Glutathione depletion causes cytochrome c release even in the absence of cell commitment to apoptosis

The d-mannose/l-galactose pathway is the dominant ascorbate biosynthetic route in the moss Physcomitrium patens

Ascorbate is an abundant and indispensable redox compound in plants. Genetic and biochemical studies have established the d-mannose/l-galactose (d-Man/l-Gal) pathway as the predominant ascorbate biosynthetic pathway in streptophytes, while the d-galacturonate (d-GalUA) pathway is found in prasinophytes and euglenoids. Based on the presence of the complete set of genes encoding enzymes involved in the d-Man/l-Gal pathway and an orthologous gene encoding aldonolactonase (ALase) - a key enzyme for the d-GalUA pathway - Physcomitrium patens may possess both pathways. Here, we have characterized the moss ALase as a functional lactonase and evaluated the ascorbate biosynthesis capability of the two pathways using knockout mutants. Physcomitrium patens expresses two ALase paralogs, namely PpALase1 and PpALase2. Kinetic analyses with recombinant enzymes indicated that PpALase1 is a functional enzyme catalyzing the conversion of l-galactonic acid to the final precursor l-galactono-1,4-lactone and that it also reacts with dehydroascorbate as a substrate. Interestingly, mutants lacking PpALase1 (Δal1) showed 1.2-fold higher total ascorbate content than the wild type, and their dehydroascorbate content was increased by 50% compared with that of the wild type. In contrast, the total ascorbate content of mutants lacking PpVTC2-1 (Δvtc2-1) or PpVTC2-2 (Δvtc2-2), which encode the rate-limiting enzyme GDP-l-Gal phosphorylase in the d-Man/l-Gal pathway, was markedly decreased to 46 and 17%, respectively, compared with that of the wild type. Taken together, the dominant ascorbate biosynthetic pathway in P. patens is the d-Man/l-Gal pathway, not the d-GalUA pathway, and PpALase1 may play a significant role in ascorbate metabolism by facilitating dehydroascorbate degradation rather than ascorbate biosynthesis.

Truncation of the TAR DNA-binding protein 43 is not a prerequisite for cytoplasmic relocalization, and is suppressed by caspase inhibition and by introduction of the A90V sequence variant

The RNA-binding and -processing protein TAR DNA-binding protein 43 (TDP-43) is heavily linked to the underlying causes and pathology of neurodegenerative diseases such as amyotrophic lateral sclerosis and frontotemporal lobar degeneration. In these diseases, TDP-43 is mislocalized, hyperphosphorylated, ubiquitinated, aggregated and cleaved. The importance of TDP-43 cleavage in the disease pathogenesis is still poorly understood. Here we detail the use of D-sorbitol as an exogenous stressor that causes TDP-43 cleavage in HeLa cells, resulting in a 35 kDa truncated product that accumulates in the cytoplasm within one hour of treatment. We confirm that the formation of this 35 kDa cleavage product is mediated by the activation of caspases. Inhibition of caspases blocks the cleavage of TDP-43, but does not prevent the accumulation of full-length protein in the cytoplasm. Using D-sorbitol as a stressor and caspase activator, we also demonstrate that the A90V variant of TDP-43, which lies adjacent to the caspase cleavage site within the nuclear localization sequence of TDP-43, confers partial resistance against caspase-mediated generation of the 35 kDa cleavage product.

Differential Effects of Mixtures of Cholesterol Oxidation Products on Bovine Aortic Endothelial Cells and Human Monocytic U937 Cells

Cholesterol oxidation products or oxysterols are of interest due to their hypothesized role in the development of atherosclerosis. The objective of the present study was to assess the cytotoxic effects of mixtures of oxysterols: 25-hydroxycholesterol (25-OHC), 7 β-hydroxycholesterol (7 β-OHC), and cholesterol-5 β,6 β-epoxide ( β-epox) on two cell types associated with the atherosclerotic process, bovine aortic endothelial (BAE) cells and human monocytic U937 cells. Cells were exposed to 25-OHC, 7 β-OHC, or β-epox, or equimolar mixtures (30 μM) of 25-OHC and 7 β-OHC, 25-OHC and β-epox, or 7 β-OHC and β-epox for 48 h. Cell viability was assessed using the fluorescein diacetate/ethidium bromide (FDA/ EtBr) assay and nuclear morphology following staining with Hoechst 33342. 25-OHC was the least toxic of the oxysterols and did not induce apoptosis in either cell line. Both 7 β-OHC and β-epox treatments were cytotoxic and induced apoptosis in the cells. Cotreatment with 25-OHC did not alter the toxicity of 7 β-OHC and β-epox in U937 cells but did decrease the percentage apoptotic cell death. In contrast, in the BAE cells cotreatment with 25-OHC had a slight protective effect on 7 β-OHC and β-epox–induced toxicities and a marked decrease in apoptotic cell death. The 7 β-OHC and β-epox mixture induced a significant increase in apoptotic cell death in U937 cells but decreased this mode of cell death in the BAE cells. The effects of oxysterols on glutathione levels also differed between the cells with changes noted in U937 and not in BAE cells. Results demonstrate interactive effects when oxysterols are studied as mixtures rather than single compounds in vitro.

The application of aptamer in apoptosis

As an indispensable process of cell life, apoptosis is essential for keeping homeostasis at cell level. Dysregulation of apoptosis is usually involved in the pathological processes of many complex diseases including cancer. With the properties such as high affinity and specificity to their targets, easy of synthesis and modification and good biocompatibility, aptamers have been attractive molecules applied in basic research, diagnostics and therapeutics. This review mainly focuses on the recent researches on application of aptamers in interference of cell apoptosis. Key targets along the intrinsic and extrinsic apoptosis pathways were respectively dissected using aptamers as a tool, providing an insight into the pathological processes, especially for cancer.

Ethanol and Acetaminophen Synergistically Induce Hepatic Aggregation and TCH346-Insensitive Nuclear Translocation of GAPDH

The glycolytic enzyme glyceraldehyde-3-phosphate dehydrogenase (GAPDH) signals during cellular stress via several post-translational modifications that change its folding properties, protein-protein interactions and sub-cellular localization. We examined GAPDH properties in acute mouse liver injury due to ethanol and/or acetaminophen (APAP) treatment. Synergistic robust and time-dependent nuclear accumulation and aggregation of GAPDH were observed only in combined, but not individual, ethanol/APAP treatments. The small molecule GAPDH-targeting compound TCH346 partially attenuated liver damage possibly via mitochondrial mechanisms, and independent of nuclear accumulation and aggregation of GAPDH. These findings provide a novel potential mechanism for hepatotoxicity caused by combined alcohol and acetaminophen exposure.

