUVEC with SOD treatment. ICAM-1 expressions in 100 U/ml (236 +/- 20%) and 1,000 U/ml (315 +/- 36%) of catalase were increased in HPAEC, and that in 1,000 U/ml (440 +/- 209%) of catalase was increased in HUVEC. Five and 10 U/ml of NAC decreased ICAM-1 expression in HPAEC (141 +/- 26% and 113 +/- 11%) and HUVEC (119 +/- 23% and 106 +/- 7%), respectively. These results suggest that extracellular glutathione may play a role in regulating hyperoxia-induced ICAM-1 expression in HPAEC and HUVEC.

Effect of antioxidants on lipopolysaccharide-stimulated induction of mangano superoxide dismutase mRNA in bovine pulmonary artery endothelial cells

Generation of reactive oxygen species (ROS) is a common event in the pathogenesis of acute lung injury. Endothelial cells may be both a target and a source of the ROS. Exposure of bovine pulmonary endothelial cells (BPAEC) to lipopolysaccharide (LPS) has been shown to result in intracellular generation of both ROS and the antioxidant enzyme, mangano superoxide dismutase (MnSOD). The present study investigates whether alterations in intracellular oxidant state affect LPS-stimulated cytotoxicity and induction of MnSOD mRNA. BPAEC were pretreated with either the free radical scavenger, dimethylsulfoxide (DMSO), the xanthine oxidase inhibitor, allopurinol, or N-acetylcysteine (a cysteine derivate capable of increasing glutathione stores) prior to exposure to LPS (0.1 microgram/ml) for either 4, 8 or 18 hours. We found that pretreatment of BPAEC with DMSO blocked both LPS-induced cytotoxicity and induction of the MnSOD gene. Nuclear run-off experiments demonstrated that LPS-stimulated induction of the MnSOD mRNA occurred at the transcriptional level and that DMSO blocked this event. Pretreatment with allopurinol also prevented the cytotoxicity associated with LPS but, in contrast to DMSO, did not alter induction of MnSOD mRNA. N-acetylcysteine did not affect the LPS-stimulated cytotoxicity but resulted in an early and transient reduction in induction of the MnSOD gene. We conclude that LPS stimulates generation of intracellular ROS that regulate induction of the MnSOD gene at the transcriptional level further, we conclude that LPS-stimulated cytotoxicity involves both the xanthine oxidase pathway and perhaps intracellular generation of hydroxyl radicals. The difference in the protective effect between DMSO, NAC and allopurinol suggest that upregulation of the MnSOD gene does not contribute to LPS-induced cytotoxicity.

N-acetylcysteine increases the glutathione content and protects rat alveolar type II cells against paraquat-induced cytotoxicity

A protective effect of N-acetylcysteine in oxidative lung damage was reported by a number of workers; however, the mechanism underlying this effect was not thoroughly elucidated. The present research investigates the protection by N-acetylcysteine against paraquat-induced cytotoxicity to alveolar type II cells, which are known to be specific targets of paraquat toxicity in vivo. We found that addition of 1 mM N-acetylcysteine to alveolar type II cells incubated with 1 mM paraquat reduced the cytotoxic index from 17.4 +/- 1.3% to 9.3 +/- 1.5%. This effect could not be explained by the interference of N-acetylcysteine with the active uptake of paraquat by type II cells. Incubation of these cells with N-acetylcysteine enhances their glutathione content, thus reducing the paraquat- induced depletion of glutathione in these cells. These results suggest that N-acetylcysteine exerts its protective effect by acting as a precursor for glutathione in alveolar type II cells.

A serum-free, pyruvate-free medium that supports neonatal neural/glial cultures

Tissue culture media with serum generally cause excessive astrocyte proliferation in neonatal brain cultures, and often fail to support neonatal neurons. Published serum-free media for brain cultures contain sodium pyruvate, which interferes with lactate dehydrogenase (LDH) assays for cell death. We wanted to use neonatal neural-glial cultures in LDH assays while avoiding astrocyte proliferation, so we developed a serum-free medium without sodium pyruvate. Our initial medium was based on that of Romijn et al. (J Neurosci Methods 23:75-83, 1988), testing selected additives. Cell survival in 8-10-day-old cultures was measured using 3-[4,5-Dimethylthiazol-2-yl]-2,5-diphenyltetrazolium bromide (MTT). N-acetylcysteine, citrate, superoxide dismutase, ascorbate, supplemental amino acids, and high levels of transferrin improved survival. The optimized medium supported neonatal brain cells in reaggregates or in monolayers of 400 cells/mm2 for several weeks with large, healthy-appearing neurons and very little astrocyte proliferation. Neurons stained strongly for the neuronal marker class III beta-tubulin and the synapse marker synaptophysin. Electron microscopy of reaggregate cultures demonstrated abundant neurons with synapses in a dense neuropil. This medium will be useful for various in vitro applications, especially those using LDH assays or requiring the use of neonatal cells.

An alternative method for obtaining high-viability cell suspensions from neonatal mouse brain

Cultured brain cells have contributed greatly to our understanding of a variety of neurobiological processes. The ability to culture brain tissue is important for studying cellular processes underlying unique neural properties. Traditional culturing techniques commonly involve triturating tissue through glass Pastuer pipets, which are inappropriate for use with potentially biohazardous materials. We therefore developed an alternative method for dissociating brain tissue. The protocol combines enzymatic digestion and mechanical dissociation with additives to the dissection medium that protect the cells against other sources of injury, including glutamate neurotoxicity, oxidative damage, and excessively alkaline pH. We find this method works well with post-natal mouse brain, consistently giving cell viabilities in the range of 92-99% and an average yield of 3.1 x 10(6) cells per mouse.

Modulation of transforming growth factor-beta 1 antiproliferative effects on endothelial cells by cysteine, cystine, and N-acetylcysteine

Early passaged bovine pulmonary artery endothelial cells exposed to 0.1-2.0 ng/ml transforming growth factor-beta 1 (TGF-beta 1) showed concentration-dependent growth inhibition, as assessed by [3H]thymidine labeling and cell counts, over a 96-h interval. Most of the inhibition of [3H]thymidine labeling measured at 96 h persisted when the medium was replaced with TGF-beta 1-free medium after 24 h, but the inhibition of labeling was prevented by the presence of anti-TGF-beta 1 antibody in the replacement medium. Additions of 2 mM cysteine, 1 mM cystine, or 2 mM N-acetylcysteine at the time of the initial addition of TGF-beta 1 blocked the inhibitory effect of TGF-beta 1 on [3H]-thymidine labeling when this was assessed after 72-96 h, but not at earlier times. Prevention of the inhibitory effect on cellular proliferation produced by cysteine, cystine and N-acetylcysteine was associated with elevation of cellular glutathione that was present at 48-96 h. There was no evidence for direct inactivation of TGF-beta 1 by the thiol-amino acids. Conditioned medium from TGF-beta 1-treated endothelial cells inhibited proliferation of mink lung carcinoma (CCL64) cells, supporting a previously reported concept of autocrine production of TGF-beta 1 by the endothelial cells. The inhibitory action of the conditioned medium was partially prevented when 1 mM cysteine was added during conditioning. Thus, TGF-beta 1 treatment of endothelial cells appears to set off autocrine production by these cells of TGF-beta 1 that perpetuates the inhibition of cellular proliferation. Replenishment of cellular glutathione with thiol-amino acids counteracts the growth-inhibitory effect of TGF-beta 1 through a currently undefined mechanism.