Oxidative Stress and Antioxidant Defense

      Abstract

      Reactive oxygen species (ROS) are produced by living organisms as a result of normal cellular metabolism and environmental factors, such as air pollutants or cigarette smoke. ROS are highly reactive molecules and can damage cell structures such as carbohydrates, nucleic acids, lipids, and proteins and alter their functions. The shift in the balance between oxidants and antioxidants in favor of oxidants is termed "oxidative stress." Regulation of reducing and oxidizing (redox) state is critical for cell viability, activation, proliferation, and organ function. Aerobic organisms have integrated antioxidant systems, which include enzymatic and non-enzymatic antioxidants that are usually effective in blocking harmful effects of ROS. However, in pathological conditions, the antioxidant systems can be overwhelmed. Oxidative stress contributes to many pathological conditions and diseases, including cancer, neurological disorders, atherosclerosis, hypertension, ischemia/perfusion, diabetes, acute respiratory distress syndrome, idiopathic pulmonary fibrosis, chronic obstructive pulmonary disease, and asthma. In this review, we summarize the cellular oxidant and antioxidant systems and discuss the cellular effects and mechanisms of the oxidative stress.

      Keywords

      This article was originally published online on 11 january 2012
      Reactive oxygen species (ROS) are produced by living organisms as a result of normal cellular metabolism. At low to moderate concentrations, they function in physiological cell processes, but at high concentrations, they produce adverse modifications to cell components, such as lipids, proteins, and DNA [
      • Valko M.
      • Rhodes C.J.
      • Moncol J.
      • Izakovic M.
      • Mazur M.
      Free radicals, metals and antioxidants in oxidative stress-induced cancer.
      ,
      • Halliwell B.
      • Gutteridge J.MC.
      ,
      • Marnett L.J.
      Lipid peroxidation--DNA damage by malondialdehyde.
      ,
      • Siems W.G.
      • Grune T.
      • Esterbauer H.
      4-Hydroxynonenal formation during ischemia and reperfusion of rat small-intestine.
      ,
      • Stadtman E.R.
      Role of oxidant species in aging.
      • Wang M.Y.
      • Dhingra K.
      • Hittelman W.N.
      • Liehr J.G.
      • deAndrade M.
      • Li D.H.
      Lipid peroxidation-induced putative malondialdehyde-DNA adducts in human breast tissues.
      ]. The shift in balance between oxidant/antioxidant in favor of oxidants is termed "oxidative stress." Oxidative stress contributes to many pathological conditions, including cancer, neurological disorders, [
      • Jenner P.
      Oxidative stress in Parkinson's disease.
      ,
      • Lyras L.
      • Cairns N.J.
      • Jenner A.
      • Jenner P.
      • Halliwell B.
      An assessment of oxidative damage to proteins, lipids, and DNA in brain from patients with Alzheimer's disease.
      ,
      • Sayre L.M.
      • Smith M.A.
      • Perry G.
      Chemistry and biochemistry of oxidative stress in neurodegenerative disease.
      • Toshniwal P.K.
      • Zarling E.J.
      Evidence for increased lipid peroxidation in multiple sclerosis.
      ] atherosclerosis, hypertension, ischemia/perfusion, [
      • Dhalla N.S.
      • Temsah R.M.
      • Netticadan T.
      Role of oxidative stress in cardiovascular diseases.
      ,
      • Kasparova S.
      • Brezova V.
      • Valko M.
      • Horecky J.
      • Mlynarik V.
      • et al.
      Study of the oxidative stress in a rat model of chronic brain hypoperfusion.
      ,
      • Kerr S.
      • Brosnan M.J.
      • McIntyre M.
      • Reid J.L.
      • Dominiczak A.F.
      • Hamilton C.A.
      Superoxide anion production is increased in a model of genetic hypertension: role of the endothelium.
      • Kukreja R.C.
      • Hess M.L.
      The oxygen free-radical system: from equations through membrane-protein interactions to cardiovascular injury and protection.
      ] diabetes, acute respiratory distress syndrome, idiopathic pulmonary fibrosis, chronic obstructive pulmonary disease, [
      • Asami S.
      • Manabe H.
      • Miyake J.
      • Tsurudome Y.
      • Hirano T.
      • et al.
      Cigarette smoking induces an increase in oxidative DNA damage, 8-hydroxydeoxyguanosine, in a central site of the human lung.
      ] and asthma [
      • Andreadis A.A.
      • Hazen S.L.
      • Comhair S.A.
      • Erzurum S.C.
      Oxidative and nitrosative events in asthma.
      ,
      • Comhair S.A.
      • Ricci K.S.
      • Arroliga M.
      • Lara A.R.
      • Dweik R.A.
      • et al.
      Correlation of systemic superoxide dismutase deficiency to airflow obstruction in asthma.
      ,
      • Comhair S.A.
      • Xu W.
      • Ghosh S.
      • Thunnissen F.B.
      • Almasan A.
      • et al.
      Superoxide dismutase inactivation in pathophysiology of asthmatic airway remodeling and reactivity.
      ,
      • Dut R.
      • Dizdar E.A.
      • Birben E.
      • Sackesen C.
      • Soyer O.U.
      • Besler T.
      • Kalayci O.
      Oxidative stress and its determinants in the airways of children with asthma.
      ,
      • Ercan H.
      • Birben E.
      • Dizdar E.A.
      • Keskin O.
      • Karaaslan C.
      • et al.
      Oxidative stress and genetic and epidemiologic determinants of oxidant injury in childhood asthma.
      • Fitzpatrick A.M.
      • Teague W.G.
      • Holguin F.
      • Yeh M.
      • Brown L.A.
      Severe Asthma Research Program. Airway glutathione homeostasis is altered in children with severe asthma: evidence for oxidant stress.
      ]. Aerobic organisms have integrated antioxidant systems, which include enzymatic and nonenzymatic antioxidants that are usually effective in blocking harmful effects of ROS. However, in pathological conditions, the antioxidant systems can be overwhelmed. In this review, we summarize the cellular oxidant and antioxidant systems and regulation of the reducing and oxidizing (redox) state in health and disease states.

      Oxidants

       Endogenous Sources of ROS

      ROS are produced from molecular oxygen as a result of normal cellular metabolism. ROS can be divided into 2 groups: free radicals and nonradicals. Molecules containing one or more unpaired electrons and thus giving reactivity to the molecule are called free radicals. When 2 free radicals share their unpaired electrons, nonradical forms are created. The 3 major ROS that are of physiological significance are superoxide anion (O2-.), hydroxyl radical (●OH), and hydrogen peroxide (H2O2). ROS are summarized in Table 1.
      Table 1Major Endogenous Oxidants
      OxidantFormulaReaction Equation
      Superoxide anionO2-.NADPH + 2O2 ↔ NADP+ + 2O2-. + H+ 2O2-. + H+ → O2 + H2O2
      Hydrogen peroxideH2O2Hypoxanthine + H2O + O2 ⇋ xanthine + H2O2 Xanthine + H2O + O2 ⇋ uric acid + H2O2
      Hydroxyl radical●OHFe2+ + H2O2 → Fe3+ + OH- + ●OH
      Hypochlorous acidHOClH2O2 + Cl- → HOCl + H2O
      Peroxyl radicalsROOR + O2 → ROO
      Hydroperoxyl radicalHOO·O2- + H2O ⇋ HOO· + OH-
      Superoxide anion is formed by the addition of 1 electron to the molecular oxygen [
      • Miller D.M.
      • Buettner G.R.
      • Aust S.D.
      Transition metals as catalysts of "autoxidation" reactions.
      ]. This process is mediated by nicotine adenine dinucleotide phosphate [NAD(P)H] oxidase or xanthine oxidase or by mitochondrial electron transport system. The major site for producing superoxide anion is the mitochondria, the machinery of the cell to produce adenosine triphosphate. Normally, electrons are transferred through mitochondrial electron transport chain for reduction of oxygen to water, but approximately 1 to 3% of all electrons leak from the system and produce superoxide. NAD(P)H oxidase is found in polymorphonuclear leukocytes, monocytes, and macrophages. Upon phagocytosis, these cells produce a burst of superoxide that lead to bactericidal activity. Superoxide is converted into hydrogen peroxide by the action of superoxide dismutases (SODs, EC 1.15.1.1). Hydrogen peroxide easily diffuses across the plasma membrane. Hydrogen peroxide is also produced by xanthine oxidase, amino acid oxidase, and NAD(P)H oxidase [
      • Dupuy C.
      • Virion A.
      • Ohayon R.
      • Kaniewski J.
      • Dème D.
      • Pommier J.
      Mechanism of hydrogen peroxide formation catalyzed by NADPH oxidase in thyroid plasma membrane.
      ,
      • Granger D.N.
      Role of xanthine oxidase and granulocytes in ischemia-reperfusion injury.
      ] and in peroxisomes by consumption of molecular oxygen in metabolic reactions. In a succession of reactions called Haber-Weiss and Fenton reactions, H2O2 can breakdown to OH- in the presence of transmission metals like Fe2+ or Cu2+ [
      • Fenton H.JH.
      Oxidation of tartaric acid in the presence of iron.
      ].
      Fe3++·O2Fe2++O2Haber-WeissFe2++H2O2Fe3++OH-+·OHFentonreaction


      O2- itself Ocan also react with H2O2 and generate OH- [
      • Haber F.
      • Weiss J.J.
      The catalytic decomposition of hydrogen peroxide by iron salts.
      ,
      • Liochev S.I.
      • Fridovich I.
      The Haber-Weiss cycle--70 years later: an alternative view.
      ]. Hydroxyl radical is the most reactive of ROS and can damage proteins, lipids, and carbohydrates and DNA. It can also start lipid peroxidation by taking an electron from polyunsaturated fatty acids.
      Granulocytic enzymes further expand the reactivity of H2O2 via eosinophil peroxidase and myeloperoxidase (MPO). In activated neutrophils, H2O2 is consumed by MPO. In the presence of chloride ion, H2O2 is converted to hypochlorous acid (HOCl). HOCl is highly oxidative and plays an important role in killing of the pathogens in the airways [
      • Klebanoff S.J.
      Myeloperoxidase: friend and foe.
      ]. However, HOCl can also react with DNA and induce DNA-protein interactions and produce pyrimidine oxidation products and add chloride to DNA bases [
      • Whiteman M.
      • Jenner A.
      • Halliwell B.
      Hypochlorous acid-induced base modifications in isolated calf thymus DNA.
      ,
      • Kulcharyk P.A.
      • Heinecke J.W.
      Hypochlorous acid produced by the myeloperoxidase system of human phagocytes induces covalent cross-links between DNA and protein.
      ]. Eosinophil peroxidase and MPO also contribute to the oxidative stress by modification of proteins by halogenations, nitration, and protein cross-links via tyrosyl radicals [
      • Brennan M.L.
      • Wu W.
      • Fu X.
      • Shen Z.
      • Song W.
      • et al.
      A tale of two controversies: defining both the role of peroxidases in nitrotyrosine formation in vivo using eosinophil peroxidase and myeloperoxidase-deficient mice, and the nature of peroxidase-generated reactive nitrogen species.
      ,
      • Denzler K.L.
      • Borchers M.T.
      • Crosby J.R.
      • Cieslewicz G.
      • Hines E.M.
      • et al.
      Extensive eosinophil degranulation and peroxidase-mediated oxidation of airway proteins do not occur in a mouse ovalbumin-challenge model of pulmonary inflammation.
      • van Dalen C.J.
      • Winterbourn C.C.
      • Senthilmohan R.
      • Kettle A.J.
      Nitrite as a substrate and inhibitor of myeloperoxidase. Implications for nitration and hypochlorous acid production at sites of inflammation.
      ].
      Other oxygen-derived free radicals are the peroxyl radicals (ROO·•). Simplest form of these radicals is hydroperoxyl radical (HOO·•) and has a role in fatty acid peroxidation. Free radicals can trigger lipid peroxidation chain reactions by abstracting a hydrogen atom from a side-chain methylene carbon. The lipid radical then reacts with oxygen to produce peroxyl radical. Peroxyl radical initiates a chain reaction and transforms polyunsaturated fatty acids into lipid hydroperoxides. Lipid hydroperoxides are very unstable and easily decompose to secondary products, such as aldehydes (such as 4-hydroxy-2,3-nonenal) and malondialdehydes (MDAs). Isoprostanes are another group of lipid peroxidation products that are generated via the peroxidation of arachidonic acid and have also been found to be elevated in plasma and breath condensates of asthmatics [
      • Wood L.G.
      • Fitzgerald D.A.
      • Gibson P.G.
      • Cooper D.M.
      • Garg M.L.
      Lipid peroxidation as determined by plasma isoprostanes is related to disease severity in mild asthma.
      ,
      • Montuschi P.
      • Corradi M.
      • Ciabattoni G.
      • Nightingale J.
      • Kharitonov S.A.
      • Barnes P.J.
      Increased 8-isoprostane, a marker of oxidative stress, in exhaled condensate of asthma patients.
      ]. Peroxidation of lipids disturbs the integrity of cell membranes and leads to rearrangement of membrane structure.
      Hydrogen peroxide, superoxide radical, oxidized glutathione (GSSG), MDAs, isoprostanes, carbonyls, and nitrotyrosine can be easily measured from plasma, blood, or bronchoalveolar lavage samples as biomarkers of oxidation by standardized assays.

