Reactive Oxygen Species: A Breath of Life or Death?: Fig. 1

Oxidative quenching and degradation of polymer-encapsulated quantum dots: new insights into the long-term fate and toxicity of nanocrystals in vivo

We report quenching and chemical degradation of polymer-coated quantum dots by reactive oxygen species (ROS), a group of oxygen-containing molecules that are produced by cellular metabolism and are involved in both normal physiological and disease processes such as oxidative signaling, cancer, and atherosclerosis. A major new finding is that hypochlorous acid (HOCl) in its neutral form is especially potent in degrading encapsulated QDs, due to its small size, neutral charge, long half-life, and fast reaction kinetics under physiologic conditions. Thus, small and neutral molecules such as HOCl and hydrogen peroxide (H2O2) are believed to diffuse across the polymer coating layer, leading to chemical oxidation of sulfur or selenium atoms on the QD surface. This "etching" process first generates lattice structural defects (which cause fluorescence quenching) and then produces soluble metal (e.g., cadmium and zinc) and chalcogenide (e.g., sulfur and selenium) species. We also find that significant fluorescence quenching occurs before QD dissolution and that localized surface defects can be repaired or "annealed" by UV light illumination. These results have important implications regarding the long-term fate and potential toxicity of semiconductor nanocrystals in vivo.

Mitochondrial drugs

Mitochondria are cellular organelles that perform pivotal functions essential for ATP production, homeostasis, and metabolism. Moreover, mitochondria are integral to a variety of cell death and survival pathways. These roles identify mitochondria as a potential target for drugs to treat metabolic and hyperproliferative diseases. Differences in the redox state of pathogenic versus non-pathogenic cells may be exploited to achieve selective anti-proliferative and cytotoxic activity against target cell populations. Pro-oxidant drugs, such as Trisenox and Elesclomol, are demonstrating clinical utility in the treatment of cancer. Results obtained with Bz-423 in mice demonstrate the potential for mitochondria-targeted drugs to control disorders of immune function. Research associating an elevated oxidant state with mitochondrial damage, degenerative disease, and aging dictates the need for a better understanding of when and how pharmacological manipulation of mitochondrial function provides most therapeutic benefit.

Chronic oxidative DNA damage due to DNA repair defects causes chromosomal instability in Saccharomyces cerevisiae

Oxidative DNA damage is likely to be involved in the etiology of cancer and is thought to accelerate tumorigenesis via increased mutation rates. However, the majority of malignant cells acquire a specific type of genomic instability characterized by large-scale genomic rearrangements, referred to as chromosomal instability (CIN). The molecular mechanisms underlying CIN are not entirely understood. We utilized Saccharomyces cerevisiae as a model system to delineate the relationship between genotoxic stress and CIN. It was found that elevated levels of chronic, unrepaired oxidative DNA damage caused chromosomal aberrations at remarkably high frequencies under both selective and nonselective growth conditions. In this system, exceeding the cellular capacity to appropriately manage oxidative DNA damage resulted in a "gain-of-CIN" phenotype and led to profound karyotypic instability. These results illustrate a novel mechanism for genome destabilization that is likely to be relevant to human carcinogenesis.

Carbonyl cyanide p-(trifluoromethoxy) phenylhydrazone (FCCP) as an O2(*-) generator induces apoptosis via the depletion of intracellular GSH contents in Calu-6 cells

Carbonyl cyanide p-(trifluoromethoxy) phenylhydrazone (FCCP) is an uncoupler of mitochondrial oxidative phosphorylation in eukaryotic cells. Here, we investigated an involvement of O(2)(*-) and GSH in FCCP-induced Calu-6 cell death and examined whether ROS scavengers rescue cells from FCCP-induced cell death. Levels of intracellular O(2)(*-) were markedly increased depending on the concentrations (5-100 microM) of FCCP. A depletion of intracellular GSH content was also observed after exposing cells to FCCP. Stable SOD mimetics, Tempol and Tiron did not change the levels of intracellular O(2)(*-), apoptosis and the loss of mitochondrial membrane potential (DeltaPsi(m)). Treatment with thiol antioxidants, NAC and DTT, showed the recovery of GSH depletion and the reduction of O(2)(*-) levels in FCCP-treated cells, which were accompanied by the inhibition of apoptosis. In contrast, BSO, a well-known inhibitor of GSH synthesis, aggravated GSH depletion, oxidative stress of O(2)(*-) and cell death in FCCP-treated cells. Taken together, our data suggested that FCCP as an O(2)(*-) generator, induces apoptosis via the depletion of intracellular GSH contents in Calu-6 cells.

