High Levels of Catalase and Glutathione Peroxidase Activity Dampen H2O2Signaling in Human Alveolar Macrophages

The cGAS-STING pathway drives inflammation in Usual Interstitial Pneumonia, phagocytosis could prevent inflammation but is inhibited by the don't eat me signal CD47

BACKGROUND

Usual Interstitial Pneumonia (UIP) a fibrosing pneumonia is associated with idiopathic pulmonary fibrosis, chronic autoimmune disease (AID), or hypersensitivity pneumonia. Oxygen radicals, due to tobacco smoke, can damage DNA and might upregulate PARP1. Cytosolic DNA from dying pneumocytes activate cytosolic GMP-AMP-synthase-stimulator of interferon genes (cGAS-STING) pathway and TREX1. Prolonged inflammation induces senescence, which might be inhibited by phagocytosis, eliminating nuclear debris. We aimed to evaluate activation of cGAS-STING-TREX1 pathway in UIP, and if phagocytosis and anti-phagocytosis might counteract inflammation.

METHODS

44 cases of UIP with IPF or AID were studied for the expression of cGAS, pSTING, TREX1 and PARP1. LAMP1 and Rab7 expression served as phagocytosis markers. CD47 protecting phagocytosis and p16 to identify senescent cells were also studied.

RESULTS

Epithelial cells in remodeled areas and macrophages expressed cGAS-pSTING, TREX1; epithelia but not macrophages stained for PARP1. Myofibroblasts, endothelia, and bronchial/bronchiolar epithelial cells were all negative except early myofibroblastic foci expressing cGAS. Type II pneumocytes expressed cGAS and PARP1, but less pSTING. TREX1 although expressed was not activated. Macrophages and many regenerating epithelial cells expressed LAMP1 and Rab7. CD47, the 'don't-eat-me-signal', was expressed by macrophages and epithelial cells including senescence cells within the remodeled areas.

CONCLUSIONS

The cGAS-STING pathway is activated in macrophages and epithelial cells within remodeled areas. LikelyTREX1 because not activated cannot sufficiently degrade DNA fragments. PARP1 activation points to smoking-induced oxygen radical release, prolonging inflammation and leading to fibrosis. By expressing CD47 epithelial cells within remodeled areas protect themselves from being eliminated by phagocytosis.

Andrographolide Inhibits Lipotoxicity-Induced Activation of the NLRP3 Inflammasome in Bone Marrow-Derived Macrophages

Andrographolide is the major bioactive component of the herb Andrographis paniculata and is a potent anti-inflammatory agent. Obesity leads to an excess of free fatty acids, particularly palmitic acid (PA), in the circulation. Obesity also causes the deposition of ectopic fat in nonadipose tissues, which leads to lipotoxicity, a condition closely associated with inflammation. Here, we investigated whether andrographolide could inhibit PA-induced inflammation by activating autophagy, activating the antioxidant defense system, and blocking the activation of the NLRP3 inflammasome. Bone marrow-derived macrophages (BMDMs) were primed with lipopolysaccharide (LPS) and then activated with PA. LPS/PA treatment increased both the mRNA expression of NLRP3 and IL-1[Formula: see text] and the release of IL-1[Formula: see text] in BMDMs. Andrographolide inhibited the LPS/PA-induced protein expression of caspase-1 and the release of IL-1[Formula: see text]. Furthermore, andrographolide attenuated LPS/PA-induced mtROS generation by first promoting autophagic flux and catalase activity, and ultimately inhibiting activation of the NLRP3 inflammasome. Our results suggest that the mechanisms by which andrographolide downregulates LPS/PA-induced IL-1[Formula: see text] release in BMDMs involve promoting autophagic flux and catalase activity. Andrographolide may thus be a candidate to prevent obesity- and lipotoxicity-driven chronic inflammatory disease.

Enzyme-Mediated Alleviation of Peroxide Toxicity in Self-Oxygenating Biomaterials

Oxygen releasing biomaterials can facilitate the survival of living implants by creating environments with a viable oxygen level. Hydrophobic oxygen generating microparticles (HOGMPs) encapsulated calcium peroxide (CPO) have recently been used in tissue engineering to release physiologically relevant amounts of oxygen for several weeks. However, generating oxygen using CPO is mediated via the generation of toxic levels of hydrogen peroxide (H2 O2 ). The incorporation of antioxidants, such as catalases, can potentially reduce H2 O2 levels. However, the formulation in which catalases can most effectively scavenge H2 O2 within oxygen generating biomaterials has remained unexplored. In this study, three distinct catalase incorporation methods are compared based on their ability to decrease H2 O2 levels. Specifically, catalase is incorporated within HOGMPs, or absorbed onto HOGMPs, or freely laden into the hydrogel entrapping HOGMPs and compared with control without catalase. Supplementation of free catalase in an HOGMP-laden hydrogel significantly decreases H2 O2 levels reflecting a higher cellular viability and metabolic activity of all the groups. An HOGMP/catalase-laden hydrogel precursor solution containing cells is used as an oxygenating bioink allowing improved viability of printed constructs under severe hypoxic conditions. The combination of HOGMPs with a catalase-laden hydrogel has the potential to decrease peroxide toxicity of oxygen generating tissues.

Possible Beneficial Effects of N-Acetylcysteine for Treatment of Triple-Negative Breast Cancer

N-acetylcysteine (NAC) is a widely used antioxidant with therapeutic potential. However, the cancer-promoting effect of NAC observed in some preclinical studies has raised concerns regarding its clinical use. Reactive oxygen species (ROS) can mediate signaling that results in both cancer-promoting and cancer-suppressing effects. The beneficial effect of NAC may depend on whether the type of cancer relies on ROS signaling for its survival and metastasis. Triple-negative breast cancer (TNBC) has aggressive phenotypes and is currently treated with standard chemotherapy as the main systemic treatment option. Particularly, basal-like TNBC cells characterized by inactivated BRCA1 and mutated TP53 produce high ROS levels and rely on ROS signaling for their survival and malignant progression. In addition, the high ROS levels in TNBC cells can mediate the interplay between cancer cells and the tissue microenvironment (TME) to trigger the recruitment and conversion of stromal cells and induce hypoxic responses, thus leading to the creation of cancer-supportive TMEs and increased cancer aggressiveness. However, NAC treatment effectively reduces the ROS production and ROS-mediated signaling that contribute to cell survival, metastasis, and drug resistance in TNBC cells. Therefore, the inclusion of NAC in standard chemotherapy could probably provide additional benefits for TNBC patients.

The Role of Redox Dysregulation in the Effects of Prenatal Stress on Embryonic Interneuron Migration

Maternal stress during pregnancy is associated with increased risk of psychiatric disorders in offspring, but embryonic brain mechanisms disrupted by prenatal stress are not fully understood. Our lab has shown that prenatal stress delays inhibitory neural progenitor migration. Here, we investigated redox dysregulation as a mechanism for embryonic cortical interneuron migration delay, utilizing direct manipulation of pro- and antioxidants and a mouse model of maternal repetitive restraint stress starting on embryonic day 12. Time-lapse, live-imaging of migrating GAD67GFP+ interneurons showed that normal tangential migration of inhibitory progenitor cells was disrupted by the pro-oxidant, hydrogen peroxide. Interneuron migration was also delayed by in utero intracerebroventricular rotenone. Prenatal stress altered glutathione levels and induced changes in activity of antioxidant enzymes and expression of redox-related genes in the embryonic forebrain. Assessment of dihydroethidium (DHE) fluorescence after prenatal stress in ganglionic eminence (GE), the source of migrating interneurons, showed increased levels of DHE oxidation. Maternal antioxidants (N-acetylcysteine and astaxanthin) normalized DHE oxidation levels in GE and ameliorated the migration delay caused by prenatal stress. Through convergent redox manipula-tions, delayed interneuron migration after prenatal stress was found to critically involve redox dysregulation. Redox biology during prenatal periods may be a target for protecting brain development.

