Oxidative stress and antioxidants in the pathogenesis of pulmonary fibrosis: a potential role for Nrf2

The sexual dimorphism associated with pulmonary hypertension corresponds to a fibrotic phenotype

Although female predominance in the development of all types of pulmonary hypertension (PH) is well established, many clinical studies have confirmed that females have better prognosis and higher survival rate than males. There is no clear explanation of why sex influences the pathogenesis and progression of PH. Using a rat angioproliferative model of PH, which closely resembles the primary pathological changes observed in humans, we evaluated the role of sex in the development and progression of PH. Female rats had a more pronounced increase in medial thickness in the small pulmonary arteries. However, the infiltration of small pulmonary arteries by inflammatory cells was found only in male rats, and this corresponded to increased myeloperoxidase activity and abundant adventitial and medial fibrosis that were not present in female rats. Although the level of right ventricle (RV) peak systolic pressure was similar in both groups, the survival rate in male rats was significantly lower. Moreover, male rats presented with a more pronounced increase in RV thickness that correlated with diffuse RV fibrosis and significantly impaired right cardiac function. The reduction in fibrosis in female rats correlated with increased expression of caveolin-1 and reduced endothelial nitric oxide synthase-derived superoxide. We conclude that, in the pathogenesis of PH, female sex is associated with greater remodeling of the pulmonary arteries but greater survival. Conversely, in males, the development of pulmonary and cardiac fibrosis leads to early and severe RV failure, and this may be an important reason for the lower survival rate among males.

Effects of lettuce glycoside B in ameliorating pulmonary fibrosis induced by irradiation exposure and its anti-oxidative stress mechanism

The present research assessed the effects of lettuce glycoside B (LGB), a compound separated and purified from Pterocypsela laciniata, on irradiation-induced pulmonary fibrosis and explored the mechanism involved. Animal model of irradiation exposure inducing pulmonary fibrosis was established by Co irradiator. Rats were intraperitoneally treated with LGB (100, 200 and 400 mg/kg) once per day for a month. Lung index data were analyzed. The levels of fibrosis were assessed by hydroxyproline (Hyp) of pulmonary and lung tissue sections after irradiation exposure. Alveolitis and fibrosis levels were calculated from semi-quantitative analysis of hematoxylin and eosin and Masson's trichrome lung section staining. The serum levels of transforming growth factor β1 (TGF-β1), interleukin (IL)-6, and tumor necrosis factor-α (TNF-α) were also evaluated. Antioxidant enzymes of superoxide dismutase (SOD) were measured in serum. Moreover, we also measured serum malondialdehyde (MDA) levels, a marker of oxidative stress. Treatment with LGB significantly reduced mortality rates and lung index scores and MDA content, enhanced SOD and other antioxidant enzymes activity, and regulated serum levels of TGF-β1, IL-6, and TNF-α. These results demonstrated that LGB significantly inhibited irradiation-induced pulmonary fibrosis. Furthermore, the results suggested promising clinical effect of LGB therapies for treating irradiation-induced pulmonary fibrosis.

Inhibitory effects of hydrogen sulphide on pulmonary fibrosis in smoking rats via attenuation of oxidative stress and inflammation

Accumulating evidence has demonstrated that hydrogen sulphide (H2 S) is involved in the pathogenesis of various respiratory diseases. In the present study, we established a rat model of passive smoking and investigated whether or not H2 S has protective effects against pulmonary fibrosis induced by chronic cigarette smoke exposure. Rat lung tissues were stained with haematoxylin-eosin and Masson's trichrome. The expression of type I collagen was detected by immunohistochemistry. Oxidative stress was evaluated by detecting serum levels of malondialdehyde, superoxide dismutase and glutathione peroxidase and measuring reactive oxygen species generation in lung tissue. Inflammation was assessed by measuring serum levels of inflammatory cytokines, including high-sensitivity C-reactive protein, tumour necrosis factor-α, interleukin (IL)-1β and IL-6. The protein expression of Nrf2, NF-κB and phosphorylated mitogen-activated protein kinases (MAPKs) in the pulmonary tissue was determined by Western blotting. Our findings indicated that administration of NaHS (a donor of H2 S) could protect against pulmonary fibrosis in the smoking rats. H2 S was found to induce the nuclear accumulation of Nrf2 in lung tissue and consequently up-regulate the expression of antioxidant genes HO-1 and Trx-1 in the smoking rats. Moreover, H2 S could also reduce cigarette smoking-induced inflammation by inhibiting the phosphorylation of ERK 1/2, JNK and p38 MAPKs and negatively regulating NF-κB activation. In conclusion, our study suggests that H2 S has protective effects against pulmonary fibrosis in the smoking rats by attenuating oxidative stress and inflammation.

DSSylation, a novel protein modification targets proteins induced by oxidative stress, and facilitates their degradation in cells

Timely removal of oxidatively damaged proteins is critical for cells exposed to oxidative stresses; however, cellular mechanism for clearing oxidized proteins is not clear. Our study reveals a novel type of protein modification that may play a role in targeting oxidized proteins and remove them. In this process, DSS1 (deleted in split hand/split foot 1), an evolutionally conserved small protein, is conjugated to proteins induced by oxidative stresses in vitro and in vivo, implying oxidized proteins are DSS1 clients. A subsequent ubiquitination targeting DSS1-protein adducts has been observed, suggesting the client proteins are degraded through the ubiquitin-proteasome pathway. The DSS1 attachment to its clients is evidenced to be an enzymatic process modulated by an unidentified ATPase. We name this novel protein modification as DSSylation, in which DSS1 plays as a modifier, whose attachment may render target proteins a signature leading to their subsequent ubiquitination, thereby recruits proteasome to degrade them.

Dose-response Effects of Bleomycin on Inflammation and Pulmonary Fibrosis in Mice

Many studies have reported that bleomycin, anti-cancer drug, induces pulmonary fibrosis as a side effect. However, few investigations have focused on the dose-response effects of bleomycin on pulmonary fibrosis. Therefore, in the present study, we investigated the effects of different doses of bleomycin in male mice. ICR mice were given 3 consecutive doses of bleomycin: 1, 2, or 4 mg/kg in bleomycin-treated (BT) groups and saline only in vehicle control (VC) groups. The animals were sacrificed at 7 and 24 days postinstillation. The severity of pulmonary fibrosis was evaluated according to inflammatory cell count and lactate dehydrogenase (LDH) activity in the broncho alveolar lavage fluid (BALF) , and lung tissues were histologically evaluated after hematoxylin and eosin (H&E) , and Masson's trichrome staining. BT groups exhibited changed cellular profiles in BAL fluid compared to the VC group, which had an increased number of total cells, neutrophils, and lymphocytes and a modest increase in the number of macrophages at 7 days post-bleomycin instillation. Moreover, BT groups showed a dose-dependent increase in LDH levels and inflammatory cell counts. However, at 24 days after treatment, collagen deposition, interstitial thickening, and granulomatous lesions were observed in the alveolar spaces in addition to a decrease in inflammatory cells. These results indicate that pulmonary fibrosis induced by 4 mg/kg bleomycin was more severe than that induced by 1 or 2 mg/kg. These data will be utilized in experimental animal models and as basic data to evaluate therapeutic candidates through non-invasive monitoring using the pulmonary fibrosis mouse model established in this study.

