H2O2-induced proliferation of primary alveolar epithelial cells is mediated by MAP kinases

Temporal coordination of the transcription factor response to H2O2 stress

Oxidative stress from excess H2O2 activates transcription factors that restore redox balance and repair oxidative damage. Although many transcription factors are activated by H2O2, it is unclear whether they are activated at the same H2O2 concentration, or time. Dose-dependent activation is likely as oxidative stress is not a singular state and exhibits dose-dependent outcomes including cell-cycle arrest and cell death. Here, we show that transcription factor activation is both dose-dependent and coordinated over time. Low levels of H2O2 activate p53, NRF2 and JUN. Yet under high H2O2, these transcription factors are repressed, and FOXO1, NF-κB, and NFAT1 are activated. Time-lapse imaging revealed that the order in which these two groups of transcription factors are activated depends on whether H2O2 is administered acutely by bolus addition, or continuously through the glucose oxidase enzyme. Finally, we provide evidence that 2-Cys peroxiredoxins control which group of transcription factors are activated.

Dose-Dependent Effect of Mitochondrial Superoxide Dismutase Gene Overexpression on Radioresistance of HEK293T Cells

Over the last two decades, a multitude of gain-of-function studies have been conducted on genes that encode antioxidative enzymes, including one of the key enzymes, manganese superoxide dismutase (SOD2). The results of such studies are often contradictory, as they strongly depend on many factors, such as the gene overexpression level. In this study, the effect of altering the ectopic expression level of major transcript variants of the SOD2 gene on the radioresistance of HEK293T cells was investigated using CRISPRa technology. A significant increase in cell viability in comparison with the transfection control was detected in cells with moderate SOD2 overexpression after irradiation at 2 Gy, but not at 3 or 5 Gy. A further increase in the level of SOD2 ectopic expression up to 22.5-fold resulted in increased cell viability detectable only after irradiation at 5 Gy. Furthermore, a 15-20-fold increase in SOD2 expression raised the clonogenic survival of cells after irradiation at 5 Gy. Simultaneous overexpression of genes encoding SOD2 and Catalase (CAT) enhanced clonogenic cell survival after irradiation more effectively than separate overexpression of both. In conjunction with the literature data on the suppression of the procarcinogenic effects of superoxide dismutase overexpression by ectopic expression of CAT, the data presented here suggest the potential efficacy of simultaneous overexpression of SOD2 and CAT to reduce oxidative stress occurring in various pathological processes. Moreover, these results illustrate the importance of selecting the degree of SOD2 overexpression to obtain a protective effect.

Temporal Coordination of the Transcription Factor Response to H2O2 stress

Oxidative stress from excess H2O2 activates transcription factors (TFs) that restore redox balance and repair oxidative damage. Though many TFs are activated by H2O2, it is unknown whether they are activated at the same H2O2 concentration or time after H2O2 stress. We found TF activation is tightly coordinated over time and dose dependent. We first focused on p53 and FOXO1 and found that in response to low H2O2, p53 is activated rapidly while FOXO1 remains inactive. In contrast, cells respond to high H2O2 in two temporal phases. In the first phase FOXO1 rapidly shuttles to the nucleus while p53 remains inactive. In the second phase FOXO1 shuts off and p53 levels rise. Other TFs are activated in the first phase with FOXO1 (NF-κB, NFAT1), or the second phase with p53 (NRF2, JUN), but not both. The two phases result in large differences in gene expression. Finally, we provide evidence that 2-Cys peroxiredoxins control which TF are activated and the timing of TF activation.

Blocking Spatiotemporal Crosstalk between Subcellular Organelles for Enhancing Anticancer Therapy with Nanointercepters

The spatiotemporal characterization of signaling crosstalk between subcellular organelles is crucial for the therapeutic effect of malignant tumors. Blocking interactive crosstalk in this fashion is significant but challenging. Herein, a communication interception strategy is reported, which blocks spatiotemporal crosstalk between subcellular organelles for cancer therapy with underlying molecular mechanisms. Briefly, amorphous-core@crystalline-shell Fe@Fe₃ O₄ nanoparticles (ACFeNPs) are fabricated to specifically block the crosstalk between lysosomes and endoplasmic reticulum (ER) by hydroxyl radicals generated along with their trajectory through heterogeneous Fenton reaction. ACFeNPs initially enter lysosomes and trigger autophagy, then continuous lysosomal damage blocks the generation of functional autolysosomes, which mediates ER-lysosome crosstalk, thus the autophagy is paralyzed. Thereafter, released ACFeNPs from lysosomes induce ER stress. Without the alleviation by autophagy, the ER-stress-associated apoptotic pathway is fully activated, resulting in a remarkable therapeutic effect. This strategy provides a wide venue for nanomedicine to exert biological advantages and confers new perspective for the design of novel anticancer drugs.

Temporal Coordination of the Transcription Factor Response to H2O2 stress

The p53 and FOXO transcription factors (TFs) share many similarities despite their distinct evolutionary origins. Both TFs are activated by a variety of cellular stresses and upregulate genes in similar pathways including cell-cycle arrest and apoptosis. Oxidative stress from excess H2O2 activates both FOXO1 and p53, yet whether they are activated at the same time is unclear. Here we found that cells respond to high H2O2 levels in two temporal phases. In the first phase FOXO1 rapidly shuttles to the nucleus while p53 levels remain low. In the second phase FOXO1 exits the nucleus and p53 levels rise. We found that other oxidative stress induced TFs are activated in the first phase with FOXO1 (NF-κB, NFAT1), or the second phase with p53 (NRF2, JUN) but not both following H2O2 stress. The two TF phases result in large differences in gene expression patterns. Finally, we provide evidence that 2-Cys peroxiredoxins control the timing of the TF phases in response to H2O2.

Epidermal Growth Factor Receptor Inhibition Is Protective in Hyperoxia-Induced Lung Injury

Aims

Studies have linked severe hyperoxia, or prolonged exposure to very high oxygen levels, with worse clinical outcomes. This study investigated the role of epidermal growth factor receptor (EGFR) in hyperoxia-induced lung injury at very high oxygen levels (>95%).

Results

Effects of severe hyperoxia (100% oxygen) were studied in mice with genetically inhibited EGFR and wild-type littermates. Despite the established role of EGFR in lung repair, EGFR inhibition led to improved survival and reduced acute lung injury, which prompted an investigation into this protective mechanism. Endothelial EGFR genetic knockout did not confer protection. EGFR inhibition led to decreased levels of cleaved caspase-3 and poly (ADP-ribosyl) polymerase (PARP) and decreased terminal dUTP nick end labeling- (TUNEL-) positive staining in alveolar epithelial cells and reduced ERK activation, which suggested reduced apoptosis in vivo. EGFR inhibition decreased hyperoxia (95%)-induced apoptosis and ERK in murine alveolar epithelial cells in vitro, and CRISPR-mediated EGFR deletion reduced hyperoxia-induced apoptosis and ERK in human alveolar epithelial cells in vitro. Innovation. This work defines a protective role of EGFR inhibition to decrease apoptosis in lung injury induced by 100% oxygen. This further characterizes the complex role of EGFR in acute lung injury and outlines a novel hyperoxia-induced cell death pathway that warrants further study.

Conclusion

In conditions of severe hyperoxia (>95% for >24 h), EGFR inhibition led to improved survival, decreased lung injury, and reduced cell death. These findings further elucidate the complex role of EGFR in acute lung injury.

