Nitric oxide activation of Keap1/Nrf2 signaling in human colon carcinoma cells

A nitrogen dioxide delivery system for biological media

Nitrogen dioxide is formed endogenously via the oxidation of NO by O(2) or O(2)(-) and from NO(2)(-) via peroxidases, among other pathways. This radical has many potential biological targets and its concentration, like that of NO and other reactive nitrogen species, is thought to be elevated at sites of inflammation. To investigate the specific cytotoxic or mutagenic effects of NO(2), it is desirable to be able to maintain its concentration at constant, predictable, and physiological levels in cell cultures, in the absence of NO. To do this, a delivery system was constructed in which NO(2)-containing gas mixtures contact a liquid within a small (110 ml) stirred reactor. In such gas mixtures NO(2) is present in equilibrium with its dimer, N(2)O(4). The uptake of NO(2) and N(2)O(4) was characterized by measuring the accumulation rates of NO(2)(-) and NO(3)(-), the stable products of N(2)O(4) hydrolysis, in buffered aqueous solutions. In some experiments NO(2)-reactive 2,2'-azino-bis(3-ethyl-benzothiazoline-6-sulfonate) (ABTS) was included and formation of the stable ABTS radical was measured. A reaction-diffusion model was developed that predicts the accumulation rates of all three products to within 15% for gas-phase concentrations of NO(2) spanning 3 orders of magnitude. The model also provides estimates for the NO(2) concentration in the liquid. This system should be useful for exposing cells to NO(2) concentrations similar to those in vivo.

The chronic effects of low lead level on the expressions of Nrf2 and Mrp1 of the testes in the rats

Lead is linked to many reproductive problems. This study was to explore the chronic effects of low lead level on expressions of Nrf2 and Mrp1 in rats' testes. Maternal SD rats were administered lead acetate from 10 days before gestation to weaning at three doses respectively after randomization. From each group, 15 male offsprings were then chosen and administrated lead acetate from weaning to six months old at the doses of 0, 0.3 and 0.9g/L respectively. The dose administrations were through drinking water freely. The methods of RT-PCR, Western blotting and immunohistochemistry were used for Mrp1 and Nrf2 of the testes. Compared with control group, significant increases were observed in the expressions of Mrp1 and Nrf2 in two lead groups (P<0.05); nucleus translocation of Nrf2 was observed; both GST and GSH was decreased with increasing the lead dose. In conclusion, Mrp1 might play important roles in lead detoxification by Nrf2.

Quinone-induced activation of Keap1/Nrf2 signaling by aspirin prodrugs masquerading as nitric oxide

The promising therapeutic potential of the NO-donating hybrid aspirin prodrugs (NO-ASA) includes induction of chemopreventive mechanisms and has been reported in almost 100 publications. One example, NCX-4040 (pNO-ASA), is bioactivated by esterase to a quinone methide (QM) electrophile. In cell cultures, pNO-ASA and QM-donating X-ASA prodrugs that cannot release NO rapidly depleted intracellular GSH and caused DNA damage; however, induction of Nrf2 signaling elicited cellular defense mechanisms including upregulation of NAD(P)H:quinone oxidoreductase-1 (NQO1) and glutamate-cysteine ligase (GCL). In HepG2 cells, the "NO-specific" 4,5-diaminofluorescein reporter, DAF-DA, responded to NO-ASA and X-ASA, with QM-induced oxidative stress masquerading as NO. LC-MS/MS analysis demonstrated efficient alkylation of Cys residues of proteins including glutathione-S-transferase-P1 (GST-P1) and Kelch-like ECH-associated protein 1 (Keap1). Evidence was obtained for alkylation of Keap1 Cys residues associated with Nrf2 translocation to the nucleus, nuclear translocation of Nrf2, activation of antioxidant response element (ARE), and upregulation of cytoprotective target genes. At least in cell culture, pNO-ASA acts as a QM donor, bioactivated by cellular esterase activity to release salicylates, NO(3)(-), and an electrophilic QM. Finally, two novel aspirin prodrugs were synthesized, both potent activators of ARE, designed to release only the QM and salicylates on bioactivation. Current interest in electrophilic drugs acting via Nrf2 signaling suggests that QM-donating hybrid drugs can be designed as informative chemical probes in drug discovery.