Peroxisomal Hydrogen Peroxide Metabolism and Signaling in Health and Disease

Hydrogen peroxide (H₂O₂), a non-radical reactive oxygen species generated during many (patho)physiological conditions, is currently universally recognized as an important mediator of redox-regulated processes. Depending on its spatiotemporal accumulation profile, this molecule may act as a signaling messenger or cause oxidative damage. The focus of this review is to comprehensively evaluate the evidence that peroxisomes, organelles best known for their role in cellular lipid metabolism, also serve as hubs in the H₂O₂ signaling network. We first briefly introduce the basic concepts of how H₂O₂ can drive cellular signaling events. Next, we outline the peroxisomal enzyme systems involved in H₂O₂ metabolism in mammals and reflect on how this oxidant can permeate across the organellar membrane. In addition, we provide an up-to-date overview of molecular targets and biological processes that can be affected by changes in peroxisomal H₂O₂ metabolism. Where possible, emphasis is placed on the molecular mechanisms and factors involved. From the data presented, it is clear that there are still numerous gaps in our knowledge. Therefore, gaining more insight into how peroxisomes are integrated in the cellular H₂O₂ signaling network is of key importance to unravel the precise role of peroxisomal H₂O₂ production and scavenging in normal and pathological conditions.

Peroxisomes as Modulators of Cellular Protein Thiol Oxidation: A New Model System

AIMS

Peroxisomes are ubiquitous, single-membrane-bounded organelles that contain considerable amounts of enzymes involved in the production or breakdown of hydrogen peroxide (H₂O₂), a key signaling molecule in multiple biological processes and disease states. Despite this, the role of this organelle in cross-compartmental H₂O₂ signaling remains largely unclear, mainly because of the difficulty to modulate peroxisomal H₂O₂ production in a selective manner. This study aimed at establishing and validating a cellular model suitable to decipher the complex signaling processes associated with peroxisomal H₂O₂ release.

RESULTS

Here, we report the development of a human cell line that can be used to selectively generate H₂O₂ inside peroxisomes in a time- and dose-controlled manner. In addition, we provide evidence that peroxisome-derived H₂O₂ can oxidize redox-sensitive cysteine residues in multiple proteins within (e.g., peroxiredoxin-5 [PRDX5]) and outside (e.g., nuclear factor kappa B subunit 1 [NFKB1] and subunit RELA proto-oncogene [RELA], phosphatase and tensin homolog [PTEN], forkhead box O3 [FOXO3], and peroxin 5 [PEX5]) the peroxisomal compartment. Furthermore, we show that the extent of protein oxidation depends on the subcellular location of the target protein and is inversely correlated to catalase activity and cellular glutathione content. Finally, we demonstrate that excessive H₂O₂ production inside peroxisomes does not induce their selective degradation, at least not under the conditions examined.

INNOVATION

This study describes for the first time a powerful model system that can be used to examine the role of peroxisome-derived H₂O₂ in redox-regulated (patho)physiological processes, a research area in need of further investigation and innovative approaches.

CONCLUSION

Our results provide unambiguous evidence that peroxisomes can serve as regulatory hubs in thiol-based signaling networks.

Redox Signaling from and to Peroxisomes: Progress, Challenges, and Prospects

SIGNIFICANCE

Peroxisomes are organelles that are best known for their role in cellular lipid and hydrogen peroxide (H₂O₂) metabolism. Emerging evidence suggests that these organelles serve as guardians and modulators of cellular redox balance, and that alterations in their redox metabolism may contribute to aging and the development of chronic diseases such as neurodegeneration, diabetes, and cancer. Recent Advances: H₂O₂ is an important signaling messenger that controls many cellular processes by modulating protein activity through cysteine oxidation. Somewhat surprisingly, the potential involvement of peroxisomes in H₂O₂-mediated signaling processes has been overlooked for a long time. However, recent advances in the development of live-cell approaches to monitor and modulate spatiotemporal fluxes in redox species at the subcellular level have opened up new avenues for research in redox biology and boosted interest in the concept of peroxisomes as redox signaling platforms.

CRITICAL ISSUES

This review first introduces the reader to what is known about the role of peroxisomes in cellular H₂O₂ production and clearance, with a focus on mammalian cells. Next, it briefly describes the benefits and drawbacks of current strategies used to investigate the complex interplay between peroxisome metabolism and cellular redox state. Furthermore, it integrates and critically evaluates literature dealing with the interrelationship between peroxisomal redox metabolism, cell signaling, and human disease.

FUTURE DIRECTIONS

As the precise molecular mechanisms underlying many of these associations are still poorly understood, a key focus for future research should be the identification of primary targets for peroxisome-derived H₂O₂.

Peroxisomes and Cellular Oxidant/Antioxidant Balance: Protein Redox Modifications and Impact on Inter-organelle Communication

Disturbances in cellular redox balance have been associated with pro-aging mechanisms and increased risk for various chronic disease states. Multiple lines of evidence indicate that peroxisomes are central players in cellular redox metabolism. Nevertheless, the potential role of this organelle as intracellular redox signaling platform has been largely overlooked for a long time. Fortunately, this situation is now changing. This review provides a snapshot of the current progress in the field, with an emphasis on the situation in mammals. We first briefly introduce the basics of redox biology and how reactive oxygen and nitrogen species can drive cellular signaling events. Next, we discuss current evidence linking peroxisome (dys)function to redox signaling, both in health and disease. We also highlight what is currently known about the downstream targets of peroxisome-derived oxidants. In addition, we present an extensive list of proteins that are involved in peroxisome functioning and have been identified as being responsive to oxidative stress in large scale redox proteomics studies. Finally, we address how changes in peroxisomal redox state may impact on functional mechanisms underlying inter-organelle communication. Gaining more insight into these mechanisms is key to our understanding of how peroxisomes are embedded in cellular signaling networks implicated in aging and diseases such as cancer, diabetes, and neurodegenerative disorders.

Role of macrophages in age-related oxidative stress and lipofuscin accumulation in mice

The age-related changes in the immune functions (immunosenescence) may be mediated by an increase of oxidative stress and damage affecting leukocytes. Although the “oxidation-inflammation” theory of aging proposes that phagocytes are the main immune cells contributing to “oxi-inflamm-aging”, this idea has not been corroborated. The aim of this work was to characterize the age-related changes in several parameters of oxidative stress and immune function, as well as in lipofuscin accumulation (“a hallmark of aging”), in both total peritoneal leukocyte population and isolated peritoneal macrophages. Adult, mature, old and long-lived mice (7, 13, 18 and 30 months of age, respectively) were used. The xanthine oxidase (XO) activity-expression, basal levels of superoxide anion and ROS, catalase activity, oxidized (GSSG) and reduced (GSH) glutathione content and lipofuscin levels, as well as both phagocytosis and digestion capacity were evaluated. The results showed an age-related increase of oxidative stress and lipofuscin accumulation in murine peritoneal leukocytes, but especially in macrophages. Macrophages from old mice showed lower antioxidant defenses (catalase activity and GSH levels), higher oxidizing compounds (XO activity/expression and superoxide, ROS and GSSG levels) and lipofuscin levels, together with an impaired macrophage functions, in comparison to adults. In contrast, long-lived mice showed in their peritoneal leukocytes, and especially in macrophages, a well-preserved redox state and maintenance of their immune functions, all which could account for their high longevity. Interestingly, macrophages showed higher XO activity and lipofuscin accumulation than lymphocytes in all the ages analyzed. Our results support that macrophages play a central role in the chronic oxidative stress associated with aging, and the fact that phagocytes are key cells contributing to immunosenescence and “oxi-inflamm-aging”. Moreover, the determination of oxidative stress and immune function parameters, together with the lipofuscin quantification, in macrophages, can be used as useful markers of the rate of aging and longevity.

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Peritoneal macrophages from old mice have higher oxidant levels than lymphocytes.

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Long-lived mice have a well-preserved redox state in both macrophages and lymphocytes.

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Peritoneal macrophages have higher lipofuscin levels than lymphocytes along aging.