A ROS-dependent mechanism promotes CDK2 phosphorylation to drive progression through S phase

Reactive oxygen species (ROS) at the right concentration promote cell proliferation in cell culture, stem cells, and model organisms. However, the mystery of how ROS signaling is coordinated with cell cycle progression and integrated into the cell cycle control machinery on the molecular level remains unsolved. Here, we report increasing levels of mitochondrial ROS during the cell cycle in human cell lines that target cyclin-dependent kinase 2 (CDK2). Chemical and metabolic interferences with ROS production decrease T-loop phosphorylation on CDK2 and so impede its full activation and thus its efficient DNA replication. ROS regulate CDK2 activity through the oxidation of a conserved cysteine residue near the T-loop, which prevents the binding of the T-loop phosphatase KAP. Together, our data reveal how mitochondrial metabolism is coupled with DNA replication and cell cycle progression via ROS, thereby demonstrating how KAP activity toward CDKs can be cell cycle regulated.

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Mitochondrial ROS drive cell cycle progression and proliferation

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Cyclin-dependent kinase 2 (CDK2) is increasingly oxidized during the cell cycle

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The oxidation state of a conserved cysteine on CDK2 regulates KAP binding

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CDK2 oxidation promotes T-loop phosphorylation and DNA replication

Redox and catalase-like activities of four widely used carbon monoxide releasing molecules (CO-RMs)

The pathophysiological roles of the endogenous signaling molecule, carbon monoxide (CO), have been extensively studied and validated in cell culture and animal models. Further, evidence supporting the therapeutic effects of CO in various human diseases has been mounting over the last two decades. Along this line, there has been intensive interest in developing various delivery forms including CO gas, CO in solution, metal–carbonyl complexes widely known as CO-releasing molecules (CO-RMs), and organic CO prodrugs. Among them, two ruthenium-based carbonyl complexes, CORM-2 and -3, occupy a very special place because they have been used in over 500 published studies. One of the mechanisms for CO's actions is known to be through attenuation of oxidative stress and regulation of production of reactive oxygen species (ROS). For this reason, it is important that CO delivery forms do not have intrinsic chemical redox properties. Herein, we describe our findings of catalase-like activities of CORM-2 and -3 in a CO-independent fashion, leading to the rapid degradation of hydrogen peroxide (H₂O₂) in PBS buffer (pH = 7.4) and in cell culture media. Further, we have found that CORM-2 and CORM-3 possess potent radical scavenging abilities. We have also studied two other widely used CO donors: CORM-401 and CORM-A1. Both showed chemical reactivity with ROS, but to a lesser degree than CORM-2 and -3. Because of the central role of ROS in some of the proposed mechanisms of actions for CO biology, the discovery of intrinsic chemical redox properties for these CO-RMs means that additional attention in designing proper controls is needed in future biological experiments using these CO-RMs for their CO-donating functions. Further, much more work is needed to understand the true implications of the chemical reactivity of these CO-RMs in cell-culture and animal-model studies of CO biology.

Four CO-releasing molecules are found to degrade H₂O₂ and free radicals either catalytically (CORM-2 and -3) or through direct reactions (CORM-401 and -A1) in solution under near-physiological conditions.

The alveolar epithelial cells are involved in pulmonary vascular remodeling and constriction of hypoxic pulmonary hypertension

BACKGROUND

Hypoxic pulmonary hypertension (HPH) is a common type of pulmonary hypertension and characterized by pulmonary vascular remodeling and constriction. Alveolar epithelial cells (AECs) primarily sense alveolar hypoxia, but the role of AECs in HPH remains unclear. In this study, we explored whether AECs are involved in pulmonary vascular remodeling and constriction.

METHODS

In the constructed rat HPH model, hemodynamic and morphological characteristics were measured. By treating AECs with hypoxia, we further detected the levels of superoxide dismutase 2 (SOD2), catalase (CAT), reactive oxygen species (ROS) and hydrogen peroxide (H2O2), respectively. To detect the effects of AECs on pulmonary vascular remodeling and constriction, AECs and pulmonary artery smooth cells (PASMCs) were co-cultured under hypoxia, and PASMCs and isolated pulmonary artery (PA) were treated with AECs hypoxic culture medium. In addition, to explore the mechanism of AECs on pulmonary vascular remodeling and constriction, ROS inhibitor N-acetylcysteine (NAC) was used.

RESULTS

Hypoxia caused pulmonary vascular remodeling and increased pulmonary artery pressure, but had little effect on non-pulmonary vessels in vivo. Meanwhile, in vitro, hypoxia promoted the imbalance of SOD2 and CAT in AECs, leading to increased ROS and hydrogen peroxide (H2O2) production in the AECs culture medium. In addition, AECs caused the proliferation of co-cultured PASMCs under hypoxia, and the hypoxic culture medium of AECs enhanced the constriction of isolated PA. However, treatment with ROS inhibitor NAC effectively alleviated the above effects.

CONCLUSION

The findings of present study demonstrated that AECs were involved in pulmonary vascular remodeling and constriction under hypoxia by paracrine H2O2 into the pulmonary vascular microenvironment.

Testosterone induces up-regulation of mitochondrial gene expression in murine C2C12 skeletal muscle cells accompanied by an increase of nuclear respiratory factor-1 and its downstream effectors

The reduction in muscle mass and strength with age, sarcopenia, is a prevalent condition among the elderly, linked to skeletal muscle dysfunction and cell apoptosis. We demonstrated that testosterone protects against H₂O₂-induced apoptosis in C2C12 muscle cells. Here, we analyzed the effect of testosterone on mitochondrial gene expression in C2C12 skeletal muscle cells. We found that testosterone increases mRNA expression of genes encoded by mitochondrial DNA, such as NADPH dehydrogenase subunit 1 (ND1), subunit 4 (ND4), cytochrome b (CytB), cytochrome c oxidase subunit 1 (Cox1) and subunit 2 (Cox2) in C2C12. Additionally, the hormone induced the expression of the nuclear respiratory factors 1 and 2 (Nrf-1 and Nrf-2), the mitochondrial transcription factors A (Tfam) and B2 (TFB2M), and the optic atrophy 1 (OPA1). The simultaneous treatment with testosterone and the androgen receptor antagonist, Flutamide, reduced these effects. H₂O₂-oxidative stress induced treatment, significantly decreased mitochondrial gene expression. Computational analysis revealed that mitochondrial DNA contains specific sequences, which the androgen receptor could recognize and bind, probably taking place a direct regulation of mitochondrial transcription by the receptor. These findings indicate that androgen plays an important role in the regulation of mitochondrial transcription and biogenesis in skeletal muscle.

Hydroxytyrosol: A natural compound with promising pharmacological activities

Hydroxytyrosol is a phenolic phytochemical with antioxidant properties in vitro. It is a natural compound that can be found in olive leaves and oil. The main dietary source of hydroxytyrosol is extra virgin olive oil. Due to its bioavailability, chemical properties and easy formulation along with its lack of toxicity, hydroxytyrosol is considered an excellent food supplement by the nutraceutical and food industries. The purpose of this review is to discuss the potential therapeutic effects of hydroxytyrosol in vivo. To do so, we conducted an electronic search in PubMed and other literature databases using "hydroxytyrosol", "beneficial effect/s", "pharmacology" as key-words. From this search, we found that hydroxytyrosol has anti-inflammatory, anti-tumor, antiviral, antibacterial and antifungal properties. Hydroxytyrosol also improves endothelial dysfunction, decreases oxidative stress, and is neuro- and cardio-protective. Due to all these biological properties, hydroxytyrosol is currently the most actively investigated natural phenol. The evidence presented in this review suggests that hydroxytyrosol has great pharmacological potential.

