Induction of apoptosis by chemotherapeutic drugs without generation of reactive oxygen species

Auraptene-induced cytotoxic effects in acute myeloid leukemia cell lines

Acute myeloid leukemia is one of the most commonly identified hematological malignancies with poor prognosis. This research was planned to identify the cytotoxic effects of Auraptene on HL60 and U937 cell lines. The cytotoxic effects of Auraptene were measured by AlamarBlue assay (Resazurin) after 24- and 48-h treatments with different doses of Auraptene. The inductive effects of Auraptene on cellular oxidative stress were investigated by determining cellular ROS levels. The cell cycle progression and cell apoptosis were also evaluated by flow cytometry method. Our findings revealed that Auraptene decreased HL60 and U937 cellular proliferation by downregulation of Cyclin D1. Auraptene also induces cellular oxidative stress by upregulation of cellular ROS levels. Auraptene induces cell cycle arrest the early and late phases of apoptosis by upregulation of Bax and p53 proteins. Our data suggest that the anti-tumor function of Auraptene can be mediated by promoting apoptosis and cell cycle arrest and inducing cellular oxidative stress in HL60 and U937 cell lines. These results support that Auraptene may be used as a potent anti-tumor agent against hematologic malignancies in the further studies.

Knockdown of Peroxiredoxin V increased the cytotoxicity of non-thermal plasma-treated culture medium to A549 cells

Administration of non-thermal plasma therapy via the use of plasma-activated medium (PAM) might be a novel strategy for cancer treatment, as it induces apoptosis by increasing reactive oxygen species (ROS) levels. Peroxiredoxin V (PRDX5) scavenges ROS and reactive nitrogen species and is known to regulate several physiological and pathological reactions. However, its role in lung cancer cells exposed to PAM is unknown. Here, we investigated the effect of PRDX5 in PAM-treated A549 lung cancer cells and determined the mechanism underlying its cytotoxicity. Cell culture medium was treated with low temperature plasma at 16.4 kV for 0, 60, 120, or 180 s to develop PAM. PRDX5 was knocked down in A549 cells via transfection with short hairpin RNA targeting PRDX5. Colony formation and wound healing assays, flow cytometry, fluorescence microscopy, and western blotting were performed to detect the effect of PRDX5 knockdown on PAM-treated A549 cells. PAM showed higher cytotoxicity in lung cancer cells than in control cells, downregulated the mitogen-activated protein kinase signaling pathway, and induced apoptosis. PRDX5 knockdown significantly inhibited cell colony formation and migration, increased ROS accumulation, and reduced mitochondrial membrane potential in lung cancer cells. Hence, PRDX5 knockdown combined with PAM treatment represents an effective option for lung cancer treatment.

The role of PSMB5 in sodium arsenite-induced oxidative stress in L-02 cells

Endemic arsenism is widely distributed in the world, which can damage multiple organs, especially in skin and liver. The etiology is clear, but the mechanisms involved remain unknown. Ubiquitin-proteasome pathway (UPP) is the main pathway regulating protein degradation of which proteasome subunit beta type-5(PSMB5) plays a dominant role. This paper aims to study the role and mechanism of PSMB5 in sodium arsenite (NaAsO2)-induced oxidative stress liver injury in L-02 cells. Firstly, L-02 cells were exposed to different concentrations of NaAsO2 to establish a liver injury model of oxidative stress, and then mechanisms of oxidative stress were studied with carbobenzoxyl-leucyl-leucl-leucll-line (MG132) and knockdown PSMB5 (PSMB5-siRNA). The oxidative stress indicators, levels of 20S proteasome, the transcription and protein expression levels of PSMB5, Cu-Zn superoxide dismutase (SOD1), and glutathione peroxidase 1 (GPx1) were detected. The results demonstrated that NaAsO2 could induce oxidative stress-induced liver injury and the activity of 20S proteasome and the protein expression of PSMB5, SOD1, and GPx1 decreased. After MG132 or PSMB5-siRNA pretreatment, the gene expression of PSMB decreased. After MG132 or PSMB5-siRNA pretreatment, and then L-02 cells were treated with NaAsO2, the gene expression of PSMB remarkably decreased; however, the protein expression of SOD1 and GPx1 increased. Overall, NaAsO2 exposure could induce oxidative stress liver injury and low expression of PSMB5 in L-02 cells, and PSMB5 might play an important role in the regulation of oxidative stress by regulating the expression of SOD1 and Gpx1.

Low-dose doxorubicin with carotenoids selectively alters redox status and upregulates oxidative stress-mediated apoptosis in breast cancer cells

The combination of carotenoids and doxorubicin (DOX) selectively alters oxidative stress-mediated apoptosis in breast cancer cells. Primarily, cytotoxic efficiency of carotenoids (β-carotene, BC; lutein, LUT; astaxanthin, AST; or fucoxanthin, FUCO) either with or without a minimal cytotoxic dose of DOX was evaluated in MCF-7 (0.12 μM) and MDA-MB-231 cells (0.28 μM). The higher cell growth inhibition of BC and/or LUT with DOX was selected for testing in further cell-based assays. Low-dose DOX significantly enhanced cytotoxicity in carotenoid (<5 μM)-treated cells compared to high-dose DOX (>1 μM) or carotenoid (20 μM) treatment alone. Depleted glutathione, increased lipid peroxides and increased ROS levels in cells confirmed the cytotoxic effect. Furthermore, mitochondrial dysfunction, cell growth arrest at G0/G1 phase and caspase cascades as well as up- and down-regulated expression levels of related proteins (p21, p27, Bax, p53, Bcl-2, and cyclin D1) revealed the synergistic effect of carotenoid and DOX treatment on ROS-mediated apoptosis. These observations demonstrated increased apoptosis in BC + DOX/LUT + DOX-treated cells due to the pronounced pro-oxidant action. Interestingly, normal breast epithelial cells (MCF 10A) exposed to similar treatments resulted in non-significant cytotoxicity. These newly observed mechanistic differences of anticancer drugs on the mitigation of toxicity with carotenoids may provide insight into the targeting of cancer therapy.