Serum Proteomics Analysis in Rats of Immunosuppression Induced by Chronic Stress

The immune system can be damaged by chronic stress. However, for this process, the involved molecular alterations and their regulatory roles played in immunosuppression still remain unclear. This study was aimed to identify the differences in serum protein expressions that are closely associated with the effect of chronic stress on immune function. Serum protein levels of rats in control group and chronic stress group were measured by iTRAQ analysis. Subsequently, among the 121 differentially expressed proteins screened between the two groups, 46 proteins were upregulated (>1.5-fold, P < 0.05), while 75 proteins were downregulated (<0.67-fold, P < 0.05). Bioinformatics analysis revealed that most of the differentially expressed proteins were in relation with the metabolic, cellular, response stimulus and immune system processes. The significantly differential expression of ceruloplasmin, haptoglobin, catalase and peroxiredoxin-1 were picked out for reconfirmation by ELISA analysis. The results were consistent with those obtained by iTRAQ. What is more, the roles of above-mentioned four proteins, apolipoprotein B-100 and heat-shock protein 90 in immunosuppression induced by chronic stress were discussed. Taken together, these findings may provide a new insight into better understanding the molecular mechanisms of immunosuppression induced by chronic stress.

MnTE-2-PyP modulates thiol oxidation in a hydrogen peroxide-mediated manner in a human prostate cancer cell

To improve the treatment of advanced prostate cancer, the development of effective and innovative antitumor agents is needed. Our previous work demonstrated that the ROS (reactive oxygen species) scavenger, MnTE-2-PyP, inhibited human prostate cancer growth and also inhibited prostate cancer migration and invasion. We showed that MnTE-2-PyP treatment altered the affinity of the histone acetyltransferase enzyme, p300, to bind to DNA. We speculate that this may be one mechanism by which MnTE-2-PyP inhibits prostate cancer progression. Specifically, MnTE-2-PyP decreased p300/HIF-1/CREB complex (p300/hypoxia-inducible factor-1/cAMP response element-binding protein) binding to a specific hypoxia-response element (HRE) motif within the plasminogen activator inhibitor-1 (PAI-1) gene promoter region, and consequently, repressed PAI-1 expression. However, it remains unclear how MnTE-2-PyP reduces p300 complex binding affinity to the promoter region of specific genes. In this study, we found that overexpression of Cu/ZnSOD (superoxide dismutase 1, SOD1) significantly suppressed PAI-1 gene expression and p300 complex binding to the promoter region of PAI-1 gene, just as was observed in cells treated with MnTE-2-PyP. Furthermore, catalase (CAT) overexpression rescued the inhibition of PAI-1 expression and p300 binding by MnTE-2-PyP. Taken together, the above findings suggest that hydrogen peroxide (H₂O₂) is likely the mediator through which MnTE-2-PyP inhibits the PAI-1 expression and p300 complex binding in PC3 cells. To confirm this, we measured the production of H₂O₂ following overexpression of SOD1 or catalase with MnTE-2-PyP treatment in the presence or absence of radiation. We found that MnTE-2-PyP increased the intracellular steady-state levels of H₂O₂ and increased nuclear H₂O₂ levels. As expected, catalase overexpression significantly decreased the levels of intracellular H₂O₂ induced by MnTE-2-PyP. We then determined if this increased H₂O₂ production could result in oxidized protein thiol groups. In the presence of MnTE-2-PyP, there was a significant increase in oxidized thiols in PC3 cell lysates and this was reversed with catalase overexpression. Specifically, we showed that p300 was oxidized after MnTE-2-PyP treatment, indicating that MnTE-2-PyP is creating a more oxidizing environment and this is altering the oxidation state of p300 thiol residues. Our data provide an in depth mechanism by which MnTE-2-PyP regulates gene transcription through induced H₂O₂ mediated oxidation of particular proteins, supporting an important role for MnTE-2-PyP as an effective and innovative antitumor agent to enhance treatment outcomes in prostate cancer radiotherapy.

Protein Thiol Redox Signaling in Monocytes and Macrophages

SIGNIFICANCE

Monocyte and macrophage dysfunction plays a critical role in a wide range of inflammatory disease processes, including obesity, impaired wound healing diabetic complications, and atherosclerosis. Emerging evidence suggests that the earliest events in monocyte or macrophage dysregulation include elevated reactive oxygen species production, thiol modifications, and disruption of redox-sensitive signaling pathways. This review focuses on the current state of research in thiol redox signaling in monocytes and macrophages, including (i) the molecular mechanisms by which reversible protein-S-glutathionylation occurs, (ii) the identification of bona fide S-glutathionylated proteins that occur under physiological conditions, and (iii) how disruptions of thiol redox signaling affect monocyte and macrophage functions and contribute to atherosclerosis. Recent Advances: Recent advances in redox biochemistry and biology as well as redox proteomic techniques have led to the identification of many new thiol redox-regulated proteins and pathways. In addition, major advances have been made in expanding the list of S-glutathionylated proteins and assessing the role that protein-S-glutathionylation and S-glutathionylation-regulating enzymes play in monocyte and macrophage functions, including monocyte transmigration, macrophage polarization, foam cell formation, and macrophage cell death.

CRITICAL ISSUES

Protein-S-glutathionylation/deglutathionylation in monocytes and macrophages has emerged as a new and important signaling paradigm, which provides a molecular basis for the well-established relationship between metabolic disorders, oxidative stress, and cardiovascular diseases.

FUTURE DIRECTIONS

The identification of specific S-glutathionylated proteins as well as the mechanisms that control this post-translational protein modification in monocytes and macrophages will facilitate the development of new preventive and therapeutic strategies to combat atherosclerosis and other metabolic diseases. Antioxid. Redox Signal. 25, 816-835.

Novel Role of Endogenous Catalase in Macrophage Polarization in Adipose Tissue

Macrophages are important components of adipose tissue inflammation, which results in metabolic diseases such as insulin resistance. Notably, obesity induces a proinflammatory phenotypic switch in adipose tissue macrophages, and oxidative stress facilitates this switch. Thus, we examined the role of endogenous catalase, a key regulator of oxidative stress, in the activity of adipose tissue macrophages in obese mice. Catalase knockout (CKO) exacerbated insulin resistance, amplified oxidative stress, and accelerated macrophage infiltration into epididymal white adipose tissue in mice on normal or high-fat diet. Interestingly, catalase deficiency also enhanced classical macrophage activation (M1) and inflammation but suppressed alternative activation (M2) regardless of diet. Similarly, pharmacological inhibition of catalase activity using 3-aminotriazole induced the same phenotypic switch and inflammatory response in RAW264.7 macrophages. Finally, the same phenotypic switch and inflammatory responses were observed in primary bone marrow-derived macrophages from CKO mice. Taken together, the data indicate that endogenous catalase regulates the polarization of adipose tissue macrophages and thereby inhibits inflammation and insulin resistance.

Lung inflammation caused by inhaled toxicants: a review

Exposure of the lungs to airborne toxicants from different sources in the environment may lead to acute and chronic pulmonary or even systemic inflammation. Cigarette smoke is the leading cause of chronic obstructive pulmonary disease, although wood smoke in urban areas of underdeveloped countries is now recognized as a leading cause of respiratory disease. Mycotoxins from fungal spores pose an occupational risk for respiratory illness and also present a health hazard to those living in damp buildings. Microscopic airborne particulates of asbestos and silica (from building materials) and those of heavy metals (from paint) are additional sources of indoor air pollution that contributes to respiratory illness and is known to cause respiratory illness in experimental animals. Ricin in aerosolized form is a potential bioweapon that is extremely toxic yet relatively easy to produce. Although the aforementioned agents belong to different classes of toxic chemicals, their pathogenicity is similar. They induce the recruitment and activation of macrophages, activation of mitogen-activated protein kinases, inhibition of protein synthesis, and production of interleukin-1 beta. Targeting either macrophages (using nanoparticles) or the production of interleukin-1 beta (using inhibitors against protein kinases, NOD-like receptor protein-3, or P2X7) may potentially be employed to treat these types of lung inflammation without affecting the natural immune response to bacterial infections.