Tyrosine phosphorylation and Ras activation is required for hydrogen peroxide-mediated Raf-1 kinase activation

Reactive oxygen species (ROS), such as hydrogen peroxide (H(2)O(2)), have been shown to play a significant role in regulating transmembrane signaling pathways to modulate cell proliferation and differentiation. Here we report findings that indicate that treatment of Sf9 cells expressing Raf-1 with H(2)O(2) results in significant and sustained activation of Raf-1 kinase. The activation of Raf-1 in response to H(2)O(2) treatment of Raf-expressing Sf9 cells was found to involve tyrosine phosphorylation, detected by immunoblotting with anti-phosphotyrosine antibody. The addition of tyrosine-specific phosphatase (PTP1B) to Raf-1 immunoprecipitated from Sf9 cells infected with Raf-1 after H(2)O(2) stimulation partially decreased the kinase activity of Raf-1. In a mammalian cell system, we also identified that the overexpression of a kinase-negative Raf-1 fragment (which acts as a dominant-negative inhibitor of Ras-Raf interaction) resulted in the inhibition of the H(2)O(2)-induced activation of Raf-1. Moreover, the blocking of the Ras function by the farnesyltransferase inhibitor, alpha-hydroxyfarnesylphosphonic acid, led to a 40% or greater reduction in Raf-1 kinase activity, suggesting that Ras is involved in the signaling pathway mediating the H(2)O(2) activation of Raf-1. Taken together, these results suggest that tyrosine phosphorylation and Ras activation are essential components of the mechanism by which H(2)O(2) activates Raf-1 kinase activity.

Induction of apoptosis by lupeol and mango extract in mouse prostate and LNCaP cells

Prostate cancer (PCA) is one of the most invasive malignancy and second leading cause of cancer related deaths in United States and some other countries. Long latency period makes PCA an ideal disease for pharmacologic or nutritional chemoprevention. Lupeol, a triterpene present in mango and other fruits, has shown to possess anticancer properties in in vivo and in vitro assays. Here, we recorded the apoptogenic activity in mouse prostate by lupeol and mango pulp extract (MPE). Testosterone was injected subcutaneously (5 mg/kg body weight) for 14 consecutive days to male Swiss albino mice. Lupeol/MPE supplementation resulted in arrest of prostate enlargement in testosterone-treated animals. In mouse prostate tissue, lupeol and MPE supplementation resulted in a significantly high percentage of apoptotic cells in the hypodiploid region. The induction of apoptosis in mouse prostate cells was preceded by the loss of mitochondrial transmembrane potential and DNA laddering. In testosterone-induced mouse prostate, upregulation of antiapoptotic B-cell non-Hodgkin lymphoma-2 and downregulation of proapoptotic Bcl-2-associated X protein and caspase-3 were also recorded. We further observed apoptogenic activities of lupeol in an in vitro model using human prostate cancer cells [lymph node carcinoma of the prostate (LNCaP)]. The apoptogenic response of lupeol-induced changes in LNCaP cells can be summarized as early increase of reactive oxygen species followed by induction of mitochondrial pathway leading to cell death. Thus, the results of this study demonstrate that lupeol/MPE is effective in combating testosterone-induced changes in mouse prostate as well as causing apoptosis by modulating cell-growth regulators.