Chain elongation analog of resveratrol as potent cancer chemoprevention agent

Resveratrol is identified as a natural cancer chemoprevention agent. There has been a lot of interest in designing and developing resveratrol analogs with cancer chemoprevention activity superior to that of parent molecule and exploring their action mechanism in the past several decades. In this study, we have synthesized resveratrol analogs of compounds A-C via conjugated chain elongation based on isoprene unit retention strategy. Remarkably, cytotoxic activity analysis results indicated that compound B possesses the best proliferation inhibition activity for NCI-H460 cells in all the test compounds. Intriguingly, compound B displayed a higher cytotoxicity against human non-small cell lung cancer cells (NCI-H460) compared to normal human embryonic lung fibroblasts (MRC-5). Afterward, flow cytometry analysis showed that compound B would induce cell apoptosis. We further researched the action mechanism. When NCI-H460 cells were incubated by compound B for 6 or 9 h, respectively, the intracellular reactive oxygen species (ROS) level was enhanced obviously. With elevation of intracellular ROS level, flow cytometry measurement verified mitochondrial transmembrane potential collapse, which was accompanied by the up-regulation of Bax and down-regulation of Bcl-2. More interestingly, compound B increased the expression of caspase-9 and caspase-3, which induced cell apoptosis. Moreover, compound B arrested cell cycle in G0/G1 phase. These are all to provide useful information for designing resveratrol-based chemoprevention agent and understanding the action mechanism.

Cyclin-dependent kinase inhibitor dinaciclib potently synergizes with cisplatin in preclinical models of ovarian cancer

Ovarian cancer is one of the most lethal of woman cancers, and its clinical therapeutic outcome currently is unsatisfied. Dinaciclib, a novel small molecule inhibitor of CDK1, CDK2, CDK5 and CDK9, is assessed in clinical trials for the treatment of several types of cancers. In this study, we investigated the anticancer effects and mechanisms of dinaciclib alone or combined with cisplatin in ovarian cancer. Dinaciclib alone actively induced cell growth inhibition, cell cycle arrest and apoptosis with the increased intracellular ROS levels, which were accompanied by obvious alterations of related proteins such as CDKs, Cyclins, Mcl-1, XIAP and survivin. Pretreatment with N-acety-L-cysteine significantly blocked ROS generation but only partially rescued apoptosis triggered by dinaciclib. Moreover, the combination of dinaciclib with cisplatin synergistically promoted cell cycle arrest and apoptosis, and inhibited the subcutaneous xenograft growth of ovarian cancer in nude mice. Altogether, dinaciclib potently synergizes with cisplatin in preclinical models of ovarian cancer, indicating this beneficial combinational therapy may be a promising strategy for treatment of ovarian cancer.

Aptamer-functionalized gold nanoparticles as photoresponsive nanoplatform for co-drug delivery

Various platforms have been developed as innovative nanocarriers to deliver therapeutic agents to the diseased sites. Multifunctional surface modification allows an enhanced recognition and uptake of drug carriers by targeted cells. However, the development of drug resistance in some tumor cells plays a major role in the failure of chemotherapy. Drugs given in combination, called multidrug delivery approach, was designed to improve the therapeutic efficacy and has become an increasingly used strategy that is of great importance in clinical cancer treatments. In this study, aptamer-functionalized gold nanoparticles (Au NPs) have been used as a nanoplatform to codeliver two different anticancer drugs for improving the drug effectiveness. The surface of Au NPs (13 nm in diameter) was assembled with AS1411 aptamers, which tethered with 21-base pairs of (CGATCGA)3 sequence approached to the Au NPs. Both the photosensitizer 5,10,15,20-tetrakis(1-methylpyridinium-4-yl) porphyrin (TMPyP4) and the chemotherapeutic drug doxorubicin (Dox) were then physically attached to the AS1411-conjugated Au NPs (T/D:ds-NPs) and delivered to the target tumor cells such as HeLa and Dox-resistant MCF-7R cell lines. When exposed to a 632 nm light, reactive oxygen species induced by TMPyP4 molecules were generated inside the living cells, followed by cell damage. In addition, triggered release of the complementary drugs also occurred simultaneously during the photodynamic reaction. In the presence of Dox molecules, the toxicity toward the target cells was superior to individual drug treatment. Overall, a co-drug delivery platform was successfully established to improve the therapeutic efficacy in tumor cells. The improvement of the photodynamic-stimulated triggered release was enhanced, thus highly promising precise drug release in targeted drug delivery.

Effect of chemotherapy exposure prior to pregnancy on fetal brain tissue and the potential protective role of quercetin

Cyclophosphamide (CYC) and doxorubicin (DOX) are among the most effective and widely used anticancer chemotherapeutic drugs. Potential chemopreventive and chemotherapeutic functions have recently been attributed to flavonoids. We hypothesized that Quercetin (QR) would protect against the toxic effects of chemotherapeutic agents applied prior to pregnancy. Rats were treated with the chemotherapeutic drugs CYC (27 mg/kg) and DOX (1.8 mg/kg) applied in a single intraperitoneal dose once every 3 weeks for 10 weeks. QR was administered at a dose of 10 mg/kg/day by oral gavage. 48 h following the experimental chemotherapy exposure, female rats were transferred to cages containing male rat for mating. Fetal brain tissues were removed from fetuses extracted by cesarean section on the 20th day of gestation for evaluation of antioxidant parameters. A significant increase in superoxide dismutase and malondialdehyde activity was observed in CYC and DOX treatment groups relative to the control group (p < 0.05). Similarly, carnitine acylcarnitine translocase and Glutathione activity was significantly reduced in the CYC and DOX groups relative to the control group (p < 0.05). Our results indicate that the use of chemotherapeutic drugs before pregnancy can result in oxidative damage to fetal brain tissue. Therefore, women who have been exposed to chemotherapy and may become pregnant should be treated with antioxidant compounds such as QR to reduce the risk of damage to fetal brain tissues.

Novel aspect of chemophototherapy in treatment of cancer

The present review deals with the genetic implications of reactive oxygen species (ROS) to enhance horizons of chemophototherapy toward novel approaches for the treatment of various cancers. ROS are species of oxygen which are in a more reactive state than molecular oxygen. ROS play essential roles in vivo such as redox regulation, gene expression, immune response and many other cellular events. ROS generated by anticancer drugs during chemophototherapy may be associated with the activation of signal molecules like PKC, transcription factor NF-kappaB as well as destabilization of mitochondrial membrane inducing the release of apoptosis inducing agents like cytochrome c, resulting in toxicity to cancer cells. Thus, we suggest that anticancer drugs on exposure to light may generate oxidative stress following Fenton-like reaction generating hydroxyl radical. This may get on specific cell cycle receptors which may lead to cell cycle arrest and subsequently cytotoxic death of cancer cells.

Novel Anticancer Platinum(IV) Complexes with Adamantylamine: Their Efficiency and Innovative Chemotherapy Strategies Modifying Lipid Metabolism

The impressive impact of cisplatin on cancer on one side and severe side effects, as well as the development of drug resistance during treatment on the other side, were the factors motivating scientists to design and synthesize new more potent analogues lacking disadvantages of cisplatin. Platinum(IV) complexes represent one of the perspective groups of platinum-based drugs. In this review, we summarize recent findings on both in vitro and in vivo effects of platinum(IV) complexes with adamantylamine. Based on a literary overview of the mechanisms of activity of platinum-based cytostatics, we discuss opportunities for modulating the effects of novel platinum complexes through interactions with apoptotic signaling pathways and with cellular lipids, including modulations of the mitochondrial cell death pathway, oxidative stress, signaling of death ligands, lipid metabolism/signaling, or intercellular communication. These approaches might significantly enhance the efficacy of both novel and established platinum-based cytostatics.