Microgel Bioreactors for Cancer Cell Targeting by pH-Dependent Generation of Radicals

The lack of specificity of traditional cytostatics and increasing resistance of cancer cells represent important challenges in cancer therapy. One of the characteristics of cancer cells is their intrinsic oxidative stress caused by higher metabolic activity, mitochondrial malfunction, and oncogene stimulation. This feature can be exploited in the pursuit of more selective cancer therapy, as there is increasing evidence that cancer cells are more sensitive to elevated concentrations of reactive oxygen species than normal cells. In this study, we demonstrate a new concept for cancer cell targeting by in situ production of radicals under physiological conditions. The biologically active radicals are produced in the milieu of cancer cells by enzymatic conversion from an inactive precursor, 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid)diammonium salt, by using miniature bioreactors represented by cell-sized microgels containing immobilized laccase. We utilize the pH-dependent activity of laccase to generate radicals only at a lower pH (5.7-6.1) that is characteristic of the tumor microenvironment. The composition of the microgels was optimized so as to allow sufficient substrate and radical diffusion, high enzyme activity, and stability under physiological conditions. The functionality of this system was evaluated on three cancer cell lines (HeLa, HT-29, and DLD1) and the cytotoxicity of in situ-produced radicals was successfully proven in all cases. These results demonstrate that cancer cell targeting by in situ-generated radicals using miniature enzymatic reactors may represent an alternative to traditional cytostatics. In particular, the pH-dependence of radical generation and their short-lived nature can ensure localized functionality in the tumor microenvironment and thereby reduce systemic side-effects.

Reactive Oxygen Species and Pulmonary Vasculature During Hypobaric Hypoxia

An increasing number of people are living or working at high altitudes (hypobaric hypoxia) and therefore suffering several physiological, biochemical, and molecular changes. Pulmonary vasculature is one of the main and first responses to hypoxia. These responses imply hypoxic pulmonary vasoconstriction (HPV), remodeling, and eventually pulmonary hypertension (PH). These events occur according to the type and extension of the exposure. There is also increasing evidence that these changes in the pulmonary vascular bed could be mainly attributed to a homeostatic imbalance as a result of increased levels of reactive oxygen species (ROS). The increase in ROS production during hypobaric hypoxia has been attributed to an enhanced activity and expression of nicotinamide adenine dinucleotide phosphate oxidase (NADPH oxidase), though there is some dispute about which subunit is involved. This enzymatic complex may be directly induced by hypoxia-inducible factor-1α (HIF-1α). ROS has been found to be related to several pathways, cells, enzymes, and molecules in hypoxic pulmonary vasculature responses, from HPV to inflammation, and structural changes, such as remodeling and, ultimately, PH. Therefore, we performed a comprehensive review of the current evidence on the role of ROS in the development of pulmonary vasculature changes under hypoxic conditions, with a focus on hypobaric hypoxia. This review provides information supporting the role of oxidative stress (mainly ROS) in the pulmonary vasculature’s responses under hypobaric hypoxia and depicting possible future therapeutics or research targets. NADPH oxidase-produced oxidative stress is highlighted as a major source of ROS. Moreover, new molecules, such as asymmetric dimethylarginine, and critical inflammatory cells as fibroblasts, could be also involved. Several controversies remain regarding the role of ROS and the mechanisms involved in hypoxic responses that need to be elucidated.

Polymorphisms of the murine mitochondrial ND4, CYTB and COX3 genes impact hematopoiesis during aging

During aging, mitochondrial DNA (mtDNA) can accumulate mutations leading to increasing levels of reactive oxygen species (ROS). Increased ROS were described to activate formerly quiescent hematopoietic stem cells (HSC). Mutations in mtDNA were shown to enhance the risk for myelodysplastic syndrome and leukemia. However, the complex relationship between mtDNA variations, ROS and aging of the hematopoietic system is not fully understood.

Herein, three mouse strains with mtDNA polymorphisms in genes of respiratory chain complexes I (ND4), III (CYTB) and IV (COX3) were compared to a reference strain during aging. Analysis focused on ROS and ATP levels, bone marrow composition and blood counts. Additionally, hematopoietic restoration capacity following cytotoxic stress was tested.

Mice with polymorphisms in ND4 and CYTB gene had significantly decreasing ROS levels in bone marrow cells during aging, without effecting ATP levels. In addition, the frequency of stem and progenitor cells increased during aging but the amount of lymphocytes in the peripheral blood decreased during aging.

In summary, the presence of mtDNA polymorphisms affecting the respiratory chain complexes I, III and IV was associated with altered ROS levels as well as changes in BM and peripheral blood composition during aging.

Testosterone modulates FoxO3a and p53-related genes to protect C2C12 skeletal muscle cells against apoptosis

The loss of muscle mass and strength with aging, sarcopenia, is a prevalent condition among the elderly, associated with skeletal muscle dysfunction and enhanced muscle cell apoptosis. We have previously demonstrated that testosterone protects against H₂O₂-induced apoptosis in C2C12 muscle cells, at different levels: morphological, biochemical and molecular. Since we have observed that testosterone reduces p-p53 and maintains the inactive state of FoxO3a transcription factor, induced by H₂O₂, we analyzed if the hormone was exerting its antiapoptotic effect at transcriptional level, by modulating pro and antiapoptotic genes associated to them. We detected the upregulation of the proapoptotic genes Puma, PERP and Bim, and MDM2 in response to H₂O₂ at different periods of the apoptotic process, and the downregulation of the antiapoptotic gene Bcl-2, whereas testosterone was able to modulate and counteract H₂O₂ effects. Furthermore, ERK and JNK kinases have been demonstrated to be linked to FoxO3a phosphorylation and thus its subcellular distribution. This work show some transcription level components, upstream of the classical apoptotic pathway, that are activated during oxidative stress and that are points where testosterone exerts its protective action against apoptosis, exposing some of the puzzle pieces of the intricate network that aged skeletal muscle apoptosis represents.

Non-linear actions of physiological agents: Finite disarrangements elicit fitness benefits

Finite disarrangements of important (vital) physiological agents and nutrients can induce plethora of beneficial effects, exceeding mere attenuation of the specific stress. Such response to disrupted homeostasis appears to be universally conserved among species. The underlying mechanism of improved fitness and longevity, when physiological agents act outside their normal range is similar to hormesis, a phenomenon whereby toxins elicit beneficial effects at low doses. Due to similarity with such non-linear response to toxins described with J-shaped curve, we have coined a new term “mirror J-shaped curves” for non-linear response to finite disarrangement of physiological agents. Examples from the clinical trials and basic research are provided, along with the unifying mechanisms that tie classical non-linear response to toxins with the non-linear response to physiological agents (glucose, oxygen, osmolarity, thermal energy, calcium, body mass, calorie intake and exercise). Reactive oxygen species and cytosolic calcium seem to be common triggers of signaling pathways that result in these beneficial effects. Awareness of such phenomena and exploring underlying mechanisms can help physicians in their everyday practice. It can also benefit researchers when designing studies and interpreting growing number of scientific data showing non-linear responses to physiological agents.

