Oxidant stress responses in influenza virus pneumonia: gene expression and transcription factor activation

Kynurenine Pathway in Respiratory Diseases

The kynurenine pathway is the primary route for tryptophan catabolism and has received increasing attention as its association with inflammation and the immune system has become more apparent. This review provides a broad overview of the kynurenine pathway in respiratory diseases, from the initial observations to the characterization of the different cell types involved in the synthesis of kynurenine metabolites and the underlying immunoregulatory mechanisms. With a focus on respiratory infections, the various attempts to characterize the kynurenine/tryptophan (K/T) ratio as an inflammatory marker are reviewed. Its implication in chronic lung inflammation and its exacerbation by respiratory pathogens is also discussed. The emergence of preclinical interventional studies targeting the kynurenine pathway opens the way for the future development of new therapies.

Autonomic Function Recovery and Physical Activity Levels in Post-COVID-19 Young Adults after Immunization: An Observational Follow-Up Case-Control Study

Coronavirus disease 2019 (COVID-19) has detrimental multi-system consequences. Symptoms may appear during the acute phase of infection, but the literature on long-term recovery of young adults after mild to moderate infection is lacking. Heart rate variability (HRV) allows for the observation of autonomic nervous system (ANS) modulation post-SARS-CoV-2 infection. Since physical activity (PA) can help improve ANS modulation, investigating factors that can influence HRV outcomes after COVID-19 is essential to advancements in care and intervention strategies. Clinicians may use this research to aid in the development of non-medication interventions. At baseline, 18 control (CT) and 20 post-COVID-19 (PCOV) participants were observed where general anamnesis was performed, followed by HRV and PA assessment. Thus, 10 CT and 7 PCOV subjects returned for follow-up (FU) evaluation 6 weeks after complete immunization (two doses) and assessments were repeated. Over the follow-up period, a decrease in sympathetic (SNS) activity (mean heart rate: p = 0.0024, CI = -24.67--3.26; SNS index: p = 0.0068, CI = -2.50--0.32) and increase in parasympathetic (PNS) activity (mean RR: p = 0.0097, CI = 33.72-225.51; PNS index: p = 0.0091, CI = -0.20-1.47) were observed. At follow-up, HRV was not different between groups (p > 0.05). Additionally, no differences were observed in PA between moments and groups. This study provides evidence of ANS recovery after SARS-CoV-2 insult in young adults over a follow-up period, independent of changes in PA.

Role of Body Mass and Physical Activity in Autonomic Function Modulation on Post-COVID-19 Condition: An Observational Subanalysis of Fit-COVID Study

The harmful effects of coronavirus disease 2019 (COVID-19) can reach the autonomic nervous system (ANS) and endothelial function. Therefore, the detrimental multiorgan effects of COVID-19 could be induced by deregulations in ANS that may persist after the acute SARS-CoV-2 infection. Additionally, investigating the differences in ANS response in overweight/obese, and physically inactive participants who had COVID-19 compared to those who did not have the disease is necessary. The aim of the study was to analyze the autonomic function of young adults after mild-to-moderate infection with SARS-CoV-2 and to assess whether body mass index (BMI) and levels of physical activity modulates autonomic function in participants with and without COVID-19. Patients previously infected with SARS-CoV-2 and healthy controls were recruited for this cross-sectional observational study. A general anamnesis was taken, and BMI and physical activity levels were assessed. The ANS was evaluated through heart rate variability. A total of 57 subjects were evaluated. Sympathetic nervous system activity in the post-COVID-19 group was increased (stress index; p = 0.0273). They also presented lower values of parasympathetic activity (p < 0.05). Overweight/obese subjects in the post-COVID-19 group presented significantly lower parasympathetic activity and reduced global variability compared to non-obese in control group (p < 0.05). Physically inactive subjects in the post-COVID-19 group presented significantly higher sympathetic activity than active subjects in the control group. Parasympathetic activity was significantly increased in physically active subjects in the control group compared to the physically inactive post-COVID-19 group (p < 0.05). COVID-19 promotes changes in the ANS of young adults, and these changes are modulated by overweight/obesity and physical activity levels.

Redox control in the pathophysiology of influenza virus infection

Triggered in response to external and internal ligands in cells and animals, redox homeostasis is transmitted via signal molecules involved in defense redox mechanisms through networks of cell proliferation, differentiation, intracellular detoxification, bacterial infection, and immune reactions. Cellular oxidation is not necessarily harmful per se, but its effects depend on the balance between the peroxidation and antioxidation cascades, which can vary according to the stimulus and serve to maintain oxygen homeostasis. The reactive oxygen species (ROS) that are generated during influenza virus (IV) infection have critical effects on both the virus and host cells. In this review, we outline the link between viral infection and redox control using IV infection as an example. We discuss the current state of knowledge on the molecular relationship between cellular oxidation mediated by ROS accumulation and the diversity of IV infection. We also summarize the potential anti-IV agents available currently that act by targeting redox biology/pathophysiology.

Understanding neuromuscular disorders in chronic fatigue syndrome

Muscle failure has been demonstrated in patients with myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS). Neurophysiological tools demonstrate the existence of both central and peripheral fatigue in these patients. Central fatigue is deduced from the reduced amplitude of myopotentials evoked by transcranial magnetic stimulation of the motor cortex as well as by the muscle response to interpolated twitches during sustained fatiguing efforts. An impaired muscle membrane conduction velocity assessed by the reduced amplitude and lengthened duration of myopotentials evoked by direct muscle stimulation is the defining feature of peripheral fatigue. Some patients with ME/CFS show an increased oxidative stress response to exercise. The formation of lipid hydroperoxides in the sarcolemma, which alters ionic fluxes, could explain the reduction of muscle membrane excitability and potassium outflow often measured in these patients. In patients with ME/CFS, the formation of heat shock proteins (HSPs) is also reduced. Because HSPs protect muscle cells against the deleterious effects of reactive oxygen species, the lack of their production could explain the augmented oxidative stress and the consecutive alterations of myopotentials which could open a way for future treatment of ME/CFS.

