Rapid and specific efflux of reduced glutathione during apoptosis induced by anti-Fas/APO-1 antibody

Selective antiproliferative and apoptotic effects of flavonoids purified from Rhus verniciflua Stokes on normal versus transformed hepatic cell lines

Considerable attention is being concentrated on dietary flavonoids in developing novel cancer-preventive approaches due to their potential ability to induce selective apoptosis of cancer cells. In this study, we prepared a flavonoid-containing fraction from a crude acetone extract of Rhus verniciflua Stokes (RVS), traditionally used as a food additive and as an herbal medicine, and named RVS chloroform-methanol fraction (RCMF). We evaluated the effects of RCMF on proliferation and apoptosis using mouse embryonic primary hepatic cells (MPHC), embryonic normal hepatic cell line (BNL CL.2), and its SV40-mediated transformed cell line (BNL SV A.8). We also investigated the effects of RCMF on the antioxidant defense system in those cells. This study demonstrated that RCMF exhibited a selective growth inhibition and apoptosis induction on transformed cells. BNL SV A.8 cells were more sensitive to RCMF-mediated cytotoxicity than were MPHC or BNL CL.2. RCMF-mediated reduction of MnSOD activity and glutathione (GSH) content in BNL SV A.8 cells is thought to be associated with RCMF-induced apoptosis. Our findings suggest that RCMF is an agent which may be capable of inducing growth inhibition and apoptosis of hepatic tumor cells.

Differential sensitivity to resveratrol-induced apoptosis of human chronic myeloid (K562) and acute lymphoblastic (HSB-2) leukemia cells

The in vitro effects of resveratrol (RES) on apoptotic pathway in human chronic myeloid (K562) and acute lymphoblastic (HSB-2) leukemia cells were investigated. RES treatment of both cell types significantly and irreversibly inhibited their growth, associated with extensive apoptosis and increase in hypodiploid cells. Cell cycle analysis showed accumulation in G(1) phase in HSB-2 drug exposed cells, while only K562-treated cells exhibited a marked accumulation in S phase with a concomitant decrease in G(1) and G(2)/M at 24 h. Moreover, RES caused internucleosomal DNA fragmentation, even if K562 cells were found less sensitive to the drug, as compared to HSB-2 cells, which also reacted earlier to the treatment. RES-induced apoptosis was associated with an increase of Bax expression and a marked release of cytochrome c from mitochondria. Interestingly, K562 cells exhibited a basal content of glutathione 10-fold that of HSB-2 cells, which increased after 24-48 h RES exposure, together with increment of glutathione reductase and peroxidase activities. However, the major resistance to apoptosis of K562 cells cannot be attributed to their higher pool of reducing power, since neither the inhibition of glutathione synthesis by buthionine sulphoximine nor glutathione depletion by diethylmaleate, sensitized these cells. In addition, glutathione enrichment of HSB-2 cells by N-acetylcysteine did not prevent the apoptotic effects of RES. Our data indicate that RES commitment to apoptosis in both cell lines is independent from the intracellular content of glutathione, while it is associated with either the enhanced expression of Bax and cytochrome c release.

Control of Atm-/- thymic lymphoma cell proliferation in vitro and in vivo by dexamethasone

AIM

Ataxia telangiectasia (A-T) is an autosomal recessive disease in humans caused by mutations in the Atm (A-T mutated) gene. The disease involves multiple organ systems, and is associated with a high incidence of leukemias and lymphomas that develop in childhood. We have reported previously that thymic lymphoma development in Atm knockout (Atm-/-) mice is associated with elevated spontaneous DNA synthesis in thymocytes, and that dexamethasone (Dex) attenuates the elevated DNA synthesis and prevents thymic lymphoma development. The primary objectives of the present study were (1) to investigate possible mechanisms underlying the tumor-suppressing effect of Dex on Atm-/- thymic lymphoma cells, and (2) to determine whether Dex is an effective tumor-suppressing treatment in mice bearing transplanted Atm-/- thymic tumors.

METHODS

Establishment of a number of Atm-/- thymic lymphoma (ATL) cell lines from Atm-/- mice, cell proliferation assays, cell cycle analyses, Western blotting and Hoechst nuclear staining were used to analyze the effects of Dex on Atm-/- thymic lymphoma cells. Atm-/- tumor cells were transplanted into the right flanks of Atm+/+ mice prior to the initiation of Dex treatment.

RESULTS

Atm-/- tumor cells were highly sensitive to Dex, both in culture and in vivo as ectopic tumors in mice. In cultured ATL-1 cells, Dex induced apoptosis, arrested the cell cycle at the G1 phase and downregulated NF-kappaB and multiple cell cycle regulators, while upregulating the NF-kappaB inhibitor IkappaBalpha. In Atm+/+ mice transplanted subcutaneously with ATL-1 cells, tumor growth was either prevented completely or significantly suppressed by Dex treatment.

CONCLUSIONS

Our findings identify potential mechanisms by which Dex affects the proliferation and survival of ATL-1 cells in culture, and provide evidence that Dex can suppress the proliferation of Atm-/- thymic lymphoma cells growing in the body. Together these results add to our earlier published data suggesting that the cellular pathways regulated by Dex may be promising therapeutic targets for prevention and treatment of thymic lymphomas in A-T individuals.

Perforin and Fas act together in the induction of apoptosis, and both are critical in the clearance of lymphocytic choriomeningitis virus infection

In this report we questioned the current view that the two principal cytotoxic pathways, the exocytosis and the Fas ligand (FasL)/Fas-mediated pathway, have largely nonoverlapping biological roles. For this purpose we have analyzed the response of mice that lack Fas as well as granzyme A (gzmA) and gzmB (FasxgzmAxB(-/-)) to infection with lymphocytic choriomeningitis virus (LCMV). We show that FasxgzmAxB(-/-) mice, in contrast to B6, Fas(-/-), and gzmAxB(-/-) mice, do not recover from a primary infection with LCMV, in spite of the expression of comparable numbers of LCMV-immune and gamma interferon-producing cytotoxic T lymphocytes (CTL) in all mouse strains tested. Ex vivo-derived FasxgzmAxB(-/-) CTL lacked nucleolytic activity and expressed reduced cytolytic activity compared to B6 and Fas(-/-) CTL. Furthermore, virus-immune CTL with functional FasL and perforin (gzmAxB(-/-)) are more potent in causing target cell apoptosis in vitro than those expressing FasL alone (perfxgzmAxB(-/-)). This synergistic effect of perforin on Fas-mediated nucleolysis of target cells is indicated by the fact that, compared to perfxgzmAxB(-/-) CTL, gzmAxB(-/-) CTL induced (i) an accelerated decrease in mitochondrial transmembrane potential, (ii) increased generation of reactive oxygen species, and (iii) accelerated phosphatidylserine exposure on plasma membranes. We conclude that perforin does not mediate recovery from LCMV by itself but plays a vital role in both gzmA/B and FasL/Fas-mediated CTL activities, including apoptosis and control of viral infections.