Mild mitochondrial metabolic deficits by α-ketoglutarate dehydrogenase inhibition cause prominent changes in intracellular autophagic signaling: Potential role in the pathobiology of Alzheimer's disease

Brain activities of the mitochondrial enzyme α-ketoglutarate dehydrogenase complex (KGDHC) are reduced in Alzheimer's disease and other age-related neurodegenerative disorders. The goal of the present study was to test the consequences of mild impairment of KGDHC on the structure, protein signaling and dynamics (mitophagy, fusion, fission, biogenesis) of the mitochondria. Inhibition of KGDHC reduced its in situ activity by 23-53% in human neuroblastoma SH-SY5Y cells, but neither altered the mitochondrial membrane potential nor the ATP levels at any tested time-points. The attenuated KGDHC activity increased translocation of dynamin-related protein-1 (Drp1) and microtubule-associated protein 1A/1B-light chain 3 (LC3) from the cytosol to the mitochondria, and promoted mitochondrial cytochrome c release. Inhibition of KGDHC also increased the negative surface charges (anionic phospholipids as assessed by Annexin V binding) on the mitochondria. Morphological assessments of the mitochondria revealed increased fission and mitophagy. Taken together, our results suggest the existence of the regulation of the mitochondrial dynamism including fission and fusion by the mitochondrial KGDHC activity via the involvement of the cytosolic and mitochondrial protein signaling molecules. A better understanding of the link among mild impairment of metabolism, induction of mitophagy/autophagy and altered protein signaling will help to identify new mechanisms of neurodegeneration and reveal potential new therapeutic approaches.

H2S Synthesizing Enzymes: Biochemistry and Molecular Aspects

Hydrogen sulfide (H2S) is a biologically active gas that is synthesized naturally by three enzymes, cystathionine γ-lyase (CSE), cystathionine β-synthetase (CBS) and 3-mercaptopyruvate sulfurtransferase (3-MST). These enzymes are constitutively present in a wide array of biological cells and tissues and their expression can be induced by a number of disease states. It is becoming increasingly clear that H2S is an important mediator of a wide range of cell functions in health and in disease. This review therefore provides an overview of the biochemical and molecular regulation of H2S synthesizing enzymes both in physiological conditions and their modulation in disease states with particular focus on their regulation in asthma, atherosclerosis and diabetes. The importance of small molecule inhibitors in the study of molecular pathways, the current use of common H2S synthesizing enzyme inhibitors and the relevant characteristics of mice in which these enzymes have been genetically deleted will also be summarized. With a greater understanding of the molecular regulation of these enzymes in disease states, as well as the availability of novel small molecules with high specificity targeted towards H2S producing enzymes, the potential to regulate the biological functions of this intriguing gas H2S for therapeutic effect can perhaps be brought one step closer.

Abnormal Glucose Metabolism in Alzheimer's Disease: Relation to Autophagy/Mitophagy and Therapeutic Approaches

Diminished glucose metabolism accompanies many neurodegenerative diseases including Alzheimer's disease. An understanding of the relation of these metabolic changes to the disease will enable development of novel therapeutic strategies. Following a metabolic challenge, cells generally conserve energy to preserve viability. This requires activation of many cellular repair/regenerative processes such as mitophagy/autophagy and fusion/fission. These responses may diminish cell function in the long term. Prolonged fission induces mitophagy/autophagy which promotes repair but if prolonged progresses to mitochondrial degradation. Abnormal glucose metabolism alters protein signaling including the release of proteins from the mitochondria or migration of proteins from the cytosol to the mitochondria or nucleus. This overview provides an insight into the different mechanisms of autophagy/mitophagy and mitochondrial dynamics in response to the diminished metabolism that occurs with diseases, especially neurodegenerative diseases such as Alzheimer's disease. The review discusses multiple aspects of mitochondrial responses including different signaling proteins and pathways of mitophagy and mitochondrial biogenesis. Improving cellular bioenergetics and mitochondrial dynamics will alter protein signaling and improve cellular/mitochondrial repair and regeneration. An understanding of these changes will suggest new therapeutic strategies.

Glutathione: new roles in redox signaling for an old antioxidant

The physiological roles played by the tripeptide glutathione have greatly advanced over the past decades superimposing the research on free radicals, oxidative stress and, more recently, redox signaling. In particular, GSH is involved in nutrient metabolism, antioxidant defense, and regulation of cellular metabolic functions ranging from gene expression, DNA and protein synthesis to signal transduction, cell proliferation and apoptosis. This review will be focused on the role of GSH in cell signaling by analysing the more recent advancements about its capability to modulate nitroxidative stress, autophagy, and viral infection.

Deferoxamine blocks death induced by glutathione depletion in PC 12 cells

The purpose of the present work was to investigate the mechanisms by which glutathione depletion induced by treatment with buthionine sulfoximine (BSO) led within 24-30 h to PC 12 cells apoptosis. Our results showed that treatment by relatively low concentrations (10-30 μM) of deferoxamine (DFx), a natural iron-specific chelator, almost completely shielded the cells from BSO-induced toxicity and that DFx still remained protective when added up to 9-12h after BSO treatment. On the other hand, phosphopeptides derived from milk casein and known to carry iron across cell membranes, markedly potentiated the toxic action of BSO when loaded with iron but were ineffective in sodium form. Kept for 24 h in serum-free medium, the cells underwent a decrease in glutathione content after BSO treatment, but remained viable. However, these BSO-pre-treated cells showed a rapid (90-120 min) decrease in cell viability when incubated with low doses of iron, whereas a great proportion of them remained viable in the presence of higher concentrations of copper and zinc. We also observed in PC 12 cells an early (4-8 h) and transient increase in the expression of ferritin subunits following BSO addition. Taken together these results suggest that BSO-induced glutathione depletion leads to an alteration of cellular iron homeostasis, which may contribute to its toxicity.

The redox state of cytochrome c modulates resistance to methotrexate in human MCF7 breast cancer cells

Background

Methotrexate is a chemotherapeutic agent used to treat a variety of cancers. However, the occurrence of resistance limits its effectiveness. Cytochrome c in its reduced state is less capable of triggering the apoptotic cascade. Thus, we set up to study the relationship among redox state of cytochrome c, apoptosis and the development of resistance to methotrexate in MCF7 human breast cancer cells.

Results

Cell incubation with cytochrome c-reducing agents, such as tetramethylphenylenediamine, ascorbate or reduced glutathione, decreased the mortality and apoptosis triggered by methotrexate. Conversely, depletion of glutathione increased the apoptotic action of methotrexate, showing an involvement of cytochrome c redox state in methotrexate-induced apoptosis. Methotrexate-resistant MCF7 cells showed increased levels of endogenous reduced glutathione and a higher capability to reduce exogenous cytochrome c. Using functional genomics we detected the overexpression of GSTM1 and GSTM4 in methotrexate-resistant MCF7 breast cancer cells, and determined that methotrexate was susceptible of glutathionylation by GSTs. The inhibition of these GSTM isoforms caused an increase in methotrexate cytotoxicity in sensitive and resistant cells.

Conclusions

We conclude that overexpression of specific GSTMs, GSTM1 and GSTM4, together with increased endogenous reduced glutathione levels help to maintain a more reduced state of cytochrome c which, in turn, would decrease apoptosis, thus contributing to methotrexate resistance in human MCF7 breast cancer cells.