Cytoprotective and Cytotoxic Effects of Rice Bran Extracts in Rat H9c2(2-1) Cardiomyocytes

This study was aimed at preliminarily assessing the cytoprotective and antioxidative effects of rice bran extracts (RBEs) from a Sarawak local rice variety (local name: "BJLN") and a commercial rice variety, "MR219," on oxidative stress in rat H9c2(2-1) cardiomyocytes. The cardiomyocytes were incubated with different concentrations of RBE and hydrogen peroxide (H2O2), respectively, to identify their respective IC50 values and safe dose ranges. Two nonlethal and close-to-IC50 doses of RBE were selected to evaluate their respective effects on H2O2 induced oxidative stress in cardiomyocytes. Both RBEs showed dose-dependent cytotoxicity effects on cardiomyocytes. H2O2 induction of cardiomyocytes pretreated with RBE further revealed the dose-dependent cytoprotective and antioxidative effects of RBE via an increase in IC50 values of H2O2. Preliminary analyses of induction effects of RBE and H2O2 on cellular antioxidant enzyme, catalase (CAT), also revealed their potential in regulating these activities and expression profile of related gene on oxidative stress in cardiomyocytes. Pretreated cardiomyocytes significantly upregulated the enzymatic activity and expression level of CAT under the exposure of H2O2 induced oxidative stress. This preliminary study has demonstrated the potential antioxidant effects of RBE in alleviating H2O2-mediated oxidative injuries via upregulation in enzymatic activities and expression levels of CAT.

Redox interplay between mitochondria and peroxisomes

Reduction-oxidation or “redox” reactions are an integral part of a broad range of cellular processes such as gene expression, energy metabolism, protein import and folding, and autophagy. As many of these processes are intimately linked with cell fate decisions, transient or chronic changes in cellular redox equilibrium are likely to contribute to the initiation and progression of a plethora of human diseases. Since a long time, it is known that mitochondria are major players in redox regulation and signaling. More recently, it has become clear that also peroxisomes have the capacity to impact redox-linked physiological processes. To serve this function, peroxisomes cooperate with other organelles, including mitochondria. This review provides a comprehensive picture of what is currently known about the redox interplay between mitochondria and peroxisomes in mammals. We first outline the pro- and antioxidant systems of both organelles and how they may function as redox signaling nodes. Next, we critically review and discuss emerging evidence that peroxisomes and mitochondria share an intricate redox-sensitive relationship and cooperate in cell fate decisions. Key issues include possible physiological roles, messengers, and mechanisms. We also provide examples of how data mining of publicly-available datasets from “omics” technologies can be a powerful means to gain additional insights into potential redox signaling pathways between peroxisomes and mitochondria. Finally, we highlight the need for more studies that seek to clarify the mechanisms of how mitochondria may act as dynamic receivers, integrators, and transmitters of peroxisome-derived mediators of oxidative stress. The outcome of such studies may open up exciting new avenues for the community of researchers working on cellular responses to organelle-derived oxidative stress, a research field in which the role of peroxisomes is currently highly underestimated and an issue of discussion.

Melatonin in testes of infertile men: evidence for anti-proliferative and anti-oxidant effects on local macrophage and mast cell populations

Melatonin acting through the hypothalamus and pituitary regulates testicular function. In addition, direct actions of melatonin at the testicular level have been recently suggested. We have described that melatonin inhibits androgen production in hamster Leydig cells via melatonin subtype 1a (mel1a) receptors and the local corticotrophin-releasing hormone (CRH) system. The initial events of the melatonin/CRH signalling pathway have also been established. Melatonin and all components of the melatonergic/CRH system were also detected in Leydig cells of infertile men. This study attempted to search for additional targets of melatonin in the human testis, and to investigate the effects of melatonin on proliferation and the oxidative state in these novel target cells. To this aim, evaluation of human testicular biopsies of patients suffering from hypospermatogenesis or Sertoli cell only syndrome and cell culture studies were performed. Melatonergic receptors were found in macrophages (MACs) and mast cells (MCs) of the human testis. In biopsies of patients suffering idiopathic infertility, melatonin testicular concentrations were negatively correlated with MAC number per mm(2) and TNFα, IL1β and COX2 expression, but positively correlated with the expression of the anti-oxidant enzymes SOD1, peroxiredoxin 1 and catalase. Melatonin inhibited proliferation and the expression of pro-inflammatory cytokines and cyclooxygenase 2 (COX2) in both the human non-testicular THP-1 MAC cell line and primary cell cultures of hamster testicular MACs. In the human HMC-1 MC line, melatonin increased the expression of anti-oxidant enzymes and decreased reactive oxygen species (ROS) generation. The results reveal new testicular targets of melatonin and describe anti-proliferative and anti-inflammatory effects of this hormone on testicular MACs. Furthermore, melatonin might provide protective effects against oxidative stress in testicular MCs.

Oxidants and redox signaling in acute lung injury

Acute lung injury (ALI) and its more severe form of clinical manifestation, the acute respiratory distress syndrome is associated with significant dysfunction in air exchange due to inflammation of the lung parenchyma. Several factors contribute to the inflammatory process, including hypoxia (inadequate oxygen), hyperoxia (higher than normal partial pressure of oxygen), inflammatory mediators (such as cytokines), infections (viral and bacterial), and environmental conditions (such as cigarette smoke or noxious gases). However, studies over the past several decades suggest that oxidants formed in the various cells of the lung including endothelial, alveolar, and epithelial cells as well as lung macrophages and neutrophils in response to the factors mentioned above mediate the pathogenesis of ALI. Oxidants modify cellular proteins, lipids, carbohydrates, and DNA to cause their aberrant function. For example, oxidation of lipids changes membrane permeability. Interestingly, recent studies also suggest that spatially and temporally regulated production of oxidants plays an important role antimicrobial defense and immunomodulatory function (such as transcription factor activation). To counteract the oxidants an arsenal of antioxidants exists in the lung to maintain the redox status, but when overwhelmed tissue injury and exacerbation of inflammation occurs. We present below the current understanding of the pathogenesis of oxidant-mediated ALI.

Peroxisome degradation in mammals: mechanisms of action, recent advances, and perspectives

Peroxisomes are remarkably dynamic organelles that participate in a diverse array of cellular processes, including the metabolism of lipids and reactive oxygen species. In order to regulate peroxisome function in response to changing nutritional and environmental stimuli, new organelles need to be formed and superfluous and dysfunctional organelles have to be selectively removed. Disturbances in any of these processes have been associated with the etiology and progression of various congenital neurodegenerative and age-related human disorders. The aim of this review is to critically explore our current knowledge of how peroxisomes are degraded in mammalian cells and how defects in this process may contribute to human disease. Some of the key issues highlighted include the current concepts of peroxisome removal, the peroxisome quality control mechanisms, the initial triggers for peroxisome degradation, the factors for dysfunctional peroxisome recognition, and the regulation of peroxisome homeostasis. We also dissect the functional and mechanistic relationship between different forms of selective organelle degradation and consider how lysosomal dysfunction may lead to defects in peroxisome turnover. In addition, we draw lessons from studies on other organisms and extrapolate this knowledge to mammals. Finally, we discuss the potential pathological implications of dysfunctional peroxisome degradation for human health.

The role of metal coordination complexes in cytosolic cellular defense

The metal coordination complexes are known to induce cytotoxic effects on various cell lines and shown to have great potential for therapeutic interventions. Their main mechanism of action is through the mediation of enzyme activities in signaling pathways essential for cellular functioning. The overall cellular responses are dose-dependent and require high exposure levels and duration to overcome cellular defense against external toxicants. However, their effect through signal transduction components is limited due to the conferred drug resistance associated with glutathione transferase (GST)-mediated mechanisms. The GST family of enzymes is not only related to anticancer drug resistance, but also associated with cancer development where they may also contribute kinase signaling events including non-receptor protein tyrosine kinase (PTK)-related pathways. In the current study, we evaluated the effect of symmetrical and mononuclear complexes of Pd(II), Pt(II), and Ni(II) with organic ligands on cytosolic targets involved in glutathione utilization, antioxidant defense, and kinase signaling by virtue of acellular in vitro analyses.

