Glutamyl transferase deficiency results in lung oxidant stress in normoxia (original) (raw)
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Gamma-glutamyl transferase deficiency results in lung oxidant stress in normoxia
American journal of physiology. Lung cellular and molecular physiology, 2002
gamma-Glutamyl transferase (GGT) is critical to glutathione homeostasis by providing substrates for glutathione synthesis. We hypothesized that loss of GGT would cause oxidant stress in the lung. We compared the lungs of GGT(enu1) mice, a genetic model of GGT deficiency, with normal mice in normoxia to study this hypothesis. We found GGT promoter 3 (P3) alone expressed in normal lung but GGT P3 plus P1, an oxidant-inducible GGT promoter, in GGT(enu1) lung. Glutathione content was barely decreased in GGT(enu1) lung homogenate and elevated nearly twofold in epithelial lining fluid, but the fraction of oxidized glutathione was increased three- and fourfold, respectively. Glutathione content in GGT(enu1) alveolar macrophages was decreased nearly sixfold, and the oxidized glutathione fraction was increased sevenfold. Immunohistochemical studies showed glutathione deficiency together with an intense signal for 3-nitrotyrosine in nonciliated bronchiolar epithelial (Clara) cells and express...
Glutathione Reductase Targeted to Type II Cells Does Not Protect Mice from Hyperoxic Lung Injury
American Journal of Respiratory Cell and Molecular Biology, 2008
Exposure of the lung epithelium to reactive oxygen species without adequate antioxidant defenses leads to airway inflammation, and may contribute to lung injury. Glutathione peroxidase catalyzes the reduction of peroxides by oxidation of glutathione (GSH) to glutathione disulfide (GSSG), which can in turn be reduced by glutathione reductase (GR). Increased levels of GSSG have been shown to correlate negatively with outcome after oxidant exposure, and increased GR activity has been protective against hyperoxia in lung epithelial cells in vitro. We tested the hypothesis that increased GR expression targeted to type II alveolar epithelial cells would improve outcome in hyperoxia-induced lung injury. Human GR with a mitochondrial targeting sequence was targeted to mouse type II cells using the SPC promoter. Two transgenic lines were identified, with Line 2 having higher lung GR activities than Line 1. Both transgenic lines had lower lung GSSG levels and higher GSH/GSSG ratios than wild-type. Six-week-old wild-type and transgenic mice were exposed to greater than 95% O 2 or room air (RA) for 84 hours. After exposure, Line 2 mice had higher right lung/body weight ratios and lavage protein concentrations than wild-type mice, and both lines 1 and 2 had lower GSSG levels than wild-type mice. These findings suggest that GSSG accumulation in the lung may not play a significant role in the development of hyperoxic lung injury, or that compensatory responses to unregulated GR expression render animals more susceptible to hyperoxic lung injury.
The American Journal of Pathology, 2009
␥-Glutamyl transferase (GGT) regulates glutathione metabolism and cysteine supply. GGT inactivation in GGT enu1 mice limits cysteine availability causing cellular glutathione deficiency. In lung, the resultant oxidant burden is associated with increased nitric oxide (NO) production, yet GGT enu1 mice still exhibit higher mortality in hyperoxia. We hypothesized that NO metabolism is altered under severe oxidant stress and contributes to lung cellular injury and death. We compared lung injury, NO synthase (NOS) expression, nitrate/nitrite production, nitroso product formation, peroxynitrite accumulation, and cell death in wild-type and GGT enu1 mice in normoxia and hyperoxia. The role of NOS activity in cell death was determined by NOS inhibition. Exposure of wild-type mice to hyperoxia caused increased lung injury, altered NO metabolism, and induction of cell death compared with normoxia, which was attenuated by NOS inhibition. Each of these lung injury indices were magnified in hyperoxia-exposed GGT enu1 mice except nitrosation , which showed a diminished decrease compared with wild-type mice. NOS inhibition attenuated cell death only slightly , likely due to further exacerbation of oxidant stress. Taken together , these data suggest that apoptosis in hyperoxia is partially NO-dependent and reiterate the importance of cellular glutathione in lung antioxidant defense. Therefore, reduced denitrosylation of proteins, possibly resulting in impaired cellular repair, and excessive apoptotic cell death likely contribute to increased lung injury and mortality of GGT enu1 mice in hyperoxia.