Purine nucleoside analog--sulfinosine modulates diverse mechanisms of cancer progression in multi-drug resistant cancer cell lines

Achieving an effective treatment of cancer is difficult, particularly when resistance to conventional chemotherapy is developed. P-glycoprotein (P-gp) activity governs multi-drug resistance (MDR) development in different cancer cell types. Identification of anti-cancer agents with the potential to kill cancer cells and at the same time inhibit MDR is important to intensify the search for novel therapeutic approaches. We examined the effects of sulfinosine (SF), a quite unexplored purine nucleoside analog, in MDR (P-gp over-expressing) non-small cell lung carcinoma (NSCLC) and glioblastoma cell lines (NCI-H460/R and U87-TxR, respectively). SF showed the same efficacy against MDR cancer cell lines and their sensitive counterparts. However, it was non-toxic for normal human keratinocytes (HaCaT). SF induced caspase-dependent apoptotic cell death and autophagy in MDR cancer cells. After SF application, reactive oxygen species (ROS) were generated and glutathione (GSH) concentration was decreased. The expression of key enzyme for GSH synthesis, gamma Glutamyl-cysteine-synthetase (γGCS) was decreased as well as the expression of gst-π mRNA. Consequently, SF significantly decreased the expression of hif-1α, mdr1 and vegf mRNAs even in hypoxic conditions. SF caused the inhibition of P-gp (coded by mdr1) expression and activity. The accumulation of standard chemotherapeutic agent – doxorubicin (DOX) was induced by SF in concentration- and time-dependent manner. The best effect of SF was obtained after 72 h when it attained the effect of known P-gp inhibitors (Dex-verapamil and tariquidar). Accordingly, SF sensitized the resistant cancer cells to DOX in subsequent treatment. Furthermore, SF decreased the experssion of vascular endothelial growth factor (VEGF) on mRNA and protein level and modulated its secretion. In conclusion, the effects on P-gp (implicated in pharmacokinetics and MDR), GSH (implicated in detoxification) and VEGF (implicated in tumor-angiogenesis and progression) qualify SF as multi-potent anti-cancer agent, which use must be considered, in particular for resistant malignancies.

Glutathione efflux and cell death

SIGNIFICANCE

Glutathione (GSH) depletion is a central signaling event that regulates the activation of cell death pathways. GSH depletion is often taken as a marker of oxidative stress and thus, as a consequence of its antioxidant properties scavenging reactive species of both oxygen and nitrogen (ROS/RNS).

RECENT ADVANCES

There is increasing evidence demonstrating that GSH loss is an active phenomenon regulating the redox signaling events modulating cell death activation and progression.

CRITICAL ISSUES

In this work, we review the role of GSH depletion by its efflux, as an important event regulating alterations in the cellular redox balance during cell death independent from oxidative stress and ROS/RNS formation. We discuss the mechanisms involved in GSH efflux during cell death progression and the redox signaling events by which GSH depletion regulates the activation of the cell death machinery.

FUTURE DIRECTIONS

The evidence summarized here clearly places GSH transport as a central mechanism mediating redox signaling during cell death progression. Future studies should be directed toward identifying the molecular identity of GSH transporters mediating GSH extrusion during cell death, and addressing the lack of sensitive approaches to quantify GSH efflux.

Targeting mitochondria in the infection strategy of the hepatitis C virus

Hepatitis C virus (HCV) infection induces a state of oxidative stress more pronounced than that observed in many other inflammatory diseases. Here, we propose a temporal sequence of events in the HCV-infected cell whereby the primary alteration consists of a release of Ca(2+) from the endoplasmic reticulum, followed by uptake into mitochondria. This ensues successive mitochondrial dysfunction leading to the generation of reactive oxygen species and a progressive metabolic adaptive response. Evidence is provided for a positive feed-back mechanism between alterations of calcium and redox homeostasis. This likely involves deregulation of the mitochondrial permeability transition and induces progressive dysfunction of cellular bioenergetics. Pathogenetic implications of the model and new opportunities for therapeutic intervention are discussed. This article is part of a Directed Issue entitled: Bioenergetic dysfunction, adaptation and therapy.

Elevated skeletal muscle apoptotic signaling following glutathione depletion

Oxidative stress has a well-established role in numerous intracellular signaling pathways, including apoptosis. Glutathione is an important cellular antioxidant and is the most abundant low molecular weight thiol in the cell. Although previous work has shown a link between glutathione and apoptosis, this relationship has not been defined in skeletal muscle. The present investigation examined the effect of glutathione depletion on skeletal muscle apoptotic signaling, and mitochondrial apoptotic-susceptibility. Administration of L: -buthionine-[S,R]-sulfoximine (BSO; 30 mM in drinking water for 10 days) caused glutathione depletion in whole muscle and isolated mitochondria, as well as elevated muscle catalase protein content and reactive oxygen species (ROS) generation. Glutathione depletion was associated with elevated DNA fragmentation, mitochondrial Bax levels, Poly(ADP-ribose) polymerase (PARP) cleavage, and calpain activity; however, caspase-3, -8, and -9 activity were not altered. BSO administration was also associated with higher cytosolic and nuclear protein levels of apoptosis-inducing factor (AIF), but not cytochrome c, second mitochondria-derived activator of caspase (Smac), or endonuclease G (EndoG). In addition, isolated mitochondria from BSO animals demonstrated significantly lower membrane potential, increased Ca(2+)-induced permeability transition pore opening, and greater basal and ROS-induced AIF and cytochrome c release. These results demonstrate that glutathione depletion in skeletal muscle increases caspase-independent signaling, as well as augments mitochondrial-associated apoptotic events to subsequent cell death stimuli.

The cyclophilin inhibitor alisporivir prevents hepatitis C virus-mediated mitochondrial dysfunction

Alisporivir (Debio-025) is an analogue of cyclosporine A and represents the prototype of a new class of non-immunosuppressive cyclophilin inhibitors. In vitro and in vivo studies have shown that alisporivir inhibits hepatitis C virus (HCV) replication, and ongoing clinical trials are exploring its therapeutic potential in patients with chronic hepatitis C. Recent data suggest that the antiviral effect is mediated by inhibition of cyclophilin A, which is an essential host factor in the HCV life cycle. However, alisporivir also inhibits mitochondrial permeability transition by binding to cyclophilin D. Because HCV is known to affect mitochondrial function, we explored the effect of alisporivir on HCV protein-mediated mitochondrial dysfunction. Through the use of inducible cell lines, which allow to investigate the effects of HCV polyprotein expression independent from viral RNA replication and which recapitulate the major alterations of mitochondrial bioenergetics observed in infectious cell systems, we show that alisporivir prevents HCV protein-mediated decrease of cell respiration, collapse of mitochondrial membrane potential, overproduction of reactive oxygen species and mitochondrial calcium overload. Strikingly, some of the HCV-mediated mitochondrial dysfunctions could even be rescued by alisporivir.

CONCLUSION

These observations provide new insights into the pathogenesis of HCV-related liver disease and reveal an additional mechanism of action of alisporivir that is likely beneficial in the treatment of chronic hepatitis C.