Aging, age-related diseases and peroxisomes

Human aging is considered as one of the biggest risk factors for the development of multiple diseases such as cancer, type-2 diabetes, and neurodegeneration. In addition, it is widely accepted that these age-related diseases result from a combination of various genetic, lifestyle, and environmental factors. As biological aging is a complex and multifactorial phenomenon, the molecular mechanisms underlying disease initiation and progression are not yet fully understood. However, a significant amount of evidence supports the theory that oxidative stress may act as a primary etiologic factor. Indeed, many signaling components like kinases, phosphatases, and transcription factors are exquisitely sensitive to the cellular redox status, and a chronic or severe disturbance in redox homeostasis can promote cell proliferation or trigger cell death. Now, almost 50 years after their discovery, there is a wealth of evidence that peroxisomes can function as a subcellular source, sink, or target of reactive oxygen and nitrogen molecules. Yet, the possibility that these organelles may act as a signaling platform for a variety of age-related processes has so far been underestimated and largely neglected. In this review, we will critically discuss the possible role of peroxisomes in the human aging process in light of the available data.

α-Tocopherol prevents lymphoma by improving antioxidant defence system of mice

Increased level of ROS causes oxidative stress and leads to various pathological conditions including cancer. Therefore antioxidants should contribute to cancer prevention by improving antioxidant defense system and thereby protecting the cell from oxidative damage. In the present study we have validated the hypothesis by evaluating the antioxidant action of α-tocopherol. The effect of α-tocopherol is analyzed on oxidative stress as well as its regulation on antioxidant defense system. Oxidative stress is measured in terms of reduced glutathione and protein carbonylation. To evaluate the role of α-tocopherol on antioxidant defense system, the activities and expressions of antioxidant enzymes like glutathione peroxidase, catalase and superoxide dismutase are analyzed by activity gel assay and by RT-PCR respectively. These enzyme activities and/or expressions are found to be improved by α-tocopherol in lymphoma bearing mice which brings down the oxidative stress as reflected by increased level of reduced glutathione as well as decreased protein carbonylation. The effect of α-tocopherol is further analyzed on general characteristics of lymphoma growth like body weight, longevity, accumulation of ascites fluid, angiogenesis in peritoneum, morphology of liver and abundance of lymphocytes. The antioxidant α-tocopherol is found to check lymphoma growth. The results suggest that α-tocopherol contributes to lymphoma prevention by improving antioxidant defence system of mice.

The Redox System in C. elegans, a Phylogenetic Approach

Oxidative stress is a toxic state caused by an imbalance between the production and elimination of reactive oxygen species (ROS). ROS cause oxidative damage to cellular components such as proteins, lipids, and nucleic acids. While the role of ROS in cellular damage is frequently all that is noted, ROS are also important in redox signalling. The "Redox Hypothesis" has been proposed to emphasize a dual role of ROS. This hypothesis suggests that the primary effect of changes to the redox state is modified cellular signalling rather than simply oxidative damage. In extreme cases, alteration of redox signalling can contribute to the toxicity of ROS, as well as to ageing and age-related diseases. The nematode species Caenorhabditis elegans provides an excellent model for the study of oxidative stress and redox signalling in animals. We use protein sequences from central redox systems in Homo sapiens, Drosophila melanogaster, and Saccharomyces cerevisiae to query Genbank for homologous proteins in C. elegans. We then use maximum likelihood phylogenetic analysis to compare protein families between C. elegans and the other organisms to facilitate future research into the genetics of redox biology.

Molecular cloning, characterization and gene expression of an antioxidant enzyme catalase (MrCat) from Macrobrachium rosenbergii

In this study, we reported a full length of catalase gene (designated as MrCat), identified from the transcriptome database of freshwater prawn Macrobrachium rosenbergii. The complete gene sequence of the MrCat is 2504 base pairs in length, and encodes 516 amino acids. The MrCat protein contains three domains such as catalase 1 (catalase proximal heme-ligand signature) at 350-358, catalase 2 (catalase proximal active site signature) at 60-76 and catalase 3 (catalase family profile) at 20-499. The mRNA expressions of MrCat in healthy and the infectious hypodermal and hematopoietic necrosis virus (IHHNV) challenged M. rosenbergii were examined using quantitative real time polymerase chain reaction (qRT-PCR). The MrCat is highly expressed in digestive tract and all the other tissues (walking leg, gills, muscle, hemocyte, hepatopancreas, pleopods, brain and eye stalk) of M. rosenbergii taken for analysis. The expression is strongly up-regulated in digestive tract after IHHNV challenge. To understand its biological activity, the recombinant MrCat gene was constructed and expressed in Escherichia coli BL21 (DE3). The recombinant MrCat existed in high thermal stability and broad spectrum of pH, which showed over 95% enzyme activity between pH 5 and 10.5, and was stable from 40 °C to 70 °C, and exhibited 85-100% enzyme activity from 30 °C to 40 °C.

Anti-carcinogenic action of curcumin by activation of antioxidant defence system and inhibition of NF-κB signalling in lymphoma-bearing mice

NF-κB (nuclear factor κB) plays a significant role in inflammation, immunity, cell proliferation, apoptosis and malignancy. ROS (reactive oxygen species) are among the most important regulating factors of NF-κB. Intracellular ROS are mainly regulated by an endogenous antioxidant defence system. Any disruption of redox balance leads to oxidative stress, which causes a number of pathological conditions including inflammation and malignancy. Increased metabolic activity in cancerous cells leads to oxidative stress, which is further enhanced due to depletion of the endogenous antioxidant defence system. However, the activation and signalling of NF-κB are reported to be inhibited by overexpression and induced activity of antioxidant enzymes. Therefore the present study focuses on the correlation between the endogenous antioxidant defence system, ROS and NF-κB activation during lymphoma growth in mice. The study highlights the anti-carcinogenic role of curcumin by modulation of NF-κB activation and oxidative stress via the endogenous antioxidant defence system. Oxidative stress was monitored by lipid peroxidation, protein carbonylation and antioxidant enzyme activity. NF-κB-mediated signalling was tested by DNA-binding activity. The results reflect that intracellular production of H2O2 in oxidative tumour micro-environment regulates NF-κB activation. Curcumin inhibits oxidative state in the liver of lymphoma-bearing mice by enhancing the transcription and activities of antioxidant enzymes, which in turn modulate activation of NF-κB, leading to a decrease in lymphoma growth. Morphological changes as well as cell proliferation and cell survival assays confirmed reduced lymphoma growth. Thus curcumin contributes to cancer prevention by disrupting the vicious cycle of constant ROS production, responsible for a high oxidative micro-environment for tumour growth.

Mitochondrial Cu,Zn-superoxide dismutase mediates pulmonary fibrosis by augmenting H2O2 generation

The release of H(2)O(2) from alveolar macrophages has been linked to the development of pulmonary fibrosis, but little is known about its source or mechanism of production. We found that alveolar macrophages from asbestosis patients spontaneously produce high levels of H(2)O(2) and have high expression of Cu,Zn-superoxide dismutase (SOD). Because Cu,Zn-SOD is found in the mitochondrial intermembrane space (IMS), we hypothesized that mitochondrial Cu,Zn-SOD-mediated H(2)O(2) generation contributed to pulmonary fibrosis. Asbestos-induced translocation of Cu,Zn-SOD to the IMS was unique to macrophages and dependent on functional mitochondrial respiration and the presence of at least one of the conserved cysteines required for disulfide bond formation. These conserved cysteine residues were also necessary for enzyme activation and H(2)O(2) generation. Cu,Zn-SOD-mediated H(2)O(2) generation was inhibited by knockdown of the iron-sulfur protein, Rieske, in complex III. The role of Cu,Zn-SOD was biologically relevant in that Cu,Zn-SOD(-/-) mice generated significantly less H(2)O(2) and had less oxidant stress in bronchoalveolar lavage fluid and lung parenchyma. Furthermore, Cu,Zn-SOD(-/-) mice did not develop pulmonary fibrosis, and knockdown of Cu,Zn-SOD in monocytes attenuated collagen I deposition by lung fibroblasts. Our findings demonstrate a novel mechanism for the pathogenesis of pulmonary fibrosis where the antioxidant enzyme Cu,Zn-SOD translocates to the mitochondrial IMS to increase H(2)O(2) generation in alveolar macrophages.