       Exogenous Source of Oxidants

       Cigarette Smoke

      Cigarette smoke contains many oxidants and free radicals and organic compounds, such as superoxide and nitric oxide [
      • Church D.F.
      • Pryor W.A.
      Free-radical chemistry of cigarette smoke and its toxicological implications.
      ]. In addition, inhalation of cigarette smoke into the lung also activates some endogenous mechanisms, such as accumulation of neutrophils and macrophages, which further increase the oxidant injury.

       Ozone Exposure

      Ozone exposure can cause lipid peroxidation and induce influx of neutrophils into the airway epithelium. Short-term exposure to ozone also causes the release of inflammatory mediators, such as MPO, eosinophil cationic proteins and also lactate dehydrogenase and albumin [
      • Hiltermann J.T.
      • Lapperre T.S.
      • van Bree L.
      • Steerenberg P.A.
      • Brahim J.J.
      • et al.
      Ozone-induced inflammation assessed in sputum and bronchial lavage fluid from asthmatics: a new noninvasive tool in epidemiologic studies on air pollution and asthma.
      ]. Even in healthy subjects, ozone exposure causes a reduction in pulmonary functions [
      • Nightingale J.A.
      • Rogers D.F.
      • Barnes P.J.
      Effect of inhaled ozone on exhaled nitric oxide, pulmonary function, and induced sputum in normal and asthmatic subjects.
      ]. Cho et al [
      • Cho A.K.
      • Sioutas C.
      • Miguel A.H.
      • Kumagai Y.
      • Schmitz D.A.
      • et al.
      Redox activity of airborne particulate matter at different sites in the Los Angeles Basin.
      ] have shown that particulate matter (mixture of solid particles and liquid droplets suspended in the air) catalyzes the reduction of oxygen.

       Hyperoxia

      Hyperoxia refers to conditions of higher oxygen levels than normal partial pressure of oxygen in the lungs or other body tissues. It leads to greater production of reactive oxygen and nitrogen species [
      • Comhair S.A.
      • Thomassen M.J.
      • Erzurum S.C.
      Differential induction of extracellular glutathione peroxidase and nitric oxide synthase 2 in airways of healthy individuals exposed to 100% O(2) or cigarette smoke.
      ,
      • Matthay M.A.
      • Geiser T.
      • Matalon S.
      • Ischiropoulos H.
      Oxidant-mediated lung injury in the acute respiratory distress syndrome.
      ].

       Ionizing Radiation

      Ionizing radiation, in the presence of O2, converts hydroxyl radical, superoxide, and organic radicals to hydrogen peroxide and organic hydroperoxides. These hydroperoxide species react with redox active metal ions, such as Fe and Cu, via Fenton reactions and thus induce oxidative stress [
      • Biaglow J.E.
      • Mitchell J.B.
      • Held K.
      The importance of peroxide and superoxide in the X-ray response.
      ,
      • Chiu S.M.
      • Xue L.Y.
      • Friedman L.R.
      • Oleinick N.L.
      Copper ion-mediated sensitization of nuclear matrix attachment sites to ionizing radiation.
      ]. Narayanan et al [
      • Narayanan P.K.
      • Goodwin E.H.
      • Lehnert B.E.
      Alpha particles initiate biological production of superoxide anions and hydrogen peroxide in human cells.
      ] showed that fibroblasts that were exposed to alpha particles had significant increases in intracellular O2-. and H2O2 production via plasma membrane-bound NADPH oxidase [
      • Narayanan P.K.
      • Goodwin E.H.
      • Lehnert B.E.
      Alpha particles initiate biological production of superoxide anions and hydrogen peroxide in human cells.
      ]. Signal transduction molecules, such as extracellular signal-regulated kinase 1 and 2 (ERK1/2), c-Jun N-terminal kinase (JNK), and p38, and transcription factors, such as activator protein-1 (AP-1), nuclear factor-κB (NF-κB), and p53, are activated, which result in the expression of radiation response-related genes [
      • Tuttle S.W.
      • Varnes M.E.
      • Mitchell J.B.
      • Biaglow J.E.
      Sensitivity to chemical oxidants and radiation in CHO cell lines deficient in oxidative pentose cycle activity.
      ,
      • Guo G.
      • Yan-Sanders Y.
      • Lyn-Cook B.D.
      • Wang T.
      • Tamae D.
      • et al.
      Manganese superoxide dismutase-mediated gene expression in radiation-induced adaptive responses.
      ,
      • Azzam E.I.
      • de Toledo S.M.
      • Spitz D.R.
      • Little J.B.
      Oxidative metabolism modulates signal transduction and micronucleus formation in bystander cells from a-particle irradiated normal human fibroblasts.
      ,
      • Leach J.K.
      • Van Tuyle G.
      • Lin P.S.
      • Schmidt-Ullrich R.
      • Mikkelsen R.B.
      Ionizing radiation-induced, mitochondria-dependent generation of reactive oxygen/nitrogen.
      ,
      • Dent P.
      • Yacoub A.
      • Fisher P.B.
      • Hagan M.P.
      • Grant S.
      MAPK pathways in radiation responses.
      • Wei S.J.
      • Botero A.
      • Hirota K.
      • Bradbury C.M.
      • Markovina S.
      • et al.
      Thioredoxin nuclear translocation and interaction with redox factor-1 activates the AP-1 transcription factor in response to ionizing radiation.
      ]. Ultraviolet A (UVA) photons trigger oxidative reactions by excitation of endogenous photosensitizers, such as porphyrins, NADPH oxidase, and riboflavins. 8-Oxo-7,8-dihydroguanine (8-oxoGua) is the main UVA-mediated DNA oxidation product formed by the oxidation of ●OH radical, 1-electron oxidants, and singlet oxygen that mainly reacts with guanine [
      • Cadet J.
      • Douki T.
      • Gasparutto D.
      • Ravanat J.L.
      Oxidative damage to DNA: formation, measurement and biochemical features.
      ]. The formation of guanine radical cation in isolated DNA has been shown to efficiently occur through the direct effect of ionizing radiation [
      • Yokoya A.
      • Cunniffe S.M.
      • O'Neill P.
      Effect of hydration on the induction of strand breaks and base lesions in plasmid DNA films by gamma-radiation.
      ,
      • Janssen Y.M.
      • Van Houten B.
      • Borm P.J.
      • Mossman B.T.
      Cell and tissue responses to oxidative damage.
      ]. After exposure to ionizing radiation, intracellular level of glutathione (GSH) decreases for a short term but then increases again [
      • Iwanaga M.
      • Mori K.
      • Iida T.
      • Urata Y.
      • Matsuo T.
      • et al.
      Nuclear factor kappa B dependent induction of gamma glutamylcysteine synthetase by ionizing radiation in T98G human glioblastoma cells.
      ].

       Heavy Metal Ions

      Heavy metal ions, such as iron, copper, cadmium, mercury, nickel, lead, and arsenic, can induce generation of reactive radicals and cause cellular damage via depletion of enzyme activities through lipid peroxidation and reaction with nuclear proteins and DNA [
      • Stohs S.J.
      • Bagchi D.
      Oxidative mechanisms in the toxicity of metal ions.
      ].
      One of the most important mechanisms of metal-mediated free radical generation is via a Fenton-type reaction. Superoxide ion and hydrogen peroxide can interact with transition metals, such as iron and copper, via the metal catalyzed Haber-Weiss/Fenton reaction to form OH radicals.
      Metal3++·O2Metal2++O2Haber-WeissMetal2++H2O2Metal3++OH-+·OHFentonreaction


      Besides the Fenton-type and Haber-Weiss-type mechanisms, certain metal ions can react directly with cellular molecules to generate free radicals, such as thiol radicals, or induce cell signaling pathways. These radicals may also react with other thiol molecules to generate O2-.. O2-. is converted to H2O2, which causes additional oxygen radical generation. Some metals, such as arsenite, induce ROS formation indirectly by activation of radical producing systems in cells [
      • Leonard S.S.
      • Harris G.K.
      • Shi X.
      Metal-induced oxidative stress and signal transduction.
      ].
      Arsenic is a highly toxic element that produces a variety of ROS, including superoxide (O2•-), singlet oxygen (1O2), peroxyl radical (ROO), nitric oxide (NO), hydrogen peroxide (H2O2), and dimethylarsinic peroxyl radicals [(CH3)2AsOO] [
      • Shi H.
      • Shi X.
      • Liu K.J.
      Oxidative mechanism of arsenic toxicity and carcinogenesis.
      ,
      • Pi J.
      • Horiguchi S.
      • Sun Y.
      • Nikaido M.
      • Shimojo N.
      • Hayashi T.
      A potential mechanism for the impairment of nitric oxide formation caused by prolonged oral exposure to arsenate in rabbits.
      • Rin K.
      • Kawaguchi K.
      • Yamanaka K.
      • Tezuka M.
      • Oku N.
      • Okada S.
      DNA-strand breaks induced by dimethylarsinic acid, a metabolite of inorganic arsenics, are strongly enhanced by superoxide anion radicals.
      ]. Arsenic (III) compounds can inhibit antioxidant enzymes, especially the GSH-dependent enzymes, such as glutathione-S-transferases (GSTs), glutathione peroxidase (GSH-Px), and GSH reductase, via binding to their sulfhydryl (-SH) groups [
      • Waalkes M.P.
      • Liu J.
      • Ward J.M.
      • Diwan L.A.
      Mechanisms underlying arsenic carcinogenesis: hypersensitivity of mice exposed to inorganic arsenic during gestation.
      ,
      • Schiller C.M.
      • Fowler B.A.
      • Woods J.S.
      Effects of arsenic on pyruvate dehydrogenase activation.
      ].
      Lead increases lipid peroxidation [
      • Monterio H.P.
      • Bechara E.JH.
      • Abdalla D.SP.
      Free radicals involvement in neurological porphyrias and lead poisoning.
      ]. Significant decreases in the activity of tissue SOD and brain GPx have been reported after lead exposure [
      • Tripathi R.M.
      • Raghunath R.
      • Mahapatra S.
      Blood lead and its effect on Cd, Cu, Zn, Fe and hemoglobin levels of children.
      ,
      • Nehru B.
      • Dua R.
      The effect of dietary selenium on lead neurotoxicity.
      ]. Replacement of zinc, which serves as a cofactor for many enzymes by lead, leads to inactivation of such enzymes. Lead exposure may cause inhibition of GST by affecting tissue thiols.
      ROS generated by metal-catalyzed reactions can modify DNA bases. Three base substitutions, G → C, G → T, and C → T, can occur as a result of oxidative damage by metal ions, such as Fe2+, Cu2+, and Ni2+. Reid et al [
      • Reid T.M.
      • Feig D.I.
      • Loeb L.A.
      Mutagenesis by metal-induced oxygen radicals.
      ] showed that G → C was predominantly produced by Fe2+while C → T substitution was by Cu2+and Ni2+.

