Redox regulation of pro-inflammatory cytokines and IkappaB-alpha/NF-kappaB nuclear translocation and activation

L-gamma-Glutamyl-L-cysteinyl-glycine (glutathione; GSH) and GSH-related enzymes in the regulation of pro- and anti-inflammatory cytokines: a signaling transcriptional scenario for redox(y) immunologic sensor(s)?

Of the antioxidant/prooxidant mechanisms mediating the regulation of inflammatory mediators, particularly cytokines, oxidative stress-related pathways remain a cornerstone. It is conspicuous that there is a strong association between free radical accumulation (ROS/RNS; oxidative stress) and the evolution of inflammation and inflammatory-related responses. The scenario that upholds a consensus on the aforementioned is still evolving to unravel, from an immunologic perspective, the molecular mechanisms associated with ROS/RNS-dependent inflammation. Cytokines are keynote players when it comes to defining an intimate relationship among reduction-oxidation (redox) signals, oxidative stress and inflammation. How close we are to identifying the molecular basis of this intricate association should be weighed against the involvement of specific signaling molecules and, potentially, transcription factors. L-gamma-Glutamyl-L-cysteinyl-glycine, or glutathione (GSH), an antioxidant thiol, has shaped, and still is refining, the face of oxidative signaling in terms of regulating the milieu of inflammatory mediators, ostensibly via the modulation (expression/repression) of oxygen- and redox-responsive transcription factors, hence termed redox(y)-sensitive cofactors. When it comes to the arena of oxygen sensing, oxidative stress and inflammation, nuclear factor-kappaB (NF-kappaB) and hypoxia-inducible factor-1alpha (HIF-1alpha) are key players that determine antioxidant/prooxidant responses with oxidative challenge. It is the theme therein to underlie current understanding of the molecular association hanging between oxidative stress and the evolution of inflammation, walked through an elaborate discussion on the role of transcription factors and cofactors. Would that classify glutathione and other redox signaling cofactors as potential anti-inflammatory molecules emphatically remains of particular interest, especially in the light of identifying upstream and downstream molecular pathways for conceiving therapeutic, alleviating strategy for oxidant-mediated, inflammatory-related disease conditions.

Celastrol inhibits pro-inflammatory cytokine secretion in Crohn's disease biopsies

Crohn's disease is a chronic intestinal inflammatory process. In modern therapy, TNF-alpha inhibition is the main goal. The aim here is to characterize the effects of Celastrol, a pentacyclic-triterpene, on the secretion of inflammatory cytokines by LPS-activated human cells. Celastrol dose-dependently inhibited the secretion of all tested pro-inflammatory cytokines with IC(50) in the nanomolar range. Effect not related to glucocorticoid receptor activity is shown by competition experiments with the steroid antagonist RU486. Celastrol inhibited the pro-inflammatory cytokine secretion from mucosal inflammatory biopsies from Crohn's disease patients. Cytometry emphasized that for all tested pro-inflammatory cytokines, CD33(+) cells are the most sensitive. Quantitative-PCR and confocal analysis on a human monocytic cell line indicated that Celastrol acts at the transcriptional level by inhibiting LPS-induced NF-kappaB translocation. Celastrol might be a putative anti-inflammatory drug in the treatment of inflammatory diseases, given its inhibition of cytokine production by intestinal biopsies from Crohn's disease patients.

Roles of NF-kappaB and SP-1 in oxidative stress-mediated induction of platelet-derived growth factor-B by TNFalpha in human endothelial cells