Protein cysteine sulfinic acid reductase (sulfiredoxin) as a regulator of cell proliferation and drug response

Sulfiredoxin (Srx) is one of a family of low molecular weight sulfur containing proteins linked with maintenance of cellular redox balance. One function of Srx is the reduction of cysteine sulfinic acid to sulfenic acid in proteins subject to oxidative stress. Other redox active protein families have multiple functions in regulating redox and controlling proliferation/death pathways; increased Srx has been linked with oncogenic transformation. To explore the biological functions of Srx in tumors, we established cell lines that overexpress Srx. Enhanced levels of Srx promoted cell proliferation and enhanced cell death following cisplatin. Srx overexpression triggered an alteration in expression and phosphorylation of cell cycle regulators p21, p27 and p53; stabilized the phosphatase PTEN and, importantly, interacted directly with, and enhanced the activity of, phosphatase PTP1B. In turn, this promoted Src kinase activity by dephosphorylating its inhibitory tyrosine residue (Y530). Srx expression was stimulated by cell exposure to certain growth factors. These data support a role for Srx in controlling the phosphorylation status of key regulatory kinases through effects upon phosphatase activity with an ultimate effect on pathways that influence cell proliferation.

Fullerenol C60(OH)24 effects on antioxidative enzymes activity in irradiated human erythroleukemia cell line

Radiotherapy-induced toxicity is a major dose-limiting factor in anti-cancer treatment. Ionizing radiation leads to the formation of reactive oxygen and nitrogen species (ROS/RNS) that are associated with radiation-induced cell death. Investigations of biological effects of fullerenol have provided evidence for its ROS/RNS scavenger properties in vitro and radioprotective efficiency in vivo. Therefore we were interested to evaluate its radioprotective properties in vitro in the human erythroleukemia cell line. Pre-treatment of irradiated cells by fullerenol exerted statistically significant effects on cell numbers and the response of antioxidative enzymes to X-ray irradiation-induced oxidative stress in cells. Our study provides evidence that the pre-treatment with fullerenol enhanced the enzymatic activity of superoxide dismutase and glutathione peroxidase in irradiated K562 cells.

Many forks in the path: cycling with FoxO

FoxO transcription factors are an evolutionary conserved subfamily of the forkhead transcription factors, characterized by the forkhead DNA-binding domain. FoxO factors regulate a number of cellular processes involved in cell-fate decisions in a cell-type- and environment-specific manner, including metabolism, differentiation, apoptosis and proliferation. A key mechanism by which FoxO determines cell fate is through regulation of the cell cycle machinery, and as such the cellular consequence of FoxO deregulation is often manifested through perturbation of the cell cycle. Consequently, the deregulation of FoxO factors is implicated in the development of numerous proliferative diseases, in particular cancer.

Alpha-lipoic acid induces apoptosis in hepatoma cells via the PTEN/Akt pathway

We report here that alpha-lipoic acid (alpha-LA), a naturally-occurring antioxidant, scavenges reactive oxygen species (ROS) followed by an increase in apoptosis of human hepatoma cells. Apoptosis induced by alpha-LA was dependent upon the activation of the caspase cascade and the mitochondrial death pathway. alpha-LA induced increases in caspase-9 and caspase-3 but had no significant effect on caspase-8 activity. Apoptosis induced by alpha-LA was found to be mediated through the tensin homologue deleted on chromosome 10 (PTEN)/Akt pathway. Prior to cell apoptosis, PTEN was activated and its downstream target Akt was inhibited. Our findings indicate that increasing ROS scavenging could be a therapeutic strategy to treat cancer.

Reactive oxygen species in tumor metastasis

Tumor metastasis is attributed not only to the abnormalities of cancer cells, but also to changes induced by the interaction of cancer cells and surrounding cells/tissues. The host immune response to cancer cells may contribute to an increased incidence of tumor metastasis. Surgical removal of tumor tissues can trigger tumor recurrence and metastatic tumor growth in distant organs. An important class of molecules involved in these events is the reactive oxygen species (ROS), which have been identified as involved in not only to tumor metastasis but also most disease processes. ROS will contribute to various aspects of malignant tumors, including carcinogenesis, aberrant growth, metastasis, and angiogenesis. High-level ROS, which can be reached by several anti-cancer treatments, suppresses tumor metastasis by destroying cancer cells because of the oxidative nature of the molecules. On the other hand, sublethal levels of ROS can induce additional changes in DNA of tumor cells to make those cells malignant, stimulate the proliferation of cancer cells, and activate the expression of various molecules, some of which assist cancer cells to form metastatic colonies. Thus, a precise understanding how ROS are generated and involved in tumor metastasis will help us to design better strategies to overcome such life-threatening events.