Glutaredoxin 2 Catalyzes the Reversible Oxidation and Glutathionylation of Mitochondrial Membrane Thiol Proteins

The redox poise of the mitochondrial glutathione pool is central in the response of mitochondria to oxidative damage and redox signaling, but the mechanisms are uncertain. One possibility is that the oxidation of glutathione (GSH) to glutathione disulfide (GSSG) and the consequent change in the GSH/GSSG ratio causes protein thiols to change their redox state, enabling protein function to respond reversibly to redox signals and oxidative damage. However, little is known about the interplay between the mitochondrial glutathione pool and protein thiols. Therefore we investigated how physiological GSH/GSSG ratios affected the redox state of mitochondrial membrane protein thiols. Exposure to oxidized GSH/GSSG ratios led to the reversible oxidation of reactive protein thiols by thiol-disulfide exchange, the extent of which was dependent on the GSH/GSSG ratio. There was an initial rapid phase of protein thiol oxidation, followed by gradual oxidation over 30 min. A large number of mitochondrial proteins contain reactive thiols and most of these formed intraprotein disulfides upon oxidation by GSSG; however, a small number formed persistent mixed disulfides with glutathione. Both protein disulfide formation and glutathionylation were catalyzed by the mitochondrial thiol transferase glutaredoxin 2 (Grx2), as were protein deglutathionylation and the reduction of protein disulfides by GSH. Complex I was the most prominent protein that was persistently glutathionylated by GSSG in the presence of Grx2. Maintenance of complex I with an oxidized GSH/GSSG ratio led to a dramatic loss of activity, suggesting that oxidation of the mitochondrial glutathione pool may contribute to the selective complex I inactivation seen in Parkinson's disease. Most significantly, Grx2 catalyzed reversible protein glutathionylation/deglutathionylation over a wide range of GSH/GSSG ratios, from the reduced levels accessible under redox signaling to oxidized ratios only found under severe oxidative stress. Our findings indicate that Grx2 plays a central role in the response of mitochondria to both redox signals and oxidative stress by facilitating the interplay between the mitochondrial glutathione pool and protein thiols.

Detection of apoptotic caspase activation in sera from patients with chronic HCV infection is associated with fibrotic liver injury

Chronic hepatitis C virus (HCV) infection is characterized by inflammatory liver damage and is associated with a high risk of development of cirrhosis and hepatocellular carcinoma. Although histological examination of liver biopsies is currently the gold standard for the detection of early liver damage, there is a strong need for better noninvasive methods. We recently demonstrated that the proapoptotic activation of caspases is considerably enhanced in histological sections from HCV-infected liver tissue, suggesting an important role of apoptosis in liver damage. Here, we investigated whether caspase activation is detectable also in sera from patients with chronic HCV infection. Using a novel enzyme-linked immunosorbent assay that selectively recognizes a proteolytic neoepitope of the caspase substrate cytokeratin-18, we demonstrate that caspase activity is markedly increased in the sera of HCV patients. Interestingly, while 27% of patients with chronic HCV infection showed normal aminotransferase levels despite inflammatory and fibrotic liver damage, more than 50% of those patients exhibited already elevated serum caspase activity. Moreover, 30% of patients with normal aminotransferase but elevated caspase activity revealed higher stages of fibrosis. In conclusion, compared with conventional surrogate markers such as aminotransferases, detection of caspase activity in serum might be a more sensitive method of detecting early liver injury. Thus, measurement of caspase activity might provide a novel diagnostic tool, especially for patients with normal aminotransferases but otherwise undiagnosed histologically active hepatitis and progressive fibrosis.

Increased efflux of glutathione conjugate in acutely diabetic cardiomyocytes

In diabetes, cell death and resultant cardiomyopathy have been linked to oxidative stress and depletion of antioxidants like glutathione (GSH). Although the de novo synthesis and recycling of GSH have been extensively studied in the chronically diabetic heart, their contribution in modulating cardiac oxidative stress in acute diabetes has been largely ignored. Additionally, the possible contribution of cellular efflux in regulating GSH levels during diabetes is unknown. We used streptozotocin to make Wistar rats acutely diabetic and after 4 days examined the different processes that regulate cardiac GSH. Reduction in myocyte GSH in diabetic rats was accompanied by increased oxidative stress, excessive reactive oxygen species, and an elevated apoptotic cell death. The effect on GSH was not associated with any change in either synthesis or recycling, as both γ-glutamylcysteine synthetase gene expression (responsible for bio syn thesis) and glutathione reductase activity (involved with GSH recycling) remained unchanged. However, gene expression of multidrug resistance protein 1, a transporter implicated in effluxing GSH during oxidative stress, was elevated. GSH conjugate efflux mediated by multidrug resistance protein 1 also increased in diabetic cardiomyocytes, an effect that was blocked using MK-571, a specific inhibitor of this transporter. As MK-571 also decreased oxidative stress in diabetic cardiomyocytes, an important role can be proposed for this transporter in GSH and reactive oxygen species homeostasis in the acutely diabetic heart. Key words: cardiomyocytes, apoptosis, multidrug resistance protein, reactive oxygen species.

Selective effects of quercetin on the cell growth and antioxidant defense system in normal versus transformed mouse hepatic cell lines

Quercetin is a dietary anticancer chemical that is capable of inducing apoptosis in tumor cells. However, little is known about its biological effect on nonmalignant cells, although the effect is one of the critical criteria to evaluate the clinical efficacy of the anticancer agent. In this study, we investigated the effects of quercetin on cell growth and apoptosis using embryonic normal hepatic cell line (BNL CL.2) and its SV40-transformed cell line (BNL SV A.8). We also evaluated the effects of quercetin on the antioxidant defense system in those cells. BNL SV A.8 cells were more sensitive to quercetin-mediated cytotoxicity than BNL CL.2 cells. In addition, the enzyme assays showed that quercetin actively stimulated the antioxidant defense systems including superoxide dismutase, catalase, glutathione, and glutathione reductase only in the BNL CL.2 cells. In particular, quercetin significantly reduced superoxide dismutase activity and increased the malonaldehyde content in BNL SV A.8 cells. These are thought to be closely related to quercetin-mediated apoptosis. Our findings suggest that quercetin is a dietary flavonoid that is capable of inducing selective growth inhibition and apoptosis in hepatic tumor cells, but not in normal cells.

Verapamil and its derivative trigger apoptosis through glutathione extrusion by multidrug resistance protein MRP1

This study demonstrates that verapamil and a newly synthesized verapamil derivative, NMeOHI(2), behave as apoptogens in multidrug resistance protein 1 (MRP1)-expressing cells. When treated with either verapamil or NMeOHI(2), surprisingly, baby hamster kidney-21 (BHK) cells transfected with human MRP1 were killed. Because parental BHK cells were not, as well as cells expressing an inactive (K1333L) MRP1 mutant, this indicated that cell death involved functional MRP1 transporter. Cell death was identified as apoptosis by using annexin V-fluorescein labeling and was no longer observed in the presence of the caspase inhibitor Z-Val-Ala-Asp(OMe)-CH(2)F (Z-VAD-FMK). In vitro, both verapamil and its derivative inhibited leukotriene C4 transport by MRP1-enriched membrane vesicles in a competitive manner, with a K(i) of 48.6 microm for verapamil and 5.5 microm for NMeOHI(2,) and stimulated reduced glutathione (GSH) transport 3-fold and 9-fold, respectively. Treatment of MRP1-expressing cells with either verapamil or the derivative quickly depleted intracellular GSH content with a strong decrease occurring in the first hour of treatment, which preceded cell death beginning at 8-16 h. Furthermore, addition of GSH to the media efficiently prevented cell death. Therefore, verapamil and its derivative trigger apoptosis through stimulation of GSH extrusion mediated by MRP1. This new information on the mechanism of induced apoptosis of MDR cells may represent a novel approach in the selective treatment of MRP1-positive tumors.