Role of nrf2 in oxidative stress and toxicity

Organismal life encounters reactive oxidants from internal metabolism and environmental toxicant exposure. Reactive oxygen and nitrogen species cause oxidative stress and are traditionally viewed as being harmful. On the other hand, controlled production of oxidants in normal cells serves useful purposes to regulate signaling pathways. Reactive oxidants are counterbalanced by complex antioxidant defense systems regulated by a web of pathways to ensure that the response to oxidants is adequate for the body's needs. A recurrent theme in oxidant signaling and antioxidant defense is reactive cysteine thiol-based redox signaling. The nuclear factor erythroid 2-related factor 2 (Nrf2) is an emerging regulator of cellular resistance to oxidants. Nrf2 controls the basal and induced expression of an array of antioxidant response element-dependent genes to regulate the physiological and pathophysiological outcomes of oxidant exposure. This review discusses the impact of Nrf2 on oxidative stress and toxicity and how Nrf2 senses oxidants and regulates antioxidant defense.

Suppression of nuclear factor erythroid 2-related factor 2 via extracellular signal-regulated kinase contributes to bleomycin-induced oxidative stress and fibrogenesis

Pulmonary fibrosis is a serious and irreversible lung injury with obscure etiologic mechanisms and no effective treatment to date. This study explored a crucial link between oxidative stress and pulmonary fibrogenesis, focusing on nuclear factor erythroid 2-related factor 2 (Nrf2), a core transcription factor in antioxidative regulation systems. Treatment of C57 BL/6 mice with bleomycin increased fibroblast viability and collagen production and significantly downregulated Nrf2. In addition, prominent oxidative stress was indicated by changes in superoxide dismutase, catalase activity, and glutathione and thiobarbituric acid-reactive substance levels. In a cell-based model, bleomycin suppressed Nrf2 activation via extracellular signal-related kinase phosphorylation, enhancing intracellular reactive oxygen species in lung fibroblasts and stimulating abnormal cell proliferation and collagen secretion. To confirm this novel mechanism of bleomycin-induced fibrogenesis, we attempted to upregulate Nrf2 and related antioxidant proteins in bleomycin-treated fibroblasts using a putative Nrf2 activator, caffeic acid phenethyl ester, and the results showed that bleomycin-induced fibroblast proliferation and collagen content were attenuated through improved redox balance. Collectively, these results disclose a potential regulatory mechanism in pulmonary fibrosis that will aid the development of new therapies.

Reductive stress linked to small HSPs, G6PD, and Nrf2 pathways in heart disease

SIGNIFICANCE

Aerobic organisms must exist between the dueling biological metabolic processes for energy and respiration and the obligatory generation of reactive oxygen species (ROS) whose deleterious consequences can reduce survival. Wide fluctuations in harmful ROS generation are circumvented by endogenous countermeasures (i.e., enzymatic and nonenzymatic antioxidants systems) whose capacity decline with aging and are enhanced by disease states.

RECENT ADVANCES

Substantial efforts on the cellular and molecular underpinnings of oxidative stress has been complemented recently by the discovery that reductive stress similarly predisposes to inheritable cardiomyopathy, firmly establishing that the biological extremes of the redox spectrum play essential roles in disease pathogenesis.

CRITICAL ISSUES

Because antioxidants by nutritional or pharmacological supplement to prevent or mitigate disease states have been largely disappointing, we hypothesize that lack of efficacy of antioxidants might be related to adverse outcomes in responders at the reductive end of the redox spectrum. As emerging concepts, such as reductive, as opposed, oxidative stress are further explored, there is an urgent and critical gap for biochemical phenotyping to guide the targeted clinical applications of therapeutic interventions.

FUTURE DIRECTIONS

New approaches are vitally needed for characterizing redox states with the long-term goal to noninvasively assess distinct clinical states (e.g., presymptomatic, end-stage) with the diagnostic accuracy to guide personalized medicine.

Effect of resveratrol on treatment of bleomycin-induced pulmonary fibrosis in rats

Resveratrol has a preventive potential on bleomycin-induced pulmonary fibrosis in prophylactic use; however, it was not studied in the treatment of the fibrosis. This study investigated the role of resveratrol on the treatment of bleomycin-induced pulmonary fibrosis. Intratracheal bleomycin (2.5 mg/kg) was given in fibrosis groups and saline in controls. First dose of resveratrol was given 14 days after bleomycin and continued until sacrifice. On 29th day, fibrosis in lung was estimated by Aschoft's criteria and hydroxyproline content. Bleomycine increased the fibrosis score (3.70 ± 1.04) and hydroxyproline levels (4.99 ± 0.90 mg/g tissue) as compared to control rats (1.02 ± 0.61 and 1.88 ± 0.59 mg/g), respectively. These were reduced to 3.16 ± 1.58 (P = 0.0001) and 3.08 ± 0.73 (P > 0.05), respectively, by resveratrol. Tissue malondialdehyde levels in the bleomycin-treated rats were higher (0.55 ± 0.22 nmol/mg protein) than that of control rats (0.16 ± 0.07; P = 0.0001) and this was reduced to 0.16 ± 0.06 by resveratrol (P = 0.0001). Tissue total antioxidant capacity is reduced (0.027 ± 0.01) by bleomycine administration when compared control rats (0.055 ± 0.012 mmol Trolox Equiv/mg protein; P = 0.0001) and increased to 0.041 ± 0.008 (P = 0.001) by resveratrol. We concluded that resveratrol has some promising potential on the treatment of bleomycin-induced pulmonary fibrosis in rats. However, different doses of the drug should be further studied.

Ankaflavin, a novel Nrf-2 activator for attenuating allergic airway inflammation

The role of inflammation-induced oxidative stress in the pathogenesis and progression of chronic inflammatory airways diseases has received increasing attention in recent years. Nuclear factor-erythroid 2 related factor 2 (Nrf-2) is the primary transcription factor that regulates the expression of antioxidant and detoxifying enzymes. In this study, yellow pigment ankaflavin (AK), derived from Monascus-fermented products, elevated nuclear Nrf-2 protein translocation in both the A549 lung cell line and the lungs of ovalbumin (OVA)-challenged mice. Furthermore, AK increased the mRNA expression of antioxidant enzymes regulated by Nrf-2, leading to a reduction in allergen-driven airway inflammation, mucus cell hyperplasia, and eosinophilia in OVA-challenged mice. Additionally, AK prevented T-cell infiltration and Th2 cytokines including interleukin (IL)-4, IL-5, and IL-13 generation in bronchial alveolar lavage fluid. The adhesion molecules ICAM-1, VCAM-1, and eotaxin were substantially reduced by AK treatment. Importantly, the inhibitory effect of AK on adhesion molecule production and immune cell infiltration was abolished by Nrf-2 small interfering RNA. This is the first study to illustrate that AK acts as a novel Nrf-2 activator for modulating the oxidative stress pathway to improve the lung injury and ameliorate the development of airway inflammation.