Xanthohumol inhibits PRRSV proliferation and alleviates oxidative stress induced by PRRSV via the Nrf2-HMOX1 axis

Porcine reproductive and respiratory syndrome virus (PRRSV) is a prevalent and endemic swine pathogen that causes significant economic losses in the global swine industry. Commercial vaccines provide limited protection against this virus, and no highly effective therapeutic drugs are yet available. In this study, we first screened a library of 386 natural products and found that xanthohumol (Xn), a prenylated flavonoid found in hops, displayed high anti-PRRSV activity by inhibiting PRRSV adsorption onto and internalization into cells. Transcriptome sequencing revealed that Xn treatment stimulates genes associated with the antioxidant response in the nuclear factor-erythroid 2-related factor 2 (Nrf2) signalling pathway. Xn causes increased expression of Nrf2, HMOX1, GCLC, GCLM, and NQO1 in Marc-145 cells. The action of Xn against PRRSV proliferation depends on Nrf2 in Marc-145 cells and porcine alveolar macrophages (PAMs). This finding suggests that Xn significantly inhibits PRRSV proliferation and decreases viral-induced oxidative stress by activating the Nrf2–HMOX1 pathway. This information should be helpful for developing a novel prophylactic and therapeutic strategy against PRRSV infection.

DMO-CAP inhibits influenza virus replication by activating heme oxygenase-1-mediated IFN response

Background

As a leading cause of respiratory disease, influenza A virus (IAV) infection remains a pandemic threat in annual seasonal outbreaks. Given the limitation of existing anti-influenza therapeutic drugs, development of new drugs is urgently required. Flavonoids extracted from Artemisia rupestris L. have an inhibitory effect on virus infections. Despite this fact, the antiviral properties of 6-demethoxy-4′-O-methylcapillarisin (DMO-CAP), one of such flavonoids, against the influenza virus have not been reported. Thus, the aim of this study is to investigate the anti-IAV virus efficacy and antiviral mechanism of DMO-CAP.

Methods

The inhibitory activity of DMO-CAP against IAV was detected in vitro using viral titers by Western blot analysis, qRT-PCR, and immunofluorescence assays. The mechanism of DMO-CAP against influenza virus was analyzed by Western blot analysis, qRT-PCR, and luciferase assay.

Results

DMO-CAP exhibits broad spectrum of antiviral activities against IAV in vitro. Mechanistically, DMO-CAP treatment induced the phosphorylation of p38 mitogen-activated protein kinase (MAPK), JNK MAPK, and ERK MAPK, which led to the activation of Nrf2/heme oxygenase-1 (HO-1) pathway. Then, the up-regulation of HO-1 expression activated the IFN response and induced the expression of IFN-stimulated genes, thereby leading to efficient anti-IAV effects.

Conclusions

DMO-CAP inhibited IAV replication by activating HO-1-mediated IFN response. DMO-CAP may be a potential agent or supplement against IAV infection.

Proteomics of Bronchoalveolar Lavage Fluid Reveals a Lung Oxidative Stress Response in Murine Herpesvirus-68 Infection

Murine herpesvirus-68 (MHV-68) productively infects mouse lungs, exhibiting a complex pathology characteristic of both acute viral infections and chronic respiratory diseases. We sought to discover proteins differentially expressed in bronchoalveolar lavage (BAL) from mice infected with MHV-68. Mice were infected intranasally with MHV-68. After nine days, as the lytic phase of infection resolved, differential BAL proteins were identified by two-dimensional (2D) electrophoresis and mass spectrometry. Of 23 unique proteins, acute phase proteins, vitamin A transport, and oxidative stress response factors Pdx6 and EC-SOD (Sod3) were enriched. Correspondingly, iNOS2 was induced in lung tissue by seven days post-infection. Oxidative stress was partly a direct result of MHV-68 infection, as reactive oxygen species (ROS) were induced in cultured murine NIH3T3 fibroblasts and human lung A549 cells infected with MHV-68. Finally, mice infected with a recombinant MHV-68 co-expressing inflammatory cytokine murine interleukin 6 (IL6) showed exacerbated oxidative stress and soluble type I collagen characteristic of tissue recovery. Thus, oxidative stress appears to be a salient feature of MHV-68 pathogenesis, in part caused by lytic replication of the virus and IL6. Proteins and small molecules in lung oxidative stress networks therefore may provide new therapeutic targets to ameliorate respiratory virus infections.

Redox Biology of Respiratory Viral Infections

Respiratory viruses cause infections of the upper or lower respiratory tract and they are responsible for the common cold—the most prevalent disease in the world. In many cases the common cold results in severe illness due to complications, such as fever or pneumonia. Children, old people, and immunosuppressed patients are at the highest risk and require fast diagnosis and therapeutic intervention. However, the availability and efficiencies of existing therapeutic approaches vary depending on the virus. Investigation of the pathologies that are associated with infection by respiratory viruses will be paramount for diagnosis, treatment modalities, and the development of new therapies. Changes in redox homeostasis in infected cells are one of the key events that is linked to infection with respiratory viruses and linked to inflammation and subsequent tissue damage. Our review summarizes current knowledge on changes to redox homeostasis, as induced by the different respiratory viruses.

Heme oxygenase-1 regulates sirtuin-1-autophagy pathway in liver transplantation: From mouse to human

Liver ischemia-reperfusion injury (IRI) represents a major risk factor of early graft dysfunction and a key obstacle to expanding the donor pool in orthotopic liver transplantation (OLT). Although graft autophagy is essential for resistance against hepatic IRI, its significance in clinical OLT remains unknown. Despite recent data identifying heme oxygenase-1 (HO-1) as a putative autophagy inducer, its role in OLT and interactions with sirtuin-1 (SIRT1), a key autophagy regulator, have not been studied. We aimed to examine HO-1-mediated autophagy induction in human OLT and in a murine OLT model with extended (20 hours) cold storage, as well as to analyze the requirement for SIRT1 in autophagy regulation by HO-1. Fifty-one hepatic biopsy specimens from OLT patients were collected under an institutional review board protocol 2 hours after portal reperfusion, followed by Western blot analyses. High HO-1 levels correlated with well-preserved hepatocellular function and enhanced SIRT1/LC3B expression. In mice, HO-1 overexpression by genetically modified HO-1 macrophage therapy was accompanied by decreased OLT damage and increased SIRT1/LC3B expression, whereas adjunctive inhibition of SIRT1 signaling diminished HO-1-mediated hepatoprotection and autophagy induction. Our translational study confirms the clinical relevance of HO-1 cytoprotection and identifies SIRT1-mediated autophagy pathway as a new essential regulator of HO-1 function in IR-stressed OLT.