      Antioxidants

      The human body is equipped with a variety of antioxidants that serve to counterbalance the effect of oxidants. For all practical purposes, these can be divided into 2 categories: enzymatic (Table 2) and nonenzymatic (Table 3).
      Table 2Enzymatic Scavenger of Antioxidant Defense
      Name of ScavengerAcronymCatalyzed Reaction
      Superoxide dismutaseSODM(n+1)+-SOD + O2- → Mn+-SOD + O2 Mn+-SOD + O2- + 2H+ → M(n+1)+-SOD + H2O2
      CatalaseCAT2 H2O2 → O2 + 2 H2OH2O2 + Fe(III)-E → H2O + O = Fe(IV)-E(·+) H2O2 + O = Fe(IV)-E(·+)→ H2O + Fe(III)-E + O2
      Glutathione peroxidaseGTPx2GSH +H2O2 → GSSG +2H2O2GSH+ ROOH → GSSG + ROH + H2O
      ThioredoxinTRXAdenosine monophosphate + sulfite + thioredoxin disulfide = 5'-adenylyl sulfate + thioredoxin Adenosine 3',5'-bisphosphate + sulfite + thioredoxin disulfide = 3'-phosphoadenyly+ sulfate + thioredoxin
      PeroxiredoxinPRX2 R'-SH + ROOH = R'-S-S-R' + H2O + ROH
      Glutathione transferaseGSTRX + GSH = HX + R-S-GSH
      Table 3Nonenzymatic Scavenger of Antioxidant Defenses
      Chemical Name of ScavengerName of ScavengerStructure
      All trans retinol 2Vitamin A
      Ascorbic acidVitamin C
      α-TocopherolVitamin E
      β-Carotene
      Glutathione

       Enzymatic Antioxidants

      The major enzymatic antioxidants of the lungs are SODs (EC 1.15.1.11), catalase (EC 1.11.1.6), and GSH-Px (EC 1.11.1.9). In addition to these major enzymes, other antioxidants, including heme oxygenase-1 (EC 1.14.99.3), and redox proteins, such as thioredoxins (TRXs, EC 1.8.4.10), peroxiredoxins (PRXs, EC 1.11.1.15), and glutaredoxins, have also been found to play crucial roles in the pulmonary antioxidant defenses.
      Since superoxide is the primary ROS produced from a variety of sources, its dismutation by SOD is of primary importance for each cell. All 3 forms of SOD, that is, CuZn-SOD, Mn-SOD, and EC-SOD, are widely expressed in the human lung. Mn-SOD is localized in the mitochondria matrix. EC-SOD is primarily localized in the extracellular matrix, especially in areas containing high amounts of type I collagen fibers and around pulmonary and systemic vessels. It has also been detected in the bronchial epithelium, alveolar epithelium, and alveolar macrophages [
      • Kinnula V.L.
      • Crapo J.D.
      Superoxide dismutases in the lung and human lung diseases.
      ,
      • Kinnula V.L.
      Production and degradation of oxygen metabolites during inflammatory states in the human lung.
      ]. Overall, CuZn-SOD and Mn-SOD are generally thought to act as bulk scavengers of superoxide radicals. The relatively high EC-SOD level in the lung with its specific binding to the extracellular matrix components may represent a fundamental component of lung matrix protection [
      • Zelko I.N.
      • Mariani T.J.
      • Folz R.J.
      Superoxide dismutase multigene family: a comparison of the CuZn-SOD (SOD1), Mn-SOD (SOD2), and EC-SOD (SOD3) gene structures, evolution, and expression.
      ].
      H2O2 that is produced by the action of SODs or the action of oxidases, such as xanthine oxidase, is reduced to water by catalase and the GSH-Px. Catalase exists as a tetramer composed of 4 identical monomers, each of which contains a heme group at the active site. Degradation of H2O2 is accomplished via the conversion between 2 conformations of catalase-ferricatalase (iron coordinated to water) and compound I (iron complexed with an oxygen atom). Catalase also binds NADPH as a reducing equivalent to prevent oxidative inactivation of the enzyme (formation of compound II) by H2O2 as it is reduced to water [
      • Kirkman H.N.
      • Rolfo M.
      • Ferraris A.M.
      • Gaetani G.F.
      Mechanisms of protection of catalase by NADPH. Kinetics and stoichiometry.
      ].
      Enzymes in the redox cycle responsible for the reduction of H2O2 and lipid hydroperoxides (generated as a result of membrane lipid peroxidation) include the GSH-Pxs [
      • Flohé L.
      Glutathione peroxidase.
      ]. The GSH-Pxs are a family of tetrameric enzymes that contain the unique amino acid selenocysteine within the active sites and use low-molecular-weight thiols, such as GSH, to reduce H2O2 and lipid peroxides to their corresponding alcohols. Four GSH-Pxs have been described, encoded by different genes: GSH-Px-1 (cellular GSH-Px) is ubiquitous and reduces H2O2 and fatty acid peroxides, but not esterified peroxyl lipids [
      • Arthur J.R.
      The glutathione peroxidases.
      ]. Esterified lipids are reduced by membrane-bound GSH-Px-4 (phospholipid hydroperoxide GSH-Px), which can use several different low-molecular-weight thiols as reducing equivalents. GSH-Px-2 (gastrointestinal GSH-Px) is localized in gastrointestinal epithelial cells where it serves to reduce dietary peroxides [
      • Chu F.F.
      • Doroshow J.H.
      • Esworthy R.S.
      Expression, characterization, and tissue distribution of a new cellular selenium-dependent glutathione peroxidase, GSHPx-GI.
      ]. GSH-Px-3 (extracellular GSH-Px) is the only member of the GSH-Px family that resides in the extracellular compartment and is believed to be one of the most important extracellular antioxidant enzyme in mammals. Of these, extracellular GSH-Px is most widely investigated in the human lung [
      • Comhair S.A.
      • Bhathena P.R.
      • Farver C.
      • Thunnissen F.B.
      • Erzurum S.C.
      Extracellular glutathione peroxidase induction in asthmatic lungs: evidence for redox regulation of expression in human airway epithelial cells.
      ].
      In addition, disposal of H2O2 is closely associated with several thiol-containing enzymes, namely, TRXs (TRX1 and TRX2), thioredoxin reductases (EC 1.8.1.9) (TRRs), PRXs (which are thioredoxin peroxidases), and glutaredoxins [
      • Gromer S.
      • Urig S.
      • Becker K.
      The thioredoxin system--from science to clinic.
      ]. Two TRXs and TRRs have been characterized in human cells, existing in both cytosol and mitochondria. In the lung, TRX and TRR are expressed in bronchial and alveolar epithelium and macrophages. Six different PRXs have been found in human cells, differing in their ultrastructural compartmentalization. Experimental studies have revealed the importance of PRX VI in the protection of alveolar epithelium. Human lung expresses all PRXs in bronchial epithelium, alveolar epithelium, and macrophages [
      • Kinnula V.L.
      • Lehtonen S.
      • Kaarteenaho-Wiik R.
      • Lakari E.
      • Pääkkö P.
      • et al.
      Cell specific expression of peroxiredoxins in human lung and pulmonary sarcoidosis.
      ]. PRX V has recently been found to function as a peroxynitrite reductase, [
      • Dubuisson M.
      • Vander Stricht D.
      • Clippe A.
      • Etienne F.
      • Nauser T.
      • et al.
      Human peroxiredoxin 5 is a peroxynitrite reductase.
      ] which means that it may function as a potential protective compound in the development of ROS-mediated lung injury [
      • Holmgren A.
      Antioxidant function of thioredoxin and glutaredoxin systems.
      ].
      Common to these antioxidants is the requirement of NADPH as a reducing equivalent. NADPH maintains catalase in the active form and is used as a cofactor by TRX and GSH reductase (EC 1.6.4.2), which converts GSSG to GSH, a co-substrate for the GSH-Pxs. Intracellular NADPH, in turn, is generated by the reduction of NADP+ by glucose-6-phosphate dehydrogenase, the first and rate-limiting enzyme of the pentose phosphate pathway, during the conversion of glucose-6-phosphate to 6-phosphogluconolactone. By generating NADPH, glucose-6-phosphate dehydrogenase is a critical determinant of cytosolic GSH buffering capacity (GSH/GSSG) and, therefore, can be considered an essential, regulatory antioxidant enzyme [
      • Dickinson D.A.
      • Forman H.J.
      Glutathione in defense and signaling: lessons from a small thiol.
      ,
      • Sies H.
      Glutathione and its role in cellular functions.
      ].
      GSTs (EC 2.5.1.18), another antioxidant enzyme family, inactivate secondary metabolites, such as unsaturated aldehydes, epoxides, and hydroperoxides. Three major families of GSTs have been described: cytosolic GST, mitochondrial GST, [
      • Ladner J.E.
      • Parsons J.F.
      • Rife C.L.
      • Gilliland G.L.
      • Armstrong R.N.
      Parallel evolutionary pathways for glutathione transferases: structure and mechanism of the mitochondrial class kappa enzyme rGSTK1-1.
      ,
      • Robinson A.
      • Huttley G.A.
      • Booth H.S.
      • Board P.G.
      Modelling and bioinformatics studies of the human kappa class glutathione transferase predict a novel third transferase family with homology to prokaryotic 2-hydroxychromene-2-carboxylate isomerases.
      ] and membrane-associated microsomal GST that has a role in eicosanoid and GSH metabolism [
      • Jakobsson P-J
      • Morgenstern R.
      • Mancini J.
      • Ford-Hutchinson A.
      • Persson B.
      Common structural features of MAPEG--a widespread superfamily of membrane associated proteins with highly divergent functions in eicosanoid and glutathione metabolism.
      ]. Seven classes of cytosolic GST are identified in mammalian, designated Alpha, Mu, Pi, Sigma, Theta, Omega, and Zeta [
      • Hayes J.D.
      • Pulford D.J.
      The glutathione S-transferase supergene family: regulation of GST and the contribution of the isoenzymes to cancer chemoprotection and drug resistance.
      ,
      • Armstrong R.N.
      Structure, catalytic mechanism, and evolution of the glutathione transferases.
      ,
      • Hayes J.D.
      • McLellan L.I.
      Glutathione and glutathione-dependent enzymes represent a co-ordinately regulated defence against oxidative stress.
      • Sheehan D.
      • Meade G.
      • Foley V.M.
      • Dowd C.A.
      Structure, function and evolution of glutathione transferases: implications for classification of nonmammalian members of an ancient enzyme superfamily.
      ]. During nonstressed conditions, class Mu and Pi GSTs interact with kinases Ask1 and JNK, respectively, and inhibit these kinases [
      • Cho S-G
      • Lee Y.H.
      • Park H-S
      • Ryoo K.
      • Kang K.W.
      • et al.
      Glutathione S-transferase Mu modulates the stress activated signals by suppressing apoptosis signal-regulating kinase 1.
      ,
      • Dorion S.
      • Lambert H.
      • Landry J.
      Activation of the p38 signaling pathway by heat shock involves the dissociation of glutathione S-transferase Mu from Ask1.
      • Adler V.
      • Yin Z.
      • Fuchs S.Y.
      • Benezra M.
      • Rosario L.
      • et al.
      Regulation of JNK signalling by GSTp.
      ]. It has been shown that GSTP1 dissociates from JNK in response to oxidative stress [
      • Adler V.
      • Yin Z.
      • Fuchs S.Y.
      • Benezra M.
      • Rosario L.
      • et al.
      Regulation of JNK signalling by GSTp.
      ]. GSTP1 also physically interacts with PRX VI and leads to recovery of PRX enzyme activity via glutathionylation of the oxidized protein [
      • Manevich Y.
      • Feinstein S.I.
      • Fisher A.B.
      Activation of the antioxidant enzyme 1-CYS peroxiredoxin requires glutathionylation mediated by heterodimerization with pGST.
      ].