PARP-1 inhibition induces a late increase in the level of reactive oxygen species in cells after ionizing radiation

Poly(ADP-ribose) polymerase 1 (PARP1), an enzyme activated by DNA strand breaks, synthesizes polymers of poly(ADP-ribose) (PAR) that modify chromatin and other proteins and play a role in DNA repair. Inhibition of PARP1 activity is considered a potentially important strategy in clinical practice, especially to sensitize tumor cells to chemo- and radio-therapy. Here we examined the influence of inhibition of PARP1 on formation of reactive oxygen species (ROS) and on DNA repair in cells exposed to ionizing radiation (IR). K562 (human myelogenous leukaemia) cells were grown and exposed to 4 or 12 Gy of ionizing radiation in presence or absence of the PARP inhibitor NU1025 (100 μM). Intracellular ROS were assayed using the probe 2,7-dichlorofluorescein with detection by flow cytometry and the rejoining of DNA strand breaks were followed by alkaline single cell gel electrophoresis (comet) assays. In untreated cells a significant increase in PAR formation occurred during the first 5 min after IR, followed by a gradual decrease up to 30 min. Addition of a PARP inhibitor arrested the production of PAR almost completely and decreased the rate of rejoining of DNA strand breaks significantly; however, 3h after irradiation we observed no difference in the amount of DNA strand breaks between PARP inhibitor-treated and untreated cells. Twelve to 48 h after irradiation, an increase of ROS concentration was observed in irradiated cells and ROS levels in PARP inhibitor-treated cells were significantly higher than in cells without inhibitor. Irradiated cells grown in the presence or absence of PARP inhibitor did not differ in the frequencies of apoptotic and necrotic cells or in the activity of caspases at 24, 48 and 72 h after irradiation. Poly(ADP-ribosylation) and inhibition of PARP1 appeared to modulate DNA strand break rejoining and influence the concentration of ROS in irradiated cells.

Redox regulation in plant programmed cell death

Programmed cell death (PCD) is a genetically controlled process described both in eukaryotic and prokaryotic organisms. Even if it is clear that PCD occurs in plants, in response to various developmental and environmental stimuli, the signalling pathways involved in the triggering of this cell suicide remain to be characterized. In this review, the main similarities and differences in the players involved in plant and animal PCD are outlined. Particular attention is paid to the role of reactive oxygen species (ROS) as key inducers of PCD in plants. The involvement of different kinds of ROS, different sites of ROS production, as well as their interaction with other molecules, is crucial in activating PCD in response to specific stimuli. Moreover, the importance is stressed on the balance between ROS production and scavenging, in various cell compartments, for the activation of specific steps in the signalling pathways triggering this cell suicide process. The review focuses on the complexity of the interplay between ROS and antioxidant molecules and enzymes in determining the most suitable redox environment required for the occurrence of different forms of PCD.

Ce³+ ions determine redox-dependent anti-apoptotic effect of cerium oxide nanoparticles

Antioxidant therapy is the novel frontier to prevent and treat an impressive series of severe human diseases, and the search for adequate antioxidant drugs is fervent. Cerium oxide nanoparticles (nanoceria) are redox-active owing to the coexistence of Ce(3+) and Ce(4+) oxidation states and to the fact that Ce(3+) defects, and the compensating oxygen vacancies, are more abundant at the surface. Nanoceria particles exert outstanding antioxidant effects in vivo acting as well-tolerated anti-age and anti-inflammatory agents, potentially being innovative therapeutic tools. However, the biological antioxidant mechanisms are still unclear. Here, the analysis on two leukocyte cell lines undergoing apoptosis via redox-dependent or independent mechanisms revealed that the intracellular antioxidant effect is the direct cause of the anti-apoptotic and prosurvival effects of nanoceria. Doping with increasing concentrations of Sm(3+), which progressively decreased Ce(3+) without affecting oxygen vacancies, blunted these effects, demonstrating that Ce(3+)/Ce(4+) redox reactions are responsible for the outstanding biological properties of nanoceria.

Pulmonary function and oxidative stress in workers exposed to styrene in plastic factory: occupational hazards in styrene-exposed plastic factory workers

Styrene is a volatile organic compound used in factories for synthesis of plastic products. The pneumotoxicity of styrene in experimental animals is known. The aim of the present study was to study the effect of styrene on lung function and oxidative stress in occupationally exposed workers in plastic factory. Thirty-four male workers, between 18 and 40 years of age, exposed to styrene for atleast 8 hours a day for more than a year were studied, while 30 age- and sex-matched healthy subjects not exposed to styrene served as controls. Assessment of lung functions showed a statistically significant reduction (p < 0.05) in most of the lung volumes, capacities (FVC, FEV(1), VC, ERV, IRV, and IC) and flow rates (PEFR, MEF(75%), and MVV) in the study group (workers) as compared to controls. Malondialdehyde (MDA) was observed to be significantly high (p < 0.05) while ferric-reducing ability of plasma (FRAP) was significantly low (p < 0.05) in styrene-exposed subjects. Reduced glutathione (GSH) level was significantly depleted in exposed subjects as compared to control group. The mean value of serum cytochrome c in styrene-exposed subjects was found to be 1.1 ng/ml (0.89-1.89) while in control its levels were under detection limit (0.05 ng/ml). It shows that styrene inhalation by workers leads to increased level of oxidative stress, which is supposed to be the cause of lung damage.

Role of glutathione in augmenting the anticancer activity of pyrroloquinoline quinone (PQQ)

Pyrroloquinoline quinone (PQQ), a bacterial redox co-factor and antioxidant, is highly reactive with nucleophilic compounds present in biological fluids. PQQ induced apoptosis in human promonocytic leukemia U937 cells and this was accompanied by depletion of the major cellular antioxidant glutathione and increase in intracellular reactive oxygen species (ROS). Treatment with glutathione (GSH) or N-acetyl-L-cysteine (NAC) did not spare PQQ toxicity but resulted in a 2-5-fold increase in PQQ-induced apoptosis in U937 cells. Cellular GSH levels increased following treatment by NAC alone but were severely depleted by co-treatment with NAC and PQQ. This was accompanied by an increase in intracellular ROS. Alternatively, depletion of glutathione also resulted in increased PQQ cytotoxicity. However, the cells underwent necrosis as evidenced by dual labeling with annexin V and propidium iodide. PQQ-induced cytotoxicity is thus critically regulated by the cellular redox status. An increase in GSH can augment apoptosis and its depletion can switch the mode of cell death to necrosis in the presence of PQQ. Our data suggest that modulation of intracellular GSH can be used as an effective strategy to potentiate cytotoxicity of quinones like PQQ.

Multistep and multitask Bax activation

Bax is a pro-apoptotic protein allowing apoptosis to occur through the intrinsic, damage-induced pathway, and amplifying that one occurring via the extrinsic, receptor mediated pathway. Bax is present in viable cells and activated by pro-apoptotic stimuli. Activation implies structural changes, consisting of exposure of the N terminus and hydrophobic domains; changes in localization, consisting in migration from cytosol to mitochondria and endoplasmic reticulum membranes; changes in the aggregation status, from monomer to dimer and multimer. Bax has multiple critical domains, namely the N terminus exposed after activation; two hydrophobic stretches exposed for membrane anchorage; two reactive cysteines allowing multimerization; the BH3 domain for interactions with the Bcl-2 family members; alpha helix 1 for t-Bid interaction. Bax has also multiple functions: it releases different mitochondrial factors such as cytochrome c, SMAC/diablo; it regulates mitochondrial fission, the mitochondrial permeability transition pore; it promotes Ca(2+) leakage through ER membrane. Altogether, Bax activation is a complex multi-step phenomenon. Here, we analyze these events as logically separable or alternative steps, attempting to assess their role, timing and reciprocal relation.