Respiratory syncytial virus infection down-regulates antioxidant enzyme expression by triggering deacetylation-proteasomal degradation of Nrf2

Respiratory syncytial virus (RSV) is the most important cause of viral acute respiratory tract infections and hospitalizations in children, for which no vaccine or treatment is available. RSV infection in cells, mice, and children leads to rapid generation of reactive oxygen species, which are associated with oxidative stress and lung damage, due to a significant decrease in the expression of airway antioxidant enzymes (AOEs). Oxidative stress plays an important role in the pathogenesis of RSV-induced lung disease, as antioxidants ameliorate clinical disease and inflammation in vivo. The aim of this study is to investigate the unknown mechanism(s) of virus-induced inhibition of AOE expression. RSV infection is shown to induce a progressive reduction in nuclear and total cellular levels of the transcription factor NF-E2-related factor 2 (Nrf2), resulting in decreased binding to endogenous AOE gene promoters and decreased AOE expression. RSV induces Nrf2 deacetylation and degradation via the proteasome pathway in vitro and in vivo. Histone deacetylase and proteasome inhibitors block Nrf2 degradation and increase Nrf2 binding to AOE endogenous promoters, resulting in increased AOE expression. Known inducers of Nrf2 are able to increase Nrf2 activation and subsequent AOE expression during RSV infection in vitro and in vivo, with significant amelioration of oxidative stress. This is the first study to investigate the mechanism(s) of virus-induced inhibition of AOE expression. RSV-induced inhibition of Nrf2 activation, due to deacetylation and proteasomal degradation, could be targeted for therapeutic intervention aimed to increase airway antioxidant capacity during infection.

1H NMR-based profiling reveals differential immune-metabolic networks during influenza virus infection in obese mice

Obese individuals are at greater risk for death from influenza virus infection. Paralleling human evidence, obese mice are also more susceptible to influenza infection mortality. However, the underlying mechanisms driving greater influenza severity in the obese remain unclear. Metabolic profiling has been utilized in infectious disease models to enhance prognostic or diagnostic methods, and to gain insight into disease pathogenesis by providing a more global picture of dynamic infection responses. Herein, metabolic profiling was used to develop a deeper understanding of the complex processes contributing to impaired influenza protection in obese mice and to facilitate generation of new explanatory hypotheses. Diet-induced obese and lean mice were infected with influenza A/Puerto Rico/8/34. ¹H nuclear magnetic resonance-based metabolic profiling of urine, feces, lung, liver, mesenteric white adipose tissue, bronchoalveolar lavage fluid and serum revealed distinct metabolic signatures in infected obese mice, including perturbations in nucleotide, vitamin, ketone body, amino acid, carbohydrate, choline and lipid metabolic pathways. Further, metabolic data was integrated with immune analyses to obtain a more comprehensive understanding of potential immune-metabolic interactions. Of interest, uncovered metabolic signatures in urine and feces allowed for discrimination of infection status in both lean and obese mice at an early influenza time point, which holds prognostic and diagnostic implications for this methodology. These results confirm that obesity causes distinct metabolic perturbations during influenza infection and provide a basis for generation of new hypotheses and use of this methodology in detection of putative biomarkers and metabolic patterns to predict influenza infection outcome.

Respiratory Viral Infections and Subversion of Cellular Antioxidant Defenses

Reactive oxygen species (ROS) formation is part of normal cellular aerobic metabolism, due to respiration and oxidation of nutrients in order to generate energy. Low levels of ROS are involved in cellular signaling and are well controlled by the cellular antioxidant defense system. Elevated levels of ROS generation due to pollutants, toxins and radiation exposure, as well as infections, are associated with oxidative stress causing cellular damage. Several respiratory viruses, including respiratory syncytial virus (RSV), human metapneumovirus (hMPV) and influenza, induce increased ROS formation, both intracellularly and as a result of increased inflammatory cell recruitment at the site of infection. They also reduce antioxidant enzyme (AOE) levels and/or activity, leading to unbalanced oxidative-antioxidant status and subsequent oxidative cell damage. Expression of several AOE is controlled by the activation of the nuclear transcription factor NF-E2-related factor 2 (Nrf2), through binding to the antioxidant responsive element (ARE) present in the AOE gene promoters. While exposure to several pro-oxidant stimuli usually leads to Nrf2 activation and upregulation of AOE expression, respiratory viral infections are associated with inhibition of AOE expression/activity, which in the case of RSV and hMPV is associated with reduced Nrf2 nuclear localization, decreased cellular levels and reduced ARE-dependent gene transcription. Therefore, administration of antioxidant mimetics or Nrf2 inducers represents potential viable therapeutic approaches to viral-induced diseases, such as respiratory infections and other infections associated with decreased cellular antioxidant capacity.

Genome-wide fitness profiling reveals adaptations required by Haemophilus in coinfection with influenza A virus in the murine lung

Bacterial coinfection represents a major cause of morbidity and mortality in epidemics of influenza A virus (IAV). The bacterium Haemophilus influenzae typically colonizes the human upper respiratory tract without causing disease, and yet in individuals infected with IAV, it can cause debilitating or lethal secondary pneumonia. Studies in murine models have detected immune components involved in susceptibility and pathology, and yet few studies have examined bacterial factors contributing to coinfection. We conducted genome-wide profiling of the H. influenzae genes that promote its fitness in a murine model of coinfection with IAV. Application of direct, high-throughput sequencing of transposon insertion sites revealed fitness phenotypes of a bank of H. influenzae mutants in viral coinfection in comparison with bacterial infection alone. One set of virulence genes was required in nonvirally infected mice but not in coinfection, consistent with a defect in anti-bacterial defenses during coinfection. Nevertheless, a core set of genes required in both in vivo conditions indicated that many bacterial countermeasures against host defenses remain critical for coinfection. The results also revealed a subset of genes required in coinfection but not in bacterial infection alone, including the iron-sulfur cluster regulator gene, iscR, which was required for oxidative stress resistance. Overexpression of the antioxidant protein Dps in the iscR mutant restored oxidative stress resistance and ability to colonize in coinfection. The results identify bacterial stress and metabolic adaptations required in an IAV coinfection model, revealing potential targets for treatment or prevention of secondary bacterial pneumonia after viral infection.

FABP5 deficiency enhances susceptibility to H1N1 influenza A virus-induced lung inflammation

The early inflammatory response to influenza A virus infection contributes to severe lung disease and continues to pose a serious threat to human health. The mechanisms by which inflammatory cells invade the respiratory tract remain unclear. Uncontrolled inflammation and oxidative stress cause lung damage in response to influenza A infection. We have previously shown that the fatty acid binding protein 5 (FABP5) has anti-inflammatory properties. We speculate that, as a transporter of fatty acids, FABP5 plays an important protective role against oxidative damage to lipids during infection as well. Using FABP5-/- and wild-type (WT) mice infected with influenza A virus, we showed that FABP5-/- mice had increased cell infiltration of macrophages and neutrophils compared with WT mice. FABP5-/- mice presented lower viral burden but lost as much weight as WT mice. The adaptive immune response was also increased in FABP5-/- mice as illustrated by the accumulation of T and B cells in the lung tissues and increased levels of H1N1-specific IgG antibodies. FABP5 deficiency greatly enhanced oxidative damage and lipid peroxidation following influenza A infection and presented with sustained tissue inflammation. Interestingly, FABP5 expression decreased following influenza A infection in WT lung tissues that corresponded to a decrease in the anti-inflammatory molecule PPAR-γ activity. In conclusion, our results demonstrate a previously unknown contribution of FABP5 to influenza A virus pathogenesis by controlling excessive oxidative damage and inflammation. This property could be exploited for therapeutic purposes.