Antibacterial and anti-atrophic effects of a highly soluble, acid stable UDCA formula in Helicobacter pylori-induced gastritis

Helicobacter pylori is one of the main causes of atrophic gastritis and gastric carcinogenesis. Gastritis can also occur in the absence of H. pylori as a result of bile reflux suggesting the eradication of H. pylori by bile acids. However, the bile salts are unable to eradicate H. pylori due to their low solubility and instability at acidic pH. This study examined the effect of a highly soluble and acid stable ursodeoxycholic acid (UDCA) formula on H. pylori-induced atrophic gastritis. The H. pylori infection decreased the body weight, mitochondrial membrane potential and ATP level in vivo. Surprisingly, H. pylori-induced expression of malate dehydrogenase (MDH), a key enzyme in the tricarboxylic acid cycle, at both the protein and mRNA levels. However, the UDCA formula repressed MDH expression and increased the membrane potential thereby increasing the ATP level and body weight in vivo. Moreover, UDCA scavenged the reactive oxygen species (ROS), increased the membrane potential, and inhibited apoptosis in AGS cells exposed to H(2)O(2) in vitro through the mitochondria-mediated pathway. Taken together, UDCA decreases the MDH and ROS levels, which can prevent apoptosis in H. pylori-induced gastritis.

Cytotoxic activity of 3,3',4,4',5,5'-hexahydroxystilbene against breast cancer cells is mediated by induction of p53 and downregulation of mitochondrial superoxide dismutase

The phytochemical resveratrol, which is found in grapes and red wine, has been reported to have a variety of biological properties. It was shown in our previous research that introduction of additional hydroxyl groups into the stilbene structure increases the biological activity of resveratrol. In this study, the activity of 3,3',4,4',5,5'-hexahydroxystilbene (M8) was investigated in ZR-75-1, MDA-MB-231 and T47D human breast cancer cells. For evaluation of cytotoxic activity of M8, clonogenic and cell proliferation assays were used. The IC50 values obtained in the clonogenic assay were 0.846 microM for T47D, 8.53 microM for ZR-75-1 cells and 25.5 microM for MDA-MB-231, while IC50 values obtained in the cell proliferation assay were significantly higher: 90.1 microM, 98.4 microM, 127.8 microM for T47D, ZR-75-1 and MDA-MB-231 cells, respectively. Compound M8 caused the activation of caspase-8 in MDA-MB-231 cells (marker of extrinsic apoptotic pathway), while activities of caspase-9 (marker of intrinsic apoptotic pathway) and caspase-3 were increased in all 3 tested cell lines. Activation of caspase-9 and caspase-3 was connected with loss of mitochondrial potential and increase of p53, which could have an impact on downregulation of mitochondrial superoxide dismutase (MnSOD) seen in our experiments. MnSOD is a key enzyme providing antioxidative defense in mitochondria - the cellular center of reactive oxygen species' generation. Downregulation of MnSOD can therefore cause a significant decrease of antioxidant defense in cancer cells. An increase of oxidative stress conditions was suggested by loss of reduced glutathione in tested cells. Since cancer cells are usually under permanent oxidative stress, additional increased ROS generation as a result of the interaction of M8 with the mitochondrial respiratory chain and a decrease in oxidative defense can therefore be a promising method for selective elimination of cancer cells.