Peroxiredoxin II restrains DNA damage-induced death in cancer cells by positively regulating JNK-dependent DNA repair

The 2-Cys peroxiredoxins (Prx) belong to a family of antioxidant enzymes that detoxify reactive oxygen and nitrogen species and are distributed throughout the intracellular and extracellular compartments. However, the presence and role of 2-Cys Prxs in the nucleus have not been studied. This study demonstrates that the PrxII located in the nucleus protects cancer cells from DNA damage-induced cell death. Although the two cytosolic 2-Cys Prxs, PrxI and PrxII, were found in the nucleus, only PrxII knockdown selectively and markedly increased cell death in the cancer cells treated with DNA-damaging agents. The increased death was completely reverted by the nuclearly targeted expression of PrxII in an activity-independent manner. Furthermore, the antioxidant butylated hydroxyanisole did not influence the etoposide-induced cell death. Mechanistically, the knockdown of Prx II expression impaired the DNA repair process by reducing the activation of the JNK/c-Jun pathway. These results suggest that PrxII is likely to be attributed to a tumor survival factor positively regulating JNK-dependent DNA repair with its inhibition possibly sensitizing cancer cells to chemotherapeutic agents.

DNA damage detected with gammaH2AX in endometrioid adenocarcinoma cell lines

Phosphorylation of histone H2AX (gammaH2AX) is a sensitive marker of DNA damage, particularly induction of DNA double-strand breaks. Using multiparameter cytometry we explored the effects of doxorubicin (DOX), cisplatin (CDDP) and 5-fluorouracil (5-FU) on four types of endometrioid adenocarcinoma cell lines (HEC-1A, HEC-1B, Ishikawa, KLE) correlating the drug-induced increases in phosphorylated H2AX (gammaH2AX) with cell cycle phase, induction of apoptosis and induction of cell senescence, the latter detected by analysis of beta-galactosidase. The study revealed significant differences among the cell lines in the effects of DNA damage vis-a-vis cell cycle phase specificity, induction of apoptosis or senescence following drug treatment. DOX treatment showed little cell cycle specificity in terms of induction of gammaH2AX, and its mechanism, which is similar to another anthracycline DNA topoisomerase II inhibitor mitoxantrone, may involve oxidative DNA damage modulated by other factors. Treatment with CDDP and 5-FU led to phosphorylation of H2AX preferentially in S-phase cells, consistent with the induction of replication stress. The response of Ishikawa cells expressing wt p53 was different compared to other cell lines. The data suggest that the treatment of endometrioid adenocarcinoma with these drugs may have to be customized to individual patients. The flow cytometric bivariate analysis of gammaH2AX and DNA content is a useful technique for better understanding the effects of antitumor agents and may contribute to customized patient treatments.

TIP47 protects mitochondrial membrane integrity and inhibits oxidative-stress-induced cell death

We found that overexpression of tail interacting protein of 47 kDa (TIP47), but not its truncated form (t-TIP47) protected NIH3T3 cells from hydrogen-peroxide-induced cell death, prevented the hydrogen-peroxide-induced mitochondrial depolarization determined by 5,50,6,60-tetrachloro-1,10,3,30-tetraethyl-benzimidazolylcarbocyanine iodide (JC1), while suppression of TIP47 in HeLa cells facilitated oxidative-stress-induced cell death. TIP47 was located to the cytoplasm of untreated cells, but some was associated to mitochondria in oxidative stress. Recombinant TIP47, but not t-TIP47 increased the mitochondrial membrane potential (Deltapsi), and partially prevented Ca2+ induced depolarization. It is assumed that TIP47 can bind to mitochondria in oxidative stress, and inhibit mitochondria mediated cell death by protecting mitochondrial membrane integrity.

Transcriptional control of Flt3 ligand targeted by fluorouracil-induced Egr-1 promoter in hematopoietic damage

BACKGROUND

Ionizing radiation (IR) activate the early growth response-1 (Egr-1) promoter by production of radical oxygen intermediates (ROIs). Egr-EF, an expression vector pCIneo containing Egr-1 promoter cloned upstream of the cDNA for Flt3 ligand, was used to treat hematopoietic damage. 5-fluorouracil, a commonly used chemotherapeutic agent, cause tumor cell death by producing DNA damage and generating ROIs. We therefore hypothesized that clinically employed chemotherapeutic agents that increase ROIs could also be employed to activate Egr-EF in a chemoinducible gene therapy strategy. The goal of this study was to explore the effect of Flt3 Ligand gene transcription regulated by fluorouracil-induced Egr-1 promoter on hematopoietic recovery.

METHODS

Human Flt3 Ligand (FL) cDNA and enhanced green fluorescent protein (EGFP) cDNA were linked together with IRES and inserted into the expression vector pCI-neo under control of the Egr-1 promoter (Egr-EF). The vector was transfected into the HFCL human bone marrow stromal cell line, and these cells were exposed to 5-FU, a chemotherapeutic drug. Expression of FL by HFCL/EF cells after 5-FU treatment was determined with ELISA, western blot and RT-PCR assays. In addition, the effect of FL from HFCL/EF cell culture supernatants on growth of CD34+ cells from cord blood was also studied. HFCL/EF cells were injected into CB-17 combined immunodeficient (SCID) mice with B16 melanoma. 5-FU was given three days after injection of the HFCL/EF cells. In the recipient mice, white blood cell levels in peripheral blood and expression of EGFP and FL in human stromal cells were measured. Tumor volumes in tumor-bearing mice were also measured.

RESULTS

5-FU treatment increased EGFP levels and secreted FL levels in HFCL/EF cells. Supernatants from HFCL/EF cell cultures treated with 5-FU increased CD34+ cell growth significantly. HFCL/EF exhibited an increase in the number of white blood cells after chemotherapy.

CONCLUSION

The data presented here support the use of transcriptional control mediated by chemoinducible gene therapy to reduce hematopoietic injury associated with 5-FU.