Comparison of glutathione reductase activity and the intracellular glutathione reducing effects of 13 derivatives of 1'-acetoxychavicol acetate in Ehrlich ascites tumor cells

In a previous study, we showed that (1'S)-acetoxychavicol acetate ((S)-ACA) caused a rapid decrease in glutathione (GSH) levels less than 15 min after exposure. (S)-ACA-induced cell death was reversed by the addition of N-acetylcysteine. In the current study, we investigated the inhibitory activities of 13 derivatives of (S)-ACA on tumor cell viability, intracellular GSH level and GR activity. Correlations were found among a decrease in cell viability, intracellular GSH levels and the activity of GR in Ehrlich ascites tumor cells treated with the various ACA analogues. A test of the 13 derivatives revealed that the structural factors regulating activity were as follows: (1) the para or 1'-position of acetoxyl group (or other acyl group) was essential, (2) the presence of a C2'-C3' double or triple bond was essential, and (3) the S configuration of the 1'-acetoxyl group was preferable.

Proteomic analysis of the protective effects of Platycodi Radix in liver of chronically alcoholic rats

In this study, we examined the effect of Platycodi Radix (PR) supplementation in chronically alcoholic rats. Sprague-Dawley rats were divided into three groups: control group (no alcohol), alcohol group (36.8% of total calories), and 0.3% PR group. The levels of serum alanine aminotransferase (ALT) and aspartate aminotransferase (AST) were increased by alcohol treatment, and PR supplementation normalized the AST level. Moreover, alcohol-induced cytochrome P450 2E1 was decreased by PR treatment. Proteomic analysis of liver tissues of alcohol-exposed rats and PR-supplemented rats revealed that 50 different proteins functionally characterized as involved with cytoskeleton regulation, signal transduction, cytokine, apoptosis, and reactive oxygen species metabolism showed significant quantitative changes. The expression levels of glutathione S-transferase mu, Bcl-2-like protein, and peroxiredoxin IV were decreased in the alcoholic group, whereas the levels of these proteins were increased more than threefold in the PR group. However, the expression levels of smooth muscle actin, cytochrome P450 2D, mitogen-activated protein kinase 8, and 3alpha-hydroxysteroid dehydrogenase were increased in the alcohol group and were decreased in the PR group. These data suggest that the antioxidant enzymes may play a protective role against alcohol-induced damage via oxidative stress defense mechanisms induced by PR supplementation.

Antiapoptotic effects of dietary antioxidants towards N-nitrosopiperidine and N-nitrosodibutylamine-induced apoptosis in HL-60 and HepG2 cells

The aim of this work was to determine the effect of vitamin C, diallyl disulfide (DADS) and dipropyl disulfide (DPDS) towards N-nitrosopiperidine (NPIP) and N-nitrosodibutylamine (NDBA)-induced apoptosis in human leukemia (HL-60) and hepatoma (HepG2) cell lines using the terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling assay. None of the vitamin C (5-50 microm), DADS and DPDS (1-5 microm) concentrations selected induced a significant percentage of apoptosis. In simultaneous treatments, vitamin C, DADS and DPDS reduced the apoptosis induced by NPIP and NDBA in HL-60 and HepG2 cells (around 70% of reduction). We also investigated its scavenging activities towards reactive oxygen species (ROS) produced by NPIP and NDBA using 2',7'-dichlorodihydrofluorescein diacetate in both cell lines. ROS production induced by both N-nitrosamine was reduced to control levels by vitamin C (5-50 microm) in a dose-dependent manner. However, DADS (5 microm) increased ROS levels induced by NPIP and NDBA in HL-60 (40 and 20% increase, respectively) and HepG2 cells (18% increase), whereas DPDS was more efficient scavenger of ROS at the lowest concentration (1 microm) in both HL-60 (52 and 25% reduction, respectively) and HepG2 cells (24% reduction). The data demonstrated that the scavenging ability of vitamin C and DPDS could contribute to inhibition of the NPIP- and NDBA-induced apoptosis. However, more than one mechanism, such as inhibition of phase I and/or induction of phase II enzymes, could be implicated in the protective effect of dietary antioxidants towards NPIP- and NDBA-induced apoptosis in HL-60 and HepG2 cells.

Oxidative stress in non-small cell lung cancer: role of nicotinamide adenine dinucleotide phosphate oxidase and glutathione

BACKGROUND

Cigarette smoke is strongly associated with NSCLC, but the carcinogenesis of NSCLC is poorly understood.

METHODS

To discover the role of oxidative stress and anti-oxidative defense in NSCLC, we measured NADPH oxidase (NOX) activity, myeloperoxidase activity, 8-OHdG, and glutathione content from lung specimens. These came from 32 patients: 22 NSCLC patients and ten controls without cancer.

RESULTS

In NSCLC patients, NOX activity was significantly higher both in the malignant (p = 0.001) and non-malignant (p = 0.044) samples from NSCLC patients, than in the control specimens. Myeloperoxidase activity was lower (p = 0.001) and glutathione content (p = 0.009) higher in malignant tissue. No significant difference was observable in 8-OHdG content between patient groups.

CONCLUSIONS

Increase in NOX activity in the malignant tissues was independent of smoking history and myeloperoxidase activity, suggesting its independent role in NSCLC pathogenesis.

Redox control of asthma: molecular mechanisms and therapeutic opportunities

An imbalance in reducing and oxidizing (redox) systems favoring a more oxidative environment is present in asthma and linked to the pathophysiology of the defining symptoms and signs including airflow limitation, hyper-reactivity, and airway remodeling. High levels of hydrogen peroxide, nitric oxide ((*)NO), and 15-F(2t)-isoprostane in exhaled breath, and excessive oxidative protein products in lung epithelial lining fluid, peripheral blood, and urine provide abundant evidence for pathologic oxidizing processes in asthma. Parallel studies document loss of reducing potential by nonenzymatic and enzymatic antioxidants. The essential first line antioxidant enzymes superoxide dismutases (SOD) and catalase are reduced in asthma as compared to healthy individuals, with lowest levels in those patients with the most severe asthma. Loss of SOD and catalase activity is related to oxidative modifications of the enzymes, while other antioxidant gene polymorphisms are linked to susceptibility to develop asthma. Monitoring of exhaled (*)NO has entered clinical practice because it is useful to optimize asthma care, and a wide array of other biochemical oxidative and nitrative biomarkers are currently being evaluated for asthma monitoring and phenotyping. Novel therapeutic strategies that target correction of redox abnormalities show promise for the treatment of asthma.

Apoptotic and necrotic action mechanisms of trimethyltin in human hepatoma G2 (HepG2) cells

In evaluating the cytotoxic effects and the mechanisms of the apoptotic and necrotic actions of trimethyltin chloride (TMT) on human hepatoma G2 (HepG2) cells, the present study focused on the involvement of antiproliferation, DNA damage, cell death, apoptosis-related proteins, and p53-dependent transcriptional activity. Twenty-four hour TMT treatments (4-64 microM) induced apoptosis and necrosis in HepG2 cells. Thirty-two micromolar and higher concentration significantly increases cell death. DNA damage was observed at 8 microM. Additionally, TMT increased the activity of cellular caspase-3 and the release of mitochondrial cytochrome c in a concentration-dependent manner. Our data demonstrated that the Bcl-2 family of proteins was involved in the apoptotic process but that p53 expression level was not affected. The results of luciferase reporter assay indicated that TMT-induced apoptosis seemed to adopt a transcription-dependent route, by activating p53 target genes such as PUMA and p21.