Integrated activation of MAP3Ks balances cell fate in response to stress

In vivo, tissues and organs are exposed to numerous stressors that require cells to respond appropriately for viability and homeostasis. Cells respond to these stressors, which range from UV irradiation, heat shock, chemicals, and changes in osmolality, to oxidative stress and inflammatory cytokines, by activating pathways that protect cells from damage. If the stress is too great, cells commit to undergo apoptosis. Such cell fate decisions involve the stress-mediated activation of mitogen-activated protein kinase (MAPK) networks, ultimately under the control of MAPK kinase kinases, or MAP3Ks. It is the MAP3Ks that coordinate the localization, duration and magnitude of MAPK activation in response to cell stress. A single stressor may activate several MAP3Ks, each of which impacts the balance between survival and apoptotic signaling. In this prospect article, we review the specific MAP3Ks that integrate the physiological response to cell stressors. The interrelationships among different stressors are discussed, with an emphasis on how the balance of signaling through MAP3Ks controls the MAPK response to determine cell fate.

Prevention of atrial fibrillation following cardiac surgery: basis for a novel therapeutic strategy based on non-hypoxic myocardial preconditioning

Atrial fibrillation is the most common complication of cardiac surgical procedures performed with cardiopulmonary bypass. It contributes to increased hospital length of stay and treatment costs. At present, preventive strategies offer only suboptimal benefits, despite improvements in anesthesia, surgical technique, and medical therapy. The pathogenesis of postoperative atrial fibrillation is considered to be multifactorial. However oxidative stress is a major contributory factor representing the unavoidable consequences of ischemia/reperfusion cycle occurring in this setting. Considerable evidence suggests the involvement of reactive oxygen species (ROS) in the pathogenic mechanism of this arrhythmia. Interestingly, the deleterious consequences of high ROS exposure, such as inflammation, cell death (apoptosis/necrosis) or fibrosis, may be abrogated by a myocardial preconditioning process caused by previous exposure to moderate ROS concentration known to trigger survival response mechanisms. The latter condition may be created by n-3 PUFA supplementation that could give rise to an adaptive response characterized by increased expression of myocardial antioxidant enzymes and/or anti-apoptotic pathways. In addition, a further reinforcement of myocardial antioxidant defenses could be obtained through vitamins C and E supplementation, an intervention also known to diminish enzymatic ROS production. Based on this paradigm, this review presents clinical and experimental evidence supporting the pathophysiological and molecular basis for a novel therapeutic approach aimed to diminish the incidence of postoperative atrial fibrillation through a non-hypoxic preconditioning plus a reinforcement of the antioxidant defense system in the myocardial tissue.

Expression of myeloperoxidase enhances the chemosensitivity of leukemia cells through the generation of reactive oxygen species and the nitration of protein

Myeloperoxidase (MPO), a pivotal lineage marker for acute myeloid leukemia (AML), has been also shown to have a prognostic value: a high percentage of MPO-positive blasts correlates to favorable prognosis. To understand the relationship between the expression of MPO in leukemia cells and the response to chemotherapeutic agents, we established MPO-expressing K562 leukemia cell lines and then treated them with cytosine arabinocide (AraC). Cells expressing wild-type MPO, but not mutant MPO that could not mature, died earlier of apoptosis than control K562 cells. Reactive oxygen species (ROS) were generated more in leukemia cells expressing MPO, and the generation was abrogated by MPO inhibitors or antioxidants. Tyrosine nitration of cellular protein also increased more in MPO-expressing K562 cells than control cells after treatment with AraC. In clinical samples, CD34-positive AML cells from high-MPO cases showed a tendency to be sensitive to AraC in the colony-formation assay, and the generation of ROS and the nitration of protein were observed only when the percentage of MPO-expressing cells was high. These data suggest that MPO enhances the chemosensitivity of AML through the generation of ROS and the nitration of proteins.