Oxidant-induced apoptosis is mediated by oxidation of the actin-regulatory protein cofilin

Physiological oxidants that are generated by activated phagocytes comprise the main source of oxidative stress during inflammation. Oxidants such as taurine chloramine (TnCl) and hydrogen peroxide (H(2)O(2)) can damage proteins and induce apoptosis, but the role of specific protein oxidation in this process has not been defined. We found that the actin-binding protein cofilin is a key target of oxidation. When oxidation of this single regulatory protein is prevented, oxidant-induced apoptosis is inhibited. Oxidation of cofilin causes it to lose its affinity for actin and to translocate to the mitochondria, where it induces swelling and cytochrome c release by mediating opening of the permeability transition pore (PTP). This occurs independently of Bax activation and requires both oxidation of cofilin Cys residues and dephosphorylation at Ser 3. Knockdown of endogenous cofilin using targeted siRNA inhibits oxidant-induced apoptosis, which is restored by re-expression of wild-type cofilin but not by cofilin containing Cys to Ala mutations. Exposure of cofilin to TnCl results in intramolecular disulphide bonding and oxidation of Met residues to Met sulphoxide, but only Cys oxidation causes cofilin to induce mitochondrial damage.

Bcl-2 family proteins as regulators of oxidative stress

The Bcl-2 family of proteins includes pro- and anti-apoptotic factors acting at mitochondrial and microsomal membranes. An impressive body of published studies, using genetic and physical reconstitution experiments in model organisms and cell lines, supports a view of Bcl-2 proteins as the critical arbiters of apoptotic cell death decisions in most circumstances (excepting CD95 death receptor signaling in Type I cells). Evasion of apoptosis is one of the hallmarks of cancer [Hanahan D, Weinberg RA. The hallmarks of cancer. Cell 2000;100:57-70], relevant to tumorigenesis as well as resistance to cytotoxic drugs, and deregulation of Bcl-2 proteins is observed in many cancers [Manion MK, Hockenbery DM. Targeting BCL-2-related proteins in cancer therapy. Cancer Biol Ther. 2003;2:S105-14; Olejniczak ET, Van Sant C, Anderson MG, Wang G, Tahir SK, Sauter G, et al. Integrative genomic analysis of small-cell lung carcinoma reveals correlates of sensitivity to bcl-2 antagonists and uncovers novel chromosomal gains. Mol Cancer Res. 2007;5:331-9]. The rekindled interest in aerobic glycolysis as a cancer trait raises interesting questions as to how metabolic changes in cancer cells are integrated with other essential alterations in cancer, e.g. promotion of angiogenesis and unbridled growth signals. Apoptosis induced by multiple different signals involves loss of mitochondrial homeostasis, in particular, outer mitochondrial membrane integrity, releasing cytochrome c and other proteins from the intermembrane space. This integrative process, controlled by Bcl-2 family proteins, is also influenced by the metabolic state of the cell. In this review, we consider the role of reactive oxygen species, a metabolic by-product, in the mitochondrial pathway of apoptosis, and the relationships between Bcl-2 functions and oxidative stress.

Bcl-2 family proteins as regulators of oxidative stress

The Bcl-2 family of proteins includes pro- and anti-apoptotic factors acting at mitochondrial and microsomal membranes. An impressive body of published studies, using genetic and physical reconstitution experiments in model organisms and cell lines, supports a view of Bcl-2 proteins as the critical arbiters of apoptotic cell death decisions in most circumstances (excepting CD95 death receptor signaling in Type I cells). Evasion of apoptosis is one of the hallmarks of cancer [Hanahan D, Weinberg RA. The hallmarks of cancer. Cell 2000;100:57-70], relevant to tumorigenesis as well as resistance to cytotoxic drugs, and deregulation of Bcl-2 proteins is observed in many cancers [Manion MK, Hockenbery DM. Targeting BCL-2-related proteins in cancer therapy. Cancer Biol Ther. 2003;2:S105-14; Olejniczak ET, Van Sant C, Anderson MG, Wang G, Tahir SK, Sauter G, et al. Integrative genomic analysis of small-cell lung carcinoma reveals correlates of sensitivity to bcl-2 antagonists and uncovers novel chromosomal gains. Mol Cancer Res. 2007;5:331-9]. The rekindled interest in aerobic glycolysis as a cancer trait raises interesting questions as to how metabolic changes in cancer cells are integrated with other essential alterations in cancer, e.g. promotion of angiogenesis and unbridled growth signals. Apoptosis induced by multiple different signals involves loss of mitochondrial homeostasis, in particular, outer mitochondrial membrane integrity, releasing cytochrome c and other proteins from the intermembrane space. This integrative process, controlled by Bcl-2 family proteins, is also influenced by the metabolic state of the cell. In this review, we consider the role of reactive oxygen species, a metabolic by-product, in the mitochondrial pathway of apoptosis, and the relationships between Bcl-2 functions and oxidative stress.

Antioxidant activity of N-acetylcysteine, flavonoids and α-tocopherol on endometrial cells in culture

An appropriate local environment is necessary for successful implantation. Oxidative stress is implicated in the pathogenesis of several pathologies, and may contribute to early pregnancy failure. Antioxidant therapies have been studied in infertility. In this study, we have assessed the antioxidant activity of N-acetylcysteine (NAC), flavonoids (quercetin, catechin) and alpha-tocopherol in an oxidative model of endometrial cells (RL95). Endometrial cells were incubated at several hydrogen peroxide concentrations. Antioxidant effects of NAC (15 mM), quercetin (150 microM), catechin (150 microM) and alpha-tocopherol included in liposomes (1.6 microg) were assessed by measuring cell viability by the MTT assay. Alpha-tocopherol-liposomes taken up by endometrial cells were assessed by HPLC. All liposomes used were able to introduce alpha-tocopherol into cells. The antioxidant effect of NAC and quercetin improved the viability of oxidised cells, and this effect was observed when the oxidant and antioxidant were coincubated. No viability change occurred when the antioxidant was added before or after the oxidant. The antioxidant effect of NAC was better than that of quercetin. When catechin or alpha-tocopherol were used in the same conditions, no antioxidant effect was detected in cells in culture. These results demonstrate that NAC and quercetin are good H2O2 scavengers.

Cytoprotective effect of Panax ginseng on gallic acid-induced toxicity in TM3 mouse Leydig cells

Our previous study had demonstrated cytotoxicity of gallic acid on testicular cells with increasing the intracellular production of hydrogen peroxide. In the present study, the Panax ginseng root aqueous extract showed the cytoprotective effect on gallic acid-induced toxicity in TM3 mouse Leydig cells with decreasing the intracellular production of hydrogen peroxide.

