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

Cardiac volume overload rapidly induces oxidative stress-mediated myocyte apoptosis and hypertrophy

Oxidative stress stimulates both growth and apoptosis in cardiac myocytes in vitro. We investigated the role of oxidative stress in the initial phases of cardiac remodeling induced in an animal model by volume overload. As plausible candidates for a connection between oxidative stress and cardiomyocyte apoptosis or hypertrophy, we explored the behaviour of two MAPKs, specifically JNK and ERK. At 48 h of overload, the greatest increase in oxidative stress coincided with a peak of cardiomyocyte apoptosis. This was possibly induced through the mitochondrial metabolism, as evidenced by the release of cytochrome c and a significant increase in the active forms of caspase-9 and -3, but not caspase-8. Oxidative stress markers significantly decreased at 96 h of overload, combined with a marked attenuation of apoptosis and the appearance of hypertrophy. The highest levels of JNK and the lowest levels of ERK phosphorylation were observed at 48 h of overload. Conversely, a sharp increase in ERK phosphorylation was detected at 96 h of overload coinciding with the hypertrophic response. Together these results show that oxidative stress is an early and transient event in myocardial volume overload. They suggest that oxidative stress mediates amplitude dependent apoptotic and hypertrophic responses in cardiomyocytes through the selective activation of, respectively, JNK and ERK.

Oxidative Bax dimerization promotes its translocation to mitochondria independently of apoptosis

Bax is a cytosolic protein, which in response to stressing apoptotic stimuli, is activated and translocates to mitochondria, thus initiating the intrinsic apoptotic pathway. In spite of many studies and the importance of the issue, the molecular mechanisms that trigger Bax translocation are still obscure. We show by computer simulation that the two cysteine residues of Bax may form disulfide bridges, producing conformational changes that favor Bax translocation. Oxidative, nonapoptogenic treatments produce an up-shift of Bax migration compatible with homodimerization, which is reverted by reducing agents; this is accompanied by translocation to mitochondria. Dimers also appear in pure cytosolic fractions of cell lysates treated with H2O2, showing that Bax dimerization may take place in the cytosol. Bax dimer-enriched lysates support Bax translocation to isolated mitochondria much more efficiently than untreated lysates, indicating that dimerization may promote Bax translocation. The absence of apoptosis in our system allows the demonstration that Bax moves because of oxidations, even in the absence of apoptosis. This provides the first evidence that Bax dimerization and translocation respond to oxidative stimuli, suggesting a novel role for Bax as a sensor of redox imbalance.

Sensitization of Glioma Cells to Fas-Dependent Apoptosis by Chemotherapy-Induced Oxidative Stress

A prominent feature of glioblastoma is its resistance to death from Fas pathway activation. In this study, we explored the modulation of Fas-induced glioblastoma death with chemotherapeutic agents. Camptothecin significantly increased the glioblastoma cell death response to Fas receptor activation regardless of p53 status. Sublethal concentrations of camptothecin reduced the IC50 of agonistic anti-Fas antibody (CH-11) 10-fold, from 500 to 50 ng/mL, in human U87 glioblastoma cells (p53 wild-type). Cell viability in response to camptothecin, CH-11 alone, and the combination of camptothecin + CH-11 was found to be 84%, 85%, and 47% (P < 0.001), respectively. A similar pattern of relative cytotoxicity was found in U373 cells (p53 mutant). We further examined the pathways and mechanisms involved in this apparent synergistic cytotoxic response. Cell death was found to be predominantly apoptotic involving both extrinsic and intrinsic pathways as evidenced by annexin V staining, cleavage of caspases (3, 8, and 9), increased caspase activities, Smac release, and cytoprotection by caspase inhibitors. Expression of Fas-associated death domain, and not Fas, Fas ligand, or caspase proteins, increased following cell treatment with camptothecin + CH-11. Camptothecin treatment enhanced c-jun-NH2-kinase activation in response to CH-11, but inhibition of c-jun-NH2-kinase did not prevent cell death induced by the combination treatment. Reactive oxygen species, especially H2O2, were elevated following camptothecin treatment; and H2O2 enhanced cell death induced by CH-11. The antioxidants glutathione and N-acetyl-cysteine prevented cell death induced by camptothecin + CH-11. These findings show that camptothecin synergizes with Fas activation to induce glioblastoma apoptosis via a mechanism involving reactive oxygen species and oxidative stress pathways.

Antioxidant enzymes and apoptosis

The role of antioxidant enzymes can be interpreted in terms of fine tuning of the concentration of reactive oxygen species which are required in the redox regulation of the cell cycle and of programmed cell death. This review summarizes findings from papers published in the last few years which deal with the relation between apoptosis and the two antioxidant enzymes, manganous superoxide dismutase (MnSOD) and catalase. With respect to MnSOD, the literature is much in favor of an inhibitory action in apoptosis. Increased MnSOD activity has been shown to prevent cell death via the receptor-mediated apoptotic pathway as well as cell death via the mitochondrial pathway. The literature on the influence of catalase activity on apoptosis is less consistent. Evidence for both an antiapoptotic and a proapoptotic role of catalase can be found. From the results reviewed here, two schemes for the involvement of MnSOD and catalase in the regulation of apoptosis can be extracted: 1) Both MnSOD and catalase inhibit apoptosis by removing superoxide anion radicals or H2O2, respectively, because these reactive oxygen species are mediators required for the apoptotic program or inhibit a survival pathway. 2) An increase in H2O2 by downregulation or inhibition of catalase activity and/or upregulation of MnSOD activity inhibits apoptosis while a decrease in H2O2 by upregulation of catalase activity and/or downregulation of MnSOD activity supports apoptosis, possibly because of a supportive role of H2O2 in a survival pathway. The data reported so far do not allow for an explanation why some cell models appear to fit the first scheme while the second scheme appears to correctly describe other cell models. The present state of the literature reveals that antioxidant enzymes play a more intricate role in cell physiology than previously assumed.