Free radical generation induces epithelial-to-mesenchymal transition in lung epithelium via a TGF-β1-dependent mechanism

Fibrotic remodelling of lung parenchymal and airway compartments is the major contributor to life-threatening organ dysfunction in chronic lung diseases such as idiopathic pulmonary fibrosis (IPF) and Chronic Obstructive Pulmonary Disease (COPD). Since transforming growth factor-β1 (TGF-β1) is believed to play a key role in disease pathogenesis and markers of oxidative stress are also commonly detected in bronchoalveolar lavage (BAL) from such patients we sought to investigate whether both factors might be interrelated. Here we investigated the hypothesis that oxidative stress to the lung epithelium promotes fibrotic repair by driving epithelial-to-mesenchymal transition (EMT) via the augmentation of TGF-β1. We show that in response to 400μM hydrogen peroxide (H(2)O(2)) A549 cells, used a model for alveolar epithelium, and human primary bronchial epithelial cells (PBECs) undergo EMT displaying morphology changes, decreased expression of epithelial markers (E-cadherin and ZO-1), increased expression of mesenchymal markers (vimentin and α-smooth muscle actin) as well as increased secretion of extracelluar matrix components. The same oxidative stress also promotes expression of TGF-β1. Inhibition of TGF-β1 signalling as well as treatment with antioxidants such as phenyl tert-butylnitrone (PBN) and superoxide dismutase 3 (SOD3) prevent the oxidative stress driven EMT-like changes described above. Interventions also inhibited EMT-like changes. This study identifies a link between oxidative stress, TGF-β1 and EMT in lung epithelium and highlights the potential for antioxidant therapies to limit EMT and its potential contribution to chronic lung disease.

Effect of oxidative stress on development of silicosis

AIM: To investigate the changes of oxidative stress indicators in the serum of silicosis patients and explore the mechanism of silicosis development.

METHODS: Two hundred workers who were exposed to silica dust for more than one year were recruited as dust-exposed group, 100 non-dust-exposed subjects served as control group, 32 patients with suspected 0⁺ silicosis as observation group, and 130 silicosis patients were taken as the silicosis group. Indicators of oxidative stress, including superoxide dismutase (SOD), nitric oxide (NO), serum glutathione peroxidase (GSH-Px), total antioxidant capacity (T-AOC), nitric oxide synthase (NOS), and lipid malondialdehyde (MDA), were determined in all the groups.

RESULTS: Compared with the control group, NO and GSH-Px in dust-exposed group and silicosis group increased, and SOD decreased significantly (81.162 ± 35.176, 270.469 ± 39.228 and 68.209 ± 21.528, respectively, P = 0.004, P = 0.002, P = 0.005). Compared with the control and dust-exposed group, T-AOC, NOS and MDA in silicosis group increased significantly (13.048 ± 4.153, 36.201 ± 7.782 and 5.054 ± 1.204, respectively, P = 0.018, P = 0.022, P = 0.011). Compared with dust-exposed group, GSH-Px in the silicosis group increased significantly (270.469 ± 39.228, P = 0.002). GSH-Px in phase III silicosis was significantly higher than in phase I silicosis (290.750 ± 39.129, P = 0.021). Pearson correlation analysis showed that serum GSH-Px was positively correlated with silicosis staging, length of dust exposure and type of occupation (47.109 ± 8.015, P = 0.001).

CONCLUSION: The imbalance of oxidative and anti-oxidation system is associated with the development of silicosis. The surveillance of oxidative stress indicators will benefit the prognosis of silicosis patients.

Caveolin-1 deficiency protects from pulmonary fibrosis by modulating epithelial cell senescence in mice

Idiopathic pulmonary fibrosis is associated with a decreased expression of caveolin-1 (cav-1), yet its role remains unclear. To investigate the role of cav-1, we induced pulmonary fibrosis in wild-type (WT) and cav-1-deficient (cav-1(-/-)) mice using intratracheal instillation of bleomycin. Contrary to expectations, significantly less collagen deposition was measured in tissue from cav-1(-/-) mice than in their WT counterparts, consistent with reduced mRNA expression of procollagen1a2 and procollagen3a1. Moreover, cav-1(-/-) mice demonstrated 77% less α-smooth muscle actin staining, suggesting reduced mesenchymal cell activation. Levels of pulmonary injury, assessed by tenascin-C mRNA expression and CD44v10 detection, were significantly increased at Day 21 after injury in WT mice, an effect significantly attenuated in cav-1(-/-) mice. The apparent protective effect against bleomycin-induced fibrosis in cav-1(-/-) mice was attributed to reduce cellular senescence and apoptosis in cav-1(-/-) epithelial cells during the early phase of lung injury. Reduced matrix metalloproteinase (MMP)-2 and MMP-9 expressions indicated a low profile of senescence-associated secretory phenotype (SASP) in the bleomycin-injured cav-1(-/-) mice. However, IL-6 and macrophage inflammatory protein 2 were increased in WT and cav-1(-/-) mice after bleomycin challenge, suggesting that bleomycin-induced inflammatory response substantiated the SASP pool. Thus, loss of cav-1 attenuates early injury response to bleomycin by limiting stress-induced cellular senescence/apoptosis in epithelial cells. In contrast, decreased cav-1 expression promotes fibroblast activation and collagen deposition, effects that may be relevant in later stages of reparative response. Hence, therapeutic strategies to modulate the expression of cav-1 should take into account cell-specific effects in the regenerative responses of the lung epithelium to injury.

Effect of diallyl sulfide on in vitro and in vivo Nrf2-mediated pulmonic antioxidant enzyme expression via activation ERK/p38 signaling pathway

Increasing oxidative stress is intimately involved in the pathogenesis of lung failure. Nuclear factor-erythroid 2 related factor 2 (Nrf2) is a key element in redox homeostasis. Nrf2 regulates antioxidant-associated genes that are often the target of phytochemicals in chemoprevention. This study evaluated the effect of diallyl sulfide (DAS), which is present in garlic, on the expression of antioxidant enzymes in the rat lung and the Nrf2 modulation in MRC-5 lung cells. DAS increased the activities of glutathione S-transferase, glutathione reductase, and catalase as well as the GSH/GSSG ratio compared with the lung of untreated control rats (p < 0.05). The pulmonic superoxide dismutase, glutathione peroxidase, NAD(P)H:quinone oxidoreductase 1, and catalase mRNA levels were also significantly increased (p < 0.05) after DAS treatment. Following DAS treatment, DAS level was measured in the plasma after 7 days of oral administration, and the C(max) value was 15 ± 4.2 μM. The total amount of pulmonic Nrf2 and the nuclear translocation of Nrf2 were elevated in DAS-treated rats, clarifying the effect of DAS on the modulation of antioxidant enzymes. Furthermore, DAS could induce nuclear translocation of Nrf2 via ERK/p38 signaling pathway in lung MRC-5 cells. This study demonstrates that DAS administration can significantly induce the activity of antioxidant enzymes in rat lungs and suggests a possible use for DAS as a dietary preventive agent against oxidative stress-induced lung injury.

Human alveolar epithelial cell injury induced by cigarette smoke

Background

Cigarette smoke (CS) is a highly complex mixture and many of its components are known carcinogens, mutagens, and other toxic substances. CS induces oxidative stress and cell death, and this cell toxicity plays a key role in the pathogenesis of several pulmonary diseases.