Doxorubicin degradation in cardiomyocytes

Antitumor therapy with the anthracycline doxorubicin is limited by a severe cardiotoxicity, which seems to correlate with the cardiac levels of doxorubicin and its metabolization to reactive oxygen species. Previous biochemical studies showed that hydrogen peroxide-activated myoglobin caused an oxidative degradation of doxorubicin; however, a pharmacological evaluation of this metabolic pathway was precluded by the lack of safe and specific inhibitors of doxorubicin degradation. We found that tert-butoxycarbonyl-alanine inhibited doxorubicin degradation induced in vitro by hydrogen peroxide-activated oxyferrous myoglobin. When assessed in H9c2 cardiomyocytes, tert-butoxycarbonyl-alanine neither stimulated the cellular uptake of doxorubicin nor diminished its efflux; moreover, tert-butoxycarbonyl-alanine did not cause toxicity per se nor did it augment the toxicity induced by hydrogen peroxide or chemical agents that increased the cellular levels of reactive oxygen species. Nonetheless, tert-butoxycarbonyl-alanine increased the cellular levels of doxorubicin, its conversion to reactive oxygen species, and its concentration-related toxicity. tert-Butoxycarbonyl-alanine also aggravated the toxicity of a degradation-prone anthracycline analog, daunorubicin, but it caused a minor effect on the toxicity of a degradation-resistant analog, aclarubicin. These results suggested that tert-butoxycarbonyl-alanine increased the cellular levels and toxicity of doxorubicin by inhibiting its oxidative degradation to harmless products. Accordingly, doxorubicin samples that had been oxidized in vitro with hydrogen peroxide and oxyferrous myoglobin lacked toxicity to cardiomyocytes. The effects of tert-butoxycarbonyl-alanine were most evident at 0.1 to 1 microM doxorubicin, which may be relevant to clinical conditions. These studies identify an oxidative degradation of doxorubicin as a possible salvage mechanism for diminishing its levels and toxicity in cardiomyocytes.

On the potential of thioredoxin reductase inhibitors for cancer therapy

Thioredoxin reductase (TrxR)-as part of a major thiol regulating system-allows redox metabolism to adjust to cellular requirements. Therefore, changes at the redox level reflect as a pars pro toto changes concerning the entire cell. Three different TrxR isoenzymes, TrxR1 as cytosolic, TrxR2 as mitochondrial, and TrxR3 as testis-specific thiol regulator are known. All three enzymes contain a reactive and solvent accessible selenocysteine residue which is located on a flexible C-terminal arm of the protein. This selenocysteine is essentially involved in the catalytic cycle of TrxR and thus represents an attractive binding site for inhibitors. Many tumor cells have elevated TrxR levels and TrxR has been shown to play a major role in drug resistance. Inhibition of TrxR and its related redox reactions may thus contribute to a successful single, combinatory or adjuvant cancer therapy. A great number of effective natural and synthetic TrxR inhibitors are now available possessing antitumor potential ranging from induction of oxidative stress to cell cycle arrest and apoptosis. This article summarizes the present knowledge on the potential of TrxR inhibitors and TrxR as anticancer drug target.

Induction of necrotic cell death and mitochondrial permeabilization by heme binding protein 2/SOUL

We found that heme-binding protein 2/SOUL sensitised NIH3T3 cells to cell death induced by A23187 and etoposide, but it did not affect reactive oxygen species formation. In the presence of sub-threshold calcium, recombinant SOUL provoked mitochondrial permeability transition (mPT) in vitro that was inhibited by cyclosporine A (CsA). This effect was verified in vivo by monitoring the dissipation of mitochondrial membrane potential. Flow cytometry analysis showed that SOUL promoted necrotic death in A23187 and etoposide treated cells, which effect was prevented by CsA. These data suggest that besides its heme-binding properties SOUL promotes necrotic cell death by inducing mPT.

The effect of intracellular ascorbate on the susceptibility of HL60 and Jurkat cells to chemotherapy agents

Chemotherapy agents initiate tumour cell apoptosis and this is thought to involve oxidative stress. In this study we have investigated the effect of the important antioxidant Vitamin C (ascorbate) on the response of HL60 and Jurkat cells to three chemotherapy drugs, namely etoposide, melphalan and arsenic trioxide (As(2)O(3)). Cells grown in routine culture media are deficient in ascorbate and to determine its effect on chemotherapy drug-induced apoptosis we supplemented the cells prior to drug exposure. We found that ascorbate had a varied effect on apoptosis and cell cycle progression. Etoposide-induced apoptosis in HL60 cells was significantly increased in ascorbate-loaded cells as measured by caspase-3 activation and DNA degradation, and this appeared to reflect a decrease in the number of necrotic cells rather than increased cytotoxicity. In contrast, ascorbate had no effect on etoposide-induced apoptosis in Jurkat cells. In both cell types melphalan-induced apoptosis was unaffected by intracellular ascorbate, whereas both apoptosis and growth arrest with low concentrations of As(2)O(3) were diminished. These results indicate that intracellular ascorbate can affect cell responses to chemotherapy drugs in a complex and somewhat unpredictable manner and that it may play an important role in the responsiveness of tumour cells to chemotherapy regimes.

Ionizing radiation: a genetic switch for cancer therapy

Gene therapy of cancer represents a promising but challenging area of therapeutic research. The discovery of radiation-inducible genes led to the concept and development of radiation-targeted gene therapy. In this approach, promoters of radiation-inducible genes are used to drive transcription of transgenes in the response to radiation. Constructs in which the radiation-inducible promoter elements activate a transgene encoding a cytotoxic protein are delivered to tumors by adenoviral vectors. The tumoricidal effects are then localized temporally and spatially by X-rays. We review the conceptual development of TNFerade, an adenoviral vector containing radiation-inducible elements of the early growth response-1 promoter upstream of a cDNA encoding human tumor necrosis factor-alpha. We also summarize the preclinical work and clinical trials utilizing this vector as a treatment for diverse solid tumors.

Gold(III) Porphyrin 1a Induced Apoptosis by Mitochondrial Death Pathways Related to Reactive Oxygen Species

Apoptosis is a tightly controlled multistep mechanism of cell death, and mitochondria are considered to play a central role in this process. Mitochondria initiate two distinct apoptosis pathways, one caspase-dependent and the other caspase-independent. In addition, mitochondrial production of reactive oxygen species (ROS) seems to play a role in cell death. Most chemotherapeutic agents induce apoptosis through at least one of these pathways. The post-initiation mechanisms of gold(III) porphyrin 1a were investigated in this study. HONE1 cells exposed to gold(III) porphyrin 1a underwent apoptosis after 24 hours. Functional proteomic studies revealed the alteration of several cytoplasmic protein expressions in HONE1 cells after treatment with the drug. These proteins include enzymes participating in energy production and proteins involved in cellular redox balance. There was a quick attenuation of mitochondrial membrane potential (DeltaPsi(m)) with the alterations of Bcl-2 family proteins, the release of cytochrome c, and apoptosis-inducing factor (AIF) following gold(III) porphyrin 1a treatment. Cytochrome c in turn activated caspase-9 and caspase-3. Cotreatment with caspase inhibitor (zVAD-fmk) showed that the activated caspases worked in conjunction with AIF-initiated apoptosis pathways. Further study showed that ROS played a part in gold(III) porphyrin 1a-induced apoptosis by regulating DeltaPsi(m). In summary, gold(III) porphyrin 1a induced apoptosis through both caspase-dependent and caspase-independent mitochondrial pathways, and intracellular oxidation affected gold(III) porphyrin 1a-induced apoptosis. These results support a role for gold(III) porphyrin 1a as a promising anticancer drug lead and as a possible novel therapeutic agent directed toward the mitochondria.