The protective mechanism of quercetin-3-O-β-D-glucuronopyranoside (QGC) in H2O2-induced injury of feline esophageal epithelial cells

Quercetin-3-O-β-D-glucuronopyranoside (QGC) is a flavonoid glucoside extracted from Rumex Aquaticus. Recent studies have shown that QGC exhibits anti-inflammatory, anti-oxidateve effect in vivo and cytoprotective effect in vitro. Reactive oxygen species (ROS), at low concentration, play role as a primary signal or second messenger, however, at high concentration, ROS are cytotoxic. In this study, we investigated the protective mechanism of QGC in H2O2-induced injury of Feline Esophageal Epithelial Cells. Primary-cultured feline esophagus cells were identified by an indirect immunofluorescent staining method using a cytokeratin monoclonal antibody. Cell viability was determined by the conventional MTT reduction assay. Western blot analysis was performed with specific antibodies to investigate the activation of MAPKs, NF-κB, and IκB-α, and the expression of COX-2. When the cells were exposed to 600 μM H2O2 medium for 24 h, cell viability decreased to 54 %. However, when cells were pretreated with 50-150 μM QGC for 12 h, the viability of cells exposed to H2O2 significantly increased in the dose dependent manner. QGC (50 μM, 12 h) also inhibited the expression of COX-2 induced by 10 μM H2O2 for 24 h. We found that treatment of H2O2 activated p38 MAPK and JNK, but not ERK. However QGC inhibited the H2O2-induced p38 MAPK and JNK phosphorylation. In addition, NF-κB was activated by H2O2 and translocated into the nucleus, but QGC inhibited the activation of NF-κB by blocking degradation of IκB. These data suggest that QGC reduces H2O2-induced COX-2 production by modulating the p38 MAPK, JNK, NF-κB signal pathway in feline esophageal epithelial cells.

HIF-1α induction, proliferation and glycolysis of Theileria-infected leukocytes

Within 2 h of infection by Theileria annulata sporozoites, bovine macrophages display a two- to fourfold increase in transcription of hypoxia inducible factor (HIF-1α). Twenty hours post-invasion sporozoites develop into multi-nucleated macroschizonts that transform the infected macrophage into an immortalized, permanently proliferating, hyper-invasive and disease-causing leukaemia-like cell. Once immortalized Theileria-infected leukocytes can be propagated as cell lines and even though cultivated under normoxic conditions, both infected B cells and macrophages display sustained activation of HIF-1α. Attenuated macrophages used as live vaccines against tropical theileriosis also display HIF-1α activation even though they have lost their tumorigenic phenotype. Here, we review data that ascribes HIF-1α activation to the proliferation status of the infected leukocyte and discuss the possibility that Theileria may have lost its ability to render its host macrophage virulent due to continuous parasite replication in a high Reactive Oxygen Species (ROS) environment. We propose a model where uninfected macrophages have low levels of H2 O2 output, whereas virulent-infected macrophages produce high amounts of H2 O2 . Further increase in H2 O2 output leads to dampening of infected macrophage virulence, a characteristic of disease-resistant macrophages. At the same time exposure to H2 O2 sustains HIF-1α that induces the switch from mitochondrial oxidative phosphorylation to Warburg glycolysis, a metabolic shift that underpins uncontrolled infected macrophage proliferation. We propose that as macroschizonts develop into merozoites and infected macrophage proliferation arrests, HIF-1α levels will decrease and glycolysis will switch back from Warburg to oxidative glycolysis. As Theileria infection transforms its host leukocyte into an aggressive leukaemic-like cell, we propose that manipulating ROS levels, HIF-1α induction and oxidative over Warburg glycolysis could contribute to improved disease control. Finally, as excess amounts of H2 O2 drive virulent Theileria-infected macrophages towards attenuation it highlights how infection-induced pathology and redox balance are intimately linked.

A fullerene colloidal suspension stimulates the growth and denitrification ability of wastewater treatment sludge-derived bacteria

Fullerene (C60) is a nanoparticle that has been widely studied and applied in numerous commodities. However, there are concerns regarding its potential negative impact on the environment. A fullerene colloidal suspension (nC60) is known for its property of selectively inhibiting the growth of microorganisms. In this study, using denaturing gradient gel electrophoresis fingerprinting technology, we found that fullerene altered the structure of a sludge-derived microbial community. Specifically, the bacteria from Bacillus, Acidovorax and Cloacibacterium genera were enriched in abundance when supplemented with nC60 at pH 6.5 under aerobic conditions. The effects of the fullerene colloidal suspension on a strain of Bacillus isolated from the same microbial community were evaluated to further characterize the growth-stimulating effect of nC60. The biomass of cultures of this strain incubated with nC60 concentrations ranging from 3 mg L(-1) to 7 mg L(-1) was approximately twice that of the control during the stationary phase. The fullerene also induced higher superoxide dismutase activity in Bacillus cereus. Furthermore, the nitrate removal rate of B. cereus increased to nearly 55% in the presence of 5 mg L(-1) nC60, compared to 35% for the control. Meanwhile, the cumulative loading amount of nitrite was reduced from 33 μg mL(-1) to 25 μg mL(-1) by the addition of 5 mg L(-1) nC60. Our results demonstrate that the fullerene colloidal suspension is conditionally capable of promoting the growth and denitrification metabolism of certain bacteria, such as B. cereus. Fullerene might have both inhibitory and stimulatory effects on microorganisms in various environments.

Protective role of peroxisome proliferator-activated receptor β/δ in acute lung injury induced by prolonged hyperbaric hyperoxia in rats

Peroxisome proliferator-activated receptor (PPAR)-β/δ is a transcription factor that belongs to the PPAR family, but the role of PPAR-β/δ in acute lung injury (ALI) induced by hyperbaric oxygen is unknown. In this study we investigated if PPAR-β/δ activation protects from hyperoxia-induced ALI in a rat model. ALI was induced by prolonged hyperbaric oxygen (HBO2) (2.3ATA, 100% O2) for 8h. Administration of PPAR-β/δ agonist GW0742 (0.3mg/kg, i.p.) at 1 and 6h prior to HBO2 exposure significantly reduced the (1) lung injury, (2) proinflammatory cytokines (TNF-α, IL-1β, IL-6), (3) apoptosis (Bax/Bcl-2, cleaved-caspase-3 and TUNEL), (4) nuclear factor (NF)-κB expression level and DNA binding activity in the nucleus, and (5) extracellular signal-regulated kinase (ERK)1/2 phosphorylation and markedly elevated (6) superoxide dismutase and glutathione peroxidase activities as well as (7) IκB expression. However, administration of the PPAR-β/δ antagonist GSK0660 abolished these protective effects. These findings indicate that activation of PPAR-β/δ ameliorates hyperoxia-induced ALI in rats by up-regulating antioxidant enzyme activity as well as suppressing inflammation and apoptosis.