Usurping the mitochondrial supremacy: extramitochondrial sources of reactive oxygen intermediates and their role in beta cell metabolism and insulin secretion

Insulin secretion from pancreatic beta cells is a process dependent on metabolism. While oxidative stress is a well-known inducer of beta cell toxicity and impairs insulin secretion, recent studies suggest that low levels of metabolically-derived reactive oxygen intermediates (ROI) also play a positive role in insulin secretion. Glucose metabolism is directly correlated with ROI production, particularly in beta cells in which glucose uptake is proportional to the extracellular concentration of glucose. Low levels of exogenously added ROI or quinones, which stimulate ROI production, positively affect insulin secretion, while antioxidants block insulin secretion, suggesting that ROI activate unidentified redox-sensitive signal transduction components within these cells. The mitochondria are one source of ROI: increased metabolic flux increases mitochondrial membrane potential resulting in electron leakage and adventitious ROI production. A second source of ROI are cytosolic and plasma membrane oxidoreductases which oxidize NAD(P)H and directly produce ROI through the reduction of molecular oxygen. The mechanism of ROI-mediated potentiation of insulin secretion remains an important topic for future study.

Effect of Sargassum thunbergii on ROS mediated oxidative damage and identification of polyunsaturated fatty acid components

In this study, we examined protective effect of Sargassum thunbergii on reactive oxygen species (ROS) mediated oxidative stress in cellular systems. In addition, polyunsaturated fatty acids from S. thunbergii were identified and quantified by gas chromatography mass spectroscopy. Intracellular ROS levels were measured using a oxidation sensitive dye, 2',7'-dichlorofluorescein diacetate (DCFH-DA). Treatment with S. thunbergii significantly reduced intracellular ROS mediated cell damage and inhibited myeloperoxidase (MPO) activity assessed in tumor necrosis factor-alpha (TNF-alpha) stimulated human monocytic leukemia in a concentration-dependent manner. Moreover, antioxidative mechanisms by S. thunbergii were evaluated by measuring the expression levels of antioxidative enzymes such as superoxide dismutase (SOD-1), catalase, glutathione peroxidase and glutathione reductase. SOD-1 and glutathione reductase were up-regulated by S. thunbergii. Furthermore, S. thunbergii contains polyunsaturated fatty acids such as arachidonic acid, arachidic acid, palmitic acid, elaidic acid, linoleic acid, stearic acid and cis-5,8,11,14,17-eicosanoic acid. Therefore, these results suggested that S. thunbergii has nutraceutical effectiveness in prevention of ROS-induced tissue damage and potential natural antioxidant related to oxidative stress, which can be traceable to polyunsaturated fatty acids contained in S. thunbergii.

Modulation of reactive oxygen species by Rac1 or catalase prevents asbestos-induced pulmonary fibrosis

The release of reactive oxygen species (ROS) and cytokines by alveolar macrophages has been demonstrated in asbestos-induced pulmonary fibrosis, but the mechanism linking alveolar macrophages to the pathogenesis is not known. The GTPase Rac1 is a second messenger that plays an important role in host defense. In this study, we demonstrate that Rac1 null mice are protected from asbestos-induced pulmonary fibrosis, as determined by histological and biochemical analysis. We hypothesized that Rac1 induced pulmonary fibrosis via generation of ROS. Asbestos increased TNF-alpha and ROS in a Rac1-dependent manner. TNF-alpha was elevated only 1 day after exposure, whereas ROS generation progressively increased in bronchoalveolar lavage cells obtained from wild-type (WT) mice. To determine whether ROS generation contributed to pulmonary fibrosis, we overexpressed catalase in WT monocytes and observed a decrease in ROS generation in vitro. More importantly, administration of catalase to WT mice attenuated the development of fibrosis in vivo. For the first time, these results demonstrate that Rac1 plays a crucial role in asbestos-induced pulmonary fibrosis. Moreover, it suggests that a simple intervention may be useful to prevent progression of the disease.

ASBESTOS-INDUCED ACTIVATION OF CELL SIGNALING PATHWAYS IN HUMAN BRONCHIAL EPITHELIAL CELLS

Using respiratory epithelial cells transfected with either superoxide dismutase (SOD) or catalase, the authors tested the hypothesis that the activation of the epidermal growth factor (EGF) receptor signal pathway after asbestos exposure involves an oxidative stress. Western blotting using phospho-specific antibodies demonstrated that the EGF receptor kinase inhibitor PD153035 decreased both the phosphorylation of extracellular signal-regulated kinase (ERK)1/2 and its upstream signal pathway, including mitogen-activate protein kinase/ERK kinase (MEK)1/2. Similarly, the MEK1/2 kinase inhibitor PD98059 also demonstrated the ability to decrease phosphorylation of ERK1/2. Crocidolite-induced phosphorylation of EGF receptor, ERK1/2, and MEK1/2 was reduced by transfection of BEAS-2B cells with a catalase vector, supporting a participation of oxidative stress in this pathway. These results show that crocidolite can activate the phosphorylation of EGF receptor and its downstream cell signal pathway in BEAS-2B cells and this is associated with the oxidative stress presented by the fibers.

Effect of garlic on lipid peroxidation and antioxidation enzymes in DMBA-induced skin carcinoma

OBJECTIVE

Naturally occurring phytochemicals display an active cancer preventive strategy to inhibit, delay, or reverse human carcinogenesis. Studies have indicated that certain daily-consumed dietary phytochemicals have cancer protective effects mediated by carcinogens. Lipid peroxide plays a detrimental role in all cancers including skin carcinogenesis. Garlic, a phytochemical, has acquired a special position in the folklore of many cultures as a formidable prophylactic and therapeutic medicinal agent. In this report, we pursue the chemopreventive effect of aqueous garlic on skin carcinogenesis.

METHODS

"Swiss albino mice" were divided into five groups depending on the combination of skin cancer-inducing 7,12-dimethylbenz[a]anthracene and garlic treatments. Histology of the affected skin and biochemical assays for lipid peroxide, catalase, superoxide dismutase, glutathione-S-transferase, and glutathione peroxidase were performed to demonstrate the effect of garlic in mice. Immunoblotting was performed with cyclo-oxygenase-2, p53, and caspase-3 to demonstrate expressions of the respective proteins in skin lysates.

RESULTS

Garlic extracts inhibited the oxidative modification of lipids, thus protecting cells from injury by the oxidized molecules. The best chemopreventive action of garlic was observed in mice in which garlic treatment was performed before and after the induction of skin carcinogenesis. Garlic ingestion delayed formation of skin papillomas in animals and simultaneously decreased the size and number of papillomas, which was also reflected in the skin histology of the mice treated.

CONCLUSION

The protective effects against skin cancer elicited by garlic in mice are believed to be due at least in part to the induction cellular defense systems.