       Nonenzymatic Antioxidants

      Nonenzymatic antioxidants include low-molecular-weight compounds, such as vitamins (vitamins C and E), β-carotene, uric acid, and GSH, a tripeptide (L-γ-glutamyl-L-cysteinyl-L-glycine) that comprise a thiol (sulfhydryl) group.

       Vitamin C (Ascorbic Acid)

      Water-soluble vitamin C (ascorbic acid) provides intracellular and extracellular aqueous-phase antioxidant capacity primarily by scavenging oxygen free radicals. It converts vitamin E free radicals back to vitamin E. Its plasma levels have been shown to decrease with age [
      • Bunker V.W.
      Free radicals, antioxidants and ageing.
      ,
      • Mezzetti A.
      • Lapenna D.
      • Romano F.
      • Costantini F.
      • Pierdomenico S.D.
      • et al.
      Systemic oxidative stress and its relationship with age and illness.
      ].

       Vitamin E (α-Tocopherol)

      Lipid-soluble vitamin E is concentrated in the hydrophobic interior site of cell membrane and is the principal defense against oxidant-induced membrane injury. Vitamin E donates electron to peroxyl radical, which is produced during lipid peroxidation. α-Tocopherol is the most active form of vitamin E and the major membrane-bound antioxidant in cell. Vitamin E triggers apoptosis of cancer cells and inhibits free radical formations [
      • White E.
      • Shannon J.S.
      • Patterson R.E.
      Relationship between vitamin and calcium supplement use and colon cancer.
      ].

       Glutathione

      GSH is highly abundant in all cell compartments and is the major soluble antioxidant. GSH/GSSG ratio is a major determinant of oxidative stress. GSH shows its antioxidant effects in several ways [
      • Masella R.
      • Di Benedetto R.
      • Vari R.
      • Filesi C.
      • Giovannini C.
      Novel mechanisms of natural antioxidant compounds in biological systems: involvement of glutathione and glutathione-related enzymes.
      ]. It detoxifies hydrogen peroxide and lipid peroxides via action of GSH-Px. GSH donates its electron to H2O2 to reduce it into H2O and O2. GSSG is again reduced into GSH by GSH reductase that uses NAD(P)H as the electron donor. GSH-Pxs are also important for the protection of cell membrane from lipid peroxidation. Reduced glutathione donates protons to membrane lipids and protects them from oxidant attacks [
      • Curello S.
      • Ceconi C.
      • Bigoli C.
      • Ferrari R.
      • Albertini A.
      • Guarnieri C.
      Changes in the cardiac glutathione status after ischemia and reperfusion.
      ].
      GSH is a cofactor for several detoxifying enzymes, such as GSH-Px and transferase. It has a role in converting vitamin C and E back to their active forms. GSH protects cells against apoptosis by interacting with proapoptotic and antiapoptotic signaling pathways [
      • Masella R.
      • Di Benedetto R.
      • Vari R.
      • Filesi C.
      • Giovannini C.
      Novel mechanisms of natural antioxidant compounds in biological systems: involvement of glutathione and glutathione-related enzymes.
      ]. It also regulates and activates several transcription factors, such as AP-1, NF-κB, and Sp-1.

       Carotenoids (β-Carotene)

      Carotenoids are pigments found in plants. Primarily, β-carotene has been found to react with peroxyl (ROO●), hydroxyl (●OH), and superoxide (O2-.) radicals [
      • El-Agamey A.
      • Lowe G.M.
      • McGarvey D.J.
      • Mortensen A.
      • Phillip D.M.
      • Truscott T.G.
      Carotenoid radical chemistry and antioxidant/pro-oxidant properties.
      ]. Carotenoids show their antioxidant effects in low oxygen partial pressure but may have pro-oxidant effects at higher oxygen concentrations [
      • Rice-Evans C.A.
      • Sampson J.
      • Bramley P.M.
      • Holloway D.E.
      Why do we expect carotenoids to be antioxidants in vivo?.
      ]. Both carotenoids and retinoic acids (RAs) are capable of regulating transcription factors [
      • Niles R.M.
      Signaling pathways in retinoid chemoprevention and treatment of cancer.
      ]. β-Carotene inhibits the oxidant-induced NF-κB activation and interleukin (IL)-6 and tumor necrosis factor-α production. Carotenoids also affect apoptosis of cells. Antiproliferative effects of RA have been shown in several studies. This effect of RA is mediated mainly by retinoic acid receptors and vary among cell types. In mammary carcinoma cells, retinoic acid receptor was shown to trigger growth inhibition by inducing cell cycle arrest, apoptosis, or both [
      • Donato L.J.
      • Noy N.
      Suppression of mammary carcinoma growth by retinoic acid: proapoptotic genes are targets for retinoic acid receptor and cellular retinoic acid-binding protein II signaling.
      ,
      • Niizuma H.
      • Nakamura Y.
      • Ozaki T.
      • Nakanishi H.
      • Ohira M.
      • et al.
      Bcl-2 is a key regulator for the retinoic acid-induced apoptotic cell death in neuroblastoma.
      ].

      The Effect of Oxidative Stress: Genetic, Physiological, and Biochemical Mechanisms

      Oxidative stress occurs when the balance between antioxidants and ROS are disrupted because of either depletion of antioxidants or accumulation of ROS. When oxidative stress occurs, cells attempt to counteract the oxidant effects and restore the redox balance by activation or silencing of genes encoding defensive enzymes, transcription factors, and structural proteins [
      • Dalton T.P.
      • Shertzer H.G.
      • Puga A.
      Regulation of gene expression by reactive oxygen.
      ,
      • Scandalios J.G.
      Genomic responses to oxidative stress.
      ]. Ratio between oxidized and reduced glutathione (2GSH/GSSG) is one of the important determinants of oxidative stress in the body. Higher production of ROS in body may change DNA structure, result in modification of proteins and lipids, activation of several stress-induced transcription factors, and production of proinflammatory and anti-inflammatory cytokines.

       Effects of Oxidative Stress on DNA

      ROS can lead to DNA modifications in several ways, which involves degradation of bases, single- or double-stranded DNA breaks, purine, pyrimidine or sugar-bound modifications, mutations, deletions or translocations, and cross-linking with proteins. Most of these DNA modifications (Fig. 1) are highly relevant to carcinogenesis, aging, and neurodegenerative, cardiovascular, and autoimmune diseases. Tobacco smoke, redox metals, and nonredox metals, such as iron, cadmium, chrome, and arsenic, are also involved in carcinogenesis and aging by generating free radicals or binding with thiol groups. Formation of 8-OH-G is the best-known DNA damage occurring via oxidative stress and is a potential biomarker for carcinogenesis.
      Figure thumbnail gr1
      Figure 1Base modifications introduced by reactive oxygen species.
      Promoter regions of genes contain consensus sequences for transcription factors. These transcription factor-binding sites contain GC-rich sequences that are susceptible for oxidant attacks. Formation of 8-OH-G DNA in transcription factor binding sites can modify binding of transcription factors and thus change the expression of related genes as has been shown for AP-1 and Sp-1 target sequences [
      • Ghosh R.
      • Mitchell D.L.
      Effect of oxidative DNA damage in promoter elements on transcription factor binding.
      ]. Besides 8-OH-G, 8,5'-cyclo-2'-deoxyadenosine (cyclo-dA) has also been shown to inhibit transcription from a reporter gene in a cell system if located in a TATA box [
      • Marietta C.
      • Gulam H.
      • Brooks P.J.
      A single 8, 50-cyclo-20-deoxyadeno-sine lesion in a TATA box prevents binding of the TATA binding protein and strongly reduces transcription in vivo.
      ]. The TATA-binding protein initiates transcription by changing the bending of DNA. The binding of TATA-binding protein may be impaired by the presence of cyclo-dA.
      Oxidative stress causes instability of microsatellite (short tandem repeats) regions. Redox active metal ions, hydroxyl radicals increase microsatellite instability [
      • Jackson A.L.
      • Chen R.
      • Loeb L.A.
      Induction of microsatellite instability by oxidative DNA damage.
      ]. Even though single-stranded DNA breaks caused by oxidant injury can easily be tolerated by cells, double-stranded DNA breaks induced by ionizing radiation can be a significant threat for the cell survival [
      • Caldecott K.W.
      Protein-protein interactions during mammalian DNA single-strand break repair.
      ].
      Methylation at CpG islands in DNA is an important epigenetic mechanism that may result in gene silencing. Oxidation of 5-MeCyt to 5-hydroxymethyl uracil (5-OHMeUra) can occur via deamination/oxidation reactions of thymine or 5-hydroxymethyl cytosine intermediates [
      • Cooke M.S.
      • Evans M.D.
      • Dizdaroglu M.
      • Lunec J.
      Oxidative DNA damage: mechanisms, mutation, and disease.
      ]. In addition to the modulating gene expression, DNA methylation also seems to affect chromatin organization [
      • Jones P.L.
      • Wolffe A.P.
      Relationships between chromatin organization and DNA methylation in determining gene expression.
      ]. Aberrant DNA methylation patterns induced by oxidative attacks also affect DNA repair activity.