Phospholipase D participates in H(2)O(2)-induced A549 alveolar epithelial cell migration

To investigate the effects of phospholipase D (PLD) on low-concentration hydrogen peroxide (H(2)O(2))-induced growth and migration in alveolar epithelial A549 cells, the cells were exposed to H(2)O(2) (3-100 μM) for 12-48 hours, cell proliferation was determined by MTT assay and cell migration was tested by a modified epithelial wound healing assay. We found that one bolus of H(2)O(2) (10-100 μM) did not affect proliferation, but significantly stimulated migration (143-161% of control) after a 12-hour exposure. Pretreatment with the antioxidants catalase (1000 U/ml), N-acetyl-cysteine (2 mM), or edaravone (10 μM) abolished the migration induced by 30 μM H(2)O(2); the PLD inhibitor 1-butanol (0.5%) also attenuated H(2)O(2)-induced migration to the control level; while exogenous phosphatidic acid (PA) (10(-7)-10(-4) M) mimicked the effects of PLD activation and induced migration in a dose-dependent manner. We suggest that the alveolar epithelial cell migration induced by exposure to low concentrations of H(2)O(2) benefits tissue repair during acute lung injury (ALI) and PLD is involved in the underlying mechanism.

Neutrophils augment LPS-mediated pro-inflammatory signaling in human lung epithelial cells

BACKGROUND

The role of polymorphonuclear neutrophils in pulmonary host defense is well recognized. The influence of a pre-existing inflammation driven by neutrophils (neutrophilic inflammation) on the airway epithelial response toward pro-inflammatory exogenous triggers, however, is still poorly addressed. Therefore, the aim of the present study is to investigate the effect of neutrophils on lipopolysaccharide (LPS)-induced pro-inflammatory signaling in lung epithelial cells. Additionally, underlying signaling pathways are examined.

METHODS

Human bronchial epithelial cells (BEAS-2B) were co-incubated with human peripheral blood neutrophils or bone-marrow derived neutrophils from either C57BL/6J wild type or nicotinamide adenine dinucleotide phosphate (NADPH)-oxidase deficient (p47(phox-/-)) mice. Upon stimulation with LPS, interleukin (IL)-8 production and reactive oxygen species (ROS) generation were measured. Additionally, activation of the extracellular signal-regulated kinases (ERK) 1/2 and nuclear factor (NF)-κB signaling pathways was analyzed.

RESULTS

Our studies show that the presence of neutrophils synergistically increases LPS-induced IL-8 and ROS production by BEAS-2B cells without inducing cytotoxicity. The observed IL-8 response to endotoxin increases in proportion to time, LPS-concentration and the number of neutrophils present. Moreover, this synergistic IL-8 production strongly correlated with the chemotactic properties of the co-incubations and significantly depended on a functional neutrophilic NADPH oxidase. The presence of neutrophils also augments LPS-induced phosphorylation of ERK1/2 and IκBα as well as NF-κB RelA DNA binding activity in BEAS-2B cells.

CONCLUSIONS

Our results indicate that the pro-inflammatory effects of LPS toward lung epithelial cells are amplified during a pre-existing neutrophilic inflammation. These findings support the concept that patients suffering from pulmonary neutrophilic inflammation are more susceptible toward exogenous pro-inflammatory triggers.

Testosterone exerts antiapoptotic effects against H2O2 in C2C12 skeletal muscle cells through the apoptotic intrinsic pathway

Experimental data indicate that apoptosis is activated in the aged skeletal muscle, contributing to sarcopenia. We have previously demonstrated that testosterone protects against hydrogen peroxide (H(2)O(2))-induced apoptosis in C2C12 muscle cells. Here we identified molecular events involved in the antiapoptotic effect of testosterone. At short times of exposure to H(2)O(2) cells exhibit a defense response but at longer treatment times cells undergo apoptosis. Incubation with testosterone prior to H(2)O(2) induces BAD inactivation, inhibition of poly(ADP-ribose) polymerase cleavage, and a decrease in BAX levels, and impedes the loss of mitochondrial membrane potential, suggesting that the hormone participates in the regulation of the apoptotic intrinsic pathway. Simultaneous treatment with testosterone, H(2)O(2), and the androgen receptor (AR) antagonist, flutamide, reduces the effects of the hormone, pointing to a possible participation of the AR in the antiapoptotic effect. The data presented allow us to begin to elucidate the mechanism by which the hormone prevents apoptosis in skeletal muscle.

Regulation of reactive oxygen species generation in cell signaling

Reactive oxygen species (ROS) including superoxide anion and hydrogen peroxide (H(2)O(2)) are thought to be byproducts of aerobic respiration with damaging effects on DNA, protein, and lipid. A growing body of evidence indicates, however, that ROS are involved in the maintenance of redox homeostasis and various cellular signaling pathways. ROS are generated from diverse sources including mitochondrial respiratory chain, enzymatic activation of cytochrome p450, and NADPH oxidases further suggesting involvement in a complex array of cellular processes. This review summarizes the production and function of ROS. In particular, how cytosolic and membrane proteins regulate ROS generation for intracellular redox signaling will be detailed.

Dimerumic acid inhibits SW620 cell invasion by attenuating H₂O₂-mediated MMP-7 expression via JNK/C-Jun and ERK/C-Fos activation in an AP-1-dependent manner

Reactive oxygen species (ROS) such as hydrogen peroxide (H₂O₂) in the tumor microenvironment play important roles in tumor invasion and metastasis. Recently, ROS have been reported to cause a significant increase in the production and expression of matrix metalloproteinase (MMP)-7, which is closely correlated with metastatic colorectal cancer. The present study was undertaken to evaluate the scavenging activity of dimerumic acid (DMA) for H₂O₂ isolated from Monascus-fermented rice to investigate the inhibitory effects of DMA on the invasive potential of SW620 human colon cancer cells, and to explore the mechanisms underlying both these phenomena. Our results showed that increased MMP-7 expression due to H₂O₂ exposure was mediated by activation of mitogen-activated protein kinases (MAPKs) such as Jun N-terminal kinase (JNK), extracellular-regulated kinase (ERK), and p38 kinase. DMA pretreatment suppressed activation of H₂O₂-mediated MAPK pathways and cell invasion. Moreover, H₂O₂-triggered MMP-7 production was demonstrated via JNK/c-Jun and ERK/c-Fos activation in an activating protein 1 (AP-1)-dependent manner. Taken together, these results suggest that DMA suppresses H₂O₂-induced cell invasion by inhibiting AP-1-mediated MMP-7 gene transcription via the JNK/c-Jun and ERK/c-Fos signaling pathways in SW620 human colon cancer cells. Our data suggest that DMA may be useful in minimizing the development of colorectal metastasis. In the future, DMA supplementation may be a beneficial antioxidant to enhance surgical outcomes.

Selenomethionine increases proliferation and reduces apoptosis in bovine mammary epithelial cells under oxidative stress

The decline in mammary epithelial cell number as lactation progresses may be due, in part, to oxidative stress. Selenium is an integral component of several antioxidant enzymes. The present study was conducted to examine the effect of oxidative stress and selenomethionine (SeMet) on morphology, viability, apoptosis, and proliferation of bovine mammary epithelial cells (BMEC) in primary culture. Cells were isolated from mammary glands of lactating dairy cows and grown for 3 d in a low-serum gel system containing lactogenic hormones and 0 or 100 μM H2O2 with 0, 10, 20, or 50 nM SeMet. Hydrogen peroxide stress increased intracellular H2O2 to 3 times control concentrations and induced a loss of cuboidal morphology, cell-cell contact, and viability of BMEC by 25%. Apoptotic cell number more than doubled during oxidative stress, but proliferating cell number was not affected. Supplementation with SeMet increased glutathione peroxidase activity 2-fold and restored intracellular H2O2 to control levels with a concomitant return of morphology and viability to normal. Apoptotic BMEC number was decreased 76% below control levels by SeMet and proliferating cell number was increased 4.2-fold. These findings suggest that SeMet modulated apoptosis and proliferation independently of a selenoprotein-mediated reduction of H2O2. In conclusion, SeMet supplementation protects BMEC from H2O2-induced apoptosis and increased proliferation and cell viability under conditions of oxidative stress.