Methodology/Principal Findings

We studied the effect of cigarette smoke extract (CSE) in human alveolar epithelial type I-like (ATI-like) cells. These are isolated type II cells that are differentiating toward the type I cell phenotype in vitro and have lost many type II cell markers and express type I cell markers. ATI-like cells were more sensitive to CSE than alveolar type II cells, which maintained their differentiated phenotype in vitro. We observed disruption of mitochondrial membrane potential, apoptosis and necrosis that were detected by double staining with acridine orange and ethidium bromide or Hoechst 33342 and propidium iodide and TUNEL assay after treatment with CSE. We also detected caspase 3 and caspase 7 activities and lipid peroxidation. CSE induced nuclear translocation of Nrf2 and increased expression of Nrf2, HO-1, Hsp70 and Fra1. Moreover, we found that Nrf2 knockdown sensitized ATI-like cells to CSE and Nrf2 overexpression provided protection against CSE-induced cell death. We also observed that two antioxidant compounds N-acetylcysteine and trolox protected ATI-like cells against injury by CSE.

Conclusions

Our study indicates that Nrf2 activation is a major factor in cellular defense of the human alveolar epithelium against CSE-induced toxicity and oxidative stress. Therefore, antioxidant agents that modulate Nrf2 would be expected to restore antioxidant and detoxifying enzymes and to prevent CS-related lung injury and perhaps lessen the development of emphysema.

Idiopathic pulmonary fibrosis

Idiopathic pulmonary fibrosis is a devastating, age-related lung disease of unknown cause that has few treatment options. This disease was once thought to be a chronic inflammatory process, but current evidence indicates that the fibrotic response is driven by abnormally activated alveolar epithelial cells (AECs). These cells produce mediators that induce the formation of fibroblast and myofibroblast foci through the proliferation of resident mesenchymal cells, attraction of circulating fibrocytes, and stimulation of the epithelial to mesenchymal transition. The fibroblast and myofibroblast foci secrete excessive amounts of extracellular matrix, mainly collagens, resulting in scarring and destruction of the lung architecture. The mechanisms that link idiopathic pulmonary fibrosis with ageing and aberrant epithelial activation are unknown; evidence suggests that the abnormal recapitulation of developmental pathways and epigenetic changes have a role. In this Seminar, we review recent data on the clinical course, therapeutic options, and underlying mechanisms thought to be involved in the pathogenesis of idiopathic pulmonary fibrosis.

Cytoglobin: biochemical, functional and clinical perspective of the newest member of the globin family

Since the discovery of cytoglobin (Cygb) a decade ago, growing amounts of data have been gathered to characterise Cygb biochemistry, functioning and implication in human pathologies. Its molecular roles remain under investigation, but nitric oxide dioxygenase and lipid peroxidase activities have been demonstrated. Cygb expression increases in response to various stress conditions including hypoxia, oxidative stress and fibrotic stimulation. When exogenously overexpressed, Cygb revealed cytoprotection against these factors. Cygb was shown to be upregulated in fibrosis and neurodegenerative disorders and downregulated in multiple cancer types. CYGB was also found within the minimal region of a hereditary tylosis with oesophageal cancer syndrome, and its expression was reduced in tylotic samples. Recently, Cygb has been shown to inhibit cancer cell growth in vitro, thus confirming its suggested tumour suppressor role. This article aims to review the biochemical and functional aspects of Cygb, its involvement in various pathological conditions and potential clinical utility.

[Protective role of Nrf2 in the lungs against oxidative airway diseases]

Airways are continually exposed to multiple inhaled oxidants and protect themselves with cellular and extracellular antioxidants throughout the epithelial lining fluid and tissues. Oxidative stress, resulting from the increased oxidative burden and decreased level of antioxidant proteins, is involved in cellular and tissue damage related to the pathogenesis of many acute and chronic respiratory diseases. Evidence suggested that nuclear factor erythroid-2-related factor 2 (Nrf2), a transcription factor that controls antioxidant response element (ARE)-regulated antioxidant and cytoprotective genes has an essential protective role in the lungs against oxidative airway diseases. Therefore, Nrf2 promises to be an attractive therapeutic target for intervention and prevention strategies in respiratory diseases. We have reviewed major findings on the mechanisms of lung protection against oxidative stress by Nrf2 and the current literature suggesting that Nrf2 is a valuable therapeutic target.

Ly6Chi monocytes direct alternatively activated profibrotic macrophage regulation of lung fibrosis

RATIONALE

Idiopathic pulmonary fibrosis (IPF) is a devastating disease. Antiinflammatory therapies, including corticosteroids, are of no benefit. The role of monocytes and macrophages is therefore controversial.

OBJECTIVES

To define the role of monocytes and macrophages during lung fibrogenesis and resolution, and explore the phenotype of the cells involved.

METHODS

We used multiple in vivo depletional strategies, backed up by adoptive transfer techniques. Further studies were performed on samples from patients with IPF.

MEASUREMENTS AND MAIN RESULTS

Depletion of lung macrophages during fibrogenesis reduced pulmonary fibrosis as measured by lung collagen (P = 0.0079); fibrosis score (P = 0.0051); and quantitative polymerase chain reaction for surrogate markers of fibrosis Col1 (P = 0.0083) and a-smooth muscle actin (P = 0.0349). There was an associated reduction in markers of the profibrotic alternative macrophage activation phenotype, Ym1 (P = 0.0179), and Arginase 1. The alternative macrophage marker CD163 was expressed on lung macrophages from patients with IPF. Depletion of Ly6Chi circulating monocytes reduced pulmonary fibrosis (P = 0.0052) and the number of Ym1- positive alternatively activated lung macrophages (P = 0.0310). Their adoptive transfer during fibrogenesis exacerbated fibrosis (P = 0.0304); however, adoptively transferred CD45.1 Ly6Chi cells were not found in the lungs of recipient CD45.2 mice.

CONCLUSIONS

We demonstrate the importance of circulating monocytes and lung macrophages during pulmonary fibrosis, and emphasize the importance of the alternatively activated macrophage phenotype. We show that Ly6Chi monocytes facilitate the progression of pulmonary fibrosis, but are not obviously engrafted into lungs thereafter. Finally, we provide empirical data to suggest that macrophages may have a resolution-promoting role during the reversible phase of bleomycin-induced pulmonary fibrosis.

Multiple ways to die: delineation of the unfolded protein response and apoptosis induced by Surfactant Protein C BRICHOS mutants

Epithelial cell dysfunction is now recognized as an important mechanism in the pathogenesis of interstitial lung diseases. Surfactant Protein C (SP-C), an alveolar type II cell specific protein, has contributed to this concept with the observation that heterozygous expression of SFTPC gene mutations are associated with chronic interstitial lung disease. We have shown that transient expression of aggregation prone mutant SP-C isoforms (SP-C BRICHOS) destabilize ER quality control mechanisms resulting in the intracellular accumulation of aggregating propeptide, inhibition of the ubiquitin/proteasome system, and activation of apoptosis. The goal of the present study was to define signaling pathways linking the unfolded protein response (UPR) and subsequent ER stress with intrinsic apoptosis events observed following mutant SP-C expression. In vitro expression of the SP-C BRICHOS mutant, SP-C(Δexon4), was used as a model system. Here we show stimulation of a broad ER stress response in both transfected A549 and HEK293 cells with activation of all 3 canonical sensing pathways, IRE1/XBP-1, ATF6, and PERK/eIF2α. SP-C(Δexon4) expression also resulted in activation of caspase 3, but failed to stimulate expression of the apoptosis mediating transcription factors ATF4/CHOP. However, inhibition of either caspase 4 or c-jun kinase (JNK) each blocked caspase 3 mediated cell death. Taken together, these results suggest that expression of SP-C BRICHOS mutants induce apoptosis through multiple UPR signaling pathways, and provide new therapeutic targets for the amelioration of ER stress induced cytotoxicity observed in fibrotic lung remodeling.