       Effects of Oxidative Stress on Lipids

      ROS can induce lipid peroxidation and disrupt the membrane lipid bilayer arrangement that may inactivate membrane-bound receptors and enzymes and increase tissue permeability [
      • Girotti A.W.
      Mechanisms of lipid peroxidation.
      ]. Products of lipid peroxidation, such as MDA and unsaturated aldehydes, are capable of inactivating many cellular proteins by forming protein cross-linkages [
      • Siu G.M.
      • Draper H.H.
      Metabolism of malonaldehyde in vivo and in vitro.
      ,
      • Esterbauer H.
      • Koller E.
      • Slee R.G.
      • Koster J.F.
      Possible involvement of the lipid-peroxidation product 4-hydroxynonenal in the formation of fluorescent chromolipids.
      • Hagihara M.
      • Nishigaki I.
      • Maseki M.
      • Yagi K.
      Age-dependent changes in lipid peroxide levels in the lipoprotein fractions of human serum.
      ]. 4-Hydroxy-2-nonenal causes depletion of intracellular GSH and induces of peroxide production, [
      • Keller J.N.
      • Mark R.J.
      • Bruce A.J.
      • Blanc E.
      • Rothstein J.D.
      • et al.
      4-Hydroxynonenal, an aldehydic product of membrane lipid peroxidation, impairs glutamate transport and mitochondrial function in synaptosomes.
      ,
      • Uchida K.
      • Shiraishi M.
      • Naito Y.
      • Torii Y.
      • Nakamura Y.
      • Osawa T.
      Activation of stress signaling pathways by the end product of lipid peroxidation. 4-hydroxy-2-nonenal is a potential inducer of intracellular peroxide production.
      ] activates epidermal growth factor receptor, [
      • Suc I.
      • Meilhac O.
      • Lajoie-Mazenc I.
      • Vandaele J.
      • Jurgens G.
      • Salvayre R.
      • Negre-Salvayre A.
      Activation of EGF receptor by oxidized LDL.
      ] and induces fibronectin production [
      • Tsukagoshi H.
      • Kawata T.
      • Shimizu Y.
      • Ishizuka T.
      • Dobashi K.
      • Mori M.
      4-Hydroxy-2-nonenal enhances fibronectin production by IMR-90 human lung fibroblasts partly via activation of epidermal growth factor receptor-linked extracellular signal-regulated kinase p44/42 pathway.
      ]. Lipid peroxidation products, such as isoprostanes and thiobarbituric acid reactive substances, have been used as indirect biomarkers of oxidative stress, and increased levels were shown in the exhaled breath condensate or bronchoalveolar lavage fluid or lung of chronic obstructive pulmonary disease patients or smokers [
      • Montuschi P.
      • Collins J.V.
      • Ciabattoni G.
      • Lazzeri N.
      • Corradi M.
      • Kharitonov S.A.
      • Barnes P.J.
      Exhaled 8-isoprostane as an in vivo bio-marker of lung oxidative stress in patients with COPD and healthy smokers.
      ,
      • Morrison D.
      • Rahman I.
      • Lannan S.
      • MacNee W.
      Epithelial permeability, inflammation, and oxidant stress in the air spaces of smokers.
      • Nowak D.
      • Kasielski M.
      • Antczak A.
      • Pietras T.
      • Bialasiewicz P.
      Increased content of thiobarbituric acid-reactive substances and hydrogen peroxide in the expired breath condensate of patients with stable chronic obstructive pulmonary disease: no significant effect of cigarette smoking.
      ].

       Effects of Oxidative Stress on Proteins

      ROS can cause fragmentation of the peptide chain, alteration of electrical charge of proteins, cross-linking of proteins, and oxidation of specific amino acids and therefore lead to increased susceptibility to proteolysis by degradation by specific proteases [
      • Kelly F.J.
      • Mudway I.S.
      Protein oxidation at the air-lung interface.
      ]. Cysteine and methionine residues in proteins are particularly more susceptible to oxidation [
      • Dean R.T.
      • Roberts C.R.
      • Jessup W.
      Fragmentation of extracellular and intracellular polypeptides by free radicals.
      ]. Oxidation of sulfhydryl groups or methionine residues of proteins cause conformational changes, protein unfolding, and degradation [
      • Lyras L.
      • Cairns N.J.
      • Jenner A.
      • Jenner P.
      • Halliwell B.
      An assessment of oxidative damage to proteins, lipids, and DNA in brain from patients with Alzheimer's disease.
      ,
      • Dean R.T.
      • Roberts C.R.
      • Jessup W.
      Fragmentation of extracellular and intracellular polypeptides by free radicals.
      ,
      • Keck R.G.
      The use of t-butyl hydroperoxide as a probe for methionine oxidation in proteins.
      • Davies K.J.
      Protein damage and degradation by oxygen radicals. I. General aspects.
      ]. Enzymes that have metals on or close to their active sites are especially more sensitive to metal catalyzed oxidation. Oxidative modification of enzymes has been shown to inhibit their activities [
      • Stadtman E.R.
      Metal ion-catalyzed oxidation of proteins: biochemical mechanism and biological consequences.
      ,
      • Fucci L.
      • Oliver C.N.
      • Coon M.J.
      • Stadtman E.R.
      Inactivation of key metabolic enzymes by mixed-function oxidation reactions: possible implication in protein turnover and ageing.
      ].
      In some cases, specific oxidation of proteins may take place. For example, methionine can be oxidized methionine sulfoxide [
      • Stadtman E.R.
      • Moskovitz J.
      • Levine R.L.
      Oxidation of methionine residues of proteins: biological consequences.
      ] and phenylalanine to o-tyrosine [
      • Stadtman E.R.
      • Levine R.L.
      Free radical-mediated oxidation of free amino acids and amino acid residues in proteins.
      ]; sulfhydryl groups can be oxidized to form disulfide bonds;[
      • Stadtman E.R.
      Protein oxidation in aging and age-related diseases.
      ] and carbonyl groups may be introduced into the side chains of proteins. Gamma rays, metal-catalyzed oxidation, HOCl, and ozone can cause formation of carbonyl groups [
      • Shacter E.
      Quantification and significance of protein oxidation in biological samples.
      ].

       Effects of Oxidative Stress on Signal Transduction

      ROS can induce expression of several genes involved in signal transduction [
      • Valko M.
      • Rhodes C.J.
      • Moncol J.
      • Izakovic M.
      • Mazur M.
      Free radicals, metals and antioxidants in oxidative stress-induced cancer.
      ,
      • Poli G.
      • Leonarduzzi G.
      • Biasi F.
      • Chiarpotto E.
      Oxidative stress and cell signalling.
      ]. A high ratio for GSH/GSSG is important for the protection of the cell from oxidative damage. Disruption of this ratio causes activation of redox sensitive transcription factors, such as NF-κB, AP-1, nuclear factor of activated T cells and hypoxia-inducible factor 1, that are involved in the inflammatory response. Activation of transcription factors via ROS is achieved by signal transduction cascades that transmit the information from outside to the inside of cell. Tyrosine kinase receptors, most of the growth factor receptors, such as epidermal growth factor receptor, vascular endothelial growth factor receptor, and receptor for platelet-derived growth factor, protein tyrosine phosphatases, and serine/threonine kinases are targets of ROS [
      • Neufeld G.
      • Cohen T.
      • Gengrinovitch S.
      • Poltorak Z.
      Vascular endothelial growth factor (VEGF) and its receptors.
      ,
      • Sundaresan M.
      • Yu Z.X.
      • Ferrans V.J.
      • Sulciner D.J.
      • Gutkind J.S.
      • et al.
      Regulation of reactive-oxygen species generation in fibroblasts by Rac1.
      • Sun T.
      • Oberley L.W.
      Redox regulation of transcriptional activators.
      ]. Extra-cellular signal-regulated kinases, JNK, and p38, which are the members of mitogen-activated protein kinase family and involved in several processes in cell including proliferation, differentiation, and apoptosis, also can be regulated by oxidants.
      Under oxidative stress conditions, cysteine residues in the DNA-binding site of c-Jun, some AP-1 subunits, and inhibitory κ-B kinase undergo reversible S-glutathiolation. Glutaredoxin and TRX have been reported to play an important role in regulation of redox-sensitive signaling pathways, such as NF-κB and AP-1, p38 mitogen-activated protein kinase, and JNK [
      • Klatt P.
      • Molina E.P.
      • De Lacoba M.G.
      • Padilla C.A.
      • Martinez-Galesteo E.
      • Barcena J.A.
      • Lamas S.
      Redox regulation of c-Jun DNA binding by reversible S-glutathiolation.
      ,
      • Reynaert N.L.
      • Ckless K.
      • Guala A.S.
      • Wouters E.F.
      • van der Vliet A.
      • Janssen-Heininger Y.M.
      In situ detection of S-glutathionylated proteins following glutaredoxin-1 catalyzed cysteine derivatization.
      ,
      • Reynaert N.L.
      • Wouters E.F.
      • Janssen-Heininger Y.M.
      Modulation of glu-taredoxin-1 expression in a mouse model of allergic airway disease.
      • Filomeni G.
      • Rotilio G.
      • Ciriolo M.R.
      Cell signalling and the glutathione redox system.
      ].
      NF-κB can be activated in response to oxidative stress conditions, such as ROS, free radicals, and UV irradiation [
      • Pande V.
      • Ramos M.J.
      Molecular recognition of 15-deoxydelta (12, 14)-prostaglandin J(2) by nuclear factor-kappa B and other cellular proteins.
      ]. Phosphorylation of IκB frees NF-κB and allows it to enter the nucleus to activate gene transcription [
      • Perkins N.D.
      Integrating cell-signalling pathways with NF-kappaB and IKK function.
      ]. A number of kinases have been reported to phosphorylate IκBs at the serine residues. These kinases are the targets of oxidative signals for activation of NF-κB [
      • Gilmore T.D.
      Introduction to NF-kappaB: players, pathways, perspectives.
      ]. Reducing agents enhance NF-κB DNA binding, whereas oxidizing agents inhibit DNA binding of NF-κB. TRX may exert 2 opposite actions in regulation of NF-κB: in the cytoplasm, it blocks degradation of IκB and inhibits NF-κB activation but enhances NF-κB DNA binding in the nucleus [
      • Hirota K.
      • Murata M.
      • Sachi Y.
      • Nakamura H.
      • Takeuchi J.
      • Mori K.
      • Yodoi J.
      Distinct roles of thioredoxin in the cytoplasm and in the nucleus. A two-step mechanism of redox regulation of transcription factor NF-kappaB.
      ]. Activation of NF-κB via oxidation-related degradation of IκB results in the activation of several antioxidant defense-related genes. NF-κB regulates the expression of several genes that participate in immune response, such as IL-1κ, IL-6, tumor necrosis factor-α, IL-8, and several adhesion molecules [
      • Ward P.A.
      Role of complement, chemokines and regulatory cytokines in acute lung injury.
      ,
      • Akira S.
      • Kishimoto A.
      NF-IL6 and NF-kB in cytokine gene regulation.
      ]. NF-κB also regulates angiogenesis and proliferation and differentiation of cells.
      AP-1 is also regulated by redox state. In the presence of H2O2, some metal ions can induce activation of AP-1. Increase in the ratio of GSH/GSSG enhances AP-1 binding while GSSG inhibits the DNA binding of AP-1 [
      • Meyer M.
      • Schreck R.
      • Baeuerle P.A.
      H2O2 and antioxidants have opposite effects on activation of NF-kappa B and AP-1 in intact cells: AP-1 as secondary antioxidant-responsive factor.
      ]. DNA binding of the Fos/Jun heterodimer is increased by the reduction of a single conserved cysteine in the DNA-binding domain of each of the proteins, [
      • Abate C.
      • Patel L.
      • Rausher F.J.
      • Curran T.
      Redox regulation of fos and jun DNA-binding activity in vitro.
      ] while DNA binding of AP-1 can be inhibited by GSSG in many cell types, suggesting that disulphide bond formation by cysteine residues inhibits AP-1 DNA binding [
      • Galter D.
      • Mihm S.
      • Droge W.
      Distinct effects of glutathione disulphide on the nuclear transcription factors kB and the activator protein-1.
      ,
      • Hirota K.
      • Matsui M.
      • Iwata S.
      • Nishiyama A.
      • Mori K.
      • Yodoi J.
      AP-1 transcriptional activity is regulated by a direct association between thioredoxin and Ref-1.
      ]. Signal transduction via oxidative stress is summarized in Figure 2.
      Figure thumbnail gr2
      Figure 2Effects of oxidative stress on signal transduction in the cell.

      Conclusions

      Oxidative stress can arise from overproduction of ROS by metabolic reactions that use oxygen and shift the balance between oxidant/antioxidant statuses in favor of the oxidants. ROS are produced by cellular metabolic activities and environmental factors, such as air pollutants or cigarette smoke. ROS are highly reactive molecules because of unpaired electrons in their structure and react with several biological macromolecules in cell, such as carbohydrates, nucleic acids, lipids, and proteins, and alter their functions. ROS also affects the expression of several genes by upregulation of redox-sensitive transcription factors and chromatin remodeling via alteration in histone acetylation/deacetylation. Regulation of redox state is critical for cell viability, activation, proliferation, and organ function.