Platelet-derived growth factor-B (PDGF-B) is upregulated by proinflamatory stimuli in the early stages of atherosclerosis. However, its mechanisms are not fully elucidated. In the present study, by using the antioxidant N-acetylcysteine (NAC), we investigated in human umbilical vein endothelial cells (HUVECs) the roles of oxidative stress in PDGF-B expression induced by tumor necrosis factor alpha (TNFalpha) and its underlying mechanisms. Exposure of HUVECs to TNFalpha (200 U/ml) for 24 hours caused significant increases of both the PDGF-B expression and its promoter/enhancer activity, which were abolished by NAC (20 mmol/L). Accordingly, a prolonged oxidative stress was induced by TNFalpha and that was prevented by pretreatment with NAC. Electrophoresis mobility shift assay (EMSA) and Western blot analysis showed that both the nuclear factor-kappaB (NF-kappaB) and the specificity protein-1 (SP-1) were activated by TNFalpha. However, NAC only partially inhibited the TNFalpha-induced activation of NF-kappaB, but abolished the activation of SP-1. Mutation of the NF-kappaB binding site resulted in a moderate reduction in the TNFalpha-induced activity of PDGF-B promoter/enhancer, whereas mutation of SP-1 binding site resulted in an absence of induction by TNFalpha. These results suggest that oxidative stress mediates the TNFalpha-induced expression of PDGF-B in HUVECs through redox-sensitive transcription factors, predominantly the SP-1 and possibly, to some extent of NF-kappaB.

Ascorbic acid restores sensitivity to imatinib via suppression of Nrf2-dependent gene expression in the imatinib-resistant cell line

OBJECTIVE

Imatinib, a BCR/ABL tyrosine kinase inhibitor, has shown remarkable clinical effects in chronic myelogenous leukemia. However, the leukemia cells become resistant to this drug in most blast crisis cases. The transcription factor Nrf2 regulates the gene expression of a number of detoxifying enzymes such as gamma-glutamylcysteine synthetase (gamma-GCS), the rate-limiting enzyme in glutathione (GSH) synthesis, via the antioxidant response element (ARE). In this study, we examined the involvement of Nrf2 in the acquisition of resistance to imatinib. Since oxidative stress promotes the translocation of Nrf2 from the cytoplasm to the nucleus, we also examined whether ascorbic acid, a reducing reagent, can overcome the resistance to imatinib by inhibiting Nrf2 activity.

RESULTS

Binding of Nrf2 to the ARE of the gamma-GCS light subunit (gamma-GCSl) gene promoter was much stronger in the imatinib-resistant cell line KCL22/SR than in the parental imatinib-sensitive cell line KCL22. The levels of gamma-GCSl mRNA and GSH were higher in KCL22/SR cells, a finding consistent with the observation of an increase in Nrf2-DNA binding. Addition of a GSH monoester to KCL22 cells resulted in an increase in the IC(50) value of imatinib. In contrast, addition of ascorbic acid to KCL22/SR cells resulted in a decrease in Nrf2-DNA binding and decreases in levels of gamma-GCSl mRNA and GSH. Consistent with these findings, ascorbic acid partly restored imatinib sensitivity to KCL22/SR.

CONCLUSION

Changes in the redox state caused by antioxidants such as ascorbic acid can overcome resistance to imatinib via inhibition of Nrf2-mediated gene expression.

Mercury-induced apoptosis and necrosis in murine macrophages: role of calcium-induced reactive oxygen species and p38 mitogen-activated protein kinase signaling

The current study characterizes the mechanism by which mercury, a toxic metal, induces death in murine macrophages. The cytotoxic EC(50) of mercury ranged from 62.7 to 81.1 microM by various assays in J774A.1 cultures; accordingly, we employed 70 microM of mercuric chloride in most experiments. Mercury-induced intracellular calcium modulated reactive oxygen species (ROS) production, which resulted in both cell apoptosis and necrosis indicated by annexin V binding and caspase-3 activity, and propidium-iodide binding. Calcium antagonists abolished ROS production. Mercury stimulated p38 mitogen-activated protein kinase (MAPK) and additively stimulated lipopolysaccharide-activated p38. Mercury-activated p38 was decreased by pretreatment of cells with antioxidants, N-acetylcysteine (NAC) and silymarin, indicating that mercury-induced ROS were involved in p38 activation. Mercury increased the expression of tumor necrosis factor alpha (TNFalpha); antioxidants and a specific p38 inhibitor decreased this effect. Pretreatment with antioxidants, p38 inhibitor, and anti-TNFalpha antibody decreased mercury-induced necrosis; however, anti-TNFalpha antibody did not decrease mercury-induced apoptosis. Results suggest that mercury-induced macrophage death is a mix of apoptosis and necrosis employing different pathways. P38-mediated caspase activation regulates mercury-induced apoptosis and p38-mediated TNFalpha regulates necrosis in these cells. Calcium regulates ROS production and mercury-induced ROS modulate downstream p38 that regulates both apoptosis and necrosis.