Origanum vulgare induces apoptosis in human colon cancer caco2 cells

Oregano spice is widely used in the Mediterranean diet, which is associated with a low risk for colon cancer. Although the medicinal benefits of oregano, such as the anti-inflammatory and antimicrobial activities, are well known; nonetheless, only few data are available on its effect in cancer prevention, especially concerning the mechanism of action. Here, we investigated the effect of Origanum vulgare ethanolic extracts on redox balance, cell proliferation, and cell death in colon adenocarcinoma Caco2 cells. Oregano extract leads to growth arrest and cell death in a dose- and time-dependent manner. Changes in glutathione content, as well as the increase in its oxidized form, may be involved in oregano-triggered death. Both extrinsic and intrinsic apoptotic pathways appear to be activated by spice extract. Our findings suggest that oregano amounts found in the Mediterranean diet can exert proapoptotic effects, which are selective for cancer cells. Moreover, whole extract, instead of a specific component, can be responsible for the observed cytotoxic effects.

Neurobehavioral impairments, generation of oxidative stress and release of pro-apoptotic factors after chronic exposure to sulphur mustard in mouse brain

Recent global events have focused attention on the potential threat of international and domestic chemical terrorism, as well as the possibility of chemical warfare proliferation. Sulphur mustard (SM) is one of the potent chemical warfare agents (CWA), which initiates a cascade of events that converge on the redox mechanisms common to brain injury. The present study was designed to examine the effects of chronic SM exposure on neurobehavioral impairments, mitochondrial oxidative stress in male Swiss Albino mice and its role in inducing apoptotic neuronal cell death. The animals were divided into four groups (control, low, medium and high dose) of 5 animals each. Exposure to SM was given percutaneously daily for 12 weeks. The results demonstrated impairment in neurobehavioral indices viz. rota rod, passive avoidance and water maze tests in a dose dependent manner. There was a significant increase in lipid peroxidation and protein carbonyl content whereas, decrease in the activity of manganese superoxide dismutase (MnSOD), glutathione reductase and glutathione peroxidase suggesting impaired antioxidant defense system. Immunoblotting of cytochrome c, Bcl-2, Bax and activation of caspase-3 suggest induction of apoptosis in a dose dependent manner. Finally, increased p53 expression suggests that it may target the mitochondrial pathway for inducing apoptosis in response to DNA damage signals. In conclusion, chronic SM exposure may have the potential to generate oxidative stress which may trigger the release of cytochrome c as well as caspase-3 activation in neurons leading to cell death by apoptosis in a dose dependent manner which may in the end be responsible for the disruption of cognitive functions in mice.

Neutral sphingomyelinase-induced ceramide accumulation by oxidative stress during carbon tetrachloride intoxication

Ceramide is a biologically active lipid causing apoptosis in a variety of cells. In this study, we examined the effect of CCl4 on the ceramide metabolism and indicators of oxidative stress. After 12 h of oral administration of CCl4 (4 ml/kg body weight as a 1:1 mixture of CCl4 and mineral oil) to rats, aspartate aminotransferase (AST) and alanine aminotransferase (ALT) were increased. Antioxidants such as vitamins C and E were decreased in the liver and kidney. In addition, the ratio of GSH/GSSG in the liver, plasma, kidney, and brain decreased at 2h. The total ceramide in the liver significantly increased as early as 2h after CCl4 administration. After 24 and 36 h, the total ceramide in plasma and the kidney was also augmented. In the brain, the total ceramide dramatically increased at 36 h. These results suggested that the increased ceramide in plasma was transferred to the kidney and the brain. The activity of neutral sphingomyelinase (SMase), which was reported to be enhanced by the decrease of GSH, was significantly increased after CCl4 treatment in the liver, kidney, and brain. However, acid SMase activities were not increased in the liver and kidney. Thus, the activation of neutral SMase via oxidative stress induced the increase of ceramide during CCl4 intoxication in not only the liver but also other tissues. These results suggested that the excess accumulation of ceramide causes damage in other organs including the kidney and brain during fulminant hepatic failure.

Effect of polyI:C cotreatment on halothane-induced liver injury in mice

Drug-induced liver injury (DILI) is a challenging problem in drug development and clinical practice. Patient susceptibility to DILI is multifactorial, making these reactions difficult to predict and prevent. Clinical observations have suggested that concurrent bacterial and viral infections represent an important risk factor in determining patient susceptibility to developing adverse drug reactions, although the underlying mechanism is not clear. In the present study, we employed the viral RNA mimetic (polyinosinic-polycytidylic acid [polyI:C]) to emulate viral infection and examined its effect on halothane-induced liver injury. Although pretreatment of mice with polyI:C attenuated halothane hepatotoxicity due to its inhibitory effect on halothane metabolism, posttreatment significantly exacerbated liver injury with hepatocellular apoptosis being significantly higher than that in mice treated with polyI:C alone or halothane alone. The pan-caspase inhibitor z-VAD-fmk suppressed liver injury induced by polyI:C/posthalothane cotreatment, suggesting that the increased hepatocyte apoptosis contributes to the exacerbation of liver injury. Posttreatment with polyI:C also caused activation of hepatic Kupffer cells (KCs) and natural killer (NK) cells and upregulated multiple proapoptotic factors, including tumor necrosis factor-alpha (TNF-alpha), NK receptor group 2, member D (NKG2D), and Fas ligand (FasL). These factors may play important roles in mediating polyI:C-induced hepatocyte apoptosis.

CONCLUSION

This is the first study to provide evidence that concurrent viral infection can inhibit cytochrome (CYP)450 activities and activate the hepatic innate immune system to proapoptotic factors. DILI may be attenuated or exacerbated by pathogens depending on the time of infection.

Oxidative, multistep activation of the noncanonical NF-kappaB pathway via disulfide Bcl-3/p50 complex

Buthionine sulfoximine (BSO) is a well-known inhibitor of glutathione synthesis, producing slow glutathione (GSH) depletion and oxidative stress; some "responder" cells avoid BSO-induced death by trans-activating the prosurvival protein Bcl-2. Here we show that BSO activates a noncanonical, inhibitory NF-kappaB- and p65-independent NF-kappaB pathway via a multistep process leading to the up-regulation of Bcl-2. The slow BSO-induced GSH depletion allows separation of two redox-related phases, namely, early thiol disequilibrium and late frank oxidative stress; each phase contributes to the progressive activation of a p50-p50 homodimer. The early phase, coinciding with substantial thiol depletion, produces a cytosolic preparative complex, consisting of p50 and its interactor Bcl-3 linked by interprotein disulfide bridges. The late phase, coinciding with reactive oxygen species production, is responsible, probably via p38 activation, for nuclear targeting of the complex and trans-activation of Bcl-2.