Asbestos-induced MKP-3 expression augments TNF-alpha gene expression in human monocytes

TNF-alpha is associated with the development of interstitial fibrosis. We have demonstrated that the p38 mitogen-activated protein (MAP) kinase regulates TNF-alpha expression in monocytes exposed to asbestos. In this report, we asked if extracellular signal-regulated kinase (ERK) was also involved in TNF-alpha expression in monocytes exposed to asbestos. We found that p38 and ERK were differentially activated in alveolar macrophages obtained from patients with asbestosis compared with normal subjects. More specifically, p38 was constitutively active and ERK activation was suppressed. Since the upstream pathway leading to ERK was intact, we hypothesized that an ERK-specific phosphatase was, in part, responsible for the decreased ERK activity. We evaluated whether the dual specificity phosphatase MAP kinase phosphatase (MKP)-3, which is highly expressed in the lung and specifically dephosphorylates ERK, was increased after exposure to asbestos. We found that MKP-3 increased after exposure to asbestos, and its expression was regulated by p38. We found that p38 and ERK negatively regulated one another, and MKP-3 had a role in this differential activation. We also found that p38 was a positive regulator and ERK was a negative regulator of TNF-alpha gene expression. Cells overexpressing MKP-3 had a significant increase in TNF-alpha gene expression, suggesting than an environment favoring p38 MAP kinase activation is necessary for TNF-alpha production in monocytes exposed to asbestos. Taken together, these data demonstrate that the p38 MAP kinase down-regulates ERK via activation of MKP-3 in human monocytes exposed to asbestos to enhance TNF-alpha gene expression.

The cDNA cloning and mRNA expression of cytoplasmic Cu, Zn superoxide dismutase (SOD) gene in scallop Chlamys farreri

Cu, Zn superoxide dismutases (SODs) are metalloenzymes that represent one important line of defence against reactive oxygen species (ROS). A cytoplasmic Cu, Zn SOD cDNA sequence was cloned from scallop Chlamys farreri by the homology-based cloning technique. The full-length cDNA of scallop cytoplasmic Cu, Zn SOD (designated CfSOD) was 1022 bp with a 459 bp open reading frame encoding a polypeptide of 153 amino acids. The predicted amino acid sequence of CfSOD shared high identity with cytoplasmic Cu, Zn SOD in molluscs, insects, mammals and other animals, such as cytoplasmic Cu, Zn SOD in oyster Crassostrea gigas (CAD42722), mosquito Aedes aegypti (ABF18094), and cow Bos taurus (XP_584414). A quantitative reverse transcriptase real-time PCR (qRT-PCR) assay was developed to assess the mRNA expression of CfSOD in different tissues and the temporal expression of CfSOD in scallop challenged with Listonella anguillarum, Micrococcus luteus and Candida lipolytica respectively. Higher-level mRNA expression of CfSOD was detected in the tissues of haemocytes, gill filaments and kidney. The expression of CfSOD dropped in the first 8-16 h and then recovered after challenge with L. anguillarum and M. luteus, but no change was induced by the C. lipolytica challenge. The results indicated that CfSOD was a constitutive and inducible acute-phase protein, and could play an important role in the immune responses against L. anguillarum and M. luteus infection.

Constitutive NADPH oxidase and increased mitochondrial respiratory chain activity regulate chemokine gene expression

Alveolar macrophages, which generate high levels of reactive oxygen species, especially O(2)(*-), are involved in the recruitment of neutrophils to sites of inflammation and injury in the lung, and the generation of chemotactic proteins triggers this cellular recruitment. In this study, we asked whether O(2)(*-) generation in alveolar macrophages had a role in the expression of chemokines. Specifically, we hypothesized that O(2)(*-) generation is necessary for chemokine expression in alveolar macrophages after TNF-alpha stimulation. We found that alveolar macrophages have high constitutive NADPH oxidase activity that was not increased by TNF-alpha, but TNF-alpha increased the activity of the mitochondrial respiratory chain. In addition, the mitochondrial respiratory chain increased O(2)(*-) generation if the NADPH oxidase was inhibited. O(2)(*-) generation was necessary for macrophage inflammatory protein-2 (MIP-2) gene expression, because inhibition of NADPH oxidase or the mitochondrial respiratory chain or overexpression of Cu,Zn-superoxide dismutase significantly inhibited expression of MIP-2. TNF-alpha activated the ERK MAP kinase, and ERK activity was essential for chemokine gene expression. In addition, overexpression of the MEK1-->ERK pathway significantly increased IL-8 expression, and a small interfering RNA to the NADPH oxidase inhibited ERK- and TNF-alpha-induced chemokine expression. Collectively, these results suggest that in alveolar macrophages, O(2)(*-) generation mediates chemokine expression after TNF-alpha stimulation in an ERK-dependent manner.

Primary role of functional ischemia, quantitative evidence for the two-hit mechanism, and phosphodiesterase-5 inhibitor therapy in mouse muscular dystrophy

BACKGROUND

Duchenne Muscular Dystrophy (DMD) is characterized by increased muscle damage and an abnormal blood flow after muscle contraction: the state of functional ischemia. Until now, however, the cause-effect relationship between the pathogenesis of DMD and functional ischemia was unclear. We examined (i) whether functional ischemia is necessary to cause contraction-induced myofiber damage and (ii) whether functional ischemia alone is sufficient to induce the damage.

METHODOLOGY/PRINCIPAL FINDINGS

In vivo microscopy was used to document assays developed to measure intramuscular red blood cell flux, to quantify the amount of vasodilatory molecules produced from myofibers, and to determine the extent of myofiber damage. Reversal of functional ischemia via pharmacological manipulation prevented contraction-induced myofiber damage in mdx mice, the murine equivalent of DMD. This result indicates that functional ischemia is required for, and thus an essential cause of, muscle damage in mdx mice. Next, to determine whether functional ischemia alone is enough to explain the disease, the extent of ischemia and the amount of myofiber damage were compared both in control and mdx mice. In control mice, functional ischemia alone was found insufficient to cause a similar degree of myofiber damage observed in mdx mice. Additional mechanisms are likely contributing to cause more severe myofiber damage in mdx mice, suggestive of the existence of a "two-hit" mechanism in the pathogenesis of this disease.

CONCLUSIONS/SIGNIFICANCE

Evidence was provided supporting the essential role of functional ischemia in contraction-induced myofiber damage in mdx mice. Furthermore, the first quantitative evidence for the "two-hit" mechanism in this disease was documented. Significantly, the vasoactive drug tadalafil, a phosphodiesterase 5 inhibitor, administered to mdx mice ameliorated muscle damage.

Differential expression and oxidation of MKP-1 modulates TNF-alpha gene expression

Monocytic cells are integral in the pathogenesis of inflammatory disorders. We have shown previously that asbestos-induced p38 mitogen-activated protein (MAP) kinase activation and TNF-alpha expression are mediated by H(2)O(2) in blood monocytes. Due to the high expression and activity of catalase and glutathione peroxidase, normal alveolar macrophages do not respond in a manner similar to that of blood monocytes. Since kinase activity is tightly regulated by phosphatases, we hypothesized that the dual specificity phosphatase MAP kinase phosphatase (MKP)-1 regulates p38 activity and TNF-alpha production in alveolar macrophages due to insufficient H(2)O(2) generation in response to asbestos. We found that MKP-1 was highly expressed in alveolar macrophages, while blood monocytes had minimal expression. Inhibition of expression and activity of MKP-1 or overexpression of a catalytic mutant MKP-1 recovered p38 activity in alveolar macrophages. We questioned whether MKP-1 oxidation played a role dictating the contrasting responses of these cells to asbestos exposure, and found that overexpressed wild-type MKP-1 in monocytes was oxidized, while the mutant MKP-1 remained in the reduced form. Monocytes overexpressing either catalase or wild-type MKP-1 had decreased p38 activation and TNF-alpha production, respectively. In addition, TNF-alpha gene expression was regained in alveolar macrophages overexpressing the catalytic mutant MKP-1. These data suggest that MKP-1, through increased expression and lack of oxidation, modulates the inflammatory response in alveolar macrophages exposed to asbestos.