The general case for redox control of wound repair

The orthodox view has been that reactive oxygen species are primarily damaging to cells. There is general agreement that while high (3%) doses of H(2)O(2) may serve as a clinical disinfectant, its overall effect on healing is not positive. Current work shows that at very low concentrations, reactive oxygen species may regulate cellular signaling pathways by redox-dependent mechanisms. Recent discoveries show that almost all cells of the wound microenvironment contain specialized enzymes that utilize O(2) to generate reactive oxygen species. Numerous aspects of wound healing are subject to redox control. An understanding of how endogenous reactive oxygen species are generated in wound-related cells may influence the healing process and could result in new redox-based therapeutic strategies. Current results with growth factor therapy of wounds have not met clinical expectations. Many of these growth factors, such as platelet-derived growth factor, rely on reactive oxygen species for functioning. Redox-based strategies may serve as effective adjuncts to jump-start healing of chronic wounds. The understanding of wound-site redox biology is also likely to provide novel insights into the fundamental mechanisms that would help to optimize conditions for oxygen therapy. While a window of therapeutic opportunity seems to exist under conditions of low concentrations of reactive oxygen species, high levels may complicate regeneration and remodeling of nascent tissue.

Enhanced survival effect of pyruvate correlates MAPK and NF-kappaB activation in hydrogen peroxide-treated human endothelial cells

We recently reported that pyruvate inhibited translocation and activation of p53 caused by DNA damage due to oxidant injury (Lee YJ, Kang IJ, Bünger R, and Kang YH. Microvasc Res 66: 91-101, 2003); this was associated with increased expression of apoptosis-related bcl-2 and decreased expression of bax gene. This study attempted to delineate possible regulatory sites and mechanisms of antiapoptotic pyruvate, focusing on reactive oxygen species-mediated signaling in a human umbilical vein endothelial cell model. We compared the effects of the cytosolic reductant l-lactate and malate-aspartate shuttle blocker aminooxyacetate, both of which increase cytosolic NADH, on the downstream signaling pathway. Hydrogen peroxide (0.5 mM H2O2) depleted intracellular total glutathione that was prevented by pyruvate but not by l-lactate or aminooxyacetate. Activation of caspase-3 and the cleavage of procaspase-6 and procaspase-7 were strongly inhibited by pyruvate but markedly enhanced by l-lactate and aminooxyacetate, implicating redox-related antiapoptotic mechanisms of pyruvate. Western blot analysis and immunochemical data revealed that H2O2-induced transactivation of nuclear factor-kappaB (NF-kappaB) was also inhibited by pyruvate but not by l-lactate or aminooxyacetate. In addition, H2O2 downregulated extracellular signal-regulated kinase (ERK1/2) and phosphorylated p38 mitogen-activated protein kinase (MAPK), effects that were fully reversed by pyruvate within 2 h. Collectively, these findings indicate that pyruvate can protect cellular glutathione, thus enhancing cellular antioxidant potential, and that enhanced antioxidant potential can desensitize NF-kappaB transactivation due to reactive oxygen species, suggesting possible metabolic redox relations to NF-kappaB. Furthermore, pyruvate blocked the p38 MAPK pathway and activated the ERK pathway in an apparently redox-sensitive manner, which may regulate expression of genes believed to prevent apoptosis and promote cell survival. Thus pyruvate may have therapeutic potential for reducing endothelial dysfunction and improving survival during oxidative stress.