      References

        • Valko M.
        • Rhodes C.J.
        • Moncol J.
        • Izakovic M.
        • Mazur M.
        Free radicals, metals and antioxidants in oxidative stress-induced cancer.
        Chem Biol Interact. 2006; 160: 1-40
        • Halliwell B.
        • Gutteridge J.MC.
        Free Radicals in Biology and Medicine. 3. Oxford University Press, New York1999
        • Marnett L.J.
        Lipid peroxidation--DNA damage by malondialdehyde.
        Mutat Res. 1999; 424: 83-95
        • Siems W.G.
        • Grune T.
        • Esterbauer H.
        4-Hydroxynonenal formation during ischemia and reperfusion of rat small-intestine.
        Life Sci. 1995; 57: 785-789
        • Stadtman E.R.
        Role of oxidant species in aging.
        Curr Med Chem. 2004; 11: 1105-1112
        • Wang M.Y.
        • Dhingra K.
        • Hittelman W.N.
        • Liehr J.G.
        • deAndrade M.
        • Li D.H.
        Lipid peroxidation-induced putative malondialdehyde-DNA adducts in human breast tissues.
        Cancer Epidemiol Biomarkers Prev. 1996; 5: 705-710
        • Jenner P.
        Oxidative stress in Parkinson's disease.
        Ann Neurol. 2003; 53: S26-S36
        • Lyras L.
        • Cairns N.J.
        • Jenner A.
        • Jenner P.
        • Halliwell B.
        An assessment of oxidative damage to proteins, lipids, and DNA in brain from patients with Alzheimer's disease.
        J Neurochem. 1997; 68: 2061-2069
        • Sayre L.M.
        • Smith M.A.
        • Perry G.
        Chemistry and biochemistry of oxidative stress in neurodegenerative disease.
        Curr Med Chem. 2001; 8: 721-738
        • Toshniwal P.K.
        • Zarling E.J.
        Evidence for increased lipid peroxidation in multiple sclerosis.
        Neurochem Res. 1992; 17: 205-207
        • Dhalla N.S.
        • Temsah R.M.
        • Netticadan T.
        Role of oxidative stress in cardiovascular diseases.
        J Hypertens. 2000; 18: 655-673
        • Kasparova S.
        • Brezova V.
        • Valko M.
        • Horecky J.
        • Mlynarik V.
        • et al.
        Study of the oxidative stress in a rat model of chronic brain hypoperfusion.
        Neurochem Int. 2005; 46: 601-611
        • Kerr S.
        • Brosnan M.J.
        • McIntyre M.
        • Reid J.L.
        • Dominiczak A.F.
        • Hamilton C.A.
        Superoxide anion production is increased in a model of genetic hypertension: role of the endothelium.
        Hypertension. 1999; 33: 1353-1358
        • Kukreja R.C.
        • Hess M.L.
        The oxygen free-radical system: from equations through membrane-protein interactions to cardiovascular injury and protection.
        Cardiovasc Res. 1992; 26: 641-655
        • Asami S.
        • Manabe H.
        • Miyake J.
        • Tsurudome Y.
        • Hirano T.
        • et al.
        Cigarette smoking induces an increase in oxidative DNA damage, 8-hydroxydeoxyguanosine, in a central site of the human lung.
        Carci-nogenesis. 1997; 18: 1763-1766
        • Andreadis A.A.
        • Hazen S.L.
        • Comhair S.A.
        • Erzurum S.C.
        Oxidative and nitrosative events in asthma.
        Free Radic Biol Med. 2003; 35: 213-225
        • Comhair S.A.
        • Ricci K.S.
        • Arroliga M.
        • Lara A.R.
        • Dweik R.A.
        • et al.
        Correlation of systemic superoxide dismutase deficiency to airflow obstruction in asthma.
        Am J Respir Crit Care Med. 2005; 172: 306-313
        • Comhair S.A.
        • Xu W.
        • Ghosh S.
        • Thunnissen F.B.
        • Almasan A.
        • et al.
        Superoxide dismutase inactivation in pathophysiology of asthmatic airway remodeling and reactivity.
        Am J Pathol. 2005; 166: 663-674
        • Dut R.
        • Dizdar E.A.
        • Birben E.
        • Sackesen C.
        • Soyer O.U.
        • Besler T.
        • Kalayci O.
        Oxidative stress and its determinants in the airways of children with asthma.
        Allergy. 2008; 63: 1605-1609
        • Ercan H.
        • Birben E.
        • Dizdar E.A.
        • Keskin O.
        • Karaaslan C.
        • et al.
        Oxidative stress and genetic and epidemiologic determinants of oxidant injury in childhood asthma.
        J Allergy Clin Immunol. 2006; 118: 1097-1104
        • Fitzpatrick A.M.
        • Teague W.G.
        • Holguin F.
        • Yeh M.
        • Brown L.A.
        Severe Asthma Research Program. Airway glutathione homeostasis is altered in children with severe asthma: evidence for oxidant stress.
        J Allergy Clin Immunol. 2009; 123: 146-152
        • Miller D.M.
        • Buettner G.R.
        • Aust S.D.
        Transition metals as catalysts of "autoxidation" reactions.
        Free Radic Biol Med. 1990; 8: 95-108
        • Dupuy C.
        • Virion A.
        • Ohayon R.
        • Kaniewski J.
        • Dème D.
        • Pommier J.
        Mechanism of hydrogen peroxide formation catalyzed by NADPH oxidase in thyroid plasma membrane.
        J Biol Chem. 1991; 266: 3739-3743
        • Granger D.N.
        Role of xanthine oxidase and granulocytes in ischemia-reperfusion injury.
        Am J Physiol. 1988; 255: H1269-H1275
        • Fenton H.JH.
        Oxidation of tartaric acid in the presence of iron.
        J Chem Soc. 1984; 65: 899-910
        • Haber F.
        • Weiss J.J.
        The catalytic decomposition of hydrogen peroxide by iron salts.
        Proc R Soc Lond Ser A. 1934; 147: 332-351
        • Liochev S.I.
        • Fridovich I.
        The Haber-Weiss cycle--70 years later: an alternative view.
        Redox Rep. 2002; 7: 55-57
        • Klebanoff S.J.
        Myeloperoxidase: friend and foe.
        J Leukoc Biol. 2005; 77: 598-625
        • Whiteman M.
        • Jenner A.
        • Halliwell B.
        Hypochlorous acid-induced base modifications in isolated calf thymus DNA.
        Chem Res Toxicol. 1997; 10: 1240-1246
        • Kulcharyk P.A.
        • Heinecke J.W.
        Hypochlorous acid produced by the myeloperoxidase system of human phagocytes induces covalent cross-links between DNA and protein.
        Biochemistry. 2001; 40: 3648-3656
        • Brennan M.L.
        • Wu W.
        • Fu X.
        • Shen Z.
        • Song W.
        • et al.
        A tale of two controversies: defining both the role of peroxidases in nitrotyrosine formation in vivo using eosinophil peroxidase and myeloperoxidase-deficient mice, and the nature of peroxidase-generated reactive nitrogen species.
        J Biol Chem. 2002; 277: 17415-17427
        • Denzler K.L.
        • Borchers M.T.
        • Crosby J.R.
        • Cieslewicz G.
        • Hines E.M.
        • et al.
        Extensive eosinophil degranulation and peroxidase-mediated oxidation of airway proteins do not occur in a mouse ovalbumin-challenge model of pulmonary inflammation.
        J Immunol. 2001; 167: 1672-1682
        • van Dalen C.J.
        • Winterbourn C.C.
        • Senthilmohan R.
        • Kettle A.J.
        Nitrite as a substrate and inhibitor of myeloperoxidase. Implications for nitration and hypochlorous acid production at sites of inflammation.
        J Biol Chem. 2000; 275: 11638-11644
        • Wood L.G.
        • Fitzgerald D.A.
        • Gibson P.G.
        • Cooper D.M.
        • Garg M.L.
        Lipid peroxidation as determined by plasma isoprostanes is related to disease severity in mild asthma.
        Lipids. 2000; 35: 967-974
        • Montuschi P.
        • Corradi M.
        • Ciabattoni G.
        • Nightingale J.
        • Kharitonov S.A.
        • Barnes P.J.
        Increased 8-isoprostane, a marker of oxidative stress, in exhaled condensate of asthma patients.
        Am J Respir Crit Care Med. 1999; 160: 216-220
        • Church D.F.
        • Pryor W.A.
        Free-radical chemistry of cigarette smoke and its toxicological implications.
        Environ Health Perspect. 1985; 64: 111-126
        • Hiltermann J.T.
        • Lapperre T.S.
        • van Bree L.
        • Steerenberg P.A.
        • Brahim J.J.
        • et al.
        Ozone-induced inflammation assessed in sputum and bronchial lavage fluid from asthmatics: a new noninvasive tool in epidemiologic studies on air pollution and asthma.
        Free Radic Biol Med. 1999; 27: 1448-1454
        • Nightingale J.A.
        • Rogers D.F.
        • Barnes P.J.
        Effect of inhaled ozone on exhaled nitric oxide, pulmonary function, and induced sputum in normal and asthmatic subjects.
        Thorax. 1999; 54: 1061-1069
        • Cho A.K.
        • Sioutas C.
        • Miguel A.H.
        • Kumagai Y.
        • Schmitz D.A.
        • et al.
        Redox activity of airborne particulate matter at different sites in the Los Angeles Basin.
        Environ Res. 2005; 99: 40-47
        • Comhair S.A.
        • Thomassen M.J.
        • Erzurum S.C.
        Differential induction of extracellular glutathione peroxidase and nitric oxide synthase 2 in airways of healthy individuals exposed to 100% O(2) or cigarette smoke.
        Am J Respir Cell Mol Biol. 2000; 23: 350-354
        • Matthay M.A.
        • Geiser T.
        • Matalon S.
        • Ischiropoulos H.
        Oxidant-mediated lung injury in the acute respiratory distress syndrome.
        Crit Care Med. 1999; 27: 2028-2030
        • Biaglow J.E.
        • Mitchell J.B.
        • Held K.
        The importance of peroxide and superoxide in the X-ray response.
        Int J Radiat Oncol Biol Phys. 1992; 22: 665-669
        • Chiu S.M.
        • Xue L.Y.
        • Friedman L.R.
        • Oleinick N.L.
        Copper ion-mediated sensitization of nuclear matrix attachment sites to ionizing radiation.
        Biochemistry. 1993; 32: 6214-6219
        • Narayanan P.K.
        • Goodwin E.H.
        • Lehnert B.E.
        Alpha particles initiate biological production of superoxide anions and hydrogen peroxide in human cells.
        Cancer Res. 1997; 57: 3963-3971
        • Tuttle S.W.
        • Varnes M.E.
        • Mitchell J.B.
        • Biaglow J.E.
        Sensitivity to chemical oxidants and radiation in CHO cell lines deficient in oxidative pentose cycle activity.
        Int J Radiat Oncol Biol Phys. 1992; 22: 671-675
        • Guo G.
        • Yan-Sanders Y.
        • Lyn-Cook B.D.
        • Wang T.
        • Tamae D.
        • et al.
        Manganese superoxide dismutase-mediated gene expression in radiation-induced adaptive responses.
        Mol Cell Biol. 2003; 23: 2362-2378
        • Azzam E.I.
        • de Toledo S.M.
        • Spitz D.R.
        • Little J.B.
        Oxidative metabolism modulates signal transduction and micronucleus formation in bystander cells from a-particle irradiated normal human fibroblasts.
        Cancer Res. 2002; 62: 5436-5442
        • Leach J.K.
        • Van Tuyle G.