NRF2 deficiency reduces life span of mice administered thoracic irradiation

Subsets of cancer survivors who have been subjected to thoracic irradiation face the prospect of developing pulmonary injury. Radiation-induced pulmonary fibrosis is an insidious injury that presents 6 to 24 months after irradiation and continues to progress over a period of years. TGF-β and reactive oxygen species contribute significantly to the pathogenesis of this injury. The transcription factor NRF2 controls antioxidant gene expression and therefore regulates the cellular oxidant burden. This work demonstrates an additional paradigm for NRF2: suppression of TGF-β-mediated signaling, assessed by measuring expression of a surrogate TGF-β1 target gene (PAI-1) in lung fibroblasts. Thoracic irradiation of Nfe2l2(-/-) mice resulted in rapid expression of PAI-1 and FSP-1 compared to irradiated wild-type mice. Examination of lung tissue 16 weeks after thoracic irradiation of Nfe2l2(-/-) mice revealed the presence of distended alveoli and decreased numbers of alveoli compared to wild-type mice. Suppression of NRF2 expression shortened life span in mice administered 16 Gy to the thorax. Nfe2l2(+/-) and Nfe2l2(-/-) mice exhibited a mean life span of 176 days compared to wild-type mice, which lived an average of 212 days. These novel results identify NRF2 as a susceptibility factor for the development of late tissue injury.

Novel therapeutic approaches for pulmonary fibrosis

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

New pharmacological strategies for the treatment of pulmonary fibrosis

The treatment of pulmonary fibrosis continues to pose major difficulties. Idiopathic pulmonary fibrosis (IPF), the most prevalent chronic fibrosing lung disease, is a devastating condition that carries a prognosis worse than that of many cancers. Abnormalities in multiple pathways involved in wound healing and inflammation lead to the development of this condition. High doses of corticosteroids are now contraindicated in IPF, although they have a role in other fibrosing lung diseases. More effective treatments are urgently required and a number of novel candidate therapies have been put forward, based on animal and in vitro work. As in other complex disorders, it is likely that combinations of agents, rather than single treatments, will be needed. The principle of combination therapy was recently endorsed by the guidelines of the British Thoracic Society, which make a weak recommendation for a combination of prednisolone, azathioprine and N-acetylcysteine. However, enrolment of patients into trials of new therapies is considered to be ‘best current practice’ as this offers sufferers with IPF the chance to receive new agents that may be more effective than current treatments. In pulmonary fibrotic disorders other than IPF, anti-inflammatory therapy is broadly appropriate and benefits most patients, but a clear treatment strategy is essential. The art of management is to distinguish accurately between inherently stable fibrotic disease (with treatment not required), progressive predominantly fibrotic disease (with low-dose long-term treatment warranted to retard progression) and the presence of major associated inflammation (justifying initial high-dose treatment).

NF-E2-related factor 2, a key inducer of antioxidant defenses, negatively regulates the CFTR transcription

A few studies have clearly indicated that oxidative stress suppresses the cystic fibrosis transmembrane conductance receptor (CFTR) function and expression. However, the mechanisms by which this occurs are still poorly understood. To clarify this effect, we investigated the role of NF-E2-related factor 2 (Nrf2) transcription factor, a key cellular sensor of oxidative stress. A conserved antioxidant response element (ARE) in the CFTR minimal promoter, which binds Nrf2, has been identified. Surprisingly, Nrf2 exerts an unexpected repressive role on the CFTR gene promoter activity. To decipher the molecular mechanisms involved, we evaluated the role of YY1 in the Nrf2-mediated transcriptional activity and showed cooperation between these two factors. We demonstrated that Nrf2 promotes YY1 nuclear localization and increases its binding to the CFTR promoter. To our knowledge, this study is the first to report a repressor role of Nrf2 through the cooperation with YY1 and contributes to clarify the cascade events leading to the oxidative stress-suppressed CFTR expression.

Oxidative stress targets in pulmonary emphysema: focus on the Nrf2 pathway

IMPORTANCE OF THE FIELD

Oxidative stress has been implicated in the pathogenesis of pulmonary emphysema. Nuclear factor erythroid-2-related factor 2 (Nrf2) a major antioxidant transcription factor could play a protective role in pulmonary emphysema.

AREAS COVERED IN THIS REVIEW

Nrf2 is ubiquitously expressed throughout the lung, but is predominantly found in epithelium and alveolar macrophages. Evidence suggests that Nrf2 and several Nrf2 downstream genes have an essential protective role in the lung against oxidative stress from environmental pollutants and toxicants such as cigarette smoke, a major causative factor for the development and progression of pulmonary emphysema. Application of Nrf2-deficient mice identified an extensive range of protective roles for Nrf2 against the pathogenesis of pulmonary emphysema. Therefore, Nrf2 promises to be an attractive therapeutic target for intervention and prevention strategies.

WHAT THE READER WILL GAIN

In this review, we discuss recent findings on the association of oxidative stress with pulmonary emphysema. We also address the mechanisms of Nrf2 lung protection against oxidative stress based on emerging evidence from experimental oxidative disease models and human studie.

TAKE HOME MESSAGE

The current literature suggests that among oxidative stress targets, Nrf2 is a valuable therapeutic target in pulmonary emphysema.

Nrf2 protects against pulmonary fibrosis by regulating the lung oxidant level and Th1/Th2 balance

Background

Pulmonary fibrosis is a progressive and lethal disorder. Although the precise mechanisms of pulmonary fibrosis are not fully understood, oxidant/antioxidant and Th1/Th2 balances may play an important role in many of the processes of inflammation and fibrosis. The transcription factor Nrf2 acts as a critical regulator for various inflammatory and immune responses by controlling oxidative stress. We therefore investigated the protective role of Nrf2 against the development of pulmonary fibrosis.

Methods

To generate pulmonary fibrosis, both wild-type C57BL/6 mice and Nrf2-deficient mice of the same background were administered bleomycin intratracheally.

Results

The survival of Nrf2-deficient mice after bleomycin administration was significantly lower than that of wild-type mice. The degree of bleomycin-induced initial pulmonary inflammation and pulmonary fibrosis was much more severe in Nrf2-deficient mice than in wild-type mice. The expression of antioxidant enzymes and phase II detoxifying enzymes was significantly reduced in the lungs of Nrf2-deficient mice, concomitant with an elevation of lung 8-isoprostane level, compared with wild-type mice. The expression of Th2 cytokines, such as interleukin-4 and interleukin-13, was significantly elevated in the lungs of Nrf2-deficient mice with an increase in the number of Th2 cells that express GATA-binding protein 3.

Conclusions

The results indicated that Nrf2 protects against the development of pulmonary fibrosis by regulating the cellular redox level and lung Th1/Th2 balance. Thus, Nrf2 might be an important genetic factor in the determination of susceptibility to pulmonary fibrosis.