Environmental toxicity, redox signaling and lung inflammation: The role of glutathione
Molecular Aspects of Medicine, 2009
Glutathione (γ-glutamyl-cysteinyl-glycine, GSH) is the most abundant intracellular antioxidant thiol and is central to redox defense during oxidative stress. GSH metabolism is tightly regulated and has been implicated in redox signaling and also in protection against environmental oxidant-mediated injury. Changes in the ratio of the reduced and disulfide form (GSH/GSSG) can affect signaling pathways that participate in a broad array of physiological responses from cell proliferation, autophagy and apoptosis to gene expression that involve H 2 O 2 as a second messenger. Oxidative stress due to oxidant/antioxidant imbalance and also due to environmental oxidants is an important component during inflammation and respiratory diseases such as chronic obstructive pulmonary disease, idiopathic pulmonary fibrosis, acute respiratory distress syndrome, and asthma. It is known to activate multiple stress kinase pathways and redox sensitive transcription factors such as Nrf2, NF-κB and AP-1, which differentially regulate the genes for pro-inflammatory cytokines as well as the protective antioxidant genes. Understanding the regulatory mechanisms for the induction of antioxidants, such as GSH, versus pro-inflammatory mediators at sites of oxidant-directed injuries may allow for the development of novel therapies which will allow pharmacological manipulation GSH synthesis during inflammation and oxidative injury. This article features the current knowledge about the role of GSH in redox signaling, GSH biosynthesis and particularly the regulation of transcription factor Nrf2 by GSH and downstream signaling during oxidative stress and inflammation in various pulmonary diseases. We also discussed the current therapeutic clinical trials using GSH and other thiol compounds, such as N-acetyl-L-cysteine, fudosteine, carbocysteine, erdosteine in environment-induced airways disease.
Oxidative stress and regulation of glutathione in lung inflammation
2001
Inflammatory lung diseases are characterized by chronic inflammation and oxidant/antioxidant imbalance, a major cause of cell damage. The development of an oxidant/antioxidant imbalance in lung inflammation may activate redox-sensitive transcription factors such as nuclear factor-kB, and activator protein-1 (AP-1), which regulate the genes for pro-inflammatory mediators and protective antioxidant genes. Glutathione (GSH), a ubiquitous tripeptide thiol, is a vital intra-and extracellular protective antioxidant against oxidative/nitrosative stresses, which plays a key role in the control of pro-inflammatory processes in the lungs. Recent findings have suggested that GSH is important in immune modulation, remodelling of the extracellular matrix, apoptosis and mitochondrial respiration. The rate-limiting enzyme in GSH synthesis is c-glutamylcysteine synthetase (c-GCS). The human c-GCS heavy and light subunits are regulated by AP-1 and antioxidant response elements and are modulated by oxidants, phenolic antioxidants, growth factors, and inflammatory and anti-inflammatory agents in lung cells. Alterations in alveolar and lung GSH metabolism are widely recognized as a central feature of many inflammatory lung diseases such as idiopathic pulmonary fibrosis, acute respiratory distress syndrome, cystic fibrosis and asthma. The imbalance and/or genetic variation in antioxidant c-GCS and pro-inflammatory versus antioxidant genes in response to oxidative stress and inflammation in some individuals may render them more susceptible to lung inflammation. Knowledge of the mechanisms of GSH regulation and balance between the release and expression of pro-and anti-inflammatory mediators could lead to the development of novel therapies based on the pharmacological manipulation of the production as well as gene transfer of this important antioxidant in lung inflammation and injury. This review describes the redox control and involvement of nuclear factor-kB and activator protein-1 in the regulation of cellular glutathione and c-glutamylcysteine synthetase under conditions of oxidative stress and inflammation, the role of glutathione in oxidant-mediated susceptibility/tolerance, c-glutamylcysteine synthetase genetic susceptibility and the potential therapeutic role of glutathione and its precursors in protecting against lung oxidant stress, inflammation and injury.