Chemoinducible gene therapy

Chemo-inducible cancer gene therapy is a potential new treatment for solid tumors that may in part enhance the anti-tumor effects of chemotherapy while minimizing toxicity. This approach combines viral vectors expressing cytotoxic transgenes that can be transcriptionally activated by DNA-damaging agents. The development of chemo-inducible gene therapy has numerous implications for the treatment of both localized and metastatic disease in patients with solid tumors.

Mitochondria superoxide dismutase mimetic inhibits peroxide-induced oxidative damage and apoptosis: role of mitochondrial superoxide

The purpose of this study was to test the hypothesis whether Mito-carboxy proxyl (Mito-CP), a mitochondria-targeted nitroxide, inhibits peroxide-induced oxidative stress and apoptosis in bovine aortic endothelial cells (BAEC). Glucose/glucose oxidase (Glu/GO)-induced oxidative stress was monitored by dichlorodihydrofluorescein oxidation catalyzed by intracellular H(2)O(2) and transferrin receptor-mediated iron transported into cells. Pretreatment of BAECs with Mito-CP significantly diminished H(2)O(2)- and lipid peroxide-induced intracellular formation of dichlorofluorescene and protein oxidation. Electron paramagnetic resonance (EPR) studies confirmed the selective accumulation of Mito-CP into the mitochondria. Mito-CP inhibited the cytochrome c release and caspase-3 activation in cells treated with peroxides. Mito-CP inhibited both H(2)O(2)- and lipid peroxide-induced inactivation of complex I and aconitase, overexpression of transferrin receptor (TfR), and mitochondrial uptake of (55)Fe, while restoring the mitochondrial membrane potential and proteasomal activity. In contrast, the "untargeted" carboxy proxyl (CP) nitroxide probe did not protect the cells from peroxide-induced oxidative stress and apoptosis. However, both CP and Mito-CP inhibited superoxide-induced cytochrome c reduction to the same extent in a xanthine/xanthine oxidase system. We conclude that selective uptake of Mito-CP into the mitochondria is responsible for inhibiting peroxide-mediated Tf-Fe uptake and apoptosis and restoration of the proteasomal function.

Desferal inhibits breast tumor growth and does not interfere with the tumoricidal activity of doxorubicin

Desferal is a clinically approved iron chelator used to treat iron overload. Doxorubicin is an anthracycline cancer chemotherapy drug used in the treatment of breast cancer. It can undergo redox cycling in the presence of iron to produce reactive oxygen species. The oxidant-generating activity of doxorubicin is thought to be responsible for the cardiotoxic side effects of the drug, but it is unclear whether it is also required for its anti-tumor activity. To test whether an iron-chelating antioxidant would interfere with the tumor-killing activity of doxorubicin, nude mice were transplanted with xenografts of human breast cancer MDA-MB 231 cells and then treated with doxorubicin and/or desferal. Not only did desferal not interfere with the anti-tumor activity of doxorubicin, it inhibited tumor growth on its own. In vitro studies confirmed that desferal inhibits breast tumor growth. However, it did not induce apoptosis, nor did it induce cell cycle arrest. Instead, desferal caused cytostasis, apparently through iron depletion. The cytostatic activity of desferal was partially ameliorated by pretreatment with iron-saturated transferrin, and transferrin receptor expression on breast cancer cells nearly doubled after exposure to desferal. In contrast to its effect on tumor cells, desferal did not inhibit growth of normal breast epithelial cells. The data indicate that the anti-tumor activity of doxorubicin is not dependent on iron-mediated ROS production. Furthermore, desferal may have utility as an adjunctive chemotherapy due to its ability to inhibit breast tumor growth and cardiotoxic side effects without compromising the tumor-killing activity of an anthracycline chemotherapy drug.

Novel platinum(IV) complexes induce rapid tumor cell deathin vitro

The anticancer activity of platinum complexes has been known since the discovery of classical Pt(II)-based drug cisplatin. However, Pt(IV) complexes have greater inertness than corresponding Pt(II) complexes, thus allowing the oral administration and reducing the toxicity associated with platinum-based chemotherapy. Here, we describe the in vitro antitumor activity of some novel Pt(IV)-based agents against mouse fibrosarcoma L929 cells and human astrocytoma U251 cells. The cytotoxicity of 2 Pt(IV) complexes with bidentate ethylenediamine-N,N'-di-3-propanoato esters was found to be markedly higher than that of their Pt(II) counterparts and comparable to the antitumor action of cisplatin. In contrast to cisplatin, which caused oxidative stress-independent apoptotic cell death of tumor cells, these Pt(IV) complexes induced oxygen radical-mediated tumor cell necrosis. Importantly, the cytotoxic action of novel Pt(IV) complexes was markedly more rapid than that of cisplatin, indicating their potential usefulness in anticancer therapy.

Upregulation of Daxx mediates apoptosis in response to oxidative stress

Oxidative stress induces apoptosis in a variety of cell types by as yet unclear signaling mechanisms. The Daxx protein is reportedly involved in apoptosis through its interactions with Fas, transforming growth factor-beta receptor, and promyelocytic leukemia protein (PML). Here, we explored the possible roles of Daxx in oxidative stress-induced apoptosis. We found that both the mRNA and protein levels of Daxx markedly increased when cells underwent apoptosis after H2O2 treatment. Pretreatment with the cell-permeable antioxidant, N-acetyl cysteine, prevented cells from H2O2-induced Daxx upregulation and subsequent apoptosis, indicating that the endogenous oxidant regulated Daxx expression. Furthermore, suppression of endogenous Daxx expression by antisense oligonucleotide technology inhibited oxidative stress-induced apoptosis in HeLa cells. Taken together, these results suggest that Daxx acts as an intermediary messenger of pro-apoptotic signals triggered by oxidative stress.

Chemoinducible gene therapy: A strategy to enhance doxorubicin antitumor activity

A replication-defective adenoviral vector, Ad.Egr-TNF.11D, was engineered by ligating the CArG (CC(A/T)6GG) elements of the Egr-1 gene promoter upstream to a cDNA encoding human tumor necrosis factor-α. We report here that Ad.Egr-TNF.11D is activated by the clinically important anticancer agents cisplatin, cyclophosphamide, doxorubicin, 5-fluorouracil, gemcitabine, and paclitaxel. N-acetylcysteine, a free radical scavenger, blocked induction of tumor necrosis factor-α by anticancer agents, supporting a role for reactive oxygen intermediates in activation of the CArG sequences. Importantly, resistance of PC-3 human prostate carcinoma and PROb rat colon carcinoma tumors to doxorubicin in vivo was reversed by combining doxorubicin with Ad.Egr-TNF and resulted in significant antitumor effects. Treatment with Ad.Egr-TNF.11D has been associated with inhibition of tumor angiogenesis. In this context, a significant decrease in tumor microvessel density was observed following combined treatment with doxorubicin and Ad.Egr-TNF.11D as compared with either agent alone. These data show that Ad.Egr-TNF.11D is activated by diverse anticancer drugs.