Nitric oxide produced endogenously is responsible for hypoxia-induced HIF-1α stabilization in colon carcinoma cells

Hypoxia-inducible factor-1α (HIF-1α) is a critical regulator of cellular responses to hypoxia. Under normoxic conditions, the cellular HIF-1α level is regulated by hydroxylation by prolyl hydroxylases (PHDs), ubiquitylation, and proteasomal degradation. During hypoxia, degradation decreases, and its intracellular level is increased. Exogenously administered nitric oxide (NO)-donor drugs stabilize HIF-1α; thus, NO is suggested to mimic hypoxia. However, the role of low levels of endogenously produced NO generated during hypoxia in HIF-1α stabilization has not been defined. Here, we demonstrate that NO and reactive oxygen species (ROS) produced endogenously by human colon carcinoma HCT116 cells are responsible for HIF-1α accumulation in hypoxia. The antioxidant N-acetyl-L-cysteine (NAC) and NO synthase inhibitor N(G)-monomethyl L-arginine (L-NMMA) effectively reduced HIF-1α stabilization and decreased HIF-1α hydroxylation. These effects suggested that endogenous NO and ROS impaired PHD activity, which was confirmed by reversal of L-NMMA- and NAC-mediated effects in the presence of dimethyloxaloylglycine, a PHD inhibitor. Thiol reduction with dithiothreitol decreased HIF-1α stabilization in hypoxic cells, while dinitrochlorobenzene, which stabilizes S-nitrosothiols, favored its accumulation. This suggested that ROS- and NO-mediated HIF-1α stabilization involved S-nitrosation, which was confirmed by demonstrating increased S-nitrosation of PHD2 during hypoxia. Our results support a regulatory mechanism of HIF-1α during hypoxia in which endogenously generated NO and ROS promote inhibition of PHD2 activity, probably by its S-nitrosation.

Protective action of nipradilol mediated through S-nitrosylation of Keap1 and HO-1 induction in retinal ganglion cells

Nipradilol (Nip), which has α1- and β-adrenoceptor antagonist and nitric oxide (NO)-donating properties, has clinically been used as an anti-glaucomatous agent in Japan. NO mediates cellular signaling pathways that regulate physiological functions. The major signaling mechanisms mediated by NO are cGMP-dependent signaling and protein S-nitrosylation-dependent signalings. Nip has been described as having neuroprotective effects through cGMP-dependent pathway in retinal ganglion cells (RGCs). However, the effect seems to be partial. On the other hand, whether Nip can prevent cell death through S-nitrosylation is not yet clarified. In this study, we therefore focused on the neuroprotective mechanism of Nip through S-nitrosylation. Nip showed a dramatic neuroprotective effect against oxidative stress-induced death of RGC-5 cells. However, denitro-nipradilol, which does not have NO-donating properties, was not protective against oxidative stress. Furthermore, an NO scavenger significantly reversed the protective action of Nip against oxidative stress. In addition, we demonstrated that α1- or β-adrenoceptor antagonists (prazosin or timolol) did not show any neuroprotective effect against oxidative stress in RGC-5 cells. We also demonstrated that Nip induced the expression of the NO-dependent antioxidant enzyme, heme oxygenase-1 (HO-1). S-nitrosylation of Kelch-like ECH-associated protein by Nip was shown to contribute to the translocation of NF-E2-related factor 2 to the nucleus, and triggered transcriptional activation of HO-1. Furthermore, RGC death and levels of 4-hydroxy-2-nonenal (4HNE) were increased after optic nerve injury in vivo. Pretreatment with Nip significantly suppressed RGC death and accumulation of 4HNE after injury through an HO-1 activity-dependent mechanism. These data demonstrate a novel neuroprotective action of Nip against oxidative stress-induced RGC death in vitro and in vivo.

Nitric oxide, can it be only good? Increasing the antioxidant properties of nitric oxide in hepatocytes by YC-1 compound

The aim of the study was to evaluate the effect of Nitric oxide (NO) on redox changes and fat accumulation in hepatocytes. AML-12 hepatocytes were exposed to the NO donor Diethylenetriamine-NONOate (DETA-NO). DETA-NO led to a dose- and time-dependent increase in lipid accumulation in the cells, measured by Nile red fluorescence. Exposure of the cells to 1mM DETA-NO for 24h increased reactive oxygen species production, mainly peroxides. At the same time, NO induced elevation of reduced glutathione (GSH) and a mild activation of the antioxidant transcription factors Hypoxia-inducible factor 1α (HIF1α) and NF-E2 related factor 2 (Nrf-2). We used 100 μM YC-1 to inhibit HIF1α activity and induce activation of soluble Guanylate Cyclase (sGC). YC-1 alone did not affect fat accumulation, and only moderately increased the expression of Nrf-2-targeted genes Heme oxygenase 1 (Hmox1), NAD(P)H dehydrogenase (quinone 1) (Nqo1) and Glutathione S-transferase α1 (Gstα1). However, YC-1 abolished the negative effect of NO on fat accumulation when administered together. Strikingly, YC-1 potentiated the effect of NO on Nrf-2 activation, thus increasing dramatically the antioxidant properties of NO. Moreover, YC-1 intensified the effect of NO on the expression of peroxisome-proliferator-activated receptor-gamma co-activator 1α (PGC1α) and mitochondrial biogenesis markers. This study suggests that YC-1 may shift the deleterious effects of NO into the beneficial ones, and may improve the antioxidant properties of NO.