N-Acetyl-L-cysteine prevents exercise-induced intestinal lymphocyte apoptosis by maintaining intracellular glutathione levels and reducing mitochondrial membrane depolarization

Intense exercise leads to post-exercise lymphocytopenia and immunosuppression, possibly by triggering lymphocyte apoptosis. To test the role of oxidative stress on exercise-induced lymphocyte apoptosis, we administered the antioxidant N-acetyl--cysteine (NAC) and measured apoptosis in intestinal lymphocytes (IL) from exhaustively exercised animals. Eighty-seven female C57BL/6 mice were randomly assigned to receive NAC (1 g/kg) or saline 30 min prior to treadmill exercise for 90 min at 2degrees slope (30 min at 22 m min(-1), 30 min at 25 m min(-1), and 30 min at 28 m min(-1)) and sacrificed immediately (Imm) or 24 hours (24 h) after cessation of exercise. Control mice (nonexercised) were exposed to treadmill noise and vibration without running. Exercise increased IL phosphatidylserine externalization (p<0.001), mitochondrial membrane depolarization (p<0.05), and decreased intracellular glutathione concentrations (p<0.05) immediately following exercise in saline relative to nonexercised mice. At 24 h post-exercise, saline injected mice had fewer total (p<0.001) and CD3+ (p<0.005) IL compared to nonexercised animals. NAC injection in mice maintained intracellular glutathione levels, prevented phosphatidylserine externalization, mitochondrial membrane depolarization, and loss of IL immediately and 24 h after exercise. These data suggest that lymphocyte apoptosis precedes post-exercise lymphocytopenia and may be due to oxidative stress.

Induction of apoptosis in human pancreatic cancer cells by docosahexaenoic acid

Polyunsaturated fatty acids have been indicated to induce anti-proliferative and/or apoptotic effects in various tumor cells. We showed that, at a 200- micro M concentration, both alpha-linoleic (18:2 n-6; LA) or docosahexaenoic (22:6 n-3; DHA) acid inhibited cell growth, while only DHA induced apoptosis in the human Paca-44 pancreatic cancer cell line. Investigating the mechanism underlying DHA-induced apoptosis, we showed that DHA induced a rapid and dramatic (>60%) intracellular depletion of reduced glutathione (GSH), without affecting oxidized glutathione (GSSG). Moreover, using two specific inhibitors of carrier-mediated GSH extrusion, cystathionine or methionine, we observed that GSH depletion occurred via an active GSH extrusion, and that inhibition of GSH efflux completely reversed apoptosis. These results provide the first evidence for a possible causative role of GSH depletion in DHA-induced apoptosis.

Glutathione and glutathione peroxidase in sputum samples of adult patients with cystic fibrosis

BACKGROUND

Reduced glutathione (GSH) is a major antioxidant in the lung. In cystic fibrosis (CF) patients, extracellular GSH levels of lower airways, obtained by bronchoalveolar lavage (BAL), were reported to be lower than non-CF individuals.

METHODS

Upper airway secretions of stable adult CF patients (29 spontaneous and 13 induced sputum) and non-CF individuals (14 healthy and 12 asthmatics; all induced sputum) were analyzed for total glutathione (i.e. the sum of reduced, GSH, and oxidized, GSSG, forms), GSH and GSSG levels by enzymatic kinetic assay.

RESULTS

In CF, both spontaneous and induced sputum samples were comparable in total glutathione levels which were surprisingly high (median concentration of 9.2 (range 1.4-65.2) and 11.6 (1.1-69.8) microM, respectively). In non-CF individuals, total glutathione levels were significantly lower (healthy 2.8 (1.0-12.3), asthmatics (5.3 (1.3-19.2) microM; p<0.001, both vs. CF). In CF, more than 90% of total glutathione was represented by GSH, whereas in non-CF controls, GSH made up less than 50% of total glutathione (p<0.001).

CONCLUSIONS

In contrast to BAL, CF sputum contains high levels of GSH. Sputum induction is a potentially useful procedure to monitor antioxidant levels in upper airways of CF patients.

Neuroprotective effect of fraxetin and myricetin against rotenone-induced apoptosis in neuroblastoma cells

Rotenone-induced apoptosis is considered to contribute to the etiology of Parkinson's disease (PD). We try to prevent the apoptosis induced by rotenone toxicity with 50 microM myricetin, 100 microM fraxetin and 100 microM N-acetylcysteine (NAC) that protect against reactive oxygen species (ROS), on SH-SY5Y human neuroblastoma cell line. Morphological changes induced by rotenone and intracellular ROS were assessed in live SH-SY5Y dopaminergic cells by confocal microscopy using the fluorescent dyes, dihydroethidium and 2',7'-dichlorofluorescein diacetate (DCFH-DA). DNA fragmentation was assayed as index of apoptosis. We also investigated oxidative stress parameters such as the glutathione redox status and lipid peroxidation. The exposure of the SH-SY5Y cells to rotenone 5 microM for 16 h produced severe morphological changes, DNA fragmentation and significative increases in the levels of hydrogen peroxide and superoxide anion. These increases were reduced by a 30-min pretreatment with fraxetin 100 microM or NAC 100 microM. DNA laddering produced by rotenone treatment was also inhibited by fraxetin and NAC. Treatment with 5 microM rotenone induced loss of reduced glutathione (GSH) and increased cellular levels of oxidized glutathione (GSSG). Fraxetin and NAC treatments restored glutathione redox ratio diminished after rotenone challenge and decreased the levels of lipid peroxidation. These results suggest that the natural antioxidants, such as fraxetin, may prevent the apoptotic death of dopaminergic cells induced by rotenone and mediated by oxidative stress.

Activation of plasma membrane reduced glutathione transport in death receptor apoptosis of HepG2 cells

Cells undergoing apoptosis release reduced glutathione (GSH) into the extracellular space; however, the physiological significance and the mechanism behind the GSH export remain unclear. The present study demonstrates that GSH is released by HepG2 cells undergoing Fas, tumor necrosis factor alpha (TNFalpha), or tumor necrosis factor-related apoptosis-inducing ligand (TRAIL)-stimulated cell death. GSH release was observed at times when extracellular lactate dehydrogenase (LDH) activity and propidium iodide (PI) incorporation were low, suggesting that the GSH release does not occur because of nonspecific cell damage, but is occurring through a specific transport system. Caspase 3-like proteases were activated before GSH was released, indicating that protease may be involved in signaling GSH release. To investigate the mechanism of GSH release, studies were performed in the presence of GSH transport inhibitors, as well as 25 mM GSH in the media. Two organic anion transporter inhibitors, probenecid and dibromosulfophthalein (DBSP), were effective in inhibiting Fas-stimulated GSH release. The addition of 25 mM GSH to the extracellular media also prevented the loss of intracellular GSH and delayed cell death. These findings suggest that an organic anion transporter is involved in GSH release during apoptosis, and that maintenance of intracellular GSH levels during apoptosis provides protection for the cell.