Sulforaphane generates reactive oxygen species leading to mitochondrial perturbation for apoptosis in human leukemia U937 cells

Sulforaphane, an isothiocyanate found in cruciferous vegetables, has been shown to possess growth-inhibiting and apoptosis-inducing activities in cancer cell lines in vitro. In order to further explore the critical events leading to apoptosis in sulforaphane-treated U937 human leukemia cells, the following effects of sulforaphane on components of the mitochondrial apoptotic pathway were examined: generation of reactive oxygen species (ROS), alteration of the mitochondrial membrane potential (MMP), and the expression changes of Bcl-2 family proteins. The cytotoxic effect of sulforaphane was mediated by its induction of apoptosis as characterized by the occurrence of DNA ladders, apoptotic bodies and chromosome condensation in U937 cells. The sulforaphane-induced apoptosis in U937 cells correlated with the generation of intracellular ROS, collapse of MMP, activation of caspase-3, and down-regulation of anti-apoptotic Bcl-2 expression. The quenching of ROS generation with antioxidant N-acetyl-L-cysteine conferred significant protection against sulforaphane-elicited ROS generation, disruption of the MMP, caspase-3 activation and apoptosis. In conclusion, the present study reveals that the cellular ROS generation plays a pivotal role in the initiation of sulforaphane-triggered apoptotic death in U937 cells.

Analysis of the retinal gene expression profile after hypoxic preconditioning identifies candidate genes for neuroprotection

Background

Retinal degeneration is a main cause of blindness in humans. Neuroprotective therapies may be used to rescue retinal cells and preserve vision. Hypoxic preconditioning stabilizes the transcription factor HIF-1α in the retina and strongly protects photoreceptors in an animal model of light-induced retinal degeneration. To address the molecular mechanisms of the protection, we analyzed the transcriptome of the hypoxic retina using microarrays and real-time PCR.

Results

Hypoxic exposure induced a marked alteration in the retinal transcriptome with significantly different expression levels of 431 genes immediately after hypoxic exposure. The normal expression profile was restored within 16 hours of reoxygenation. Among the differentially regulated genes, several candidates for neuroprotection were identified like metallothionein-1 and -2, the HIF-1 target gene adrenomedullin and the gene encoding the antioxidative and cytoprotective enzyme paraoxonase 1 which was previously not known to be a hypoxia responsive gene in the retina. The strongly upregulated cyclin dependent kinase inhibitor p21 was excluded from being essential for neuroprotection.

Conclusion

Our data suggest that neuroprotection after hypoxic preconditioning is the result of the differential expression of a multitude of genes which may act in concert to protect visual cells against a toxic insult.

The Role of Glucose Metabolism and Glucose-Associated Signalling in Cancer

Aggressive carcinomas ferment glucose to lactate even in the presence of oxygen. This particular metabolism, termed aerobic glycolysis, the glycolytic phenotype, or the Warburg effect, was discovered by Nobel laureate Otto Warburg in the 1920s. Since these times, controversial discussions about the relevance of the fermentation of glucose by tumours took place; however, a majority of cancer researchers considered the Warburg effect as a non-causative epiphenomenon. Recent research demonstrated, that several common oncogenic events favour the expression of the glycolytic phenotype. Moreover, a suppression of the phenotypic features by either substrate limitation, pharmacological intervention, or genetic manipulation was found to mediate potent tumour-suppressive effects. The discovery of the transketolase-like 1 (TKTL1) enzyme in aggressive cancers may deliver a missing link in the interpretation of the Warburg effect. TKTL1-activity could be the basis for a rapid fermentation of glucose in aggressive carcinoma cells via the pentose phosphate pathway, which leads to matrix acidification, invasive growth, and ultimately metastasis. TKTL1 expression in certain non-cancerous tissues correlates with aerobic formation of lactate and rapid fermentation of glucose, which may be required for the prevention of advanced glycation end products and the suppression of reactive oxygen species. There is evidence, that the activity of this enzyme and the Warburg effect can be both protective or destructive for the organism. These results place glucose metabolism to the centre of pathogenesis of several civilisation related diseases and raise concerns about the high glycaemic index of various food components commonly consumed in western diets.