Established Principles and Emerging Concepts on the Interplay between Mitochondrial Physiology and S-(De)nitrosylation: Implications in Cancer and Neurodegeneration

S-nitrosylation is a posttranslational modification of cysteine residues that has been frequently indicated as potential molecular mechanism governing cell response upon redox unbalance downstream of nitric oxide (over)production. In the last years, increased levels of S-nitrosothiols (SNOs) have been tightly associated with the onset of nitroxidative stress-based pathologies (e.g., cancer and neurodegeneration), conditions in which alterations of mitochondrial homeostasis and activation of cellular processes dependent on it have been reported as well. In this paper we aim at summarizing the current knowledge of mitochondria-related proteins undergoing S-nitrosylation and how this redox modification might impact on mitochondrial functions, whose impairment has been correlated to tumorigenesis and neuronal cell death. In particular, emphasis will be given to the possible, but still neglected implication of denitrosylation reactions in the modulation of mitochondrial SNOs and how they can affect mitochondrion-related cellular process, such as oxidative phosphorylation, mitochondrial dynamics, and mitophagy.

Role of sulfiredoxin as a regulator of peroxiredoxin function and regulation of its expression

Peroxiredoxins (Prxs) constitute a family of peroxidases in which cysteine serves as the primary site of oxidation during the reduction of peroxides. Members of the 2-Cys Prx subfamily of Prxs (Prx I to IV in mammals) are inactivated via hyperoxidation of the active-site cysteine to sulfinic acid (Cys-SO(2)H) during catalysis and are reactivated via an ATP-consuming reaction catalyzed by sulfiredoxin (Srx). This reversible hyperoxidation reaction has been proposed to protect H(2)O(2) signaling molecules from premature removal by 2-Cys Prxs or to upregulate the chaperone function of these enzymes. In addition to its sulfinic acid reductase activity, Srx catalyzes the removal of glutathione (deglutathionylation) from modified proteins. The physiological relevance of both the reversible hyperoxidation of 2-Cys Prxs and the deglutathionylation catalyzed by Srx remains unclear. Recent findings have revealed that Srx expression is induced in mammalian cells under a variety of conditions, such as in metabolically stimulated pancreatic β cells, in immunostimulated macrophages, in neuronal cells engaged in synaptic communication, in lung cells exposed to hyperoxia or cigarette smoke, in hepatocytes of ethanol-fed animals, and in several types of cells exposed to chemopreventive agents. Such induction of Srx in mammalian cells is regulated at the transcriptional level, predominantly via activator protein-1 and/or nuclear factor erythroid 2-related factor 2. Srx expression is also regulated at the translational level in Saccharomyces cerevisiae.

Identification of UV-protective activators of nuclear factor erythroid-derived 2-related factor 2 (Nrf2) by combining a chemical library screen with computer-based virtual screening

Nuclear factor erythroid-derived 2-related factor 2 (Nrf2) is a master regulator of cellular antioxidant defense systems, and activation of this transcription factor is a promising strategy for protection of skin and other organs from environmental insults. To identify efficient Nrf2 activators in keratinocytes, we combined a chemical library screen with computer-based virtual screening. Among 14 novel Nrf2 activators, the most potent compound, a nitrophenyl derivative of 2-chloro-5-nitro-N-phenyl-benzamide, was characterized with regard to its molecular mechanism of action. This compound induced the expression of cytoprotective genes in keratinocytes isolated from wild-type but not from Nrf2-deficient mice. Most importantly, it showed low toxicity and protected primary human keratinocytes from UVB-induced cell death. Therefore, it represents a potential lead compound for the development of drugs for skin protection under stress conditions. Our study demonstrates that chemical library screening combined with advanced computational similarity searching is a powerful strategy for identification of bioactive compounds, and it points toward an innovative therapeutic approach against UVB-induced skin damage.

A system for exposing molecules and cells to biologically relevant and accurately controlled steady-state concentrations of nitric oxide and oxygen

Nitric oxide (NO) plays key roles in cell signaling and physiology, with diverse functions mediated by NO concentrations varying over three orders-of-magnitude. In spite of this critical concentration dependence, current approaches to NO delivery in vitro result in biologically irrelevant and poorly controlled levels, with hyperoxic conditions imposed by ambient air. To solve these problems, we developed a system for controlled delivery of NO and O(2) over large concentration ranges to mimic biological conditions. Here we describe the fabrication, operation and calibration of the delivery system. We then describe applications for delivery of NO and O(2) into cell culture media, with a comparison of experimental results and predictions from mass transfer models that predict the steady-state levels of various NO-derived reactive species. We also determined that components of culture media do not affect the steady-state levels of NO or O(2) in the device. This system provides critical control of NO delivery for in vitro models of NO biology and chemistry.