Keap1 is a forked-stem dimer structure with two large spheres enclosing the intervening, double glycine repeat, and C-terminal domains

Keap1 is a substrate adaptor of a Cullin 3-based E3 ubiquitin ligase complex that recognizes Nrf2, and also acts as a cellular sensor for xenobiotics and oxidative stresses. Nrf2 is a transcriptional factor regulating the expression of cytoprotective enzyme genes in response to such stresses. Under unstressed conditions Keap1 binds Nrf2 and results in rapid degradation of Nrf2 through the proteasome pathway. In contrast, upon exposure to oxidative and electrophilic stress, reactive cysteine residues in intervening region (IVR) and Broad complex, Tramtrack, and Bric-à-Brac domains of Keap1 are modified by electrophiles. This modification prevents Nrf2 from rapid degradation and induces Nrf2 activity by repression of Keap1. Here we report the structure of mouse Keap1 homodimer by single particle electron microscopy. Three-dimensional reconstruction at 24-A resolution revealed two large spheres attached by short linker arms to the sides of a small forked-stem structure, resembling a cherry-bob. Each sphere has a tunnel corresponding to the central hole of the beta-propeller domain, as determined by x-ray crystallography. The IVR domain appears to surround the core of the beta-propeller domain. The unexpected proximity of IVR to the beta-propeller domain suggests that any distortions generated during modification of reactive cysteine residues in the IVR domain may send a derepression signal to the beta-propeller domain and thereby stabilize Nrf2. This study thus provides a structural basis for the two-site binding and hinge-latch model of stress sensing by the Nrf2-Keap1 system.

Endogenous antioxidants and radical scavengers

All living organisms are constantly exposed to oxidant agents deriving from both endogenous and exogenous sources capable to modify biomolecules and induce damages. Free radicals generated by oxidative stress exert an important role in the development of tissue damage and aging. Reactive species (RS) derived from oxygen (ROS) and nitrogen (RNS) pertain to free radicals family and are constituted by various forms of activated oxygen or nitrogen. RS are continuosly produced during normal physiological events but can be removed by antioxidant defence mechanism: the imbalance between RS and antioxidant defence mechanism leads to modifications in cellular membrane or intracellular molecules. In this chapter only endogenous antioxidant molecules will be critically discussed, such as Glutathione, Alpha-lipoic acid, Coenzyme Q, Ferritin, Uric acid, Bilirubin, Metallothioneine, L-carnitine and Melatonin.

Dihydro-CDDO-trifluoroethyl amide (dh404), a novel Nrf2 activator, suppresses oxidative stress in cardiomyocytes

Targeting Nrf2 signaling appears to be an attractive approach for the treatment of maladaptive cardiac remodeling and dysfunction; however, pharmacological modulation of the Nrf2 pathway in the cardiovascular system remains to be established. Herein, we report that a novel synthetic triterpenoid derivative, dihydro-CDDO-trifluoroethyl amide (dh404), activates Nrf2 and suppresses oxidative stress in cardiomyocytes. Dh404 interrupted the Keap1-Cul3-Rbx1 E3 ligase complex-mediated Nrf2 ubiquitination and subsequent degradation saturating the binding capacity of Keap1 to Nrf2, thereby rendering more Nrf2 to be translocated into the nuclei to activate Nrf2-driven gene transcription. A mutant Keap1 protein containing a single cysteine-to-serine substitution at residue 151 within the BTB domain of Keap1 was resistant to dh404-induced stabilization of Nrf2 protein. In addition, dh404 did not dissociate the interaction of Nrf2 with the Keap1-Cul3-Rbx1 E3 ligase complex. Thus, it is likely that dh404 inhibits the ability of Keap1-Cul3-Rbx1 E3 ligase complex to target Nrf2 for ubiquitination and degradation via modifying Cys-151 of Keap1 to change the conformation of the complex. Moreover, dh404 was able to stabilize Nrf2 protein, to enhance Nrf2 nuclear translocation, to activate Nrf2-driven transcription, and to suppress angiotensin II (Ang II)-induced oxidative stress in cardiomyocytes. Knockdown of Nrf2 almost blocked the anti-oxidative effect of dh404. Dh404 activated Nrf2 signaling in the heart. Taken together, dh404 appears to be a novel Nrf2 activator with a therapeutic potential for cardiac diseases via suppressing oxidative stress.

Redox control of the cell cycle in health and disease

The cellular oxidation and reduction (redox) environment is influenced by the production and removal of reactive oxygen species (ROS). In recent years, several reports support the hypothesis that cellular ROS levels could function as ''second messengers'' regulating numerous cellular processes, including proliferation. Periodic oscillations in the cellular redox environment, a redox cycle, regulate cell-cycle progression from quiescence (G(0)) to proliferation (G(1), S, G(2), and M) and back to quiescence. A loss in the redox control of the cell cycle could lead to aberrant proliferation, a hallmark of various human pathologies. This review discusses the literature that supports the concept of a redox cycle controlling the mammalian cell cycle, with an emphasis on how this control relates to proliferative disorders including cancer, wound healing, fibrosis, cardiovascular diseases, diabetes, and neurodegenerative diseases. We hypothesize that reestablishing the redox control of the cell cycle by manipulating the cellular redox environment could improve many aspects of the proliferative disorders.

Peroxisome proliferator-activated receptor-gamma ligands induce heme oxygenase-1 in lung fibroblasts by a PPARgamma-independent, glutathione-dependent mechanism

Oxidative stress plays an important role in the pathogenesis of pulmonary fibrosis. Heme oxygenase-1 (HO-1) is a key antioxidant enzyme, and overexpression of HO-1 significantly decreases lung inflammation and fibrosis in animal models. Peroxisome proliferator-activated receptor-gamma (PPARgamma) is a transcription factor that regulates adipogenesis, insulin sensitization, and inflammation. We report here that the PPARgamma ligands 15d-PGJ2 and 2-cyano-3,12-dioxoolean-1,9-dien-28-oic acid (CDDO), which have potent antifibrotic effects in vitro, also strongly induce HO-1 expression in primary human lung fibroblasts. Pharmacological and genetic approaches are used to demonstrate that induction of HO-1 is PPARgamma independent. Upregulation of HO-1 coincides with decreased intracellular glutathione (GSH) levels and can be inhibited by N-acetyl cysteine (NAC), a thiol antioxidant and GSH precursor. Upregulation of HO-1 is not inhibited by Trolox, a non-thiol antioxidant, and does not involve the transcription factors AP-1 or Nrf2. CDDO and 15d-PGJ2 contain an alpha/beta unsaturated ketone that acts as an electrophilic center that can form covalent bonds with free reduced thiols. Rosiglitazone, a PPARgamma ligand that lacks an electrophilic center, does not induce HO-1. These data suggest that in human lung fibroblasts, 15d-PGJ2 and CDDO induce HO-1 via a GSH-dependent mechanism involving the formation of covalent bonds between 15d-PGJ2 or CDDO and GSH. Inhibiting HO-1 upregulation with NAC has only a small effect on the antifibrotic properties of 15d-PGJ2 and CDDO in vitro. These results suggest that CDDO and similar electrophilic PPARgamma ligands may have great clinical potential as antifibrotic agents, not only through direct effects on fibroblast differentiation and function, but indirectly by bolstering antioxidant defenses.