        • Lin P.S.
        • Schmidt-Ullrich R.
        • Mikkelsen R.B.
        Ionizing radiation-induced, mitochondria-dependent generation of reactive oxygen/nitrogen.
        Cancer Res. 2001; 61: 3894-3901
        • Dent P.
        • Yacoub A.
        • Fisher P.B.
        • Hagan M.P.
        • Grant S.
        MAPK pathways in radiation responses.
        Oncogene. 2003; 22: 5885-5896
        • Wei S.J.
        • Botero A.
        • Hirota K.
        • Bradbury C.M.
        • Markovina S.
        • et al.
        Thioredoxin nuclear translocation and interaction with redox factor-1 activates the AP-1 transcription factor in response to ionizing radiation.
        Cancer Res. 2000; 60: 6688-6695
        • Cadet J.
        • Douki T.
        • Gasparutto D.
        • Ravanat J.L.
        Oxidative damage to DNA: formation, measurement and biochemical features.
        Mutat Res. 2003; 531: 5-23
        • Yokoya A.
        • Cunniffe S.M.
        • O'Neill P.
        Effect of hydration on the induction of strand breaks and base lesions in plasmid DNA films by gamma-radiation.
        J Am Chem Soc. 2002; 124: 8859-8866
        • Janssen Y.M.
        • Van Houten B.
        • Borm P.J.
        • Mossman B.T.
        Cell and tissue responses to oxidative damage.
        Lab Invest. 1993; 69: 261-274
        • Iwanaga M.
        • Mori K.
        • Iida T.
        • Urata Y.
        • Matsuo T.
        • et al.
        Nuclear factor kappa B dependent induction of gamma glutamylcysteine synthetase by ionizing radiation in T98G human glioblastoma cells.
        Free Radic Biol Med. 1998; 24: 1256-1268
        • Stohs S.J.
        • Bagchi D.
        Oxidative mechanisms in the toxicity of metal ions.
        Free Radic Biol Med. 1995; 18: 321-336
        • Leonard S.S.
        • Harris G.K.
        • Shi X.
        Metal-induced oxidative stress and signal transduction.
        Free Radic Biol Med. 2004; 37: 1921-1942
        • Shi H.
        • Shi X.
        • Liu K.J.
        Oxidative mechanism of arsenic toxicity and carcinogenesis.
        Mol Cell Biochem. 2004; 255: 67-78
        • Pi J.
        • Horiguchi S.
        • Sun Y.
        • Nikaido M.
        • Shimojo N.
        • Hayashi T.
        A potential mechanism for the impairment of nitric oxide formation caused by prolonged oral exposure to arsenate in rabbits.
        Free Radic Biol Med. 2003; 35: 102-113
        • Rin K.
        • Kawaguchi K.
        • Yamanaka K.
        • Tezuka M.
        • Oku N.
        • Okada S.
        DNA-strand breaks induced by dimethylarsinic acid, a metabolite of inorganic arsenics, are strongly enhanced by superoxide anion radicals.
        Biol Pharm Bull. 1995; 18: 45-58
        • Waalkes M.P.
        • Liu J.
        • Ward J.M.
        • Diwan L.A.
        Mechanisms underlying arsenic carcinogenesis: hypersensitivity of mice exposed to inorganic arsenic during gestation.
        Toxicology. 2004; 198: 31-38
        • Schiller C.M.
        • Fowler B.A.
        • Woods J.S.
        Effects of arsenic on pyruvate dehydrogenase activation.
        Environ Health Perspect. 1977; 19: 205-207
        • Monterio H.P.
        • Bechara E.JH.
        • Abdalla D.SP.
        Free radicals involvement in neurological porphyrias and lead poisoning.
        Mol Cell Biochem. 1991; 103: 73-83
        • Tripathi R.M.
        • Raghunath R.
        • Mahapatra S.
        Blood lead and its effect on Cd, Cu, Zn, Fe and hemoglobin levels of children.
        Sci Total Environ. 2001; 277: 161-168
        • Nehru B.
        • Dua R.
        The effect of dietary selenium on lead neurotoxicity.
        J Environ Pathol Toxicol Oncol. 1997; 16: 47-50
        • Reid T.M.
        • Feig D.I.
        • Loeb L.A.
        Mutagenesis by metal-induced oxygen radicals.
        Environ Health Perspect. 1994; 102: 57-61
        • Kinnula V.L.
        • Crapo J.D.
        Superoxide dismutases in the lung and human lung diseases.
        Am J Respir Crit Care Med. 2003; 167: 1600-1619
        • Kinnula V.L.
        Production and degradation of oxygen metabolites during inflammatory states in the human lung.
        Curr Drug Targets In3amm Allergy. 2005; 4: 465-470
        • Zelko I.N.
        • Mariani T.J.
        • Folz R.J.
        Superoxide dismutase multigene family: a comparison of the CuZn-SOD (SOD1), Mn-SOD (SOD2), and EC-SOD (SOD3) gene structures, evolution, and expression.
        Free Radic Biol Med. 2002; 33: 337-349
        • Kirkman H.N.
        • Rolfo M.
        • Ferraris A.M.
        • Gaetani G.F.
        Mechanisms of protection of catalase by NADPH. Kinetics and stoichiometry.
        J Biol Chem. 1999; 274: 13908-13914
        • Flohé L.
        Glutathione peroxidase.
        Basic Life Sci. 1988; 49: 663-668
        • Arthur J.R.
        The glutathione peroxidases.
        Cell Mol Life Sci. 2000; 57: 1825-1835
        • Chu F.F.
        • Doroshow J.H.
        • Esworthy R.S.
        Expression, characterization, and tissue distribution of a new cellular selenium-dependent glutathione peroxidase, GSHPx-GI.
        J Biol Chem. 1993; 268: 2571-2576
        • Comhair S.A.
        • Bhathena P.R.
        • Farver C.
        • Thunnissen F.B.
        • Erzurum S.C.
        Extracellular glutathione peroxidase induction in asthmatic lungs: evidence for redox regulation of expression in human airway epithelial cells.
        FASEB J. 2001; 15: 70-78
        • Gromer S.
        • Urig S.
        • Becker K.
        The thioredoxin system--from science to clinic.
        Med Res Rev. 2004; 24: 40-89
        • Kinnula V.L.
        • Lehtonen S.
        • Kaarteenaho-Wiik R.
        • Lakari E.
        • Pääkkö P.
        • et al.
        Cell specific expression of peroxiredoxins in human lung and pulmonary sarcoidosis.
        Thorax. 2002; 57: 157-164
        • Dubuisson M.
        • Vander Stricht D.
        • Clippe A.
        • Etienne F.
        • Nauser T.
        • et al.
        Human peroxiredoxin 5 is a peroxynitrite reductase.
        FEBS Lett. 2004; 571: 161-165
        • Holmgren A.
        Antioxidant function of thioredoxin and glutaredoxin systems.
        Antioxid Redox Signal. 2000; 2: 811-820
        • Dickinson D.A.
        • Forman H.J.
        Glutathione in defense and signaling: lessons from a small thiol.
        Ann N Y Acad Sci. 2002; 973: 488-504
        • Sies H.
        Glutathione and its role in cellular functions.
        Free Radic Biol Med. 1999; 27: 916-921
        • Ladner J.E.
        • Parsons J.F.
        • Rife C.L.
        • Gilliland G.L.
        • Armstrong R.N.
        Parallel evolutionary pathways for glutathione transferases: structure and mechanism of the mitochondrial class kappa enzyme rGSTK1-1.
        Biochemistry. 2004; 43: 52-61
        • Robinson A.
        • Huttley G.A.
        • Booth H.S.
        • Board P.G.
        Modelling and bioinformatics studies of the human kappa class glutathione transferase predict a novel third transferase family with homology to prokaryotic 2-hydroxychromene-2-carboxylate isomerases.
        Biochem J. 2004; 379: 541-552
        • Jakobsson P-J
        • Morgenstern R.
        • Mancini J.
        • Ford-Hutchinson A.
        • Persson B.
        Common structural features of MAPEG--a widespread superfamily of membrane associated proteins with highly divergent functions in eicosanoid and glutathione metabolism.
        Protein Sci. 1999; 8: 689-692
        • Hayes J.D.
        • Pulford D.J.
        The glutathione S-transferase supergene family: regulation of GST and the contribution of the isoenzymes to cancer chemoprotection and drug resistance.
        Crit Rev Biochem Mol Biol. 1995; 30: 445-600
        • Armstrong R.N.
        Structure, catalytic mechanism, and evolution of the glutathione transferases.
        Chem Res Toxicol. 1997; 10: 2-18
        • Hayes J.D.
        • McLellan L.I.
        Glutathione and glutathione-dependent enzymes represent a co-ordinately regulated defence against oxidative stress.
        Free Radic Res. 1999; 31: 273-300
        • Sheehan D.
        • Meade G.
        • Foley V.M.
        • Dowd C.A.
        Structure, function and evolution of glutathione transferases: implications for classification of nonmammalian members of an ancient enzyme superfamily.
        Biochem J. 2001; 360: 1-16
        • Cho S-G
        • Lee Y.H.
        • Park H-S
        • Ryoo K.
        • Kang K.W.
        • et al.
        Glutathione S-transferase Mu modulates the stress activated signals by suppressing apoptosis signal-regulating kinase 1.
        J Biol Chem. 2001; 276: 12749-12755
        • Dorion S.
        • Lambert H.
        • Landry J.
        Activation of the p38 signaling pathway by heat shock involves the dissociation of glutathione S-transferase Mu from Ask1.
        J Biol Chem. 2002; 277: 30792-30797
        • Adler V.
        • Yin Z.
        • Fuchs S.Y.
        • Benezra M.
        • Rosario L.
        • et al.
        Regulation of JNK signalling by GSTp.
        EMBO J. 1999; 18: 1321-1334
        • Manevich Y.
        • Feinstein S.I.
        • Fisher A.B.
        Activation of the antioxidant enzyme 1-CYS peroxiredoxin requires glutathionylation mediated by heterodimerization with pGST.
        Proc Natl Acad Sci USA. 2004; 101: 3780-3785
        • Bunker V.W.
        Free radicals, antioxidants and ageing.
        Med Lab Sci. 1992; 49: 299-312
        • Mezzetti A.
        • Lapenna D.
        • Romano F.
        • Costantini F.
        • Pierdomenico S.D.
        • et al.
        Systemic oxidative stress and its relationship with age and illness.
        J Am Geriatr Soc. 1996; 44: 823-827
        • White E.
        • Shannon J.S.
        • Patterson R.E.
        Relationship between vitamin and calcium supplement use and colon cancer.
        Cancer Epidemiol Bio-markers Prev. 1997; 6: 769-774
        • Masella R.
        • Di Benedetto R.
        • Vari R.
        • Filesi C.
        • Giovannini C.
        Novel mechanisms of natural antioxidant compounds in biological systems: involvement of glutathione and glutathione-related enzymes.
        J Nutr Biochem. 2005; 16: 577-586
        • Curello S.
        • Ceconi C.
        • Bigoli C.
        • Ferrari R.
        • Albertini A.
        • Guarnieri C.
        Changes in the cardiac glutathione status after ischemia and reperfusion.
        Experientia. 1985; 41: 42-43
        • El-Agamey A.
        • Lowe G.M.
        • McGarvey D.J.
        • Mortensen A.
        • Phillip D.M.
        • Truscott T.G.
        Carotenoid radical chemistry and antioxidant/pro-oxidant properties.
        Arch Biochem Biophys. 2004; 430: 37-48
        • Rice-Evans C.A.
        • Sampson J.
        • Bramley P.M.