Drug-induced apoptosis in yeast

In order to alter the impact of diseases on human society, drug development has been one of the most invested research fields. Nowadays, cancer and infectious diseases are leading targets for the design of effective drugs, in which the primary mechanism of action relies on the modulation of programmed cell death (PCD). Due to the high degree of conservation of basic cellular processes between yeast and higher eukaryotes, and to the existence of an ancestral PCD machinery in yeast, yeasts are an attractive tool for the study of affected pathways that give insights into the mode of action of both antitumour and antifungal drugs. Therefore, we covered some of the leading reports on drug-induced apoptosis in yeast, revealing that in common with mammalian cells, antitumour drugs induce apoptosis through reactive oxygen species (ROS) generation and altered mitochondrial functions. The evidence presented suggests that yeasts may be a powerful model for the screening/development of PCD-directed drugs, overcoming the problem of cellular specificity in the design of antitumour drugs, but also enabling the design of efficient antifungal drugs, targeted to fungal-specific apoptotic regulators that do not have major consequences for human cells.

The role of reactive oxygen species in integrin and matrix metalloproteinase expression and function

Cell adhesion and migration is largely dependent on integrin binding to extracellular matrix, and several signalling pathways involved in these processes have been shown to be modified by reactive oxygen species (ROS). In fact, integrin activation is linked to increased ROS production by NADPH-oxidases, 5-lipoxygenase, and release from mitochondria. Cell migration is intimately linked to degradation of the extracellular matrix, and activated matrix metalloproteinases (MMPs) are a prerequisite for cancer cell invasion and metastasis. In this minireview, we focus on the interplay between integrin-mediated ROS production and MMP expression as well as its biological and pathobiological significance.

Increased expression of mitochondrial glycerophosphate dehydrogenase and antioxidant enzymes in prostate cancer cell lines/cancer

The involvement of mitochondrial glycerophosphate dehydrogenase (mGPDH) has previously been established in the production of ROS in prostate cancer cell lines (LNCaP, DU145, PC3 and CL1). The current study demonstrates that the mRNA level of mGPDH in prostate cancer cells is 3.3-8.9-fold higher compared to the normal prostate epithelial cell line, PNT1A. This is consistent with the enzymatic activity and protein level of mGPDH. However, cytochrome c oxidase (COX) activity is 2.9-3.2-fold down-regulated in androgen-independent prostate cancer cell lines. The level of antioxidant enzymes, catalase, MnSOD and CuZnSOD are up-regulated in prostate cancer cell lines. Furthermore, it was observed that the activity of mGPDH is significantly higher in liver tissues from all mice with cancer compared to liver tissues from control mice. These data suggest that the up-regulation of mGPDH, due to a highly glycolytic environment, contributes to the overall increase in ROS generation and may result in the progression of the cancer.

Hydrogen peroxide induces expression and activation of AMP-activated protein kinase in a dental pulp cell line

AIM

To investigate the effects of hydrogen peroxide on cell viability and expression and activation of AMP-activated protein kinase (AMPK) in rat dental pulp cell line RPC-C2A.

METHODOLOGY

RPC-C2A cells derived from rat dental pulp were maintained in MEM supplemented with 10% FBS at 37 degrees C, in a humidified atmosphere at 5% CO(2). Cells were cultured in the presence or absence of H(2)O(2) for up to 60 min at concentrations of from 0.1 to 3.0 mmol L(-1). Cell viability was analysed by WST-1 reduction assay. Expression of AMPK subunit isoforms was analysed by Western blotting using antibodies to the catalytic alpha1 and regulatory beta1 and gamma1 subunit isoforms. The effect of silencing AMPKalpha1 on cell viability was determined using siRNA.

RESULTS

Exposure to H(2)O(2) decreased cell viability in a time- and dose-dependent manner. The catalytic AMPKalpha1 subunit and its activated form, phospho-AMPKalpha, increased with exposure to H(2)O(2) in a time- and dose-dependent manner, whereas the regulatory beta1 and gamma1 subunits showed no change. Downregulation of AMPKalpha1 resulted in a reduction in cell viability in H(2)O(2)-treated cells at a concentration of 0.1 mmol L(-1) for 30 min incubation, indicating an increased sensitivity to H(2)O(2).