NOS-2 signaling and cancer therapy

The role of NO and cGMP signaling in tumor biology has been extensively studied during the past three decades. However, whether the pathway is beneficial or detrimental in cancer is still open to question. We suggest several reasons for this ambiguity: first, although NO participates in normal signaling (e.g., vasodilation and neurotransmission), NO is also a cytotoxic or apoptotic molecule when produced at high concentrations by inducible nitric-oxide synthase (iNOS or NOS-2). In addition, the cGMP-dependent (NO/sGC/cGMP pathway) and cGMP-independent (NO oxidative pathway) components may vary among different tissues and cell types. Furthermore, solid tumors contain two compartments: the parenchyma (neoplastic cells) and the stroma (nonmalignant supporting tissues including connective tissue, blood vessels, and inflammatory cells) with different NO biology. Thus, the NO/sGC/cGMP signaling molecules in tumors as well as the surrounding tissue must be further characterized before targeting this signaling pathway for tumor therapy. In this review, we focus on the NOS-2 expression in tumor and surrounding cells and summarized research outcome in terms of cancer therapy. We propose that a normal function of the sGC-cGMP signaling axis may be important for the prevention and/or treatment of malignant tumors. Inhibiting NOS-2 overexpression and the tumor inflammatory microenvironment, combined with normalization of the sGC/cGMP signaling may be a favorable alternative to chemotherapy and radiotherapy for malignant tumors.

Nrf2 as a converging node for cellular signaling pathways of gasotransmitters

Gasotransmitters is a family of endogenous molecules of gases or gaseous signaling molecules. To date, nitric oxide (NO), carbon monoxide (CO) and hydrogen sulfide (H(2)S) have been found to be important gasotransmitters in humans. Three gasotransmitters at high concentrations have been confirmed to be detrimental to human health, while evidence shows they at low concentrations may confer protective effects. There are important interactions among three gasotransmitters. Recent evidence reveals that these gasotransmitters may converge at Nrf2, an important transcription factor able to induce the expressions of some critical antioxidant enzymes, which may attribute to the protective effects of these gasotransmitters. Thus, we hypothesize that Nrf2 serves as a converging node for cellular signaling pathways of gasotransmitters, which adds evidence on the interactions among them.

Modulation of transcription factor Nrf2 in an in vitro model of traumatic brain injury

Traumatic brain injury (TBI) afflicts approximately 1.4 million people in the United States and TBIs have been labeled a major cause of death and disability on a global scale. Regulatory responses in a variety of neuronal loss conditions have supported the protective involvement of the nuclear factor (erythroid-derived 2)-like 2 (Nrf2) transcription factor. Nrf2 regulates antioxidant enzyme genes, and an increase in Nrf2 expression may counteract oxidative damage that results from TBI. Elevated Nrf2 may ultimately act through the upregulation of downstream target genes such as thioredoxin (Trx) and heat-shock protein-70 (HSP70) and this may reduce neuronal loss. We performed multiple mild biaxial stretch injuries to neuroblastoma cells in culture, and examined the effects of the Nrf2 activator, tert-butylhydroquinone (tBHQ). We also compared the stretch injury to oxidative insult. We confirmed that Trx and HSP70 were upregulated by treatment with tBHQ. We observed that tBHQ protected neurons from either insult, and that this was evident by different measures of cell viability and a decrease in annexin V binding. Neuronal health after insult was improved approximately 50% by tBHQ, indicating that neurons exposed to TBI in vitro can be protected.

Proteomic characterization of the cellular response to nitrosative stress mediated by s-nitrosoglutathione reductase inhibition

The S-nitrosoglutathione-metabolizing enzyme, GSNO reductase (GSNOR), has emerged as an important regulator of protein S-nitrosylation. GSNOR ablation is protective in models of asthma and heart failure, raising the idea that GSNOR inhibitors might hold therapeutic value. Here, we investigated the effects of a small molecule inhibitor of GSNOR (GSNORi) in mouse RAW 264.7 macrophages. We found that GSNORi increased protein S-nitrosylation in cytokine-stimulated cells, and we utilized stable isotope labeling of amino acids in cell culture (SILAC) to quantify the cellular response to this "nitrosative stress". The expression of several cytokine-inducible immunomodulators, including osteopontin, cyclooxygenase-2, and nitric oxide synthase isoform 2 (NOS2), were decreased by GSNORi. In addition, selective targets of the redox-regulated transcription factor, nuclear factor (erythroid-derived 2)-like 2 (Nrf2)-including heme oxygenase 1 (HO-1) and glutamate cysteine ligase modulatory subunit-were induced by GSNORi in a NOS2- and Nrf2-dependent manner. In cytokine-stimulated cells, Nrf2 protected from GSNORi-induced glutathione depletion and cytotoxicity and HO-1 activity was required for down-regulation of NOS2. Interestingly, GSNORi also affected a marked increase in NOS2 protein stability. Collectively, these data provide the most complete description of the global effects of GSNOR inhibition and demonstrate several important mechanisms for inducible response to GSNORi-mediated nitrosative stress.