        • Holloway D.E.
        Why do we expect carotenoids to be antioxidants in vivo?.
        Free Radic Res. 1997; 26: 381-398
        • Niles R.M.
        Signaling pathways in retinoid chemoprevention and treatment of cancer.
        Mutat Res. 2004; 555: 81-96
        • Donato L.J.
        • Noy N.
        Suppression of mammary carcinoma growth by retinoic acid: proapoptotic genes are targets for retinoic acid receptor and cellular retinoic acid-binding protein II signaling.
        Cancer Res. 2005; 65: 8193-8199
        • Niizuma H.
        • Nakamura Y.
        • Ozaki T.
        • Nakanishi H.
        • Ohira M.
        • et al.
        Bcl-2 is a key regulator for the retinoic acid-induced apoptotic cell death in neuroblastoma.
        Oncogene. 2006; 25: 5046-5055
        • Dalton T.P.
        • Shertzer H.G.
        • Puga A.
        Regulation of gene expression by reactive oxygen.
        Ann Rev Pharmacol Toxicol. 1999; 39: 67-101
        • Scandalios J.G.
        Genomic responses to oxidative stress.
        in: Meyers R.A. Encyclopedia of Molecular Cell Biology and Molecular Medicine. 2. Wiley-VCH, Weinheim, Germany2004: 489-512
        • Ghosh R.
        • Mitchell D.L.
        Effect of oxidative DNA damage in promoter elements on transcription factor binding.
        Nucleic Acids Res. 1999; 27: 3213-3218
        • Marietta C.
        • Gulam H.
        • Brooks P.J.
        A single 8, 50-cyclo-20-deoxyadeno-sine lesion in a TATA box prevents binding of the TATA binding protein and strongly reduces transcription in vivo.
        DNA Repair (Amst). 2002; 1: 967-975
        • Jackson A.L.
        • Chen R.
        • Loeb L.A.
        Induction of microsatellite instability by oxidative DNA damage.
        Proc Natl Acad Sci USA. 1998; 95: 12468-12473
        • Caldecott K.W.
        Protein-protein interactions during mammalian DNA single-strand break repair.
        Biochem Soc Trans. 2003; 31: 247-251
        • Cooke M.S.
        • Evans M.D.
        • Dizdaroglu M.
        • Lunec J.
        Oxidative DNA damage: mechanisms, mutation, and disease.
        FASEB J. 2003; 17: 1195-1214
        • Jones P.L.
        • Wolffe A.P.
        Relationships between chromatin organization and DNA methylation in determining gene expression.
        Semin Cancer Biol. 1999; 9: 339-347
        • Girotti A.W.
        Mechanisms of lipid peroxidation.
        J Free Radic Biol Med. 1985; 1: 87-95
        • Siu G.M.
        • Draper H.H.
        Metabolism of malonaldehyde in vivo and in vitro.
        Lipids. 1982; 17: 349-355
        • Esterbauer H.
        • Koller E.
        • Slee R.G.
        • Koster J.F.
        Possible involvement of the lipid-peroxidation product 4-hydroxynonenal in the formation of fluorescent chromolipids.
        Biochem J. 1986; 239: 405-409
        • Hagihara M.
        • Nishigaki I.
        • Maseki M.
        • Yagi K.
        Age-dependent changes in lipid peroxide levels in the lipoprotein fractions of human serum.
        J Gerontol. 1984; 39: 269-272
        • Keller J.N.
        • Mark R.J.
        • Bruce A.J.
        • Blanc E.
        • Rothstein J.D.
        • et al.
        4-Hydroxynonenal, an aldehydic product of membrane lipid peroxidation, impairs glutamate transport and mitochondrial function in synaptosomes.
        Neuroscience. 1997; 806: 85-96
        • Uchida K.
        • Shiraishi M.
        • Naito Y.
        • Torii Y.
        • Nakamura Y.
        • Osawa T.
        Activation of stress signaling pathways by the end product of lipid peroxidation. 4-hydroxy-2-nonenal is a potential inducer of intracellular peroxide production.
        J Biol Chem. 1999; 274: 2234-2242
        • Suc I.
        • Meilhac O.
        • Lajoie-Mazenc I.
        • Vandaele J.
        • Jurgens G.
        • Salvayre R.
        • Negre-Salvayre A.
        Activation of EGF receptor by oxidized LDL.
        FASEB J. 1998; 12: 665-671
        • Tsukagoshi H.
        • Kawata T.
        • Shimizu Y.
        • Ishizuka T.
        • Dobashi K.
        • Mori M.
        4-Hydroxy-2-nonenal enhances fibronectin production by IMR-90 human lung fibroblasts partly via activation of epidermal growth factor receptor-linked extracellular signal-regulated kinase p44/42 pathway.
        Toxicol Appl Pharmacol. 2002; 184: 127-135
        • Montuschi P.
        • Collins J.V.
        • Ciabattoni G.
        • Lazzeri N.
        • Corradi M.
        • Kharitonov S.A.
        • Barnes P.J.
        Exhaled 8-isoprostane as an in vivo bio-marker of lung oxidative stress in patients with COPD and healthy smokers.
        Am J Respir Crit Care Med. 2000; 162: 1175-1177
        • Morrison D.
        • Rahman I.
        • Lannan S.
        • MacNee W.
        Epithelial permeability, inflammation, and oxidant stress in the air spaces of smokers.
        Am J Respir Crit Care Med. 1999; 159: 473-479
        • Nowak D.
        • Kasielski M.
        • Antczak A.
        • Pietras T.
        • Bialasiewicz P.
        Increased content of thiobarbituric acid-reactive substances and hydrogen peroxide in the expired breath condensate of patients with stable chronic obstructive pulmonary disease: no significant effect of cigarette smoking.
        Respir Med. 1999; 93: 389-396
        • Kelly F.J.
        • Mudway I.S.
        Protein oxidation at the air-lung interface.
        Amino Acids. 2003; 25: 375-396
        • Dean R.T.
        • Roberts C.R.
        • Jessup W.
        Fragmentation of extracellular and intracellular polypeptides by free radicals.
        Prog Clin Biol Res. 1985; 180: 341-350
        • Keck R.G.
        The use of t-butyl hydroperoxide as a probe for methionine oxidation in proteins.
        Anal Biochem. 1996; 236: 56-62
        • Davies K.J.
        Protein damage and degradation by oxygen radicals. I. General aspects.
        J Biol Chem. 1987; 262: 9895-9901
        • Stadtman E.R.
        Metal ion-catalyzed oxidation of proteins: biochemical mechanism and biological consequences.
        Free Radic Biol Med. 1990; 9: 315-325
        • Fucci L.
        • Oliver C.N.
        • Coon M.J.
        • Stadtman E.R.
        Inactivation of key metabolic enzymes by mixed-function oxidation reactions: possible implication in protein turnover and ageing.
        Proc Natl Acad Sci USA. 1983; 80: 1521-1525
        • Stadtman E.R.
        • Moskovitz J.
        • Levine R.L.
        Oxidation of methionine residues of proteins: biological consequences.
        Antioxid Redox Signal. 2003; 5: 577-582
        • Stadtman E.R.
        • Levine R.L.
        Free radical-mediated oxidation of free amino acids and amino acid residues in proteins.
        Amino Acids. 2003; 25: 207-218
        • Stadtman E.R.
        Protein oxidation in aging and age-related diseases.
        Ann N Y Acad Sci. 2001; 928: 22-38
        • Shacter E.
        Quantification and significance of protein oxidation in biological samples.
        Drug Metab Rev. 2000; 32: 307-326
        • Poli G.
        • Leonarduzzi G.
        • Biasi F.
        • Chiarpotto E.
        Oxidative stress and cell signalling.
        Curr Med Chem. 2004; 11: 1163-1182
        • Neufeld G.
        • Cohen T.
        • Gengrinovitch S.
        • Poltorak Z.
        Vascular endothelial growth factor (VEGF) and its receptors.
        FASEB J. 1999; 13: 9-22
        • Sundaresan M.
        • Yu Z.X.
        • Ferrans V.J.
        • Sulciner D.J.
        • Gutkind J.S.
        • et al.
        Regulation of reactive-oxygen species generation in fibroblasts by Rac1.
        Biochem J. 1996; 318: 379-382
        • Sun T.
        • Oberley L.W.
        Redox regulation of transcriptional activators.
        Free Radic Biol Med. 1996; 21: 335-348
        • Klatt P.
        • Molina E.P.
        • De Lacoba M.G.
        • Padilla C.A.
        • Martinez-Galesteo E.
        • Barcena J.A.
        • Lamas S.
        Redox regulation of c-Jun DNA binding by reversible S-glutathiolation.
        FASEB J. 1999; 13: 1481-1490
        • Reynaert N.L.
        • Ckless K.
        • Guala A.S.
        • Wouters E.F.
        • van der Vliet A.
        • Janssen-Heininger Y.M.
        In situ detection of S-glutathionylated proteins following glutaredoxin-1 catalyzed cysteine derivatization.
        Biochim Biophys Acta. 2006; 1760: 380-387
        • Reynaert N.L.
        • Wouters E.F.
        • Janssen-Heininger Y.M.
        Modulation of glu-taredoxin-1 expression in a mouse model of allergic airway disease.
        Am J Respir Cell Mol Biol. 2007; 36: 147-151
        • Filomeni G.
        • Rotilio G.
        • Ciriolo M.R.
        Cell signalling and the glutathione redox system.
        Biochem Pharmacol. 2002; 64: 1057-1064
        • Pande V.
        • Ramos M.J.
        Molecular recognition of 15-deoxydelta (12, 14)-prostaglandin J(2) by nuclear factor-kappa B and other cellular proteins.
        Bioorg Med Chem Lett. 2005; 15: 4057-4063
        • Perkins N.D.
        Integrating cell-signalling pathways with NF-kappaB and IKK function.
        Nat Rev Mol Cell Biol. 2007; 8: 49-62
        • Gilmore T.D.
        Introduction to NF-kappaB: players, pathways, perspectives.
        Oncogene. 2006; 25: 6680-6684
        • Hirota K.
        • Murata M.
        • Sachi Y.
        • Nakamura H.
        • Takeuchi J.
        • Mori K.
        • Yodoi J.
        Distinct roles of thioredoxin in the cytoplasm and in the nucleus. A two-step mechanism of redox regulation of transcription factor NF-kappaB.
        J Biol Chem. 1999; 274: 27891-27897
        • Ward P.A.
        Role of complement, chemokines and regulatory cytokines in acute lung injury.
        Ann N Y Acad Sci. 1996; 796: 104-112
        • Akira S.
        • Kishimoto A.
        NF-IL6 and NF-kB in cytokine gene regulation.
        Adv Immunol. 1997; 65: 1-46
        • Meyer M.
        • Schreck R.
        • Baeuerle P.A.
        H2O2 and antioxidants have opposite effects on activation of NF-kappa B and AP-1 in intact cells: AP-1 as secondary antioxidant-responsive factor.
        EMBO J. 1993; 12: 2005-2015
        • Abate C.
        • Patel L.
        • Rausher F.J.
        • Curran T.
        Redox regulation of fos and jun DNA-binding activity in vitro.
        Science. 1990; 249: 1157-1161
        • Galter D.
        • Mihm S.
        • Droge W.
        Distinct effects of glutathione disulphide on the nuclear transcription factors kB and the activator protein-1.
        Eur J Biochem. 1994; 221: 639-648
        • Hirota K.
        • Matsui M.
        • Iwata S.
        • Nishiyama A.
        • Mori K.
        • Yodoi J.
        AP-1 transcriptional activity is regulated by a direct association between thioredoxin and Ref-1.
        Proc Natl Acad Sci USA. 1997; 94: 3633-3638