Melatonin antagonizes the intrinsic pathway of apoptosis via mitochondrial targeting of Bcl-2

We have recently shown that melatonin antagonizes damage-induced apoptosis by interaction with the MT-1/MT-2 plasma membrane receptors. Here, we show that melatonin interferes with the intrinsic pathway of apoptosis at the mitochondrial level. In response to an apoptogenic stimulus, melatonin allows mitochondrial translocation of the pro-apoptotic protein Bax, but it impairs its activation/dimerization The downstream apoptotic events, i.e. cytochrome c release, caspase 9 and 3 activation and nuclear vesiculation are equally impaired, indicating that melatonin interferes with Bax activation within mitochondria. Interestingly, we found that melatonin induces a strong re-localization of Bcl-2, the main Bax antagonist to mitochondria, suggesting that Bax activation may in fact be antagonized by Bcl-2 at the mitochondrial level. Indeed, we inhibit the melatonin anti-apoptotic effect (i) by silencing Bcl-2 with small interfering RNAs, or with small-molecular inhibitors targeted at the BH3 binding pocket in Bcl-2 (i.e. the one interacting with Bax); and (ii) by inhibiting melatonin-induced Bcl-2 mitochondrial re-localization with the MT1/MT2 receptor antagonist luzindole. This evidence provides a mechanism that may explain how melatonin through interaction with the MT1/MT2 receptors, elicits a pathway that interferes with the Bcl-2 family, thus modulating the cell life/death balance.

Redox compartmentalization in eukaryotic cells

Diverse functions of eukaryotic cells are optimized by organization of compatible chemistries into distinct compartments defined by the structures of lipid-containing membranes, multiprotein complexes and oligomeric structures of saccharides and nucleic acids. This structural and chemical organization is coordinated, in part, through cysteine residues of proteins which undergo reversible oxidation-reduction and serve as chemical/structural transducing elements. The central thiol/disulfide redox couples, thioredoxin-1, thioredoxin-2, GSH/GSSG and cysteine/cystine (Cys/CySS), are not in equilibrium with each other and are maintained at distinct, non-equilibrium potentials in mitochondria, nuclei, the secretory pathway and the extracellular space. Mitochondria contain the most reducing compartment, have the highest rates of electron transfer and are highly sensitive to oxidation. Nuclei also have more reduced redox potentials but are relatively resistant to oxidation. The secretory pathway contains oxidative systems which introduce disulfides into proteins for export. The cytoplasm contains few metabolic oxidases and this maintains an environment for redox signaling dependent upon NADPH oxidases and NO synthases. Extracellular compartments are maintained at stable oxidizing potentials. Controlled changes in cytoplasmic GSH/GSSG redox potential are associated with functional state, varying with proliferation, differentiation and apoptosis. Variation in extracellular Cys/CySS redox potential is also associated with proliferation, cell adhesion and apoptosis. Thus, cellular redox biology is inseparable from redox compartmentalization. Further elucidation of the redox control networks within compartments will improve the mechanistic understanding of cell functions and their disruption in disease.

Conformational change in the active center region of GST P1-1, due to binding of a synthetic conjugate of DXR with GSH, enhanced JNK-mediated apoptosis

Treatment of cells with a synthetic conjugate of DXR with GSH via glutaraldehyde (GSH-DXR) caused cytochrome c to be released from the mitochondria to the cytosol following potent activation of caspase-3 and -9 by typical DNA fragmentation. This apoptosis was regulated by the JNK-signaling pathway. In the present experiment, binding of GSH-DXR to GST P1-1 allosterically led to the disappearance of its enzyme activity and activated the kinase activity of JNK without dissociation of the JNK-GST P1-1 complex. The recombinant GST P1-1 molecule with a mutation in the active center region (W38H and C47S) lost its GST activity when bound to JNK to the same degree as the wild-type, with the mutated GST P1-1 molecule failing to inhibit the activity of JNK. It has been reported that JNK-signaling is regulated by GST P1-1 via interaction with the C-terminus. We confirmed that GST P1-1 deletion mutant (Delta194-209) and a site-directed mutant (R201A) in the C-terminal region failed to bind and inhibit JNK. These results indicated that not only binding of the C-terminal region of GST P1-1 to the JNK molecule, but also the active center region of GST P1-1 play important roles in the regulation of JNK enzyme activity. The findings suggested that allosteric inhibition of GST P1-1 activity by the binding of GSH-DXR following conformational change may activate JNK and induce apoptosis via the mitochondrial pathway in the cells.

Sequential phases of Ca2+ alterations in pre-apoptotic cells

The very early events of the intrinsic, damage-induced apoptotic pathway, i.e., upstream to Bax activation, probably consist of physico-chemical alterations (i.e., redox, pH or Ca2+ changes) rather then subtle molecular interactions, and in spite of many studies they remain unclear. One problem is that cells undergo apoptosis in an asynchronous way, leading to heterogeneity in the cell population that impairs the results of bulk analyses. In this study, we present a flow cytometric approach for studying Ca2+ alteration in apoptosis at the single cell level. By means of a multiparametric analysis, we could discriminate different sub-populations, i.e., viable and apoptotic cells and cells in secondary necrosis, and separately analyse static as well as dynamic Ca2+ parameters in each sub-population. With this approach, we have identified a set of sequential Ca2+ changes; two very early ones occur prior to any other apoptotic alterations, whereas a later change coincides with the appearance of apoptosis. Interestingly, the two pre-apoptotic changes occur simultaneously in all treated cells, i.e., at fixed times post-treatment, whereas the later one occurs at varying times, i.e., within a wide time range, concomitantly with the other apoptotic events.

H2S, Endoplasmic Reticulum Stress, and Apoptosis of Insulin-secreting Beta Cells

Cystathionine gamma-lyase (CSE) is a key enzyme in the trans-sulfuration pathway, which uses L-cysteine to produce hydrogen sulfide (H2S). Functional changes of pancreatic beta cells induced by endogenous H2S have been reported, but the effect of the CSE/H2S system on pancreatic beta cell survival has not been known. In this study, we demonstrate that H2Sat physiologically relevant concentrations induced apoptosis of INS-1E cells, an insulin-secreting beta cell line. Transfection of INS-1E cells with a recombinant defective adenovirus containing the CSE gene (Ad-CSE) resulted in a significant increase in CSE expression and H2S production. Ad-CSE transfection also stimulated apoptosis. The other two end products of CSE-catalyzed enzymatic reaction, ammonium and pyruvate, had no effects on INS-1E cell apoptosis, indicating that overexpression of CSE may stimulate INS-1E cell apoptosis via increased endogenous production of H2S. Both exogenous H2S (100 microM) and Ad-CSE transfection inhibited ERK1/2 but activated p38 MAPK. Interestingly, BiP and CHOP, two indicators of endoplasmic reticulum (ER) stress, were up-regulated in H2S-and CSE-mediated apoptosis in INS-1E cells. After suppressing CHOP mRNA expression, H2S-induced apoptosis of INS-1E cells was significantly decreased. Inhibition of p38 MAPK, but not of ERK1/2, inhibited the expression of BiP and CHOP and decreased H2S-stimulated apoptosis, suggesting that p38 MAPK activation functions upstream of ER stress to initiate H2S-induced apoptosis. It is concluded that H2S induces apoptosis of insulin-secreting beta cells by enhancing ER stress via p38 MAPK activation. Our findings may help unmask a novel role of CSE/H2S system in regulating pancreatic functions under physiological condition and in diabetes.