An in vitro and in vivo investigation of the effects of diesel exhaust on human airway lining fluid antioxidants

Breathing high concentrations of diesel exhaust (DE) induces pulmonary inflammation, bronchoconstriction, increased airway reactivity, and oxidative stress in healthy subjects. To examine if these responses occur at environmentally relevant concentrations of DE, we exposed 25 healthy subjects to DE (PM(10) 100 microg/m(3), 0.6 ppm NO(2) for 2-h) and filtered air on separate occasions. Immediately following DE exposure, subjects displayed an increase in subjective symptoms and a mild bronchoconstriction. Six hours following the cessation of DE exposure neither airway inflammation, nor antioxidant depletion (ascorbate, urate, and reduced glutathione), was seen at any level of the respiratory tract. Instead, an increased flux of reduced glutathione into the bronchial (p < 0.01) and nasal airways (p < 0.05) was observed. In separate, in vitro experiments, DE was found to have comparable oxidative activity to the transition metal rich residual oil fly ash (ROFA) particle, significantly depleting lung lining fluid ascorbic acid and reduced glutathione in a transition metal and superoxide-dependent mechanism. Together, these data indicate that even though DE has marked oxidative activity, this effect is not observed to any great extent in the airways of healthy subjects. We interpret these findings as being indicative that the antioxidant network at the air-lung interface in healthy subjects is capable of dealing with the oxidative challenge posed by DE at ambient concentrations.

The cardiolipin–cytochrome c interaction and the mitochondrial regulation of apoptosis

While many studies have focused on cytochrome c release from mitochondria, little attention has been given to the specific interaction between cardiolipin (CL) and cytochrome c, the breaching of which likely represents a critical event in the initiation of mitochondrially mediated apoptosis. Mounting evidence suggests that a decrease in the level of CL affects cytochrome c binding to the inner membrane, thus leading to higher levels of soluble cytochrome c in the mitochondrial intermembrane space. Among the factors known to affect CL levels are thyroid status, plasma concentrations of free fatty acids, Ca2+ dysregulation, and reactive oxygen species (ROS). These factors, especially Ca2+ and ROS, have long been recognized as triggers of cell death and, more recently, as modulators of mitochondrially mediated apoptosis. In this review, we discuss the significance of the disruption of the CL-cytochrome c interaction for cytochrome c release and apoptosis.

Apoptosis and macrophage clearance of neutrophils: regulation by reactive oxygen species

Inflammation is a beneficial host response to foreign challenge involving numerous soluble factors and cell types, including polymorphonuclear granulocytes or neutrophils. Programmed cell death (apoptosis) of neutrophils has been documented in vitro as well as in vivo, and is thought to be important for the resolution of inflammation, as this process allows for engulfment and removal of senescent cells prior to their necrotic disintegration. Studies in recent years have begun to unravel the mechanism of macrophage clearance of apoptotic cells, and evidence has accrued for a critical role of externalization and oxidation of plasma membrane phosphatidylserine, and its subsequent recognition by macrophage receptors, in this process. Activated neutrophils generate vast amounts of reactive oxygen species for the purpose of killing ingested micro-organisms, and these reactive metabolites may also modulate the life-span, as well as the clearance, of the neutrophil itself. This review aims to address the latter topic, as well as to summarize current knowledge on the molecular mechanisms of neutrophil apoptosis and macrophage clearance of these cells at the site of inflammation.

EGF mediates protection against Fas-induced apoptosis by depleting and oxidizing intracellular GSH stocks

Several pieces of evidence have demonstrated the importance of reduction/oxidation (redox) signaling in biological processes, including sensitivity toward apoptosis. In parallel, it was recently reported that growth factors induce the generation of reactive oxygen species (ROS). Therefore, we tested the hypothesis that the anti-apoptotic effect of epidermal growth factor (EGF) was mediated by changes in the redox state of hepatocytes through changes in GSH stocks. Isolated mouse hepatocytes were cultured and exposed to anti-Fas stimulation in order to induce apoptosis. Cell death by apoptosis was assessed by Hoechst 33258 staining and by measuring caspase-3 proteolysis activity. Cell treatment with EGF significantly decreased total (GSx) and reduced (GSH) glutathione levels in the presence and the absence of anti-Fas. Furthermore, glutathione reductase activity was lower in EGF-treated cultures (by 28%) as compared to untreated cultures which lead to a significant decline in GSH/GSx ratio. These effects were found to be EGF-receptor tyrosine kinase activity dependent. Co-stimulation of cells with anti-Fas and EGF attenuated caspase-3 activation and cell death by apoptosis by 70%. GSH monoethylester (GSHmee) significantly attenuated the effect of EGF on GSH and GSH/GSx ratio. It caused an increase in caspase-3 activation and in the percentage of apoptotic cells in anti-Fas + EGF-treated cells, thus resulting in a 53% decline in the protective effect of EGF. In conclusion, EGF induces a significant and specific depletion and oxidization of intracellular GSH, paralleled by a protection against Fas-induced apoptosis. GSH repenishment partly counteracted these effects suggesting that GSH depletion contributed to the protective effect of EGF against caspase-3 activation and cell death by apoptosis.

The role of oxidative damage in the neuropathology of organic acidurias: insights from animal studies

Organic acidurias represent a group of inherited disorders resulting from deficient activity of specific enzymes of the catabolism of amino acids, carbohydrates or lipids, leading to tissue accumulation of one or more carboxylic (organic) acids. Patients affected by organic acidurias predominantly present neurological symptoms and structural brain abnormalities, of which the aetiopathogenesis is poorly understood. However, in recent years increasing evidence has emerged suggesting that oxidative stress is possibly involved in the pathology of some organic acidurias and other inborn errors of metabolism. This review addresses some of the recent developments obtained mainly from animal studies indicating oxidative damage as an important determinant of the neuropathophysiology of some organic acidurias. Recent data showing that various organic acids are capable of inducing free radical generation and decreasing brain antioxidant defences is presented. The discussion focuses on the relatively low antioxidant defences of the brain and the vulnerability of this tissue to reactive species. This offers new perspectives for potential therapeutic strategies for these disorders, which may include the early use of appropriate antioxidants as a novel adjuvant therapy, besides the usual treatment based on removing toxic compounds and using special diets and pharmacological agents, such as cofactors and L-carnitine.

Human mitochondrial glutaredoxin reduces S-glutathionylated proteins with high affinity accepting electrons from either glutathione or thioredoxin reductase

Glutaredoxins catalyze glutathione-dependent thiol disulfide oxidoreductions via a GSH-binding site and active cysteines. Recently a second human glutaredoxin (Grx2), which is targeted to either mitochondria or the nucleus, was cloned. Grx2 contains the active site sequence CSYC, which is different from the conserved CPYC motif present in the cytosolic Grx1. Here we have compared the activity of Grx2 and Grx1 using glutathionylated substrates and active site mutants. The kinetic studies showed that Grx2 catalyzes the reduction of glutathionylated substrates with a lower rate but higher affinity compared with Grx1, resulting in almost identical catalytic efficiencies (k(cat)/K(m)). Permutation of the active site motifs of Grx1 and Grx2 revealed that the CSYC sequence of Grx2 is a prerequisite for its high affinity toward glutathionylated proteins, which comes at the price of lower k(cat). Furthermore Grx2 was a substrate for NADPH and thioredoxin reductase, which efficiently reduced both the active site disulfide and the GSH-glutaredoxin intermediate formed in the reduction of glutathionylated substrates. Using this novel electron donor pathway, Grx2 reduced low molecular weight disulfides such as CoA but with particular high efficiency glutathionylated substrates including GSSG. These results suggest an important role for Grx2 in protection and recovery from oxidative stress.

Nitrite-mediated protection against hypochlorous acid-induced chondrocyte toxicity: a novel cytoprotective role of nitric oxide in the inflamed joint?

OBJECTIVE

To examine the potential consequences of overproduction of nitric oxide (NO) and nitrite (NO(2) (-)) in the inflamed rheumatoid joint.