Methylation of the KEAP1 gene promoter region in human colorectal cancer

BACKGROUND

The Keap1-Nrf2 pathway has been reported to be impaired in several cancers. However, the status of Keap1-Nrf2 system in human colorectal cancer (CRC) has not been elucidated.

METHODS

We used colorectal cancer (CRC) cell lines and surgical specimens to investigate the methylation status of the KEAP1 promoter region as well as expression of Nrf2 and its downstream antioxidative stress genes, NQO-1 and AKR1C1.

RESULTS

DNA sequencing analysis indicated that all mutations detected were synonymous, with no amino acid substitutions. We showed by bisulfite genomic sequencing and methylation-specific PCR that eight of 10 CRC cell lines had hypermethylated CpG islands in the KEAP1 promoter region. HT29 cells with a hypermethylated KEAP1 promoter resulted in decreased mRNA and protein expression but unmethylated Colo320DM cells showed higher expression levels. In addition, treatment with the DNA methyltransferase inhibitor 5-Aza-dC combined with the histone deacetylase inhibitor trichostatin A (TSA) increased KEAP1 mRNA expression. These result suggested that methylation of the KEAP1 promoter regulates its mRNA level. Time course analysis with the Nrf2-antioxidant response element (ARE) pathway activator t-BHQ treatment showed a rapid response within 24 h. HT29 cells had higher basal expression levels of NQO-1 and AKR1C1 mRNA than Colo320DM cells. Aberrant promoter methylation of KEAP1 was detected in 53% of tumor tissues and 25% of normal mucosae from 40 surgical CRC specimens, indicating that cancerous tissue showed increased methylation of the KEAP1 promoter region, conferring a protective effect against cytotoxic anticancer drugs.

CONCLUSION

Hypermethylation of the KEAP1 promoter region suppressed its mRNA expression and increased nuclear Nrf2 and downstream ARE gene expression in CRC cells and tissues.

Established Principles and Emerging Concepts on the Interplay between Mitochondrial Physiology and S-(De)nitrosylation: Implications in Cancer and Neurodegeneration

S-nitrosylation is a posttranslational modification of cysteine residues that has been frequently indicated as potential molecular mechanism governing cell response upon redox unbalance downstream of nitric oxide (over)production. In the last years, increased levels of S-nitrosothiols (SNOs) have been tightly associated with the onset of nitroxidative stress-based pathologies (e.g., cancer and neurodegeneration), conditions in which alterations of mitochondrial homeostasis and activation of cellular processes dependent on it have been reported as well. In this paper we aim at summarizing the current knowledge of mitochondria-related proteins undergoing S-nitrosylation and how this redox modification might impact on mitochondrial functions, whose impairment has been correlated to tumorigenesis and neuronal cell death. In particular, emphasis will be given to the possible, but still neglected implication of denitrosylation reactions in the modulation of mitochondrial SNOs and how they can affect mitochondrion-related cellular process, such as oxidative phosphorylation, mitochondrial dynamics, and mitophagy.

Neurovascular protection by ischaemic tolerance: role of nitric oxide

Nitric oxide (NO) has emerged as a key mediator in the mechanisms of ischaemic tolerance induced by a wide variety of preconditioning stimuli. NO is involved in the brain protection that develops either early (minutes-hours) or late (days-weeks) after the preconditioning stimulus. However, the sources of NO and the mechanisms underlying the protective effects differ substantially. While in early preconditioning NO is produced by the endothelial and neuronal isoform of NO synthase, in delayed preconditioning NO is synthesized by the inducible or 'immunological' isoform of NO synthase. Furthermore, in early preconditioning, NO acts through the canonical cGMP pathway, possibly through protein kinase G and opening of mitochondrial K(ATP) channels. In late preconditioning, the protection is mediated by peroxynitrite formed by the reaction of NO with superoxide derived from the enzyme NADPH oxidase. The mechanisms by which peroxynitrite exerts its protective effect may include improvement of post-ischaemic cerebrovascular function, leading to enhancement of blood flow to the ischaemic territory, and expression of prosurvival genes resulting in cytoprotection. The evidence suggests that NO can engage highly effective and multifunctional prosurvival pathways, which could be exploited for the prevention and treatment of cerebrovascular pathologies.