CONCLUSIONS

Reactive oxygen induced energy fuel gauge enzyme AMPKalpha expression and its activation by phosphorylation in RPC-C2A cells, suggesting that AMPK is essential for protection against H(2)O(2)-induced nonapoptotic cell death. Therefore, AMPK may be a therapeutic modulation target for treatment of the dentine-pulp complex injured by reactive oxygen.

Plumbagin induces cell cycle arrest and apoptosis through reactive oxygen species/c-Jun N-terminal kinase pathways in human melanoma A375.S2 cells

This study is the first to investigate the anticancer effect of plumbagin in human melanoma A375.S2 cells. Plumbagin exhibited effective cell growth inhibition by inducing cancer cells to undergo S-G2/M phase arrest and apoptosis. Further investigation revealed that plumbagin's inhibition of cell growth was also evident in a nude mice model. Blockade of cell cycle was associated with increased levels of p21, and reduced amounts of cyclin B1, cyclin A, Cdc2, and Cdc25C. Plumbagin also enhanced the levels of inactivated phosphorylated Cdc2 and Cdc25C. Plumbagin triggered the mitochondrial apoptotic pathway indicated by a change in Bax/Bcl-2 ratios, resulting in caspase-9 activation. We also found the generation of ROS is a critical mediator in plumbagin-induced cell growth inhibition. Plumbagin increased the activation of apoptosis signal-regulating kinase 1, JNK and extracellular signal-regulated kinase 1/2 (ERK1/2), but not p38. In addition, antioxidants vitamin C and catalase significantly decreased plumbagin-mediated c-Jun N-terminal kinase (JNK) activation and apoptosis. Moreover, blocking ERK and JNK by specific inhibitors suppressed plumbagin-triggered mitochondrial apoptotic pathway. Taken together, these results imply a critical role for ROS and JNK in the plumbagin's anticancer activity.

Regulation of erythrocyte lifespan: do reactive oxygen species set the clock?

The forkhead box O (Foxo) subfamily of transcription factors regulates expression of genes important for many cellular processes, ranging from initiation of cell cycle arrest and apoptosis to induction of DNA damage repair. Invertebrate Foxo orthologs such as DAF-16 also regulate longevity. Cellular responses inducing resistance to ROS are important for cellular survival and organism lifespan, but until recently, mammalian factors regulating resistance to oxidative stress have not been well characterized. Marinkovic and colleagues demonstrate in this issue of the JCI that Foxo3 is specifically required for induction of proteins that regulate the in vivo oxidative stress response in murine erythrocytes (see the related article beginning on page 2133). Their work offers the interesting hypothesis that in so doing, Foxo3 may regulate the lifespan of red blood cells, and underlies the importance of understanding the direct targets of this transcription factor and its regulation.

Pyruvate reduces DNA damage during hypoxia and after reoxygenation in hepatocellular carcinoma cells

Pyruvate is located at a crucial crossroad of cellular metabolism between the aerobic and anaerobic pathways. Modulation of the fate of pyruvate, in one direction or another, can be important for adaptative response to hypoxia followed by reoxygenation. This could alter functioning of the antioxidant system and have protective effects against DNA damage induced by such stress. Transient hypoxia and alterations of pyruvate metabolism are observed in tumors. This could be advantageous for cancer cells in such stressful conditions. However, the effect of pyruvate in tumor cells is poorly documented during hypoxia/reoxygenation. In this study, we showed that cells had a greater need for pyruvate during hypoxia. Pyruvate decreased the number of DNA breaks, and might favor DNA repair. We demonstrated that pyruvate was a precursor for the biosynthesis of glutathione through oxidative metabolism in HepG2 cells. Therefore, glutathione decreased during hypoxia, but was restored after reoxygenation. Pyruvate had beneficial effects on glutathione depletion and DNA breaks induced after reoxygenation. Our results provide more evidence that the alpha-keto acid promotes the adaptive response to hypoxia followed by reoxygenation. Pyruvate might thus help to protect cancer cells under such stressful conditions, which might be harmful for patients with tumors.