METHODS

Human articular chondrocytes in culture were exposed to HOCl (hypochlorous acid, a physiologic oxidant formed in increased amounts at sites of chronic inflammation), and assays of cell viability, intracellular ATP and glutathione (GSH), and lactate dehydrogenase (LDH) were performed. HOCl-induced lipid peroxidation and activation of the MAP kinases ERK-1/2, JNK-1/2, and p38 were also measured. The modulatory effects of NO-derived nitrite (NO(2) (-)) and nitrate (NO(3) (-)) on HOCl-mediated chondrocyte toxicity were investigated.

RESULTS

Exposure of human articular chondrocytes to HOCl resulted in a concentration- and time-dependent loss of viability, decrease in ATP and GSH levels, LDH leakage, and cell death. HOCl induced significant lipid peroxidation as well as activation of the MAP kinases ERK-1/2 and p38 but not JNK-1/2. However, the presence of NO(2) (-) but not NO(3) (-) substantially decreased HOCl-dependent cellular toxicity even when NO(2) (-) was added at low (microM) concentrations. In sharp contrast, NO(2) (-) (1 mM) did not inhibit superoxide-, hydroxyl radical-, H(2)O(2)-, or peroxynitrite-mediated cytotoxicity. Furthermore, culture media from cells treated with interleukin-1beta (to generate NO and NO(2) (-)) offered significantly more protection against HOCl-mediated cytotoxicity than culture media from untreated cells.

CONCLUSION

These data suggest that NO(2) (-) accumulation at chronically inflamed sites where both HOCl and NO are overproduced may be cytoprotective against damage induced by HOCl. Accumulation of NO(2) (-) could represent a novel cytoprotective role of NO in inflamed joints. A mechanism for this is suggested.

A novel redox mechanism for the glutathione-dependent reversible uptake of a fungal toxin in cells

The fungal metabolite gliotoxin is characterized by an internal disulfide bridge and can exist in either disulfide or dithiol forms. Gliotoxin and other members of the epipolythiodioxopiperazine class of toxins have immunosuppressive properties and have been implicated in human and animal mycotoxicoses. The bridged disulfide moiety is thought to be generally essential for biological activity. Here we show that only the natural (oxidized) form of gliotoxin is actively concentrated in a cell line in a glutathione-dependent manner. Intracellular levels of the toxin can be up to 1500-fold greater than the applied concentration, and toxin in the cells exists almost exclusively in the reduced form. A simple model of toxin entry followed by reduction to the cell-impermeant dithiol explains active uptake, cell density dependence of EC50 values and predicts a value for the maximum concentration of toxin at limiting cell density in agreement with the experiment. Oxidation of the intracellular toxin results in rapid efflux from the cell that also occurs when glutathione levels fall following induction of apoptotic cell death by the toxin. This mechanism allows for minimal production of the toxin while enabling maximal intracellular concentration and thus maximal efficacy of killing in a competitor organism initially present at low cell density. The toxin effluxes from the apoptotic cell exclusively in the oxidized form and can further enter and kill neighboring cells, thus acting in a pseudocatalytic way.

Apoptosis in primary lymphoid organs with aging

Age-associated changes in the immune system are responsible for an increased likelihood of infection, autoimmune diseases, and cancer in the elderly. Immunosenescence is characterized by reduced levels of the peripheral naive T cell pool derived from thymus and the loss of immature B lineage cells in the bone marrow. Primary lymphoid organs, i.e., bone marrow and thymus, exhibit a loss of cellularity with age, which is especially dramatic in the thymus. A summary of major changes associated with aging in primary lymphoid organs is described in this article. The participation of apoptosis in cell loss in the immune system, a change associated with age, as well as a description of molecular machinery involved, is presented. Finally, the involvement of different hormonal and non-hormonal agents in counteracting apoptosis in thymus and bone marrow during aging is explained. Here, we underlie the important role of glucocorticoids as immunodepressors and melatonin as an immunostimulatory agent.

The metastasis suppressor gene C33/CD82/KAI1 induces apoptosis through reactive oxygen intermediates

Here we describe the isolation of C33/CD82/KAI1 in a screen for apoptosis-inducing genes. C33 is a gene that is downregulated in many metastatic tumor cells and the expression of which can attenuate the process of metastases formation in a variety of tumors. In accordance, we observed cell death induction by C33 in many different cell types. C33 seems to promote cell death by the generation of reactive oxygen intermediates (ROIs). These ROIs, however, are not derived from the mitochondrial respiratory chain as in most other scenarios leading to apoptosis. We observed that C33 renders cells sensitive to ROIs by causing the specific release of the intracellular antioxidant glutathione (GSH) from cells. Moreover, C33 activates the GTPase Cdc42, which mediates GSH release and apoptosis induction and allows to detect the formation of ROIs.

Chromosomal DNA fragmentation in apoptosis and necrosis induced by oxidative stress

Chromosomal DNA dysfunction plays a role in mammalian cell death. Oxidative stress producing reactive oxygen species (ROS) induces chromatin dysfunction such as single- and double-strand DNA fragmentation leading to cell death through apoptosis or necrosis. More than 1 Mbp giant DNA, 200-800 or 50-300 kbp high molecular weight (HMW) DNA and internucleosomal DNA fragments are produced by oxidative stress and by some agents producing ROS during apoptosis or necrosis in several types of mammalian cells. Some nucleases involved in the chromosomal DNA fragmentation in apoptosis or necrosis are classified. ROS-mediated DNA fragmentation is caused and enhanced by polyunsaturated fatty acids (PUFAs) or their hydroperoxides through lipid peroxidation. A reduction of intracellular GSH levels induced by the inhibition of cystein transport or GSH biosynthesis leads to cell death through over production and accumulation of ROS in some types of mammalian cells. The ROS accumulation system has been used as a model of oxidative stress to discuss whether ROS-mediated DNA fragmentation associated with cell death is based on apoptosis or necrosis.

Fas-stimulated generation of reactive oxygen species or exogenous oxidative stress sensitize cells to Fas-mediated apoptosis

Inhibition of Fas-mediated apoptosis in B cell lymphomas by thiol antioxidants (glutathione and N-acetylcysteine) supported previous studies, suggesting that Fas-stimulated ROS generation may play a role in Fas-mediated apoptosis. Thus, the goal of the current study was to determine if Fas stimulation could induce ROS generation and what role, if any, it played in apoptosis. Fas crosslinking induced rapid generation of ROS (within 15 min) well before the appearance of characteristic apoptotic changes. Overexpression of catalase or superoxide dismutase suggested that Fas induced production of both superoxide anion and hydrogen peroxide. ROS generation was only observed, however, in cells that were sensitive to apoptosis and not in B cells inherently resistant to anti-Fas or in those in which resistance was induced by B cell receptor crosslinking. The exogenous addition of 250 microM hydrogen peroxide could reverse the resistant phenotype and sensitize cells to Fas-induced apoptosis. In Fas-sensitive cells, depletion of endogenous antioxidant defenses with buthionine sulfoximine increased the sensitivity to Fas-induced apoptosis, while overexpression of antioxidant enzymes and antiapoptotic proteins suggested a role for Fas-induced production of hydrogen peroxide in apoptosis. Further analysis suggested a redox-sensitive step early in Fas signaling at the level of initiator caspase (caspase-8) activation. Thus, the data suggest that the level of oxidative stress, either from exogenous sources or generated endogenously upon receptor stimulation, regulates the sensitivity to Fas-mediated apoptosis.