Nitric oxide activates an Nrf2/sulfiredoxin antioxidant pathway in macrophages

Peroxiredoxins (Prx's) are a family of peroxidases that maintain thiol homeostasis by catalyzing the reduction of organic hydroperoxides, H₂O₂, and peroxynitrite. Under conditions of oxidative stress, eukaryotic Prx's can be inactivated by the substrate-dependent oxidation of the catalytic cysteine to sulfinic acid, which may regulate the intracellular messenger function of H₂O₂. A small redox protein, sulfiredoxin (Srx), conserved only in eukaryotes, has been shown to reduce sulfinylated 2-Cys Prx's, adding to the complexity of the H₂O₂ signaling network. In this study, we addressed the regulation of Srx expression in immunostimulated primary macrophages that produce both reactive oxygen species (ROS) and nitric oxide (NO(•)). We present genetic evidence that NO-mediated Srx up-regulation is mediated by the transcription factor nuclear factor erythroid 2-related factor (Nrf2). We also show that the NO(•)/Srx pathway inhibits generation of ROS. These results reveal a link between innate immunity and H₂O₂ signaling. We propose that an NO(•)/Nrf2/Srx pathway participates in the maintenance of redox homeostasis in cytokine-activated macrophages and other inflammatory settings.

Granulocyte colony stimulating factor attenuates inflammation in a mouse model of amyotrophic lateral sclerosis

BACKGROUND

Granulocyte colony stimulating factor (GCSF) is protective in animal models of various neurodegenerative diseases. We investigated whether pegfilgrastim, GCSF with sustained action, is protective in a mouse model of amyotrophic lateral sclerosis (ALS). ALS is a fatal neurodegenerative disease with manifestations of upper and lower motoneuron death and muscle atrophy accompanied by inflammation in the CNS and periphery.

METHODS

Human mutant G93A superoxide dismutase (SOD1) ALS mice were treated with pegfilgrastim starting at the presymptomatic stage and continued until the end stage. After long-term pegfilgrastim treatment, the inflammation status was defined in the spinal cord and peripheral tissues including hematopoietic organs and muscle. The effect of GCSF on spinal cord neuron survival and microglia, bone marrow and spleen monocyte activation was assessed in vitro.

RESULTS

Long-term pegfilgrastim treatment prolonged mutant SOD1 mice survival and attenuated both astro- and microgliosis in the spinal cord. Pegfilgrastim in SOD1 mice modulated the inflammatory cell populations in the bone marrow and spleen and reduced the production of pro-inflammatory cytokine in monocytes and microglia. The mobilization of hematopoietic stem cells into the circulation was restored back to basal level after long-term pegfilgrastim treatment in SOD1 mice while the storage of Ly6C expressing monocytes in the bone marrow and spleen remained elevated. After pegfilgrastim treatment, an increased proportion of these cells in the degenerative muscle was detected at the end stage of ALS.

CONCLUSIONS

GCSF attenuated inflammation in the CNS and the periphery in a mouse model of ALS and thereby delayed the progression of the disease. This mechanism of action targeting inflammation provides a new perspective of the usage of GCSF in the treatment of ALS.

Nitric oxide activates Nrf2 through S-nitrosylation of Keap1 in PC12 cells

Nitric oxide (NO) exerts bifunctional effects on cell survival. While a high concentration of NO is cytotoxic, a relatively low concentration of NO promotes cytoprotection and cell survival. However, the molecular mechanism underlying the cytoprotective effect of NO remains poorly understood. One of the transcription factors that confer cellular protection against oxidative stress is NF-E2-related factor 2 (Nrf2), which is sequestered in the cytoplasm by forming an inactive complex with Klech-like ECH-associated protein 1 (Keap1). Previous studies suggested that various stimuli could induce the dissociation of Nrf2 from Keap1 in cytosol and/or promote its nuclear translocation by activating several upstream kinases. NO-mediated thiol modification in Keap1 has also been proposed as a possible mechanism of Nrf2 activation. Since NO can modify the function or activity of target proteins through S-nitrosylation of cysteine, we attempted to investigate whether the cytoprotective effect of NO is mediated through Nrf2 activation by directly modifying cysteine residues of Keap1. Our present study reveals that treatment of rat pheochromocytoma (PC12) cells with an NO donor S-nitroso-N-acetylpenicillamine (SNAP) induced nuclear translocation and DNA binding of Nrf2. Under the same experimental conditions, there was NO-mediated S-nitrosylation of Keap1 observed, which coincided with the Nrf2 activation. Moreover, SNAP treatment caused phosphorylation of Nrf2, and pharmacological inhibition of protein kinase C (PKC) abolished the phosphorylation and nuclear localization of Nrf2. In conclusion, NO can activate Nrf2 by S-nitrosylation of Keap1 and alternatively by PKC-catalyzed phosphorylation of Nrf2 in PC12 cells.