Inhibition of Helicobacter pylori-induced nuclear factor-kappa B activation and interleukin-8 gene expression by ecabet sodium in gastric epithelial cells

BACKGROUND

Helicobacter pylori stimulates nuclear factor-kappa B (NF-kappa B) activation and chemokine interleukin-8 (IL-8) expression in gastric epithelial cells. Ecabet sodium (ecabet), a locally acting antiulcer drug, is known to have anti-H. pylori activity. However, there is little understanding of how ecabet induces anti-inflammatory activity in gastric epithelial cells infected with H. pylori. The aim of this study was to investigate the effects of ecabet on IL-8 gene expression and NF-kappa B activation in human gastric epithelial cells infected with H. pylori.

MATERIALS AND METHODS

After Hs746T, MKN-45, or SNU-5 gastric epithelial cell lines had been infected with cagA+cytotoxin+H. pylori in the presence of ecabet, IL-8 mRNA expression was assessed by quantitative reverse transcription-polymerase chain reaction, and IL-8 secretion was measured by enzyme-linked immunosorbent assay. NF-kappa B and inhibitory kappa B-alpha (I kappa B alpha) signals were assayed by electrophoretic mobility shift assay and Western blot, respectively. The activation of NF-kappa B and IL-8 reporter genes was determined by luciferase assay.

RESULTS

Ecabet showed no antimicrobial activiy against Gram-positive or -negative bacteria. However, ecabet inhibited transcription of the IL-8 gene and secretion of IL-8 by gastric epithelial cells infected with H. pylori at a concentration of 5 micro g/ml. Moreover, ecabet inhibited the activation of NF- kappa B and the degradation of I kappa B alpha in gastric epithelial cells in response to H. pylori infection. In addition, the NF-kappa B signal inhibited by ecabet was comprised predominantly of heterodimers of p65/p50.

CONCLUSIONS

Ecabet inhibited H. pylori-induced IL-8 gene transcription and secretion by suppressing the NF-kappa B signal. This inhibition might be one pathway by which ecabet exerts its anti-inflammatory effect on H. pylori-induced gastric inflammation.

Mitochondrial DNA mutations in primary leukemia cells after chemotherapy: clinical significance and therapeutic implications

Mitochondrial DNA (mtDNA) codes for 13 respiratory chain subunits and is more vulnerable to damage than nuclear DNA due, in part, to a lack of histone protection and a weak repair capacity. While mtDNA alterations have been observed in human cancer, their roles in oncogenesis and chemosensitivity remain unclear. We investigated the relationship between mtDNA mutations, reactive oxygen species (ROS) generation, and clinical outcomes in chronic lymphocytic leukemia (CLL) patients. An analysis of mtDNA from 20 CLL patients revealed that primary CLL cells from patients with prior chemotherapy had a significantly higher frequency of heteroplasmic mutations than did those from untreated patients. Overall, mtDNA mutations appeared to be associated with increased ROS generation. Patients refractory to conventional therapeutic agents tended to have higher mutation rates than patients who responded to treatment. Analysis of paired blood samples from the same patient led to the identification of a heteroplasmic mutation in the cytochrome c oxidase II gene several months after chemotherapy. The mutation was associated with increased ROS generation. Our results suggest for the first time that chemotherapy with DNA-damaging agents may cause mtDNA mutations in primary leukemia cells, which often exist in heteroplasmy, and are associated with increased ROS generation.

Redox- and oxidant-mediated regulation of interleukin-10: an anti-inflammatory, antioxidant cytokine?

Reduction-oxidation (redox) state constitutes such a potential signaling mechanism for the regulation of an inflammatory signal associated with oxidative stress. Interleukin (IL)-10 has recently emerged as an anti-inflammatory cytokine with antioxidant properties. Interestingly, redox- and oxidant-mediated pathways positively and/or negatively regulate the expression, distribution, and functional properties of IL-10, thus, allowing the evolution of what is known as an anti-inflammatory redox-oxidant revolving axis. This axis is directly involved in regulating phosphorylation mechanisms, which eventually control gene expression and the biosynthesis of oxidative stress-related cofactors, such as reactive species and inflammatory cytokines. The association between IL-10, an anti-inflammatory antioxidant, with redox- and oxidant-related pathways governing the regulation of inflammatory and closely dependent processes is thereafter discussed.