Targeting the Nrf2 pathway against cardiovascular disease

Nuclear factor E2-related factor 2 (Nrf2) is a transcription factor that controls the basal and inducible expression of a battery of antioxidant genes and other cytoprotective Phase II detoxifying enzymes. Nrf2 is ubiquitously expressed in the cardiovascular system. While several Nrf2 downstream genes have been implicated in protection against the pathogenesis of cardiovascular diseases, the precise role of Nrf2 in the cardiovascular system remains to be elucidated. Nevertheless, mounting evidence has revealed that Nrf2 is a critical regulator of cardiovascular homeostasis via the suppression of oxidative stress, a major causative factor for the development and progression of cardiovascular diseases. Therefore, Nrf2 promises to be an attractive therapeutic target for the treatment of cardiovascular disease. Herein, we review the current literature that suggests that Nrf2 is a valuable therapeutic target for cardiovascular disease, as well as experiments that illustrate the mechanisms of Nrf2 cardioprotection.

Nrf2 protects against maladaptive cardiac responses to hemodynamic stress

BACKGROUND

Reactive oxygen species (ROS) play an important role in the maintenance of cardiovascular homeostasis. The present study sought to determine whether nuclear factor erythroid-2 related factor 2 (Nrf2), a master gene of the endogenous antioxidant defense system, is a critical regulator of the cardiac hypertrophic response to pathological stress.

METHODS AND RESULTS

Cardiac hypertrophy and dysfunction were established in mice by transverse aortic constriction (TAC). Nrf2 expression was transiently increased and then declined to the basal level while impairment of cardiac function proceeded. The knockout of Nrf2 (Nrf2(-/-)) did not cause any apparent structural and functional abnormalities in the unstressed heart. However, Nrf2(-/-) mice after TAC developed pathological cardiac hypertrophy, significant myocardial fibrosis and apoptosis, overt heart failure, and increased mortality, which were associated with elevated myocardial levels of 4-hydroxy-2-nonenal and 8-hydroxydeoxyguanosine and a complete blockade of the myocardial expression of several antioxidant genes. Overexpression of Nrf2 dramatically inhibited hypertrophic factor-induced ROS production and growth in both cardiomyocytes and cardiac fibroblasts, whereas knockdown of Nrf2 exerted opposite effects in both cells.

CONCLUSIONS

These findings demonstrate that activation of Nrf2 provides a novel mechanism to protect the murine heart against pathological cardiac hypertrophy and heart failure via suppressing oxidative stress.

C/EBP{alpha} is required for pulmonary cytoprotection during hyperoxia

A number of transcriptional pathways regulating fetal lung development are active during repair of the injured lung. We hypothesized that C/EBPalpha, a transcription factor critical for lung maturation, plays a role in protection of the alveolar epithelium following hyperoxic injury of the mature lung. Transgenic Cebpalpha(Delta/Delta) mice, in which Cebpalpha was conditionally deleted from Clara cells and type II cells after birth, were developed. While no pulmonary abnormalities were observed in the Cebpalpha(Delta/Delta) mice (7-8 wk old) under normal conditions, the mice were highly susceptible to hyperoxia. Cebpalpha(Delta/Delta) mice died within 4 days of exposure to 95% oxygen in association with severe lung inflammation, altered maturation of surfactant protein B and C, decreased surfactant lipid secretion, and abnormal lung mechanics at a time when all control mice survived. mRNA microarray analysis of isolated type II cells at 0, 2, and 24 h of hyperoxia demonstrated the reduced expression of number of genes regulating surfactant lipid and protein homeostasis, including Srebf, Scap, Lpcat1, Abca3, Sftpb, and Napsa. Genes influencing cell signaling or immune responses were induced in the lungs of Cebpalpha(Delta/Delta) mice. C/EBPalpha was required for the regulation of genes associated with surfactant lipid homeostasis, surfactant protein biosynthesis, processing and transport, defense response to stress, and cell redox homeostasis during exposure to hyperoxia. While C/EBPalpha did not play a critical role in postnatal pulmonary function under normal conditions, C/EBPalpha mediated protection of the lung during acute lung injury induced by hyperoxia.

Oxidative stress in the pathogenesis of diffuse lung diseases: a review

Oxidative stress is an imbalance between oxidants (reactive oxygen and nitrogen species) and antioxidants that may affect lipids, DNA, carbohydrates and proteins. The lung is continuously exposed to endogenous and exogenous oxidants (cigarette smoke, mineral dust, ozone, radiation). Reactive oxygen and nitrogen species are mainly produced by phagocytes as well as by polymorphonuclear, alveolar, bronchial and endothelial cells. A potential role of oxidative stress in the pathogenesis of diffuse lung diseases (particularly idiopathic pulmonary fibrosis) has been demonstrated. Increased oxidant levels and decreased antioxidant defences can contribute to the progression of idiopathic pulmonary fibrosis and other diffuse lung diseases. The growing number of papers on the different aspects of oxidant/antioxidant imbalance in diffuse lung diseases in the last decade reflects increasing interest in this topic and suggests that specific DLDs may be characterized by specific patterns of oxidation and antioxidant responses. The study of oxidative stress can provide insights into etiopathogenesis and favour the discovery of new treatments. In this review of the literature on oxidants and antioxidants in diffuse lung diseases, the focus is on idiopathic pulmonary fibrosis, sarcoidosis, pneumoconiosis and pulmonary fibrosis associated with systemic sclerosis.

Molecular phenotypes distinguish patients with relatively stable from progressive idiopathic pulmonary fibrosis (IPF)

BACKGROUND

Idiopathic pulmonary fibrosis (IPF) is a progressive, chronic interstitial lung disease that is unresponsive to current therapy and often leads to death. However, the rate of disease progression differs among patients. We hypothesized that comparing the gene expression profiles between patients with stable disease and those in which the disease progressed rapidly will lead to biomarker discovery and contribute to the understanding of disease pathogenesis.

METHODOLOGY AND PRINCIPAL FINDINGS

To begin to address this hypothesis, we applied Serial Analysis of Gene Expression (SAGE) to generate lung expression profiles from diagnostic surgical lung biopsies in 6 individuals with relatively stable (or slowly progressive) IPF and 6 individuals with progressive IPF (based on changes in DLCO and FVC over 12 months). Our results indicate that this comprehensive lung IPF SAGE transcriptome is distinct from normal lung tissue and other chronic lung diseases. To identify candidate markers of disease progression, we compared the IPF SAGE profiles in stable and progressive disease, and identified a set of 102 transcripts that were at least 5-fold up regulated and a set of 89 transcripts that were at least 5-fold down regulated in the progressive group (P-value</=0.05). The over expressed genes included surfactant protein A1, two members of the MAPK-EGR-1-HSP70 pathway that regulate cigarette-smoke induced inflammation, and Plunc (palate, lung and nasal epithelium associated), a gene not previously implicated in IPF. Interestingly, 26 of the up regulated genes are also increased in lung adenocarcinomas and have low or no expression in normal lung tissue. More importantly, we defined a SAGE molecular expression signature of 134 transcripts that sufficiently distinguished relatively stable from progressive IPF.