Respiratory syncytial virus infection: mechanisms of redox control and novel therapeutic opportunities

Respiratory syncytial virus (RSV) is one of the most important causes of upper and lower respiratory tract infections in infants and young children, for which no effective treatment is currently available. Although the mechanisms of RSV-induced airway disease remain incompletely defined, the lung inflammatory response is thought to play a central pathogenetic role. In the past few years, we and others have provided increasing evidence of a role of reactive oxygen species (ROS) as important regulators of RSV-induced cellular signaling leading to the expression of key proinflammatory mediators, such as cytokines and chemokines. In addition, RSV-induced oxidative stress, which results from an imbalance between ROS production and airway antioxidant defenses, due to a widespread inhibition of antioxidant enzyme expression, is likely to play a fundamental role in the pathogenesis of RSV-associated lung inflammatory disease, as demonstrated by a significant increase in markers of oxidative injury, which correlate with the severity of clinical illness, in children with RSV infection. Modulation of ROS production and oxidative stress therefore represents a potential novel pharmacological approach to ameliorate RSV-induced lung inflammation and its long-term consequences.

Heme oxygenase-1 regulates the immune response to influenza virus infection and vaccination in aged mice

Underlying mechanisms of individual variation in severity of influenza infection and response to vaccination are poorly understood. We investigated the effect of reduced heme oxygenase-1 (HO-1) expression on vaccine response and outcome of influenza infection. HO-1-deficient and wild-type (WT) mice (kingdom, Animalia; phylum, Chordata; genus/species, Mus musculus) were infected with influenza virus A/PR/8/34 with or without prior vaccination with an adenoviral-based influenza vaccine. A genome-wide association study evaluated the expression of single-nucleotide polymorphisms (SNPs) in the HO-1 gene and the response to influenza vaccination in healthy humans. HO-1-deficient mice had decreased survival after influenza infection compared to WT mice (median survival 5.5 vs. 6.5 d, P=0.016). HO-1-deficient mice had impaired production of antibody following influenza vaccination compared to WT mice (mean antibody titer 869 vs. 1698, P=0.02). One SNP in HO-1 and one SNP in the constitutively expressed isoform HO-2 were independently associated with decreased antibody production after influenza vaccination in healthy human volunteers (P=0.017 and 0.014, respectively). HO-1 deficient mice were paired with sex- and age-matched WT controls. HO-1 affects the immune response to both influenza infection and vaccination, suggesting that therapeutic induction of HO-1 expression may represent a novel adjuvant to enhance influenza vaccine effectiveness.

Major shifts in the spatio-temporal distribution of lung antioxidant enzymes during influenza pneumonia

With the incessant challenge of exposure to the air we breathe, lung tissue suffers the highest levels of oxygen tension and thus requires robust antioxidant defenses. Furthermore, following injury or infection, lung tissue faces the additional challenge of inflammation-induced reactive oxygen and nitrogen species (ROS/RNS). Little is known about the identity or distribution of lung antioxidant enzymes under normal conditions or during infection-induced inflammation. Using a mouse model of influenza (H1N1 influenza virus A/PR/8/34 [PR8]) in combination with bioinformatics, we identified seven lung-abundant antioxidant enzymes: Glutathione peroxidase 3 (Gpx3), Superoxide dismutase 3 (Sod3), Transferrin (Tf), peroxyredoxin6 (Prdx6), glutathione S-transferase kappa 1 (Gstk1), Catalase (Cat), and Glutathione peroxidase 8 (Gpx8). Interestingly, despite the demand for antioxidants during inflammation, influenza caused depletion in two key antioxidants: Cat and Prdx6. As Cat is highly expressed in Clara cells, virus-induced Clara cell loss contributes to the depletion in Cat. Prdx6 is also reduced due to Clara cell loss, however there is a coincident increase in Prdx6 levels in the alveoli, resulting in only a subtle reduction of Prdx6 overall. Analogously, Gpx3 shifts from the basement membranes underlying the bronchioles and blood vessels to the alveoli, thus maintaining balanced expression. Taken together, these studies identify key lung antioxidants and reveal their distribution among specific cell types. Furthermore, results show that influenza depletes key antioxidants, and that in some cases there is coincident increased expression, consistent with compensatory expression. Given that oxidative stress is known to be a key risk factor during influenza infection, knowledge about the antioxidant repertoire of lungs, and the spatio-temporal distribution of antioxidants, contributes to our understanding of the underlying mechanisms of influenza-induced morbidity and mortality.

Antioxidant components of naturally-occurring oils exhibit marked anti-inflammatory activity in epithelial cells of the human upper respiratory system

BACKGROUND

The upper respiratory tract functions to protect lower respiratory structures from chemical and biological agents in inspired air. Cellular oxidative stress leading to acute and chronic inflammation contributes to the resultant pathology in many of these exposures and is typical of allergic disease, chronic sinusitis, pollutant exposure, and bacterial and viral infections. Little is known about the effective means by which topical treatment of the nose can strengthen its antioxidant and anti-inflammatory defenses. The present study was undertaken to determine if naturally-occurring plant oils with reported antioxidant activity can provide mechanisms through which upper respiratory protection might occur.

METHODS

Controlled exposure of the upper respiratory system to ozone and nasal biopsy were carried out in healthy human subjects to assess mitigation of the ozone-induced inflammatory response and to assess gene expression in the nasal mucosa induced by a mixture of five naturally-occurring antioxidant oils--aloe, coconut, orange, peppermint and vitamin E. Cells of the BEAS-2B and NCI-H23 epithelial cell lines were used to investigate the source and potential intracellular mechanisms of action responsible for oil-induced anti-inflammatory activity.

RESULTS

Aerosolized pretreatment with the mixed oil preparation significantly attenuated ozone-induced nasal inflammation. Although most oil components may reduce oxidant stress by undergoing reduction, orange oil was demonstrated to have the ability to induce long-lasting gene expression of several antioxidant enzymes linked to Nrf2, including HO-1, NQO1, GCLm and GCLc, and to mitigate the pro-inflammatory signaling of endotoxin in cell culture systems. Nrf2 activation was demonstrated. Treatment with the aerosolized oil preparation increased baseline levels of nasal mucosal HO-1 expression in 9 of 12 subjects.