Oxidative stress: a required condition for thyroid cell proliferation

Goiter is associated with increased oxidative stress (OS). We studied the effects of an anti-inflammatory agent, 15 deoxy-Delta12,14-prostaglandin J2 (15dPGJ2) and an antioxidant, N-acetylcysteine (NAC), on OS, thyroid function, and goiter expansion in a model of goiter induced by propylthiouracil (PTU) or perchlorate. OS was assessed by the immunodetection of 4-hydroxynonenal, thyroid function by measuring thyroxin (T4) and thyrotropin (TSH) plasma levels and detecting T4-rich thyroglobulin (Tg-I), and goiter expansion by weighing the thyroids and measuring cell proliferation (PCNA and cyclin D1 immunodetection). In both PTU and perchlorate-induced goiters, OS, TSH plasma levels, thyroid weight, and cell proliferation were strongly enhanced, whereas Tg-I expression was negative. All these parameters were reversed by NAC and 15dPGJ2 in PTU-goiters. In perchlorate-goiters, TSH plasma levels remained elevated and Tg-I-negative after NAC or 15dPGJ2 treatment. OS was reduced by NAC, but not by 15dPGJ2. In addition, NAC reduced PCNA and cyclin D1 immunostainings, as well as thyroid weight, whereas 15dPGJ2 influenced neither thyroid weight nor cell proliferation. In conclusion, NAC and 15dPGJ2 overcome PTU- but not perchlorate-induced effects. The retrieval of hormonal synthesis may result from direct chemical interactions between PTU and NAC/15dPGJ2. Although 15dPGJ2 has no effect in perchlorate-goiters, the reduction of OS by NAC is associated with altered goiter development, making OS a required condition for the growth of the thyroid gland.

Effect of dihydrotestosterone on mouse embryonic stem cells exposed to H2O2-induced oxidative stress

Oxidative stresses induced by reactive oxygen species (ROS) have been shown to be involved in several physiological and pathophysiological processes, such as cell proliferation and differentiation. Steroid hormones can protect cells against apoptosis or induce cell proliferation by several mechanisms. Among androgenic hormones, dihydrotestosterone (DHT) is generated by a 5alpha- reduction of testosterone. Unlike testosterone, DHT cannot be aromatized to estradiol, therefore DHT is considered a pure androgenic steroid. This study was conducted to examine the effect of DHT (10(-7) M) on H2O2 (10(-3) M) -induced injuries in mouse embryonic stem (ES) cells. H2O2 induced ROS generation and increased lipid peroxide formation and DNA fragmentation. These effects of H2O2 were inhibited by pretreatment with DHT. H2O2 also increased the phosphorylation of p38 MAPK, SAPK/JNK and nuclear factor kappa B (NF-kappaB), but DHT blocked these effects. Moreover, H2O2 decreased DNA synthesis and the levels of cell cycle regulatory proteins [cyclin D1, cyclin E, cyclin-dependent kinase (CDK) 2, and CDK 4]. These effects of H2O2 were inhibited by pretreatment with DHT. In conclusion, DHT may partially prevent H2O2-induced cell injury through inhibition of ROS and ROS-induced activation of p38 MAPK, SAPK/JNK and NF-kappaB in mouse ES cells.

Mitochondrial AIF protein involved in skeletal muscle regeneration

The mitochondrial flavoprotein apoptosis-inducing factor (AIF) has proved to be either the main mediator of apoptosis or an anti-apoptotic factor via its putative oxidoreductase and peroxide scavenging activities. We report here that 100 muM hydrogen peroxide (H2O2) induced the proliferation of C2C12 myoblasts and over-expression of AIF simultaneously in vitro. Immunofluorescence showed that the over-expression of AIF was located in the cytoplasm. The immunopositive AIF was detected in nuclei 27 days after denervation of skeletal muscle, but in the cytoplasm it was detected 27 days after fiber-damaged skeletal muscle. AIF may be a factor involved in skeletal muscle regeneration.

Replicative senescence induced by Romo1-derived reactive oxygen species

Persistent accumulation of DNA damage induced by reactive oxygen species (ROS) is proposed to be a major contributor toward the aging process. Furthermore, an increase in age-associated ROS is strongly correlated with aging in various species, including humans. Here we showed that the enforced expression of the ROS modulator 1 (Romo1) triggered premature senescence by ROS production, and this also contributed toward induction of DNA damage. Romo1-derived ROS was found to originate in the mitochondrial electron transport chain. Romo1 expression gradually increased in proportion to population doublings of IMR-90 human fibroblasts. An increase in ROS production in these cells with high population doubling was blocked by the Romo1 knockdown using Romo1 small interfering RNA. Romo1 knockdown also inhibited the progression of replicative senescence. Based on these results, we suggest that age-related ROS levels increase, and this contributes to replicative senescence, which is directly associated with Romo1 expression.

Role of p38 mitogen-activated protein kinase in ozone-induced airway hyperresponsiveness and inflammation

Ozone is a potent oxidant and causes airway hyperresponsiveness and neutrophilia. To determine the role of p38 mitogen-activated protein kinase (MAPK) activation, we studied the effect of a p38alpha inhibitor SD-282 (Scios Inc, Fremont, CA USA) on ozone-induced airway hyperresponsiveness and neutrophilia. Balb/c mice received SD-282 (30 or 90 mg/kg i.p) or vehicle 1 h before exposure to either ozone (3 ppm, 3 h) or air. Three hours after exposure, lungs were analysed for cytokine levels and bronchoalveolar lavage was performed. Another set of mice were dosed 6 h after exposure and 1 h before assessing airway hyperresponsiveness. SD-282 (90 mg/kg) significantly inhibited ozone-induced airway hyperresponsiveness (-LogPC(150): SD-282: -1.73+/-0.14 vs. vehicle: -0.99+/-0.15, P<0.05). Bronchoalveolar lavage neutrophil numbers were time-dependently increased in vehicle-dosed, ozone-exposed mice, greatest at 20-24 h after exposure. SD-282 (30 and 90 mg/kg) significantly inhibited ozone induced neutrophil numbers at 3 h and 20-24 h after ozone SD-282 significantly inhibited ozone-induced increases in phosphorylated p38 MAPK expression, and in cyclooxygenase-2 (COX-2), interleukin-6 (IL-6) and IL-1beta but not MIP-1alpha gene expression. We conclude that p38 MAPK is involved in ozone-induced airway hyperresponsiveness and lung neutrophilia. Inhibition of p38 MAPK with small molecule kinase inhibitors may be a means of reducing ozone-induced inflammation and airway hyperresponsiveness.