Supplementation of endothelial cells with mitochondria-targeted antioxidants inhibit peroxide-induced mitochondrial iron uptake, oxidative damage, and apoptosis

The mitochondria-targeted drugs mitoquinone (Mito-Q) and mitovitamin E (MitoVit-E) are a new class of antioxidants containing the triphenylphosphonium cation moiety that facilitates drug accumulation in mitochondria. In this study, Mito-Q (ubiquinone attached to a triphenylphosphonium cation) and MitoVit-E (vitamin E attached to a triphenylphosphonium cation) were used. The aim of this study was to test the hypothesis that mitochondria-targeted antioxidants inhibit peroxide-induced oxidative stress and apoptosis in bovine aortic endothelial cells (BAEC) through enhanced scavenging of mitochondrial reactive oxygen species, thereby blocking reactive oxygen species-induced transferrin receptor (TfR)-mediated iron uptake into mitochondria. Glucose/glucose oxidase-induced oxidative stress in BAECs was monitored by oxidation of dichlorodihydrofluorescein that was catalyzed by both intracellular H(2)O(2) and transferrin iron transported into cells. Pretreatment of BAECs with Mito-Q (1 microM) and MitoVit-E (1 microM) but not untargeted antioxidants (e.g. vitamin E) significantly abrogated H(2)O(2)- and lipid peroxide-induced 2',7'-dichlorofluorescein fluorescence and protein oxidation. Mitochondria-targeted antioxidants inhibit cytochrome c release, caspase-3 activation, and DNA fragmentation. Mito-Q and MitoVit-E inhibited H(2)O(2)- and lipid peroxide-induced inactivation of complex I and aconitase, TfR overexpression, and mitochondrial uptake of (55)Fe, while restoring the mitochondrial membrane potential and proteasomal activity. We conclude that Mito-Q or MitoVit-E supplementation of endothelial cells mitigates peroxide-mediated oxidant stress and maintains proteasomal function, resulting in the overall inhibition of TfR-dependent iron uptake and apoptosis.

Doxorubicin Induces Apoptosis in Normal and Tumor Cells via Distinctly Different Mechanisms

Doxorubicin (DOX), a widely used chemotherapeutic agent, exhibits cardiotoxicity as an adverse side effect in cancer patients. DOX-mediated cardiomyopathy is linked to its ability to induce apoptosis in endothelial cells and cardiomyocytes by activation of p53 protein and reactive oxygen species. We evaluated the potential roles of H(2)O(2) and p53 in DOX-induced apoptosis in normal bovine aortic endothelial cells and adult rat cardiomyocytes and in tumor cell lines PA-1 (human ovarian teratocarcinoma) and MCF-7 (human breast adenocarcinoma). Time course measurements indicated that activation of caspase-3 preceded the stimulation of p53 transcriptional activity in endothelial cells. In contrast, DOX caused early activation of p53 in tumor cells that was followed by caspase-3 activation and DNA fragmentation. These findings suggest that the transcriptional activation of p53 in DOX-induced apoptosis in endothelial cells may not be as crucial as it is in tumor cells. Further evidence was obtained using a p53 inhibitor, pifithrin-alpha. Pifithrin-alpha completely suppressed DOX-induced activation of p53 in both normal and tumor cell lines and prevented apoptosis in tumor cell lines but not in endothelial cells and cardiomyocytes. In contrast, detoxification of H(2)O(2), either by redox-active metalloporphyrin or overexpression of glutathione peroxidase, decreased DOX-induced apoptosis in endothelial cells and cardiomyocytes but not in tumor cells. This newly discovered mechanistic difference in DOX-induced apoptotic cell death in normal versus tumor cells will be useful in developing drugs that selectively mitigate the toxic side effects of DOX without affecting its antitumor action.

Caspase 3-mediated inactivation of rac GTPases promotes drug-induced apoptosis in human lymphoma cells

The Rac members of the Rho family GTPases control signaling pathways that regulate diverse cellular activities, including cytoskeletal organization, gene transcription, and cell transformation. Rac is implicated in apoptosis, but little is known about the mechanism by which it responds to apoptotic stimuli. Here we demonstrate that endogenous Rac GTPases are caspase 3 substrates that are cleaved in human lymphoma cells during drug-induced apoptosis. Cleavage of Rac1 occurs at two unconventional caspase 3 sites, VVGD11/G and VMVD47/G, and results in inactivation of the GTPase and effector functions of the protein (binding to the p21-activated protein kinase PAK1). Expression of caspase 3-resistant Rac1 mutants in the cells suppresses drug-induced apoptosis. Thus, proteolytic inactivation of Rac GTPases represents a novel, irreversible mechanism of Rac downregulation that allows maximal cell death following drug treatment.

N-Acetylcysteine enhances UV-mediated caspase-3 activation, fragmentation of E2F-4, and apoptosis in human C8161 melanoma: inhibition by ectopic Bcl-2 expression

Redox imbalance due to oxidative stress or excessive antioxidant levels can alter apoptotic responses. Recently, antioxidants like N-acetylcysteine (NAC) were reported to inhibit H(2)O(2)-mediated necrotic cell death, although they were inactive against apoptosis induced by other agents like etoposide. NAC was also found to kill preferentially tumor cells compared to normal fibroblasts at 20-50mM, but these concentrations are lethal to normal splenocytes. We now demonstrate that 10mM NAC, a non-toxic concentration, can enhance the UV radiation-mediated apoptosis of human C8161 melanoma cells. Compared to treatment with UV radiation alone, combination treatment with NAC doubled the ratio of activated caspase-3 to pro-caspase-3 and produced greater fragmentation of the retinoblastoma protein and the E2F-4 transcription factor without affecting the E2F-1 protein. These effects of joint NAC-UV radiation treatment were counteracted by the overexpression of the bcl-2 gene. To our knowledge, this report is the first to: (i) demonstrate a synergy between DNA-damaging agents, like UV radiation, and antioxidants, like NAC, and (ii) show that a Bcl-2-inhibitable E2F-4 fragmentation occurs concurrently with caspase-3 activation and apoptosis.