Heme oxygenase-1 is induced by thyroid hormone and involved in thyroid hormone preconditioning-induced protection against renal warm ischemia in rat

Thyroid hormone pretreatment was indicated to increase tissue tolerance to ischemia-reperfusion injury (IRI) in various organs, but the underlying molecular mechanisms remains largely unknown. Induction of heme oxygenase-1 (HO-1) protects organs against IRI. The present study investigated the effect of thyroid hormone on HO-1 expression and the possible relation between HO-1 and the thyroid hormone induced renal protection. T(3) administration in rat kidneys induced HO-1 expression in a time-dependent and dose-dependent way, and its expression was accompanied with significant depletion of reduced glutathione and increase in malondialdehyde content, showing a moderate oxidative stress that turns to normal level 48 h after drug injection. Thyroid hormone pretreatment (10 μg/100g body weight) 48 h before IR procedure significantly decreased serum creatinine and urea nitrogen and preserved renal histology, with significant reduction of parameters about oxidative stress and over-expression of HO-1 compared with that of IR group. In conclusion, T(3) administration involving oxidative stress in kidney exerts significant enhancement of HO-1 expression which may, at least in part, account for the renal preconditioning induced by T(3).

Evaluation of Nrf2 and IGF-1 expression in benign, premalignant and malignant gastric lesions

The aim of this study was to investigate the expression of Nrf2 and IGF-1 in benign, premalignant, and malignant gastric lesions, and to explore the role of Nrf2 and IGF-1 in gastric carcinoma carcinogenesis. Nrf2 and IGF-1 expression was detected in normal gastric mucosa, hyperplastic polyp, intraepithelial neoplasia, and adenocarcinoma by immunohistochemistry. There was no expression of Nrf2 and IGF-1 in normal gastric mucous membrane. With the elevation of Nrf2, IGF-1 expression, their co-expressions were highly elevated from benign proliferative lesions to malignant lesions. There were significant differences between hyperplastic polyps, intraepithelial neoplasias, and adenocarcinoma (hyperplastic polys vs. intraepithelial neoplasia: P=0.012; hyperplastic polyps vs. adenocarcinoma: P=0.023; and intraepithelial neoplasia vs. adenocarcinoma: P=0.027; hyperplastic polyps vs. adenocarcinoma: P=0.0000, respectively). Nrf2 expression and IGF-1 expression were correlated positively (r=0.337, P=0.037). The increased expression of Nrf2 and IGF-1 may be related to gastric carcinogenesis. Elevated Nrf2 and IGF-1 may play important roles in promoting tumor progression.

Inhibition of heme oxygenase-1 enhances anti-cancer effects of arsenic trioxide on glioma cells

We have previously reported that arsenic trioxide (ATO) could inhibit glioma growth both in vitro and in vivo, and demonstrated its potent therapeutic effects on gliomas. In this study we showed that ATO induced cell damage and heme oxygenase-1 (HO-1) expression in glioma cells via ROS generation. HO-1 inducer clearly protected from ATO-induced cell death and ROS generation, and HO-1 inhibitor led to a significant increase in cell death and ROS generation induced by ATO. In addition, knockdown of nuclear factor (erythroid-derived 2)-like 2 (Nrf2) strongly inhibited HO-1 expression induced by ATO, and significantly enhanced ATO-induced oxidative damage. Our results demonstrated, for the first time, that HO-1 inhibition or Nrf2 knockdown significantly potentiated ATO's effects on glioma cells. Considering that HO-1 is highly expressed in glioma tissues, administration of ATO in combination with either HO-1 inhibitor or Nrf2 knockdown may act as a new approach to the treatment of glioma.

Nitric oxide delivery system for biological media

Developing an understanding of how chronically elevated levels of nitric oxide at sites of inflammation or infection can lead to cancer and other diseases requires ways to expose cells and biomolecules to controlled concentrations of NO for hours to days. To achieve this, a small (65ml) stirred reactor was fabricated that included a flat, porous poly(tetrafluoroethylene) membrane and a loop of poly(dimethylsiloxane) tubing for NO and O(2) delivery, respectively. It was equipped with probes for continuous monitoring of NO and O(2) concentrations. Transport through the membrane and tubing was characterized using separate O(2) depletion experiments. In experiments using only a 10% NO mixture and a buffer that was initially air-equilibrated, constant rates of accumulation were observed for NO(2)(-) (53±2μM/h; n=8), the end product of NO oxidation, as expected. Simultaneous delivery of NO and O(2) yielded steady NO concentrations of 0.7-2.3μM, depending on the tubing length and gas compositions. A model was developed that allows the steady NO and O(2) concentrations and the duration of the transients to be predicted to within a few percent. This system should be useful for exposing cells and biomolecules to concentrations of NO that mimic those in vivo.