A critical role for Romo1-derived ROS in cell proliferation

Low levels of endogenous reactive oxygen species (ROS) originating from NADPH oxidase have been implicated in various signaling pathways induced by growth factors and mediated by cytokines. However, the main source of ROS is known to be the mitochondria, and increased levels of ROS from the mitochondria have been observed in many cancer cells. Thus far, the mechanism of ROS production in cancer cell proliferation in the mitochondria is not well-understood. We recently identified a novel protein, ROS modulator 1 (Romo1), and reported that increased expression of Romo1-triggered ROS production in the mitochondria. The experiments conducted in the present study showed that Romo1-derived ROS were indispensable for the proliferation of both normal and cancer cells. Furthermore, whilst cell growth was inhibited by blocking the ERK pathway in cells transfected with siRNA directed against Romo1, the cell growth was recovered by addition of exogenous hydrogen peroxide. The results of this study suggest that Romo1-induced ROS may play an important role in redox signaling in cancer cells.

Hydrogen peroxide inhibits caspase-dependent apoptosis by inactivating procaspase-9 in an iron-dependent manner

Apoptosis represents a physiological form of cell death, the perturbation of which may contribute to the development of several diseases connected with accumulation of unwanted cells or excessive cell loss. We have previously shown that the continuous presence of low concentrations of H2O2 (generated by the action of glucose oxidase) was able to inhibit caspase-mediated apoptosis in Jurkat cells. The main purpose of the present study was to elucidate the exact molecular mechanism(s) underlying this inhibitory action of H2O2. The results presented show that events like outer mitochondrial membrane permeabilization, release of cytochrome c from mitochondria, oligomerization of Apaf-1, and recruitment of procaspase-9 to apoptosomes were taking place normally, but further advancement toward activation of the execution caspases was interrupted when H2O2 was present during the apoptotic process. From the results presented in this work, it emerges that the inhibition of procaspase-9 autoactivation was probably due to the reversible oxidation of sensitive cysteine residues in this molecule. Remarkably, caspase-9 activation and the ensuing caspase cascade proceeded normally in the presence of H2O2 under conditions of iron deprivation, indicating that the inhibition of procaspase-9 activation was an iron-dependent process. Collectively, these results highlighted the potential role of available intracellular iron ions in signaling mechanisms related to apoptotic cell death.

Hypoxia divergently regulates production of reactive oxygen species in human pulmonary and coronary artery smooth muscle cells

Acute hypoxia causes pulmonary vasoconstriction and coronary vasodilation. The divergent effects of hypoxia on pulmonary and coronary vascular smooth muscle cells suggest that the mechanisms involved in oxygen sensing and downstream effectors are different in these two types of cells. Since production of reactive oxygen species (ROS) is regulated by oxygen tension, ROS have been hypothesized to be a signaling mechanism in hypoxia-induced pulmonary vasoconstriction and vascular remodeling. Furthermore, an increased ROS production is also implicated in arteriosclerosis. In this study, we determined and compared the effects of hypoxia on ROS levels in human pulmonary arterial smooth muscle cells (PASMC) and coronary arterial smooth muscle cells (CASMC). Our results indicated that acute exposure to hypoxia (Po(2) = 25-30 mmHg for 5-10 min) significantly and rapidly decreased ROS levels in both PASMC and CASMC. However, chronic exposure to hypoxia (Po(2) = 30 mmHg for 48 h) markedly increased ROS levels in PASMC, but decreased ROS production in CASMC. Furthermore, chronic treatment with endothelin-1, a potent vasoconstrictor and mitogen, caused a significant increase in ROS production in both PASMC and CASMC. The inhibitory effect of acute hypoxia on ROS production in PASMC was also accelerated in cells chronically treated with endothelin-1. While the decreased ROS in PASMC and CASMC after acute exposure to hypoxia may reflect the lower level of oxygen substrate available for ROS production, the increased ROS production in PASMC during chronic hypoxia may reflect a pathophysiological response unique to the pulmonary vasculature that contributes to the development of pulmonary vascular remodeling in patients with hypoxia-associated pulmonary hypertension.

Relationship between redox activity and chemical speciation of size-fractionated particulate matter

BACKGROUND

Although the mechanisms of airborne particulate matter (PM) related health effects remain incompletely understood, one emerging hypothesis is that these adverse effects derive from oxidative stress, initiated by the formation of reactive oxygen species (ROS) within affected cells. Typically, ROS are formed in cells through the reduction of oxygen by biological reducing agents, with the catalytic assistance of electron transfer enzymes and redox active chemical species such as redox active organic chemicals and metals. The purpose of this study was to relate the electron transfer ability, or redox activity, of the PM samples to their content in polycyclic aromatic hydrocarbons and various inorganic species. The redox activity of the samples has been shown to correlate with the induction of the stress protein, hemeoxygenase-1.

RESULTS

Size-fractionated (i.e. < 0.15; < 2.5 and 2.5 - 10 microm in diameter) ambient PM samples were collected from four different locations in the period from June 2003 to July 2005, and were chemically analyzed for elemental and organic carbon, ions, elements and trace metals and polycyclic aromatic hydrocarbons. The redox activity of the samples was evaluated by means of the dithiothreitol activity assay and was related to their chemical speciation by means of correlation analysis. Our analysis indicated a higher redox activity on a per PM mass basis for ultrafine (< 0.15 microm) particles compared to those of larger sizes. The PM redox activity was highly correlated with the organic carbon (OC) content of PM as well as the mass fractions of species such as polycyclic aromatic hydrocarbons (PAH), and selected metals.

CONCLUSION

The results of this work demonstrate the utility of the dithiothreitol assay for quantitatively assessing the redox potential of airborne particulate matter from a wide range of sources. Studies to characterize the redox activity of PM from various sources throughout the Los Angeles basin are currently underway.

Hyperoxia-induced signal transduction pathways in pulmonary epithelial cells

Mechanical ventilation with hyperoxia is necessary to treat critically ill patients. However, prolonged exposure to hyperoxia leads to the generation of excessive reactive oxygen species (ROS), which can cause acute inflammatory lung injury. One of the major effects of hyperoxia is the injury and death of pulmonary epithelium, which is accompanied by increased levels of pulmonary proinflammatory cytokines and excessive leukocyte infiltration. A thorough understanding of the signaling pathways leading to pulmonary epithelial cell injury/death may provide some insights into the pathogenesis of hyperoxia-induced acute inflammatory lung injury. This review focuses on epithelial responses to hyperoxia and some of the major factors regulating pathways to epithelial cell injury/death, and proinflammatory responses on exposure to hyperoxia. We discuss in detail some of the most interesting players, such as NF-kappaB, that can modulate both proinflammatory responses and cell injury/death of lung epithelial cells. A better appreciation for the functions of these factors will no doubt help us to delineate the pathways to hyperoxic cell death and proinflammatory responses.