Alpha-tocopherol protects against cisplatin-induced toxicity without interfering with antitumor efficacy

Our aim was 2-fold: to investigate the role of alpha-tocopherol supplementation on the antitumor activity of DDP and to evaluate the effect of alpha-tocopherol on the survival and neurotoxicity of DDP-treated mice. Experiments performed on the M14 human melanoma line demonstrated that alpha-tocopherol supplementation did not influence the efficacy of DDP; the inhibition of cell survival and of the in vivo tumor growth after treatment with alpha-tocopherol and DDP combination was similar to that observed after DDP alone. Conversely, alpha-tocopherol was also able to increase survival of mice treated with a high dose of DDP. While DDP alone produced death in about 70% of mice, the combination reduced deaths to about 30%. Analysis of oxidative stress markers and peroxidative damage in organs indicated that the protective effect of alpha-tocopherol was mainly related to its antioxidant activity. A significant increase in the concentration of TBARS and decreased PUFAs and catalase activity were observed after DDP treatment, while with alpha-tocopherol the levels of these markers were comparable to those observed in untreated mice. Histologic analysis performed on peripheral nerve revealed that alpha-tocopherol also protected mice from severe neurologic damage induced by DDP treatment. In conclusion, our results demonstrate that alpha-tocopherol protects against the systemic toxicity and neurotoxicity induced by DDP without interfering with its antitumor activity and suggest that this combination is a promising strategy to improve the therapeutic index of DDP-based chemotherapy.

Catalase protects HepG2 cells from apoptosis induced by DNA-damaging agents by accelerating the degradation of p53

Oxidants such as H(2)O(2) play a role in the toxicity of certain DNA-damaging agents, a process that often involves the tumor suppressor p53. H(2)O(2) is rapidly degraded by catalase, which protects cells against oxidant injury. To study the effect of catalase on apoptosis induced by DNA-damaging agents, HepG2 cells were infected with adenovirus containing the cDNA of catalase (Ad-Cat). Forty-eight hours after infection, catalase protein and activity was increased 7-10-fold compared with control cells infected with Ad-LacZ. After treatment with Vp16 or mitomycin C, control cells underwent apoptosis in a p53-dependent manner; however, overexpression of catalase inhibited this apoptosis. Basal levels as well as Vp16- or mitomycin C-stimulated levels of p53 and p21 protein were decreased in the catalase-overexpressing cells as compared with control cells; however, p53 mRNA levels were not decreased by catalase. There was no difference in p53 protein synthesis between catalase-overexpressing cells and control cells. However, pulse-chase experiments indicated that p53 protein degradation was enhanced in the catalase-overexpressing cells. Proteasome inhibitors but not calpeptin prevented the catalase-mediated decrease of p53 content. Whereas Vp16 increased, catalase overexpression decreased the phosphorylation of p53. The protein phosphatase inhibitor okadaic acid did not prevent the catalase-mediated down-regulation of p53 or phosphorylated p53. These results demonstrate that catalase protects HepG2 cells from apoptosis induced by DNA-damaging agents in association with decreasing p53 phosphorylation; the latter may lead to an acceleration in the degradation of p53 protein by the proteasome complex. This suggests that the level of catalase may play a critical role in cell-induced resistance to the effects of anti-cancer drugs which up-regulate p53.

Emodin induces apoptosis in human promyeloleukemic HL-60 cells accompanied by activation of caspase 3 cascade but independent of reactive oxygen species production

Emodin (1,3,8-trihydroxy-6-methylanthraquinone) is an active constituent of Rheum palmatum, and showed inhibitory activity on lipopolysaccharide-induced NO production in our previous study. However, the apoptosis-inducing activity of emodin has remained undefined. Among three structurally related anthraquinones, including emodin, physcion, and chrysophanol, emodin showed the most potent cytotoxic effects on HL-60 cells, accompanied by the dose- and time-dependent appearance of characteristics of apoptosis including an increase in DNA ladder intensity, morphological changes, appearance of apoptotic bodies, and an increase in hypodiploid cells. Emodin at apoptosis-inducing concentrations causes rapid and transient induction of caspase 3/CPP32 activity, but not caspase 1 activity, according to cleavage of caspase 3 substrates poly(ADP-ribose) polymerase and D4-GDI proteins, the appearance of cleaved caspase 3 fragments being detected in emodin- but not physcion- or chrysophanol-treated HL-60 cells. A decrease in the anti-apoptotic protein, Mcl-1, was detected in emodin-treated HL-60 cells, whereas other Bcl-2 family proteins including Bax, Bcl-2, Bcl-XL, and Bad remained unchanged. The caspase 3 inhibitor, Ac-DEVD-CHO, but not the caspase 1 inhibitor, Ac-YVAD-CHO, attenuated emodin-induced DNA ladders, associated with the blockage of PARP and D4-GDI cleavage. Free radical scavenging agents including NAC, catalase, SOD, ALL, DPI, L-NAME and PDTC showed no preventive effect on emodin-induced apoptotic responses, whereas NAC, CAT and PDTC prevented HL-60 cells from ROS (H(2)O(2))-induced apoptosis through inhibition of caspase 3 cascades. Induction of catalase, but not SOD, activity was detected in emodin-treated HL-60 cells by in gel activity assays, and H(2)O(2)-induced intracellular peroxide level was significantly reduced by prior treatment of emodin in HL-60 cells. Our experiments provide evidence that emodin is an effective apoptosis inducer in HL-60 cells through activation of the caspase 3 cascade, but that it is independent of ROS production.

Hyperoxia-induced apoptosis does not require mitochondrial reactive oxygen species and is regulated by Bcl-2 proteins

Exposure of animals to hyperoxia results in lung injury that is characterized by apoptosis and necrosis of the alveolar epithelium and endothelium. The mechanism by which hyperoxia results in cell death, however, remains unclear. We sought to test the hypothesis that exposure to hyperoxia causes mitochondria-dependent apoptosis that requires the generation of reactive oxygen species from mitochondrial electron transport. Rat1a cells exposed to hyperoxia underwent apoptosis characterized by the release of cytochrome c, activation of caspase-9, and nuclear fragmentation that was prevented by the overexpression of Bcl-X(L.) Murine embryonic fibroblasts from bax(-/-) bak(-/-) mice were resistant to hyperoxia-induced cell death. The administration of the antioxidants manganese (III) tetrakis (4-benzoic acid) porphyrin, ebselen, and N-acetylcysteine failed to prevent cell death following exposure to hyperoxia. Human fibrosarcoma cells (HT1080) lacking mitochondrial DNA (rho(0) cells) that failed to generate reactive oxygen species during exposure to hyperoxia were not protected against cell death following exposure to hyperoxia. We conclude that exposure to hyperoxia results in apoptosis that requires Bax or Bak and can be prevented by the overexpression of Bcl-X(L). The mitochondrial generation of reactive oxygen species is not required for cell death following exposure to hyperoxia.