CONCLUSIONS

These data indicate that selected oil-based antioxidant preparations can effectively reduce inflammation associated with oxidant stress-related challenge to the nasal mucosa. The potential for some oils to activate intracellular antioxidant pathways may provide a powerful mechanism through which effective and persistent cytoprotection against airborne environmental exposures can be provided in the upper respiratory mucosa.

Profiles of cytokine and chemokine gene expression in human pulmonary epithelial cells induced by human and avian influenza viruses

Influenza pandemic remains a serious threat to human health. In this study, the repertoire of host cellular cytokine and chemokine responses to infections with highly pathogenic avian influenza H5N1, low pathogenicity avian influenza H9N2 and seasonal human influenza H1N1 were compared using an in vitro system based on human pulmonary epithelial cells. The results showed that H5N1 was more potent than H9N2 and H1N1 in inducing CXCL-10/IP-10, TNF-alpha and CCL-5/RANTES. The cytokine/chemokine profiles for H9N2, in general, resembled those of H1N1. Of interest, only H1N1, but none of the avian subtypes examined could induce a persistent elevation of the immune-regulatory cytokine - TGF-β2. The differential expression of cytokines/chemokines following infection with different influenza viruses could be a key determinant for clinical outcome. The potential of using these cytokines/chemokines as prognostic markers or targets of therapy is worth exploring.

Regulation of heme oxygenase-1 gene by peptidoglycan involves the interaction of Elk-1 and C/EBPalpha to increase expression

Heme oxygenase (HO)-1 is a cytoprotective enzyme with anti-inflammatory properties. HO-1 is induced during a systemic inflammatory response, and expression of HO-1 is beneficial during sepsis of a Gram-positive source. Systemic infection from Gram-positive organisms has emerged as an important cause of sepsis, with Staphylococcus aureus as a common etiology. An important mediator of Gram-positive infections is peptidoglycan (PGN), a cell wall component of these organisms. Here, we demonstrate that HO-1 played an important, protective role in vivo, as mice deficient in HO-1 were very sensitive to the lethal effects of PGN derived from S. aureus. PGN induced HO-1 protein and mRNA levels, and this regulation occurred at the level of gene transcription. The PGN-responsive region of the HO-1 promoter (from -117 to -66 bp) contains a functional EBS, and Ets proteins are known to be involved in the regulation of inflammatory responses. We showed previously that Ets factors (activators Ets-2 and Ets-1 and repressor Elk-3) regulate HO-1 expression by Gram-negative endotoxin. However, during exposure to a Gram-positive stimulus in the present study, Elk-1 was a potent activator of HO-1 in conjunction with PGN. The ability of Elk-1 to induce HO-1 promoter activity was independent of direct DNA binding, but rather occurred by interacting with the CCAAT/enhancer-binding protein-alpha (C/EBPalpha), which binds to DNA. Moreover, silencing of C/EBPalpha in macrophages prevented induction of HO-1 promoter activity by either Elk-1 or PGN. These data provide further insight into the regulation and function of HO-1 by a mediator of Gram-positive bacteria.

Role of haem oxygenase-1 in microbial host defence

Haem oxygenase (HO)-1 is a cytoprotective enzyme that plays a critical role in defending the body against oxidant-induced injury during inflammatory processes. HO catalydes the degradation of haem to carbon monoxide (CO), biliverdin and ferrous iron. Biliverdin is converted to bilirubin, a potent endogenous antioxidant. CO has a number of biological functions, including anti-inflammatory properties. In various models of disease, HO-1 is known to play a critical role by ameliorating the pathological consequences of injury. In many of these models, the beneficial effects of HO-1 and its products of haem catabolism are by suppressing an inflammatory response. However, when investigating diseases due to microbial infections, inhibition of the inflammatory response could disrupt the ability of the immune system to eradicate an invading pathogen. Thus, questions remain regarding the role of HO-1 in microbial host defence. This microreview will address our present understanding of HO-1 and its functional significance in a variety of microbial infections.

Respiratory syncytial virus induces oxidative stress by modulating antioxidant enzymes

Oxidative stress plays an important role in the pathogenesis of lung inflammation. Respiratory syncytial virus (RSV) infection induces reactive oxygen species (ROS) production in vitro and oxidative injury in lungs in vivo; however, the mechanism of RSV-induced cellular oxidative stress has not been investigated. Therefore, we determined whether RSV infection of airway epithelial cells modified the expression and/or activities of antioxidant enzymes (AOE). A549 cells, a human alveolar type II-like epithelial cell line, and small airway epithelial (SAE) cells, normal human cells derived from terminal bronchioli, were infected with RSV and harvested at various time points to measure F(2)-8 isoprostanes by enzyme-linked immunosorbent assay and total and reduced glutathione (GSH and GSSG) by colorimetric assay. Superoxide dismutase (SOD) 1, 2, and 3, catalase, glutathione peroxidase (GPx), and glutathione S-transferase (GST) expression was determined by quantitative real-time PCR and Western blot, and their activity was measured by colorimetric assays. RSV infection induced a significant increase of lipid peroxidation products as well as a significant decrease in the GSH/GSSG ratio. There was a significant decrease in SOD 1, SOD 3, catalase, and GST expression with a concomitant increase of SOD 2 in RSV-infected cells, compared with uninfected cells. Total SOD activity was increased, but catalase, GPx, and GST activities were decreased, after RSV infection. Our findings suggest that RSV-induced cellular oxidative damage is the result of an imbalance between ROS production and antioxidant cellular defenses. Modulation of oxidative stress represents a potential novel pharmacologic approach to ameliorate RSV-induced acute lung inflammation.

Decreased selenoprotein expression alters the immune response during influenza virus infection in mice

Previous work from our laboratory demonstrated that host selenium (Se) deficiency results in greater lung pathology and altered immune function in mice infected with influenza virus. Because selenoproteins play a key role in determining the oxidant status of the host, we utilized a transgenic mouse line carrying a mutant selenocysteine (Sec) tRNA ([Ser]Sec) transgene (t-trspi(6)A(-)). The levels of selenoproteins are decreased in these mice in a protein- and tissue-specific manner. Male t-trspi(6)A(-) and wild-type (WT) mice were infected with influenza and killed at various time points postinfection (p.i.). Lung mRNA levels for innate and pro-inflammatory cytokines increased with infection but did not differ between groups. However, at d 2 p.i., chemokine levels were greater in the t-trspi(6)A(-) mice compared with WT mice. Additionally, IFN-gamma was higher at d 7 p.i. in the t-trspi(6)A(-) mice and viral clearance slower. Despite these immune system changes, lung pathology was similar in t-trspi(6)A(-) and WT mice. (75)Se labeling experiments demonstrated that glutathione peroxidase (GPX)-1 and thioredoxin reductase, although greatly diminished in the lungs of t-trspi(6)A(-) mice, were not altered as a result of infection. GPX-1 activity in the lungs of the t-trspi(6)A(-) mice was approximately 82% of the WT mice. In addition, the GPX-1 activity in the lungs of Se-deficient mice was 125% less than in the t-trspi(6)A(-) mice. These results suggest that although selenoproteins are important for immune function, there is a threshold of GPX-1 activity that can prevent an increase in lung pathology during influenza infection.