Homocysteine induces mesangial cell apoptosis via activation of p38-mitogen-activated protein kinase

Hyperhomocysteinemia is prevalent among patients with chronic kidney disease (CKD) and has been linked to progressive kidney and vascular diseases. Increased glomerular mesangial cell (MC) turnover, including proliferation and apoptosis, is a hallmark of CKD. Activation of p38-mitogen-activated protein kinase (p38-MAPK) has been linked to apoptosis in many cell lines. Accordingly, we studied the effect of homocysteine (Hcy) on MC p38-MAPK signalling and apoptosis. Hcy (50 microM/24 h) increased MC apoptosis as determined by terminal deoxynucleotidyl transferase-mediated deoxyuridine triphosphate (dUTP) nick end labelling (TUNEL) and single-stranded DNA (ssDNA) analysis. In addition to increases in pro-caspase-3 protein and caspase-3 activity, cells exposed to Hcy manifested enhanced reactive oxygen species content. Hcy increased p38-MAPK activity (fivefold), with maximal effect at 50 microM and 20 min; p38-MAPK activation was attenuated by N-acetylcysteine (Nac) and catalase (Cat), further indicating that the effect was via oxidative stress. Confocal microscopy revealed activation and nuclear translocation of p38-MAPK that was attenuated by Cat. In addition, Hcy-induced apoptosis as determined by TUNEL and ssDNA assay was abrogated by Nac, Cat, and SB203580 (p38-MAPK inhibitor). We conclude that in MC, Hcy (i) activates p38-MAPK and increases p38MAPK nuclear translocation via an oxidative stress dependent mechanism and (ii) induces DNA damage and apoptosis that is dependent on oxidative stress and p38-MAPK activation.

Mitochondrial aldehyde dehydrogenase attenuates hyperoxia-induced cell death through activation of ERK/MAPK and PI3K-Akt pathways in lung epithelial cells

Oxygen toxicity is one of the major risk factors in the development of the chronic lung disease or bronchopulmonary dysplasia in premature infants. Using proteomic analysis, we discovered that mitochondrial aldehyde dehydrogenase (mtALDH or ALDH2) was downregulated in neonatal rat lung after hyperoxic exposure. To study the role of mtALDH in hyperoxic lung injury, we overexpressed mtALDH in human lung epithelial cells (A549) and found that mtALDH significantly reduced hyperoxia-induced cell death. Compared with control cells (Neo-A549), the necrotic cell death in mtALDH-overexpressing cells (mtALDH-A549) decreased from 25.3 to 6.5%, 50.5 to 9.1%, and 52.4 to 15.1% after 24-, 48-, and 72-h hyperoxic exposure, respectively. The levels of intracellular and mitochondria-derived reactive oxygen species (ROS) in mtALDH-A549 cells after hyperoxic exposure were significantly lowered compared with Neo-A549 cells. mtALDH overexpression significantly stimulated extracellular signal-regulated kinase (ERK) phosphorylation under normoxic and hyperoxic conditions. Inhibition of ERK phosphorylation partially eliminated the protective effect of mtALDH in hyperoxia-induced cell death, suggesting ERK activation by mtALDH conferred cellular resistance to hyperoxia. mtALDH overexpression augmented Akt phosphorylation and maintained the total Akt level in mtALDH-A549 cells under normoxic and hyperoxic conditions. Inhibition of phosphatidylinositol 3-kinase (PI3K) activation by LY294002 in mtALDH-A549 cells significantly increased necrotic cell death after hyperoxic exposure, indicating that PI3K-Akt activation by mtALDH played an important role in cell survival after hyperoxia. Taken together, these data demonstrate that mtALDH overexpression attenuates hyperoxia-induced cell death in lung epithelial cells through reduction of ROS, activation of ERK/MAPK, and PI3K-Akt cell survival signaling pathways.

Current concepts of redox signaling in the lungs

In the intracellular redox state (GSH/GSSG) the cell plays a key role in the regulation and potentiation of the inflammatory response in lung cells. Glutathione and thioredoxin are the important protective antioxidants in the lungs. Regulation of intracellular redox glutathione and thioredoxin levels in response to reactive oxygen/nitrogen species and in inflammation should have critical effects on different lung cells on the activation of redox sensor/signal transduction pathways and various transcription factors. Possibly via the modification of cysteine residues, oxidative stress activates multiple stress kinase pathways and transcription factors nuclear factor-kappaB and activator protein-1, which differentially regulate the genes for proinflammatory cytokines as well as the protective antioxidant genes. Emerging data suggest that protein-S-thiolation, protein-S-nitrosation, and oxidation of protein-SH (formation of sulfenic, sulfinic, and sulfonic acids) are critical in redox signaling during normal physiology and under oxidative stress in controlling the cellular processes. In this review, we discuss the recent findings in the context of redox signaling during inflammation, pathology, and the role of redox modulating agents/dietary interventions either to inhibit abnormal signaling or induce/boost the endogenous antioxidant systems. Furthermore, this also provides information as to how antioxidants are involved in redox signaling to control inflammatory and oxidative stress in the lung.

Insulin and oxidative stress modulate proliferation of rat ovarian theca-interstitial cells through diverse signal transduction pathways

Insulin and moderate oxidative stress stimulate proliferation of ovarian theca-interstitial cells. The effects of these agents on selected signal transduction pathways were examined. PD98059 (inhibitor of MAP2K1, also known as MEK-1, upstream of extracellular signal-regulated protein kinases MAPK3/1, also known as ERK1/2), wortmannin (inhibitor of PIK3C2A, also known as PI3K), and rapamycin (inhibitor of FRAP1, also known as mTOR, upstream of RPS6KB1) each significantly decreased insulin and oxidative stress-induced proliferation of theca-interstitial cells. The greatest inhibition was observed in the presence of rapamycin; this effect occurred without a significant change in cell viability. Phosphorylation of AKT was stimulated by insulin only, while phosphorylation of MAPK3/1 and RPS6KB1 was increased by insulin and oxidative stress. Insulin-induced and oxidative stress-induced phosphorylation of RPS6KB1 was partly inhibited by wortmannin and partly by PD98059; the greatest inhibition was observed in the presence of a combination of wortmannin plus PD98059. Effects of insulin and oxidative stress on phosphorylation of RPS6KB1 were confirmed by kinase activity assays. These findings indicate that actions of insulin and oxidative stress converge on MAPK3/1 and RPS6KB1. Furthermore, we speculate that activation of RPS6KB1 may be in part induced via the MAPK3/1 pathway.

Intracellular Signaling Pathways Involved in the Cell Growth Inhibition of Glioma Cells by Melatonin

Melatonin is an indolamine mostly produced in the pineal gland, soluble in water, and highly lipophilic, which allows it to readily cross the blood-brain barrier. Melatonin possesses antioxidant properties and its long-term administration in rodents has not been found to cause noteworthy side effects. In the present work, we found that millimolar concentrations of this indolamine reduced cell growth of C6 glioma cells by 70% after 72 hours of treatment, inhibiting cell progression from G(1) to S phase of the cell cycle. Intraperitoneal administration of 15 mg/kg body weight of melatonin to rats previously injected in the flank with C6 glioma cells reduces tumor growth by 50% 2 weeks after the implant. Inhibition of cell growth does not depend on melatonin membrane receptor activation whereas it seemingly relates to the reduction of intracellular basal free radical levels by 30%. Increase of basal redox state of the cells and constitutive activation of tyrosine kinase receptor [receptor tyrosine kinase (RTK)] pathways, including the extracellular signal-regulated kinase 1/2 (ERK1/2) and the Akt and protein kinase C (PKC) signaling pathways, contribute to the progression of the gliomas leading to the constitutive activation of the redox-dependent survival transcription factor nuclear factor kappaB (NF-kappaB). The antioxidant effect of melatonin in C6 cells is associated to inhibition of NF-kappaB and Akt, but not of ERK1/2. The antiproliferative effect of the indolamine on these cells is partially abolished when coincubated with the PKC activator 12-O-tetradecanoylphorbol-13-acetate, thus indicating that the ability of melatonin to change cellular redox state may be inactivating the pathway RTK/PKC/Akt/NF-kappaB.