Endogenous hydrogen peroxide in paraventricular nucleus mediating cardiac sympathetic afferent reflex and regulating sympathetic activity

We previously reported that reactive oxygen species (ROS) in paraventricular nucleus (PVN) mediated cardiac sympathetic afferent reflex (CSAR). The present study investigated the role of endogenous hydrogen peroxide (H(2)O(2)), a ROS, in the PVN in mediating the CSAR and regulating sympathetic activity. The CSAR was evaluated by the response of renal sympathetic nerve activity (RSNA) to epicardial application of bradykinin (BK) in rats. Bilateral microinjection of polyethylene glycol-catalase (PEG-CAT, an analogue of endogenous catalase) or polyethylene glycol-superoxide dismutase (PEG-SOD, an analogue of endogenous superoxide dismutase) into the PVN abolished the CSAR, decreased baseline RSNA and mean arterial pressure (MAP). Moreover, pretreatment with PEG-CAT or PEG-SOD blocked the enhanced CSAR and RSNA responses induced by exogenous angiotensin II (Ang II) in the PVN. Aminotriazole (ATZ, a catalase inhibitor) alone potentiated the CSAR, increased RSNA and MAP, but failed to augment the Ang II-induced CSAR enhancement responses. Pretreated with PEG-SOD, ATZ still increased baseline RSNA and MAP but inhibited the CSAR and Ang II-induced CSAR and RSNA enhancement responses. These results suggested that endogenous H(2)O(2) in the PVN mediated both the CSAR and Ang II-induced CSAR enhancement responses. H(2)O(2) in the PVN were involved in regulating sympathetic activity and arterial pressure.

Inhibiting catalase activity sensitizes 36B10 rat glioma cells to oxidative stress

Gliomas are extremely resistant to anticancer therapies resulting in poor patient survival, due, in part, to altered expression of antioxidant enzymes. The primary antioxidant enzyme, catalase, is elevated constitutively in gliomas compared to normal astrocytes. We hypothesized that downregulating catalase in glioma cells would sensitize these cells to oxidative stress. To test this hypothesis, we implemented two approaches. The first, a pharmacological approach, used 3-amino-1,2,4-triazole, an irreversible inhibitor that reduced catalase enzymatic activity by 75%. Pharmacological inhibition of catalase was not associated with a reduction in rat 36B10 glioma cell viability until the cells were challenged with additional oxidative stress, i.e., ionizing radiation or hydrogen peroxide (H(2)O(2)). In the second molecular approach, we generated 36B10 glioma cells stably expressing catalase shRNA; a stable cell line displayed a 75% reduction in catalase immunoreactive protein and enzymatic activity. This was accompanied by an increase in intracellular reactive oxygen species and extracellular H(2)O(2). These cells exhibited increased sensitivity to radiation and H(2)O(2), which was rescued by the antioxidant, N-acetylcysteine. These results support the hypothesis that catalase is a major participant in the defense of 36B10 glioma cells against oxidative stress mediated by anticancer agents capable of increasing steady-state levels of H(2)O(2).

Changes in the metabolic activity of macrophages under the influence of tick-borne encephalitis virus

The metabolic activity of macrophages infected with tick-borne encephalitis virus (TBEV) affecting the human nervous system has been studied for the first time. The penetration and reproduction of TBEV in the macrophages stimulated their oxygen metabolism, increasing the activity of NADPH-oxidase complex, as well as the mitochondrial enzymes lactate dehydrogenase, succinate dehydrogenase, and cytochrome oxidase. A wave-like change in the activity of these enzymes in the macrophages reflected the reaction of the cells to the penetration of the virus in the first period (within 3 h) and to the synthesis of the virus particles and their exit into the extracellular space in the second period (from 5 to 48 h). In the macrophages infected with TBEV, accumulation of NO metabolites was observed. In the late period of the examination (1-4 days), the activities of superoxide dismutase and lysosomal enzymes (nonspecific esterase and acid phosphatase) were detected. Thus, the early increase in the activity of the cell enzymes indicates the activation of the macrophages, and the subsequent increase in their activity corresponds to the enhanced synthetic activity of the macrophages.

Tumor-Induced Oxidative Stress Perturbs Nuclear Factor-κB Activity-Augmenting Tumor Necrosis Factor-α–Mediated T-Cell Death: Protection by Curcumin

Cancer patients often exhibit loss of proper cell-mediated immunity and reduced effector T-cell population in the circulation. Thymus is a major site of T-cell maturation, and tumors induce thymic atrophy to evade cellular immune response. Here, we report severe thymic hypocellularity along with decreased thymic integrity in tumor bearer. In an effort to delineate the mechanisms behind such thymic atrophy, we observed that tumor-induced oxidative stress played a critical role, as it perturbed nuclear factor-kappaB (NF-kappaB) activity. Tumor-induced oxidative stress increased cytosolic IkappaBalpha retention and inhibited NF-kappaB nuclear translocation in thymic T cells. These NF-kappaB-perturbed cells became vulnerable to tumor-secreted tumor necrosis factor (TNF)-alpha (TNF-alpha)-mediated apoptosis through the activation of TNF receptor-associated protein death domain-associated Fas-associated protein death domain and caspase-8. Interestingly, TNF-alpha-depleted tumor supernatants, either by antibody neutralization or by TNF-alpha-small interfering RNA transfection of tumor cells, were unable to kill T cell effectively. When T cells were overexpressed with NF-kappaB, the cells became resistant to tumor-induced apoptosis. In contrast, when degradation-defective IkappaBalpha (IkappaBalpha super-repressor) was introduced into T cells, the cells became more vulnerable, indicating that inhibition of NF-kappaB is the reason behind such tumor/TNF-alpha-mediated apoptosis. Curcumin could prevent tumor-induced thymic atrophy by restoring the activity of NF-kappaB. Further investigations suggest that neutralization of tumor-induced oxidative stress and restoration of NF-kappaB activity along with the reeducation of the TNF-alpha signaling pathway can be the mechanism behind curcumin-mediated thymic protection. Thus, our results suggest that unlike many other anticancer agents, curcumin is not only devoid of immunosuppressive effects but also acts as immunorestorer in tumor-bearing host.

Nitric oxide protects macrophages from hydrogen peroxide-induced apoptosis by inducing the formation of catalase

We investigated the cytoprotective effect of NO on H2O2-induced cell death in mouse macrophage-like cell line RAW264. H2O2-treated cells showed apoptotic features, such as activation of caspase-9 and caspase-3, nuclear fragmentation, and DNA fragmentation. These apoptotic features were significantly inhibited by pretreatment for 24 h with NO donors, sodium nitroprusside and 1-hydroxy-2-oxo-3,3-bis-(2-aminoethyl)-1-triazene, at a low nontoxic concentration. The cytoprotective effect of NO was abrogated by the catalase inhibitor 3-amino-1,2,4-triazole but was not affected by a glutathione synthesis inhibitor, L-buthionine-(S,R)-sulfoximine. NO donors increased the level of catalase and its activity in a concentration-dependent manner. Cycloheximide, a protein synthesis inhibitor, inhibited both the NO-induced increase in the catalase level and the cytoprotective effect of NO. These results indicate that NO at a low concentration protects macrophages from H2O2-induced apoptosis by inducing the production of catalase.

Human Alveolar Macrophages Are Deficient in PTEN

Human alveolar macrophages play a critical role in host defense and in the development of inflammation and fibrosis in the lung. Unlike their precursor cells, blood monocytes, alveolar macrophages are long-lived and tend to be resistant to apoptotic stimuli. In this study, we examined the role of differentiation in altering baseline phosphatidylinositol (PI) 3-kinase/Akt activity. We found that differentiation increased activity of pro-survival PI 3-kinase/Akt while decreasing amounts of the negative PI 3-kinase regulator, PTEN. PTEN is a lipid phosphatase with activity against phosphatidylinositol 3,4,5-trisphosphate (PI(3,4,5)P3), the major bioactive product of PI 3-kinase. Examining in vivo differentiation of alveolar macrophages (by comparing blood monocytes to alveolar macrophages from single donors), we found that differentiation resulted in increased baseline reactive oxygen species (ROS) in the alveolar macrophages. This led to a deficiency in PTEN, increased activity of Akt, and prolonged survival of alveolar macrophages. These data support the hypothesis that alterations in ROS levels contribute to macrophage homeostasis by altering the balance between PI 3-kinase/Akt and the phosphatase, PTEN.