Ten years of viral and non-bacterial serology in adults with cystic fibrosis

Viral infections are associated with pulmonary exacerbations in children with cystic fibrosis (CF), but few studies have addressed the frequency in adults. This paper investigates the frequency and impact of viral infections in adults with CF receiving intravenous antibiotics. Pre- and post-treatment spirometry, inflammatory markers and antibody titres against influenza A, influenza B, adenovirus, respiratory syncytial virus, Mycoplasma pneumoniae, Chlamydia psittaci, and Coxiella burnetti were analysed over a 10-year period. Non-bacterial infections were identified in 5.1% of 3156 courses of treatment. The annual incidence of admissions per patient associated with viral infection was 4.9%. The presence of viral infection in association with a pulmonary exacerbation did not adversely affect lung function or inflammatory markers in the short term. Adults with CF have a lower incidence of respiratory viral infections associated with pulmonary exacerbations requiring intravenous antibiotics compared to children and infants with CF.

Chromium (VI) inhibits heme oxygenase-1 expression in vivo and in arsenic-exposed human airway epithelial cells

Inhaled hexavalent chromium (Cr(VI)) promotes lung injury and pulmonary diseases through poorly defined mechanisms. One hypothesis for this lung pathogenesis is that Cr(VI) silences induction of cytoprotective genes, such as heme oxygenase-1 (HO-1), whose total lung mRNA levels were reduced 21 days after nasal instillation of potassium dichromate in C57BL/6 mice. To investigate the mechanisms for this inhibition, Cr(VI) effects on basal and arsenic (As(III))-induced HO-1 expression were examined in cultured human bronchial epithelial (BEAS-2B) cells. An effect of Cr(VI) on the low basal HO-1 mRNA and protein levels in BEAS-2B cells was not detectible. In contrast, Cr(VI) added to the cells before As(III), but not simultaneously with As(III), attenuated As(III)-induced HO-1 expression. Transient transfection with luciferase reporter gene constructs controlled by the full length ho-1 promoter or deletion mutants demonstrated that this inhibition occurred in the E1 enhancer region containing critical antioxidant response elements (ARE). Cr(VI) pretreatment inhibited As(III)-induced activity of a transiently expressed reporter construct regulated by three ARE tandem repeats. The mechanism for this Cr(VI)-attenuated transactivation appeared to be Cr(VI) reduction of the nuclear levels of the transcription factor Nrf2 and As(III)-stimulated Nrf2 transcriptional complex binding to the ARE cis element. Finally, exposing cells to Cr(VI) prior to co-exposure with As(III) synergized for apoptosis and loss of membrane integrity. These data suggest that Cr(VI) silences induction of ARE-driven genes required for protection from secondary insults. The data also have important implications for understanding the toxic mechanisms of low level, mixed metal exposures in the lung.

Role of apoptosis and cytokines in influenza virus morbidity

Influenza virus is a major human pathogen that causes epidemics and pandemics with increased morbidity and, especially in the elderly and those with pre-existing medical conditions, increased mortality. Influenza is characterised by respiratory symptoms and constitutional symptoms. Whilst knowledge of the mechanisms underlying host and tissue specificity has advanced considerably of late we still know relatively little about other aspects of influenza virus virulence. In this review, we will explore what is known about the role of apoptosis in respiratory epithelial cell damage and the role of cytokines in inflammation and constitutional symptoms with particular emphasis on the link between apoptosis, inflammation, fever and cytokine production.

Global host immune response: pathogenesis and transcriptional profiling of type A influenza viruses expressing the hemagglutinin and neuraminidase genes from the 1918 pandemic virus

To understand more fully the molecular events associated with highly virulent or attenuated influenza virus infections, we have studied the effects of expression of the 1918 hemagglutinin (HA) and neuraminidase (NA) genes during viral infection in mice under biosafety level 3 (agricultural) conditions. Using histopathology and cDNA microarrays, we examined the consequences of expression of the HA and NA genes of the 1918 pandemic virus in a recombinant influenza A/WSN/33 virus compared to parental A/WSN/33 virus and to an attenuated virus expressing the HA and NA genes from A/New Caledonia/20/99. The 1918 HA/NA:WSN and WSN recombinant viruses were highly lethal for mice and displayed severe lung pathology in comparison to the nonlethal New Caledonia HA/NA:WSN recombinant virus. Expression microarray analysis performed on lung tissues isolated from the infected animals showed activation of many genes involved in the inflammatory response, including cytokine, apoptosis, and lymphocyte genes that were common to all three infection groups. However, consistent with the histopathology studies, the WSN and 1918 HA/NA:WSN recombinant viruses showed increased up-regulation of genes associated with activated T cells and macrophages, as well as genes involved in apoptosis, tissue injury, and oxidative damage that were not observed in the New Caledonia HA/NA:WSN recombinant virus-infected mice. These studies document clear differences in gene expression profiles that were correlated with pulmonary disease pathology induced by virulent and attenuated influenza virus infections.

CDllc+ cells modulate pulmonary immune responses by production of indoleamine 2,3-dioxygenase

Interactions between antigen-presenting cells and T cells can result in T cell activation or suppression. With the use of RNA analysis, high-performance liquid chromatography, mixed leukocyte reactions (MLRs), and animal models, the current study reports that lung interstitial antigen-presenting cells (iAPCs, CDllc+) suppress T cell responses in vitro and in vivo by production of indoleamine 2,3-dioxygenase (IDO), an enzyme that catabolizes tryptophan to its byproduct, kynurenine. IDO mRNA expression was unique to lung iAPCs, as cells similarly isolated from the liver and spleen did not express IDO constitutively, or in response to interferon-gamma. Lung iAPCs suppressed proliferation of allogeneic T cells, correlating with increased kynurenine levels; and blockade of IDO activity with 1-methyl-DL-tryptohan (1-MT) or addition of exogenous tryptophan recovered T cell proliferation in MLRs. In contrast, liver and splenic iAPCs were potent stimulators of T cells in MLRs, and IDO inhibition had no effect on T cell responses. In vivo studies showed that systemic blockade of IDO resulted in spontaneous proliferation in lung T cells and pulmonary inflammation. Finally, overexpressing IDO in lung transplants abrogated acute allograft rejection, a T cell-mediated disease. Collectively these data show that lung iAPCs contribute to local regulation of cellular immune responses by production of IDO.