The cleavage mode of apoptotic nuclear vesiculation is related to plasma membrane blebbing and depends on actin reorganization

In U937 monocytic cells induced to apoptosis, plasma membrane blebbing of different intensities appears, before the development of nuclear alterations; this latter phenomenon can occur through two major pathways, namely the cleavage and the budding mode (Dini et al., 1996). Strongly blebbing cells develop deep nuclear constrictions leading to nuclear fragmentation according to the cleavage mode, while cells with milder forms of blebbing, or no blebbing at all, undergo nuclear fragmentation along the budding mode. Compounds interfering with different cytoskeletal components affect blebbing, which is completely inhibited by the actin polymerization inhibitors, cytochalasins, while disturbance of tubulin network with taxol limits blebbing to milder forms. At the same time, the cytoskeletal poisons affect the type of nuclear fragmentation, abolishing the cleavage mode, shifting all events into the budding pathway. Adherent cells, which possess a more structured cytoskeleton, do not develop strong blebs and undergo nuclear fragmentation via budding. These observations suggest that the deep cytoskeletal movements that cause the strongest forms of plasma membrane blebbing strangle the nucleus, leading to the constrictions that later evolve into nuclear fragmentation by cleavage. The trigger for the cytoskeletal movements, known to be redox-sensitive, is probably the apoptotic GSH extrusion.

Inhibition of acrolein-induced apoptosis by the antioxidant N-acetylcysteine

Acrolein is a highly electrophilic alpha,beta-unsaturated aldehyde to which humans are exposed in many situations. It is an environmental pollutant that is responsible for multiple respiratory diseases and has been implicated in neurodegenerative diseases such as Alzheimer's disease. The hypothesis of the study is that the antioxidant N-acetylcysteine (NAC), a precursor of glutathione, could protect cells against acrolein-induced apoptosis. Exposure of Chinese hamster ovary cells to a noncytotoxic dose of acrolein (4 fmol/cell) depleted intracellular glutathione to 45% of initial levels. NAC, which increased intracellular glutathione levels by 30%, afforded protection against acrolein-induced cytotoxicity (loss of cell proliferation) and apoptosis. NAC protected against apoptosis by diminishing acrolein-induced activation of the mitochondrial death pathway. NAC inhibited acrolein-induced Bad translocation from the cytosol to the mitochondria, as well as Bcl-2 translocation from mitochondria to the cytosol, as evaluated by Western blot analysis. However, NAC had no effect on acrolein-induced Bax translocation to mitochondria and cytochrome c liberation into the cytosol. Meanwhile, NAC inhibited depolarization of mitochondrial membrane potential, as evaluated by rhodamine fluorescence using flow cytometry. NAC also inhibited procaspase-9 processing, activation of enzymatic activity of caspase-9, -7, and -8, and poly(ADP-ribose) polymerase cleavage induced by acrolein. Inhibition of acrolein-induced apoptosis using NAC was confirmed morphologically by diminished condensation of nuclear chromatin, as evaluated by fluorescence microscopy. These findings suggest that NAC could be potentially useful as a protective agent for people exposed to acrolein.

NMR exposure sensitizes tumor cells to apoptosis

NMR technology has dramatically contributed to the revolution of image diagnostic. NMR apparatuses use combinations of microwaves over a homogeneous strong (1 Tesla) static magnetic field. We had previously shown that low intensity (0.3-66 mT) static magnetic fields deeply affect apoptosis in a Ca2+ dependent fashion (Fanelli et al., 1999 FASEBJ., 13;95-102). The rationale of the present study is to examine whether exposure to the static magnetic fields of NMR can affect apoptosis induced on reporter tumor cells of haematopoietic origin. The impressive result was the strong increase (1.8-2.5 fold) of damage-induced apoptosis by NMR. This potentiation is due to cytosolic Ca2+ overload consequent to NMR-promoted Ca2+ influx, since it is prevented by intracellular (BAPTA-AM) and extracellular (EGTA) Ca2+ chelation or by inhibition of plasma membrane L-type Ca2+ channels. Three-days follow up of treated cultures shows that NMR decrease long term cell survival, thus increasing the efficiency of cytocidal treatments. Importantly, mononuclear white blood cells are not sensitised to apoptosis by NMR, showing that NMR may increase the differential cytotoxicity of antitumor drugs on tumor vs normal cells. This strong, differential potentiating effect of NMR on tumor cell apoptosis may have important implications, being in fact a possible adjuvant for antitumor therapies.

Magnetic Fields Protect from Apoptosis via Redox Alteration

Magnetic fields (MFs) are receiving much attention in basic research due to their emerging ability to alter intracellular signaling. We show here that static MFs with intensity of 6 mT significantly alter the intracellular redox balance of U937 cells. A strong increase of reactive oxygen species (ROS) and a decrease of glutathione (GSH) intracellular levels were found after 2 h of MF exposure and maintained thereafter. We found that also other types of MFs, such as extremely-low-frequency (ELF) MFs affect intracellular GSH starting from a threshold at 0.09 mT. We previously reported that static MFs in the intensity range of 0.3-60 mT reduce apoptosis induced by damaging agents (Fanelli et al., 1998). Here, we show that ELF-MFs are also able to protect U937 from apoptosis. Interestingly, this ability is limited to the ELF intensities able to alter redox equilibrium, indicating a link between MF's antiapoptotic effect and the MF alteration of intracellular redox balance. This suggests that MF-produced redox alterations may be part of the signaling pathway leading to apoptosis antagonism. Thus, we tested whether MFs may still exert an antiapoptotic action in cells where the redox state was artificially altered in both directions, that is, by creating an oxidative (via GSH depletion with BSO) or a reducing (with DTT) cellular environment. In both instances, MFs fail to affect apoptosis. Thus, a correct intracellular redox state is required in order for MFs to exert their antiapoptotic effect.

Different fates of intracellular glutathione determine different modalities of apoptotic nuclear vesiculation

U937 monocytic cells show two main apoptotic nuclear morphologies, budding and cleavage, that are the result of two independent morphological routes, since they never interconvert one into the other, and are differently modulated by stressing or physiological apoptogenic agents [Exp Cell Res 1996; 223:340-347]. With the aim of understanding which biochemical alterations are at the basis of these alternative apoptotic morphologies, we performed an in situ analysis that showed that in U937 cells intracellular glutathione (GSH) is lost in cells undergoing apoptosis by cleavage, whereas it is maintained in apoptotic budding cells. Lymphoma cells BL41 lose GSH in apoptosis, and show the cleavage nuclear morphology; the same cells latently infected with Epstein Barr Virus (E2r line) undergo apoptosis without GSH depletion and show the budding nuclear morphology. GSH depletion is not only concomitant to, but is the determinant of the cleavage route, since the inhibition of apoptotic GSH efflux with cystathionine or methionine shifts the apoptotic morphology from cleavage to budding. Accordingly, cystathionine or methionine antagonizes apoptosis in the all-cleavage BL41, without affecting the all-budding E2r.

Hypoxia-targeted bioreductive tyrosine kinase inhibitors with glutathione-depleting function

Tyrosine kinase inhibitors may serve as ligands for kinases that are involved in normal cell differentiation or repair, thereby leading to toxicity. It may be possible to target such inhibitors to tumor cells by coupling them to hypoxia-activated bioreductive molecules. Such coupling can utilize or incorporate bonds that have a propensity to be preferentially oxidized by thiols such as intracellular glutathione (GSH). The resulting depletion of GSH may increase redox-mediated apoptosis. The resultant molecule is hence projected to act via multiple cell killing mechanisms: (i) inhibition of tumor kinases, (ii) tumor DNA disruption and (iii) causing increased redox-mediated apoptosis.