Kupffer cells promote lead nitrate-induced hepatocyte apoptosis via oxidative stress

BACKGROUND: Apoptosis and its modulation are crucial factors for the maintenance of liver health, allowing hepatocytes to die without provoking a potential harmful inflammatory response through a tightly controlled and regulated process. Since Kupffer cells play a key role in the maintenance of liver function, the aim of this study was to verify whether Kupffer cells are involved in the induction of liver apoptosis after i.v. injection of Pb(NO3)2 likely by secretion mechanisms. RESULTS: The in vivo hepatic apoptosis, induced by Pb(NO3)2 was prevented by a pre-treatment with gadolinium chloride (GdCl3), a Kupffer cells toxicant, that suppresses Kupffer cell activity and reduces to a half the apoptotic rate. In addition, in vivo Pb(NO3)2 administration deprives hepatocytes of reduced glutathione, whereas the loss of this important oxidation-preventing agent is considerably mitigated or abolished by pre-treatment with GdCl3. However, incubation of isolated hepatocytes and Kupffer cells and HepG2 cells with Pb(NO3)2 for 24 hours induced necrotic but not apoptotic cells. Apoptosis of hepatocytes and HepG2 cells was observed only after the addition of conditioned medium obtained from Kupffer cells cultured for 24 hours with Pb(NO3)2, thus indicating the secretion of soluble mediators of apoptosis by Kupffer cells. Apoptosis in the HepG2 cells was observed upon 24-hours incubation of HepG2 cells with 1 mM buthionine sulfoximine, a glutathione depleting agent, thus showing that there is an oxidative apoptogenic pathway in HepG2 cells. CONCLUSION: Pb(NO3)2 has, at most, a direct necrotic (but not apoptogenic) effect on hepatocytes and HepG2 cells, giving a clue about the regulatory role of Kupffer cells in the induction of liver apoptosis after a single Pb(NO3)2 injection without pre-treatment with GdCl3, probably via secreting soluble factors that trigger oxidative stress in target cells.

Cinnamaldehyde induces apoptosis by ROS-mediated mitochondrial permeability transition in human promyelocytic leukemia HL-60 cells

Cinnamaldehyde is an active compound isolated from the stem bark of Cinnamomum cassia, a traditional oriental medicinal herb, which has been shown to inhibit tumor cell proliferation. In this study, we investigated the effects of cinnamaldehyde on the cytotoxicity, induction of apoptosis and the putative pathways of its actions in human promyelocytic leukemia cells. Using apoptosis analysis, measurement of reactive oxygen species (ROS), and assessment of mitochondrial membrane potentials (DeltaPsim), we show that cinnamaldehyde is a potent inducer of apoptosis and that it transduces the apoptotic signal via ROS generation, thereby inducing mitochondrial permeability transition (MPT) and cytochrome c release to the cytosol. ROS production, mitochondrial alteration, and subsequent apoptotic cell death in cinnamaldehyde-treated cells were blocked by the antioxidant N-acetylcystein. Taken together, our data indicate that cinnamaldehyde induces the ROS-mediated mitochondrial permeability transition and resultant cytochrome c release. This is the first report on the mechanism of the anticancer effect of cinnamaldehyde.

Mitochondrial-targeted fatty acid analog induces apoptosis with selective loss of mitochondrial glutathione in promyelocytic leukemia cells

Some fatty acids and derivatives are known to induce cell death in cancer cells. Mitochondria may have important roles in the death process. Therefore, we investigated the mitochondrial contribution in cell death induced by a modified fatty acid, tetradecylthioacetic acid (TTA), which cannot be beta-oxidized. TTA treatment induced apoptosis in IPC-81 leukemia cells via depolarization of the mitochondrial membrane potential (deltapsi) and early release of cytochrome c, accompanied by depletion of mitochondrial glutathione. Caspase-3 activation and cleavage of poly (ADP-ribose) polymerase (PARP) occurred at a late stage, but the broad-spectra caspase inhibitor zVAD-fmk did not block TTA-induced apoptosis. Overexpression of Bcl-2 partially prevented TTA-induced apoptosis, whereas cAMP-induced cell death was completely blocked. In conclusion, TTA seems to trigger apoptosis through mitochondrial-mediated mechanisms and selective modulation of the mitochondrial redox equilibrium.

Interactions of mitochondrial thiols with nitric oxide

The interaction of nitric oxide (NO) with mitochondria is of pathological significance and is also a potential mechanism for the regulation of mitochondrial function. Some of the ways in which NO may affect mitochondria are by reacting with low-molecular-weight thiols such as glutathione and with protein thiols. However, the detailed mechanisms and the consequences of these interactions for mitochondria are uncertain. Here we review mitochondrial thiol metabolism, outline how NO and its metabolites interact with thiols, and discuss the implications of these reactions for mitochondrial and cell function.

Docetaxel inhibits SMMC-7721 human hepatocellular carcinoma cells growth and induces apoptosis

AIM: To investigate the in vitro anti-hepatocellular carcinoma (HCC) activity of docetaxel against SMMC-7721 HCC cells and its possible mechanism.

METHODS: The HCC cells were given different concentrations of docetaxel and their growth was measured by colony forming assay. Cell cycle and apoptosis were analyzed by flow cytometry and fluorescence microscopy (acridine orange/ethidium bromide double staining, AO/EB), as well as electronic microscopy. The SMMC-7721 HCC cell reactive oxygen species (ROS) and glutathione (GSH) were measured after given docetaxel.

RESULTS: Docetaxel inhibited the hepatocellular carcinoma cells growth in a concentration dependent manner with IC₅₀ 5 × 10^-10 M. Marked cell apoptosis and G2/M phase arrest were observed after treatment with docetaxel ≥ 10^-8 M. Docetaxel promoted SMMC-7721 HCC cells ROS generation and GSH deletion.

CONCLUSION: Docetaxel suppressed the growth of SMMC-7721 HCC cells in vitro by causing apoptosis and G2/M phase arrest of the human hepatoma cells, and ROS and GSH may play a key role in the inhibition of growth and induction of apoptosis.

Role of reduced glutathione efflux in apoptosis of immortalized human keratinocytes induced by UVA

We have investigated the role played by GSH efflux in apoptosis of human HaCaT keratinocytes induced by UVA irradiation. UVA irradiation of HaCaT cells caused a rapid rise in GSH efflux across the intact cell membrane, followed by an increase in apoptosis. GSH efflux was stimulated by glucose and was reduced by the addition of exogenous GSH and intracellular GSH depletion by buthionine sulfoximine, suggesting that GSH transport is active and is influenced by the GSH concentration gradient across the cell membrane. Verapamil and cyclosporin A, blockers of the multidrug resistance-associated protein, decreased UVA-induced GSH efflux. GSH efflux occurred within 2 h of UVA irradiation, suggesting that the stimulation of GSH efflux is due to an increase in the activity of pre-existing multidrug resistance-associated protein transporter carrier. Although inhibition of GSH efflux did not affect caspase activation and DNA fragmentation, it delayed the gradual increase in plasma membrane permeability and reduced phosphatidylserine translocation in HaCaT cells. It is therefore likely that upon UVA irradiation, GSH efflux increased the intracellular oxidative stress without intervention of reactive oxygen species, thus resulting in more phosphatidylserine externalization and membrane rearrangement. These provide targets for macrophage recognition and phagocytosis and thus minimize the potential to invoke inflammation or neoplastic transformation.