Kaposi sarcoma-associated herpesvirus (KSHV) induces heme oxygenase-1 expression and activity in KSHV-infected endothelial cells

Kaposi sarcoma (KS) is the most common AIDS-associated malignancy and is characterized by angiogenesis and the presence of spindle cells. Kaposi sarcoma-associated herpesvirus (KSHV) is consistently associated with all clinical forms of KS, and in vitro infection of dermal microvascular endothelial cells (DMVECs) with KSHV recapitulates many of the features of KS, including transformation, spindle cell proliferation, and angiogenesis. To study the molecular mechanisms of KSHV pathogenesis, we compared the protein expression profiles of KSHV-infected and uninfected DMVECs. This comparison revealed that heme oxygenase-1 (HO-1), the inducible enzyme responsible for the rate-limiting step in heme catabolism, was up-regulated in infected endothelial cells. Recent evidence suggests that the products of heme catabolism have important roles in endothelial cell biology, including apoptosis and angiogenesis. Here we show that HO-1 mRNA and protein are up-regulated in KSHV-infected cultures. Comparison of oral and cutaneous AIDS-KS tissues with normal tissues revealed that HO-1 mRNA and protein were also up-regulated in vivo. Increased HO-1 enzymatic activity in vitro enhanced proliferation of KSHV-infected DMVECs in the presence of free heme. Treatment with the HO-1 inhibitor chromium mesoporphyrin IX abolished heme-induced proliferation. These data suggest that HO-1 is a potential therapeutic target for KS that warrants further study.

Effect of Quercetin on lipid peroxidation and changes in lung morphology in experimental influenza virus infection

Influenza virus infection, induced experimentally in mice, was associated with marked changes in lung morphology viz. epithelial damage with focal areas of reactive papillary hyperplasia, infiltration of leukocytes and development of oxidative stress, as evidenced by increased superoxide radical production and lipid peroxidation (LPO) products by alveolar macrophages. These effects were observed on the 5th day after virus instillation. The levels of superoxide and LPO were measured spectrophotometrically by the nitroblue tetrazolium (NBT) assay and thiobarbituric acid reactive species (TBARS) assay, respectively. The former increased by 1.5-2 fold and the latter was raised by 85% when compared with normal control. Supplementation of intranasal viral instillation with the anti-oxidant, Quercetin, given orally, resulted in a significant decrease in the levels of both superoxide radicals and LPO products. There was also a significant decrease in the number of infiltrating cells. A mild to moderate protective effect was observed in lung morphology. Thus, Quercetin may be useful as a drug in reducing the oxidative stress induced by influenza virus infection in the lung, and protect it from the toxic effects of the free radicals.

Diminished immunoreactivity of gamma-glutamylcysteine synthetase in the airways of smokers' lung

Glutathione (GSH) plays a major role in protecting the airways against oxidative stress. The rate-limiting enzyme in de novo GSH synthesis is gamma-glutamylcysteine synthetase (gamma-GCS), which is induced by acute exposure to GSH-depleting cytokines and oxidants, but downregulated by transforming growth factor beta and prolonged oxidant exposure, at least in vitro. Cell-specific expression or regulation of gamma-GCS may play an important role both in the defense against oxidants and in the pathogenesis of oxidant-associated airway diseases. In this study, the localizations of gamma-GCS heavy (gamma-GCS-HS) and light (gamma-GCS-LS) subunits were investigated by immunohistochemistry in 22 patients with chronic obstructive pulmonary disease (COPD), 20 smokers without COPD, and 13 lifelong nonsmokers. The ultrastructural distributions of both gamma-GCS subunits were assessed by immuno-electron microscopy. Both subunits were expressed most prominently in the large airways, and their ultrastructural localization was both cytoplasmic and along the plasma membrane. The expression of gamma-GCS-HS was stronger in the central bronchial epithelium than in the peripheral bronchioli (p = 0.020), or in alveolar macrophages (p = 0.008). The expression of gamma-GCS-HS in the central bronchial epithelium showed a tendency to be higher in nonsmokers compared with all smokers (p = 0.052). Alveolar macrophages of nonsmokers had higher levels of gamma-GCS-HS (p = 0.001) and gamma-GCS-LS (p = 0.001) than did smokers. The expression of gamma-GCS-HS in the central bronchial epithelium was more marked in nonsmokers than in patients with COPD (p = 0.015), the difference between smokers and patients with COPD was not significant. In conclusion, the heavy and light subunits of gamma-GCS are mainly expressed in the large airways. Their tendency to decrease in cigarette smokers may further predispose lung cells to ongoing oxidant stress, which contributes to the progression of lung injury.

Rickettsia rickettsii infection of cultured human endothelial cells induces heme oxygenase 1 expression

Existing evidence suggests that oxidative insults and antioxidant defense mechanisms play a critical role in the host cell response during infection of endothelial cells by Rickettsia rickettsii, the causative agent of Rocky Mountain spotted fever. Heme oxygenase (HO), a rate-limiting enzyme in the pathway for heme catabolism, protects against oxidant damage in a variety of stress situations. Here, we report on the expression of the inducible and constitutive HO isozymes, HO-1 and HO-2, during R. rickettsii infection of endothelial cells. Steady-state levels for HO-1 mRNA were increased two- to threefold, as early as 4 h postinfection, whereas HO-2 mRNA was not affected. Induction of HO-1 mRNA was dependent on the dose of infection and occurred in a time-dependent manner, reaching maximal levels at 4 to 7 h. The increase in HO-1 mRNA occurred at the level of trancription as it was blocked by the transcriptional inhibitors, actinomycin D and alpha-amanitin. The eukaryotic protein synthesis inhibitor, cycloheximide, caused a >50% reduction in the infection-induced increase in HO-1 mRNA level, suggesting its dependence on de novo protein synthesis of host cell. The uptake of viable organisms appeared to be necessary, since inactivation of R. rickettsii by heat or formalin fixation, or incubation of cells with cytochalasin B to prevent entry resulted in marked inhibition of HO-1 response. N-Acetyl-L-cysteine, a known oxidant scavenger, inhibited the HO-1 induction by R. rickettsii. Finally, Western analysis with a specific monoclonal antibody revealed higher levels of HO-1 protein ( approximately 32 kDa), confirming that changes in HO-1 mRNA levels were followed by increases in the levels of protein. The findings indicate that R. rickettsii infection induces HO-1 expression in host endothelial cells and suggest an important role for this enzyme in cellular response to infection, possibly by serving a protective function against oxidative injury.