CONCLUSIONS

These findings indicate that molecular signatures from lung parenchyma at the time of diagnosis could prove helpful in predicting the likelihood of disease progression or possibly understanding the biological activity of IPF.

Alveolar oxidative stress is associated with elevated levels of nonenzymatic low-molecular-weight antioxidants in patients with different forms of chronic fibrosing interstitial lung diseases

Increasing evidence indicates that disequilibrium of the alveolar oxidant-antioxidant balance may play a role in the pathogenesis of chronic fibrosing lung diseases. Excessive production of oxidants and a differential regulation of antioxidant enzymes have been described under these conditions. We characterized for the first time numerous nonenzymatic low-molecular-weight antioxidants in bronchoalveolar lavage fluids from patients with different forms of lung fibrosis initiated either by injury to the alveolar epithelium (idiopathic pulmonary fibrosis, IPF) or by inflammation (chronic sarcoidosis/hypersensitivity pneumonitis). Footprints of oxidative stress accompanied by an increase in the majority of antioxidants assessed were observed in all patient groups: elevated levels of uric acid, ascorbic acid, retinol, and alpha-tocopherol were noted, whereas glutathione levels were unchanged. The expression of Nrf2, an important redox-sensitive transcriptional regulator of antioxidants, was increased in IPF lungs. Our findings were corroborated in the bleomycin model of lung fibrosis where--aside from uric acid--nonenzymatic antioxidants were elevated during the fibrotic phase. In conclusion, alveolar levels of nonenzymatic antioxidants are elevated in fibrosing lung diseases, but are incapable of restoring oxidative balance. This increase may be part of an adaptive response to oxidative stress. However, a leakage from the blood may also contribute to our findings.

Glutathione-S-transferases in lung and sputum specimens, effects of smoking and COPD severity

BACKGROUND

Oxidative stress plays a potential role in the pathogenesis and progression of chronic obstructive pulmonary disease (COPD). Glutathione S-transferases (GSTs) detoxify toxic compounds in tobacco smoke via glutathione-dependent mechanisms. Little is known about the regulation and expression of GSTs in COPD lung and their presence in airway secretions.

METHODS

GST alpha, pi and mu were investigated by immunohistochemistry in 72 lung tissue specimens and by Western analysis in total lung homogenates and induced sputum supernatants from non-smokers, smokers and patients with variable stages of COPD severity.

RESULTS

GST alpha was expressed mainly in the airway epithelium. The percentage of GST alpha positive epithelial cells was lower in the central airways of patients with very severe (Stage IV) COPD compared to mild/moderate COPD (p = 0.02). GST alpha by Western analysis was higher in the total lung homogenates in mild/moderate COPD compared to cases of very severe disease (p < 0.001). GST pi was present in airway and alveolar epithelium as well as in alveolar macrophages. GST mu was expressed mainly in the epithelium. Both GST alpha and pi were detectable in sputum supernatants especially in patients with COPD.

CONCLUSION

This study indicates the presence of GST alpha and pi especially in the epithelium and sputum supernatants in mild/moderate COPD and low expression of GST alpha in the epithelium in cases of very severe COPD. The presence of GSTs in the airway secretions points to their potential protective role both as intracellular and extracellular mediators in human lung.

Molecular mechanisms and clinical implications of reversible protein S-glutathionylation

Sulfhydryl chemistry plays a vital role in normal biology and in defense of cells against oxidants, free radicals, and electrophiles. Modification of critical cysteine residues is an important mechanism of signal transduction, and perturbation of thiol-disulfide homeostasis is an important consequence of many diseases. A prevalent form of cysteine modification is reversible formation of protein mixed disulfides (protein-SSG) with glutathione (GSH). The abundance of GSH in cells and the ready conversion of sulfenic acids and S-nitroso derivatives to S-glutathione mixed disulfides suggests that reversible S-glutathionylation may be a common feature of redox signal transduction and regulation of the activities of redox sensitive thiol-proteins. The glutaredoxin enzyme has served as a focal point and important tool for evolution of this regulatory mechanism, because it is a specific and efficient catalyst of protein-SSG deglutathionylation. However, mechanisms of control of intracellular Grx activity in response to various stimuli are not well understood, and delineation of specific mechanisms and enzyme(s) involved in formation of protein-SSG intermediates requires further attention. A large number of proteins have been identified as potentially regulated by reversible S-glutathionylation, but only a few studies have documented glutathionylation-dependent changes in activity of specific proteins in a physiological context. Oxidative stress is a hallmark of many diseases which may interrupt or divert normal redox signaling and perturb protein-thiol homeostasis. Examples involving changes in S-glutathionylation of specific proteins are discussed in the context of diabetes, cardiovascular and lung diseases, cancer, and neurodegenerative diseases.

Regulation of glutathione synthesis

Glutathione (GSH) is a ubiquitous intracellular peptide with diverse functions that include detoxification, antioxidant defense, maintenance of thiol status, and modulation of cell proliferation. GSH is synthesized in the cytosol of all mammalian cells in a tightly regulated manner. The major determinants of GSH synthesis are the availability of cysteine, the sulfur amino acid precursor, and the activity of the rate-limiting enzyme, glutamate cysteine ligase (GCL). GCL is composed for a catalytic (GCLC) and modifier (GCLM) subunit and they are regulated at multiple levels and at times differentially. The second enzyme of GSH synthesis, GSH synthase (GS) is also regulated in a coordinated manner as GCL subunits and its up-regulation can further enhance the capacity of the cell to synthesize GSH. Oxidative stress is well known to induce the expression of GSH synthetic enzymes. Key transcription factors identified thus far include Nrf2/Nrf1 via the antioxidant response element (ARE), activator protein-1 (AP-1) and nuclear factor kappa B (NFkappaB). Dysregulation of GSH synthesis is increasingly being recognized as contributing to the pathogenesis of many pathological conditions. These include diabetes mellitus, pulmonary fibrosis, cholestatic liver injury, endotoxemia and drug-resistant tumor cells. Manipulation of the GSH synthetic capacity is an important target in the treatment of many of these disorders.

Measurement of protein sulfhydryls in response to cellular oxidative stress using gel electrophoresis and multiplexed fluorescent imaging analysis

The significance of free radicals in biology has been established by numerous investigations spanning a period of over 40 years. Whereas there are many intracellular targets for these radical species, the importance of cysteine thiol posttranslational modification has received considerable attention. The current studies present a highly sensitive method for measurement of the posttranslational modification of protein thiols. This method is based on labeling of proteins with monofunctional maleimide dyes followed by 2D gel electrophoresis to separate proteins and multiplexed fluorescent imaging analysis. The method correctly interrogates the thiol/disulfide ratio present in commercially available proteins. Exposure of pulmonary airway epithelial cells to high concentrations of menadione or t-butyl hydroperoxide resulted in the modification of cysteines in more than 141 proteins of which 60 were subsequently identified by MALDI-TOF/TOF MS. Although some proteins were modified similarly by these two oxidants, several showed detectably different maleimide ratios in response to these two agents. Proteins that were modified by one or both oxidants include those involved in transcription, protein synthesis and folding, and cell death/growth. In conclusion, these studies provide a novel procedure for measuring the redox status of cysteine thiols on individual proteins with a clearly demonstrated applicability to interactions of chemicals with pulmonary epithelial cells.