An oxidative mechanism of interferon induced priming of the Fas pathway in Fanconi anemia cells

Hematopoietic progenitor cells from children with Fanconi anemia of the C complementation group (FA-C) are excessively apoptotic and hypersensitive to various extracellular cues including Fas-ligand, tumor necrosis factor-alpha and double-stranded RNA. Interferon (IFN)-gamma is known to augment apoptotic responses of these factors. The "priming" effect of IFN-gamma is not fully explained. In view of the strong evidence that FA cells are intolerant of oxidative stress, we tested the notion that IFN-priming involves the induction of reactive oxygen species (ROS) in two FA-C B-lymphocyte cell lines and in peripheral blood neutrophils and mononuclear cells of FA patients. We also investigated whether the combination of IFN-gamma and Fas created an intracellular environment that promoted apoptosis. Significantly lower doses of IFN-gamma induced ROS accumulation in neutrophils and mononuclear cell of FA patients compared to cells of normal individuals. Enhanced ROS accumulation and decreased intracellular glutathione levels were observed in FA-C B-cell lines primed with IFN-gamma and treated with agonistic anti-Fas antibody than in isogenic control cells corrected with FANCC. The above treatment also induced caspase-3 and -8 activation as well as apoptosis. That antioxidants reduced the priming effect of IFN-gamma in Fas and IFN-gamma-treated FA lymphoblast cells, demonstrates that ROS represent a critical effector mechanism for the exaggerated responses to IFN-gamma characteristic of FA-C cells.

Signaling mechanisms in tumor necrosis factor alpha-induced death of microvascular endothelial cells of the corpus luteum

The microvasculature of the corpus luteum (CL), which comprises greater than 50% of the total number of cells in the CL, is thought to be the first structure to undergo degeneration via apoptosis during luteolysis. These studies compared the apoptotic potential of various cytokines (tumor necrosis factor alpha, TNFalpha; interferon gamma, IFNgamma; soluble Fas ligand, sFasL), a FAS activating antibody (FasAb), and the luteolytic hormone prostaglandin F2alpha (PGF2alpha) on CL-derived endothelial (CLENDO) cells. Neither sFasL, FasAb nor PGF2alpha had any effect on CLENDO cell viability. Utilizing morphological and biochemical parameters it was evident that TNFalpha and IFNgamma initiated apoptosis in long-term cultures. However, TNFalpha was the most potent stimulus for CLENDO cell apoptosis at early time points. Unlike many other studies described in non-reproductive cell types, TNFalpha induced apoptosis of CLENDO cells occurs in the absence of inhibitors of protein synthesis. TNFalpha-induced death is typically associated with acute activation of distinct intracellular signaling pathways (e.g. MAPK and sphingomyelin pathways). Treatment with TNFalpha for 5-30 min activated MAPKs (ERK, p38, and JNK), and increased ceramide accumulation. Ceramide, a product of sphingomyelin hydrolysis, can serve as an upstream activator of members of the MAPK family independently in numerous cell types, and is a well-established pro-apoptotic second messenger. Like TNFalpha, treatment of CLENDO cells with exogenous ceramide significantly induced endothelial apoptosis. Ceramide also activated the JNK pathway, but had no effect on ERK and p38 MAPKs. Pretreatment of CLENDO cells with glutathione (GSH), an intracellular reducing agent and known inhibitor of reactive oxygen species (ROS) or TNFalpha-induced apoptosis, significantly attenuated TNFalpha-induced apoptosis. It is hypothesized that TNFalpha kills CLENDO cells through elevation of reactive oxygen species, and intracellular signals that promote apoptosis.

Glutathione Depletion or Radiation Treatment Alters Respiration and Induces Apoptosis in R3230Ac Mammary Carcinoma

Glutathione depletion by L-buthionine sulfoximine inhibits the growth of Ehrlich mouse mammary carcinoma, R3230Ac rat mammary carcinoma and the PC3 human prostrate carcinoma cells, in vitro. Inhibition of growth occurs within the first 24 hours after exposure to the drug. The cell density does not increase over the initial cell density over 7 days. A549 human lung carcinoma and the DU145 human prostrate carcinoma cells show no inhibition of growth under the same treatment conditions. A comparative study of the R323OAc and A549 cells demonstrated a marked increase in apoptosis following L-BSO treatment in R3230Ac, which was dependent on L-BSO concentration and incubation time. L-BSO did not induce apoptosis in A549 cells at any of the concentrations tested. The incidence of apoptosis for R323OAc cells following exposure to 0.1 mM L-BSO was similar to the incidence of radiation-induced apoptosis observed after exposure to 10 Gy. Treatment with L-BSO or radiation alone inhibited O2 utilization in of R323Oac, while no effect on O2 utilization was observed in A549 cells. LBSO altered the bioreductive capacity of both the R323OAc and A549 cells. These results suggest that the ability of L-BSO to block mitochondrial O2 utilization may be involved in the apoptotic response in R3230Ac cells.

Analytical methods to investigate glutathione and related compounds in biological and pathological processes

Reduced glutathione (GSH, gamma-L-glutamyl-L-cysteinylglycine) is a fundamental low-molecular mass antioxidant that serves several biological functions. Upon enzymatic and non-enzymatic oxidation, GSH forms glutathione disulfide (GSSG) and, under particular conditions, may generate other oxidative products. The determination of GSH, its precursors, and metabolites in several bio-matrices is a useful tool in studying oxidative stress. Many separative and non-separative methods have been developed and improved for the assay of GSH and related compounds. At present, high-performance liquid chromatography and capillary electrophoresis are the most used separative techniques to determine GSH and congeners. The review will deal with analytical methods developed over the last few years for the determination of GSH and related compounds, and with the procedures performed in sample pre-treatment in order to minimize analytical errors. Since GSH, GSSG, and related compounds lack of strong chromophores or fluorophores, it is advantageous, in many assays, to derivatize the compounds in order to improve the detection limit with UV-Vis and to allow fluorescence, thus the most commonly used labeling agents are also described.

Costunolide triggers apoptosis in human leukemia U937 cells by depleting intracellular thiols

We have previously demonstrated that costunolide, a biologically active compound that was isolated from the stem bark of Magnolia sieboldii, induced apoptosis in human cancer cells. In the present study, we investigated the underlying mechanisms and suggest that costunolide induces apoptosis in human promonocytic leukemia U937 cells by depleting the intracellular thiols. Costunolide treatment rapidly depleted the intracellular reduced glutathione (GSH) and protein thiols, and this preceded the occurrence of apoptosis. Pretreatment with sulfhydryl compounds such as GSH, N-acetyl-L-cysteine, dithiothreitol and 2-mercaptoethanol almost completely blocked the costunolide-induced apoptosis, highlighting the significance of the intracellular thiol level in the process. Furthermore, overexpression of Bcl-2 also significantly attenuated the effects of costunolide. The apoptosis-inducing activity of costunolide is likely to depend on the exomethylene moiety because derivatives in which this group was reduced, such as dihydrocostunolide and saussurea lactone, did not deplete the cellular thiols and showed no apoptotic activity. Taken together, the present study demonstrates that the costunolide-induced apoptosis depends on intracellular thiols contents, which are modulated by Bcl-2.