Exacerbations: etiology and pathophysiologic mechanisms

Some patients with COPD are prone to frequent exacerbations, which are an important determinant of health status. Such patients have elevated airway cytokine levels, suggesting the presence of increased inflammation that may increase their susceptibility to exacerbation. The inflammatory response during a COPD exacerbation is variable, but increases in interleukin-6 levels during the exacerbation are related to the presence of a common cold. Rhinovirus infection is the most important etiologic factor in COPD exacerbations and is an important target for preventive therapy. The reduction of COPD exacerbations will have an important impact on the considerable morbidity and mortality associated with COPD.

Influenza virus infection induces metallothionein gene expression in the mouse liver and lung by overlapping but distinct molecular mechanisms

Metallothionein I (MT-I) and MT-II have been implicated in the protection of cells against reactive oxygen species (ROS), heavy metals, and a variety of pathological and environmental stressors. Here, we show a robust increase in MT-I/MT-II mRNA level and MT proteins in the livers and lungs of C57BL/6 mice exposed to the influenza A/PR8 virus that infects the upper respiratory tract and lungs. Interleukin-6 (IL-6) had a pronounced effect on the induction of these genes in the liver but not the lung. Treatment of the animals with RU-486, a glucocorticoid receptor antagonist, inhibited induction of MT-I/MT-II in both liver and lung, revealing a direct role of glucocorticoid that is increased upon infection in this induction process. In vivo genomic footprinting (IVGF) analysis demonstrated involvement of almost all metal response elements, major late transcription factor/antioxidant response element (MLTF/ARE), the STAT3 binding site on the MT-I upstream promoter, and the glucocorticoid responsive element (GRE1), located upstream of the MT-II gene, in the induction process in the liver and lung. In the lung, inducible footprinting was also identified at a unique gamma interferon (IFN-gamma) response element (gamma-IRE) and at Sp1 sites. The mobility shift analysis showed activation of STAT3 and the glucocorticoid receptor in the liver and lung nuclear extracts, which was consistent with the IVGF data. Analysis of the newly synthesized mRNA for cytokines in the infected lung by real-time PCR showed a robust increase in the levels of IL-10 and IFN-gamma mRNA that can activate STAT3 and STAT1, respectively. A STAT1-containing complex that binds to the gamma-IRE in vitro was activated in the infected lung. No major change in MLTF/ARE DNA binding activity in the liver and lung occurred after infection. These results have demonstrated that MT-I and MT-II can be induced robustly in the liver and lung following experimental influenza virus infection by overlapping but distinct molecular mechanisms.

Global impact of influenza virus on cellular pathways is mediated by both replication-dependent and -independent events

Influenza virus, the causative agent of the common flu, is a worldwide health problem with significant economic consequences. Studies of influenza virus biology have revealed elaborate mechanisms by which the virus interacts with its host cell as it inhibits the synthesis of cellular proteins, evades the innate antiviral response, and facilitates production of viral RNAs and proteins. With the advent of DNA array technology it is now possible to obtain a large-scale view of how viruses alter the environment within the host cell. In this study, the cellular response to influenza virus infection was examined by monitoring the steady-state mRNA levels for over 4,600 cellular genes. Infections with active and inactivated influenza viruses identified changes in cellular gene expression that were dependent on or independent of viral replication, respectively. Viral replication resulted in the downregulation of many cellular mRNAs, and the effect was enhanced with time postinfection. Interestingly, several genes involved in protein synthesis, transcriptional regulation, and cytokine signaling were induced by influenza virus replication, suggesting that some may play essential or accessory roles in the viral life cycle or the host cell's stress response. The gene expression pattern induced by inactivated viruses revealed induction of the cellular metallothionein genes that may represent a protective response to virus-induced oxidative stress. Genome-scale analyses of virus infections will help us to understand the complexities of virus-host interactions and may lead to the discovery of novel drug targets or antiviral therapies.

Identification of stress-responsive genes in Caenorhabditis elegans using RT-PCR differential display

In order to identify genes that are differentially expressed as a consequence of oxidative stress due to paraquat we used the differential display technique to compare mRNA expression patterns in Caenorhabditis elegans . A C.elegans mixed stage worm population and a homogeneous larval population were treated with 100 mM paraquat, in parallel with controls. Induction of four cDNA fragments, designated L-1, M-47, M-96 and M-132, was confirmed by Northern blot analysis with RNA from stressed and unstressed worm populations. A 40-fold increase in the steady-state mRNA level in the larval population was observed for the L-1/M-47 gene, which encodes the detoxification enzyme glutathione S-transferase. A potential stress-responsive transcription factor (M-132) with C2H2-type zinc finger motifs and an N-terminal leucine zipper domain was identified. The M-96 gene encodes a novel stress-responsive protein. Since paraquat is known to generate superoxide radicals in vivo , the response of the C.elegans superoxide dismutase (SOD) genes to paraquat was also investigated in this study. The steady-state mRNA levels of the manganese-type and the copper/zinc-type SODs increased 2-fold in the larval population in response to paraquat, whereas mixed stage populations did not show any apparent increase in the levels of these SOD mRNAs.

Oxygen toxicity and iron accumulation in the lungs of mice lacking heme oxygenase-2

Heme oxygenase (HO) activity leads to accumulation of the antioxidant bilirubin, and degradation of the prooxidant heme. Moderate overexpression of the inducible form, HO-1, is associated with protection against oxidative injury. However, the role of HO-2 in oxidative stress has not been explored. We evaluated survival, indices of oxidative injury, and lung and HO expression in HO-2 null mutant mice exposed to > 95% O2 compared with wild-type controls. Similar basal levels of major lung antioxidants were observed, except that the knockouts had a twofold increase in total glutathione content. Despite increased HO-1 expression from HO-1 induction, knockout animals were sensitized to hyperoxia-induced oxidative injury and mortality, and also had significantly increased markers of oxidative injury before hyperoxic exposure. Furthermore, during hyperoxia, lung hemoproteins and iron content were significantly increased without increased ferritin, suggesting accumulation of available redox-active iron. These results demonstrate that the absence of HO-2 is associated with induction of HO-1 and increased oxygen toxicity in vivo, apparently due to accumulation of lung iron. These results suggest that HO-2 functions to augment the turnover of lung iron during oxidative stress, and that this function does not appear to be compensated for by induction of HO-1 in the knockouts.