Beryllium-stimulated reactive oxygen species and macrophage apoptosis

Beryllium (Be), the etiologic agent of chronic beryllium disease, is a toxic metal that induces apoptosis in human alveolar macrophages. We tested the hypothesis that Be stimulates the formation of reactive oxygen species (ROS) which plays a role in Be-induced macrophage apoptosis. Mouse macrophages were exposed to 100 microM BeSO4 in the absence and presence of the catalytic antioxidant MnTBAP (100 microM). Apoptosis was measured as the percentage of TUNEL+ and caspase-8+ cells. ROS production was measured by flow cytometry using the fluorescence probes, dihydroethidine (DHE) and dichlorofluorescein diacetate (DCFH-DA). Be-exposed macrophages had increased TUNEL+ cells (15+/-1% versus controls 1+/-0.2%, P<0.05) and increased caspase-8+ cells (18.7+/-2% versus controls 1.8+/-0.4%, P<0.05). Be-induced caspase-8 activation, and a 4-fold increase in ROS formation, was ameliorated by exposure to MnTBAP. Hydrogen peroxide (30 microM) exposure potentiated Be-induced caspase-8 activation, and was also attenuated by MnTBAP. Our data are the first to demonstrate that Be stimulates macrophage ROS formation which plays an important role in Be-induced macrophage apoptosis.

Estrogen-induced spermatogenic cell apoptosis occurs via the mitochondrial pathway: role of superoxide and nitric oxide

The detrimental effects of estrogen on testicular function provide a conceptual basis to examine the speculative link between increased exposure to estrogens and spermatogenic cell death. Using an in vitro model, we provide an understanding of the events leading to estrogen-induced apoptosis in cells of spermatogenic lineage. Early events associated with estrogen exposure were up-regulation of FasL and increased generation of H(2)O(2), superoxide, and nitric oxide. The ability of anti-FasL antibodies to prevent several downstream biochemical changes and cell death induced by 17beta-estradiol substantiates the involvement of the cell death receptor pathway. Evidence for the amplification of the death-inducing signals through mitochondria was obtained from the transient mitochondrial hyperpolarization observed after estradiol exposure resulting in cytochrome c release. A combination of nitric oxide and superoxide but not H(2)O(2) was responsible for the mitochondrial hyperpolarization. Mn(III) tetrakis(4-benzoic acid)porphyrin chloride, an intracellular peroxynitrite scavenger, was able to reduce mitochondrial hyperpolarization and cell death. Although nitric oxide augmentation occurred through an increase in the expression of inducible nitric-oxide synthase, superoxide up-regulation was a product of estradiol metabolism. All of the above changes were mediated through an estrogen receptor-based mechanism because tamoxifen, the estrogen receptor modulator, was able to rescue the cells from estrogen-induced alterations. This study establishes the importance of the independent capability of cells of the spermatogenic lineage to respond to estrogens and most importantly suggests that low dose estrogens can potentially cause severe spermatogenic cellular dysfunction leading to impaired fertility even without interference of the hypothalamo-hypophyseal axis.

A highly bioactive lignophenol derivative from bamboo lignin exhibits a potent activity to suppress apoptosis induced by oxidative stress in human neuroblastoma SH-SY5Y cells

Approaches to protection against neurodegenerative diseases, in which oxidative stress and inflammation are implicated, should be based on the current concept on the etiology of these diseases. Recently, a new therapeutic strategy has been proposed to protect neurons from cell death by attenuating the apoptotic signal transduction. Lignin, a durable aromatic network polymer second to cellulose in abundance, was able to be converted into highly active lignophenol derivatives with antioxidant activity by using our newly developed phase-separation technique. These lignophenol derivatives were found to show the potent neuroprotective activity against oxidative stress. Among the compounds examined, a lignocresol derivative from bamboo (lig-8) exhibited the most potent neuroprotective activity against hydrogen peroxide (H(2)O(2))-induced apoptosis in human neuroblastoma cell line SH-SY5Y by preventing the caspase-3 activation via either caspase-8 or caspase-9. Furthermore, it was found that lig-8 exerted the antiapoptotic effect by inhibiting dissipation of the mitochondrial membrane permeability transition induced by H(2)O(2) or by the peripheral benzodiazepin receptor ligand PK11195. Lig-8 was also shown to be potent in the antioxidant activity in the cells exposed to H(2)O(2), as assessed by flow cytometry using 5-(and-6)-chloromethyl-2',7'-dichlorodihydrofluorescein diacetate and in vitro reactive oxygen species-scavenging potency. These data suggest that lig-8 is a promising neuroprotector, which affects the signaling pathway of neuronal cell death and that it would be of benefit to delay the progress of neurodegenerative diseases.