Chemistry of the cysteine sensors in Kelch-like ECH-associated protein 1

The protein Kelch-like ECH-associated protein 1 (Keap1) is a cysteine-rich regulatory and scaffold protein. Human Keap1 contains 27 cysteines. Some of these cysteines are believed to mediate derepression of the transcription factor nuclear factor (erythroid-derived 2)-like 2 (Nrf2), which subsequently upregulates phase 2 enzymes, in response to electrophilic/oxidative assault. Some current models depict a highly select group of two and possibly a few more cysteine residues as key sensors. The assumptions and approaches undergirding these models are commented upon. The chemical reactivity of the cysteines of Keap1 toward an array of electrophiles and one oxidant is reviewed. A number of reports in the recent literature of molecules that putatively modify cysteines of Keap1 are also included. Insights into the current molecular basis of electrophile/oxidant activation of the Nrf2 pathway via reaction at cysteines of Keap1 are discussed. Finally, important knowns and unknowns are summarized.

Nitric oxide, oxygen, and superoxide formation and consumption in macrophages and colonic epithelial cells

Knowledge of the rates at which macrophages and epithelial cells synthesize NO is critical for predicting the concentrations of NO and other reactive nitrogen species in colonic crypts during inflammation, and elucidating the linkage between inflammatory bowel disease, NO, and cancer. Macrophage-like RAW264.7 cells, primary bone marrow-derived macrophages (BMDM), and HCT116 colonic epithelial cells were subjected to simulated inflammatory conditions, and rates of formation and consumption were determined for NO, O(2), and O(2)(-). Production rates of NO were determined in either of two ways: continuous monitoring of NO concentrations in a closed chamber with corrections for autoxidation, or NO(2)(-) accumulation measurements in an open system with corrections for diffusional losses of NO. The results obtained using the two methods were in excellent agreement. Rates of NO synthesis (2.3 +/- 0.6 pmol s(-1) 10(6) cells(-1)), NO consumption (1.3 +/- 0.3 s(-1)), and O(2) consumption (59 +/- 17 pmol s(-1) 10(6) cells(-1) when NO is negligible) for activated BMDM were indistinguishable from those of activated RAW264.7 cells. NO production rates calculated from NO(2)(-) accumulation data for HCT116 cells infected with Helicobacter cinaedi (3.9 +/- 0.1 pmol s(-1) 10(6) cells(-1)) were somewhat greater than those of RAW264.7 macrophages infected under similar conditions (2.6 +/- 0.1 pmol s(-1) 10(6) cells(-1)). Thus, RAW264.7 cells have NO kinetics nearly identical to those of primary macrophages, and stimulated epithelial cells are capable of synthesizing NO at rates comparable to those of macrophages. Using these cellular kinetic parameters, simulations of NO diffusion and reaction in a colonic crypt during inflammation predict maximum NO concentrations of about 0.2 microM at the base of a crypt.

Preventing Ca2+-mediated nitrosative stress in neurodegenerative diseases: possible pharmacological strategies

Overactivation of the NMDA-subtype of glutamate receptor is known to trigger excessive calcium influx, contributing to neurodegenerative conditions. Such dysregulation of calcium signaling results in generation of excessive free radicals, including reactive oxygen and nitrogen species (ROS/RNS), including nitric oxide (NO). In turn, we and our colleagues have shown that these free radicals trigger pathological production of misfolded proteins, mitochondrial dysfunction, and apoptotic pathways in neuronal cells. Here, we discuss emerging evidence that excessive calcium-induced NO production can contribute to the accumulation of misfolded proteins, specifically by S-nitrosylation of the ubiquitin E3 ligase, parkin, and the chaperone enzyme for nascent protein folding, protein-disulfide isomerase. Additionally, excessive calcium-induced NO generation leads to the formation of S-nitrosylated dynamin-related protein 1, which causes abnormal mitochondrial fragmentation and resultant synaptic damage. In this review, we also discuss how two novel classes of pharmacological agents hold promise to interrupt these pathological processes. Firstly, the NMDA receptor antagonists, Memantine and NitroMemantine, block excessive extrasynaptic glutamate excitation while maintaining synaptic transmission, thereby limiting excessive calcium influx and production of ROS/RNS. Secondly, therapeutic pro-electrophiles are activated in the face of oxidative insult, thus protecting cells from calcium-induced oxidative stress via the Keap1/Nrf2 transcriptional pathway.