Inhibiting Glutathione Metabolism in Lung Lining Fluid as a Strategy to Augment Antioxidant Defense
Current enzyme inhibition, 2011
Glutathione is abundant in the lining fluid that bathes the gas exchange surface of the lung. On the one hand glutathione in this extracellular pool functions in antioxidant defense to protect cells and proteins in the alveolar space from oxidant injury; on the other hand, it functions as a source of cysteine to maintain cellular glutathione and protein synthesis. These seemingly opposing functions are regulated through metabolism by gamma-glutamyl transferase (GGT, EC 2.3.2.2). Even under normal physiologic conditions, lung lining fluid (LLF) contains a concentrated pool of GGT activity exceeding that of whole lung by about 7-fold and indicating increased turnover of glutathione at the epithelial surface of the lung. With oxidant stress LLF GGT activity is amplified even further as glutathione turnover is accelerated to meet the increased demands of cells for cysteine. Mouse models of GGT deficiency confirmed this biological role of LLF GGT activity and revealed the robust expansiv...
Clinical <html_ent glyph="@amp;" ascii="&"/> Experimental Allergy, 2002
Background The bronchial epithelium is exposed to reactive oxygen species (ROS) derived from cigarette smoke, air pollutants and activated leucocytes. Glutathione (GSH) prevents ROS-mediated loss of cell function, tissue injury and in¯ammation, and its synthesis is regulated by gglutamylcysteine synthetase (g-GCS). However, the capacity of bronchial epithelial cells to adapt to oxidative stress and the mechanisms involved are not known. Objective To investigate the effects of oxidative stress on the regulation of GSH synthesis in human bronchial epithelial (NCI-H292) cells.
Biochemical Pharmacology, 2001
The airway epithelium is injured by oxidants inhaled as atmospheric pollutants or produced during inflammatory responses. We studied the effect of modulating the antioxidant intracellular glutathione, both using thiol compounds and by the adaptive effect of hyperoxia, on oxidant-induced injury and activation of the nuclear factor-kappaB (NF-B) in two cell lines: the human bronchial (16HBE) and type II alveolar epithelial cells (A549). The thiol antioxidants glutathione (GSH) and glutathione monoethyl ester (GSH-MEE) [2 mM] increased GSH levels (nmol/mg protein) in A549 cells (GSH 383 Ϯ 26 and GSH-MEE 336 Ϯ 23 vs control 171 Ϯ 13, P Ͻ 0.001) and in 16HBE cells (GSH 405 Ϯ 33, GSH-MEE 362 Ϯ 37 vs control 198 Ϯ 12, P Ͻ 0.001, N ϭ 3). Treatment of hyperoxia (95% oxygen) also increased GSH levels between 4 and 24 hr exposure compared with control (P Ͻ 0.01). Hydrogen peroxide (H 2 O 2 ) (0.01 mM) induced NF-B activation, whereas hyperoxia exposure did not affect NF-B activation in either cell line. Pretreatment with DL-buthionine (SR)sulfoximine, which decreased intracellular glutathione, increased NF-B binding induced by H 2 O 2 and increased lactate dehydrogenase (LDH) release (P Ͻ 0.001). Pretreatment with the thiol compounds and hyperoxia totally inhibited H 2 O 2 -induced NF-B binding and cell injury as measured by LDH release. These data indicate the importance of intracellular glutathione and inhibition of NF-B in both protection/tolerance against oxidant-induced epithelial cell injury, and NF-B activation in response to oxidative stress which may be important in lung inflammation. Thus, increasing intracellular glutathione may be of therapeutic relevance if able to modulate NF-B activation and hence attenuate inflammation.
American Journal of Physiology-Lung Cellular and Molecular Physiology, 2015
Oxidant-mediated tissue injury is key to the pathogenesis of acute lung injury. Glutathione- S-transferases (GSTs) are important detoxifying enzymes that catalyze the conjugation of glutathione with toxic oxidant compounds and are associated with acute and chronic inflammatory lung diseases. We hypothesized that attenuation of cellular GST enzymes would augment intracellular oxidative and metabolic stress and induce lung cell injury. Treatment of murine lung epithelial cells with GST inhibitors, ethacrynic acid (EA), and caffeic acid compromised lung epithelial cell viability in a concentration-dependent manner. These inhibitors also potentiated cell injury induced by hydrogen peroxide (H2O2), tert-butyl-hydroperoxide, and hypoxia and reoxygenation (HR). SiRNA-mediated attenuation of GST-π but not GST-μ expression reduced cell viability and significantly enhanced stress (H2O2/HR)-induced injury. GST inhibitors also induced intracellular oxidative stress (measured by dihydrorhodamine...