Glutathione influences c-Myc-induced apoptosis in M14 human melanoma cells

The objective of this article is to dissect the mechanisms by which the down-regulation of c-Myc induces programmed cell death in melanoma cells. In stable and doxycycline-inducible M14 melanoma cells, down-regulation of c-Myc induced apoptosis subsequent to a decrease in the intracellular reduced glutathione content and a concomitant accumulation of its oxidized form. This redox alteration was associated with a decrease of the enzyme activities of gamma-glutamyl-cysteine synthetase and NADPH-dependent GSSG reductase, as well as a consequent glutathione release in the extracellular medium. Cytochrome c was released into the cytosol at very early stages of apoptosis induction, long before detectable production of reactive oxygen species and activation of caspase-9 and -3. Macroarray analysis revealed that down-regulation of c-Myc produced striking changes in gene expression in the section related to metabolism, where the expression of gamma-glutamyl-cysteine synthetase and GSSG reductase was found to be significantly reduced. The addition of N-acetyl-l-cysteine or glutathione ethyl ester inhibited the apoptotic process, thus confirming the key role of glutathione in programmed cell death induced by c-Myc.

Glutathione peroxidase-1 protects from CD95-induced apoptosis

Through the induction of apoptosis, CD95 plays a crucial role in the immune response and the elimination of cancer cells. Ligation of CD95 receptor activates a complex signaling network that appears to implicate the generation of reactive oxygen species (ROS). This study investigated the place of ROS production in CD95-mediated apoptosis and the role of the antioxidant enzyme glutathione peroxidase-1 (GPx1). Anti-CD95 antibodies triggered an early generation of ROS in human breast cancer T47D cells that was blocked by overexpression of GPx1 and inhibition of initiator caspase activation. Enforced expression of GPx1 also resulted in inhibition of CD95-induced effector caspase activation, DNA fragmentation, and apoptotic cell death. Resistance to CD95-mediated apoptosis was not due to an increased expression of anti-apoptotic molecules and could be reversed by glutathione-depleting agents. In addition, whereas the anti-apoptotic protein Bcl-xL prevented CD95-induced apoptosis in MCF-7 cells, it did not inhibit the early ROS production. Moreover, Bcl-xL but not GPx1 overexpression could suppress the staurosporine-induced late generation of ROS and subsequent cell death. Altogether, these findings suggest that GPx1 functions upstream of the mitochondrial events to inhibit the early ROS production and apoptosis induced by CD95 ligation. Finally, transgenic mice overexpressing GPx1 were partially protected from the lethal effect of anti-CD95, underlying the importance of peroxide formation (and GPx1) in CD95-triggered apoptosis.

Increasing endogenous ceramide using inhibitors of sphingolipid metabolism maximizes ionizing radiation-induced mitochondrial injury and apoptotic cell killing

To enhance the killing effects of ionizing radiation, we amplified the endogenous ceramide signal in Jurkat cell cultures using 3 different inhibitors of sphingolipid metabolism: DL-PDMP, D-MAPP and imipramine. Of the various possible drug combinations, only DL-PDMP (20 microM) + imipramine (20 microM) and DL-PDMP (20 microM) + imipramine (20 microM) + D-MAPP (5 microM) induced a major increase in ceramide levels, reaching 240% and 340% of control values, respectively, after incubation for 48 hr. With these models, we demonstrate that endogenously formed ceramide triggers time- and concentration-dependent apoptosis through induction of mitochondrial injury and activation of the caspase pathway. Cellular dysfunction includes alterations to the cellular redox potential, as assessed by the generation of ROS and total glutathione depletion, and a drop in Delta Psi(m). A parallel elevation of mitochondrial ceramide levels was also observed. The combination of DL-PDMP + imipramine +/- D-MAPP with 10 Gy irradiation produced cumulative effects leading to apoptosis via mitochondrial collapse and activation of the caspase cascade. The association efficiency was confirmed in normal and acid sphingomyelinase-deficient lymphoid cell lines. Taken together, these results suggest that increasing endogenous ceramide levels may potentially be very valuable when combined with ionizing radiation in tumor therapy.

Molecular profiling of hepatotoxicity induced by a aminoguanidine carboxylate in the rat: gene expression profiling

The hepatotoxicity of the aminoguanidine carboxylate 2-[1-[hydrazino(imino)methyl]hydrazino]acetic acid was characterized using oligonucleotide micro arrays, with the goal to select compounds from the same class with lower toxicity potential. The approach included a 14-day repeated- and a single-dose study in the rat as well as in vitro studies. Common gene expression changes could be followed from in vivo to in vitro studies. Anyhow, comparing the in vivo and in vitro response of the compound on gene expression, significant discrepancies were detected. Many of the genes whose mRNA levels were increased/decreased in the livers of the animals treated with toxic doses of the compound, were expressed at higher/lower levels in control hepatocytes than in control liver. The expression of the majority of these genes was not affected by in vitro treatment. These data question the use of gene expression analysis as a marker for drug response in vitro and illustrate the need of a careful characterization of in vitro systems. The results presented show that array-based gene expression analysis can lead to a better understanding of the molecular basis of drug-induced liver injury and, potentially, be used in the selection process for compounds and in the design of safer drugs.

Early redox imbalance mediates hydroperoxide-induced apoptosis in mitotic competent undifferentiated PC-12 cells

Our recent study has demonstrated that cellular redox imbalance can directly initiate apoptosis in a mitotic competent PC-12 cell line without the involvement of reactive oxygen species (ROS). However, whether cell apoptosis induced by ROS is, in fact, mediated by a loss of redox balance caused by the oxidant is unresolved. The linkage between oxidant-mediated apoptosis and the induction of cellular redox was examined in PC-12 cells using the oxidant, tert-butylhydroperoxide (TBH). TBH caused cell apoptosis in 24 h that was preceded by an early increase (30 min) in oxidized glutathione (GSSG). Pretreatment with N-acetyl cysteine prevented TBH-induced GSSG increases and cell apoptosis. Altered Bax/BcL-2 expression and release of mitochondrial cytochrome c occurred post-redox imbalance and was kinetically linked to caspase-3 activation and poly ADP-ribose polymerase cleavage. Moreover, cell apoptosis was attenuated by inhibition of caspase-9, but not caspase-8, and blockade of mitochondrial ROS generation and permeability transition pore attenuated caspase 3 activation and cell apoptosis. Collectively, these results show that TBH-induced GSSG elevation is associated with the disruption of mitochondrial integrity, activation of caspase-3 and cell apoptosis. This redox induction of the apoptotic cascade was dissociated from cellular GSH efflux.

Resistance to Fas-induced apoptosis in hepatocytes: role of GSH depletion by cell isolation and culture

The involvement of reduction/oxidation (redox) state in cell sensitivity to apoptosis has been suggested by several studies in which induction of apoptosis was shown to require oxidative stress or GSH extrusion. On the other hand, biochemical studies of caspases revealed that their activation necessitates a reduced cysteine in their active site. This is ensured by maintaining intact intracellular glutathione status during apoptotic induction as reported by in vivo studies. Therefore, we investigated the relationship between intracellular glutathione levels and the sensitivity of mouse hepatocytes in culture to Fas-induced apoptosis as well as potential mechanisms responsible for this sensitivity. We found that total and reduced glutathione levels are decreased by one-half after cell isolation procedure and further decline by 25% during cell culture for 2 h in normal Williams' E medium. Cell culture in medium supplemented with cysteine and methionine maintains glutathione at a level similar to that measured just after cell isolation. Results show that the capacity of Fas to activate caspase-8 and to induce apoptosis requires important intracellular glutathione levels and high GSH/total glutathione ratio. In conclusion, the present study shows that intracellular glutathione plays an important role in maintaining the apoptotic machinery functional and is thus capable of transmitting the apoptotic signal.