Depletion Of Intracellular GSH Research Articles

Inhibitory Effect of Gallic Acid and Its Esters on 2,2′-Azobis(2-amidinopropane)hydrochloride (AAPH)-Induced Hemolysis and Depletion of Intracellular Glutathione in Erythrocytes

The protective effect of gallic acid and its esters, methyl, propyl, and lauryl gallate, against 2,2'-azobis(2-amidinopropane)hydrochloride (AAPH)-induced hemolysis and depletion of intracellular glutathione (GSH) in erythrocytes was studied. The inhibition of hemolysis was dose-dependent, and the esters were significantly more effective than gallic acid. Gallic acid and its esters were compared with regard to their reactivity to free radicals, using the DPPH and AAPH/pyranine free-cell assays, and no significant difference was obtained. Gallic acid and its esters not only failed to inhibit the depletion of intracellular GSH in erythrocytes induced by AAPH but exacerbated it. Similarly, the oxidation of GSH by AAPH or horseradish peroxidase/H(2)O(2) in cell-free systems was exacerbated by gallic acid or gallates. This property could be involved in the recent findings on pro-apoptotic and pro-oxidant activities of gallates in tumor cells. We provide evidence that lipophilicity and not only radical scavenger potency is an important factor regarding the efficiency of antihemolytic substances.

Structure–toxicity relationship of phenolic analogs as anti-melanoma agents: An enzyme directed prodrug approach

The aim of this study was to identify a phenolic prodrug compound that is minimally metabolized by rat liver microsomes, but yet could form quinone reactive intermediates in melanoma cells as a result of its bioactivation by tyrosinase. In current work, we investigated 24 phenolic compounds for their metabolism by tyrosinase, rat liver microsomes and their toxicity towards murine B16-F0 and human SK-MEL-28 melanoma cells. A linear correlation was found between toxicities of phenolic analogs towards SK-MEL-28 and B16-F0 melanoma cells, suggesting similar mechanisms of toxicity in both cell lines. 4-HEB was identified as the lead compound. 4-HEB (IC 50 48 h, 75 μM) showed selective toxicity towards five melanocytic melanoma cell lines SK-MEL-28, SK-MEL-5, MeWo, B16-F0 and B16-F10, which express functional tyrosinase, compared to four non-melanoma cells lines SW-620, Saos-2, PC3 and BJ cells and two amelanotic SK-MEL-24, C32 cells, which do not express functional tyrosinase. 4-HEB caused significant intracellular GSH depletion, ROS formation, and showed significantly less toxicity to tyrosinase specific shRNA transfected SK-MEL-28 cells. Our findings suggest that presence of a phenolic group in 4-HEB is critical for its selective toxicity towards melanoma cells.

Efficacy of Caffeic Acid Phenethyl Ester (CAPE) in skin B16-F0 melanoma tumor bearing C57BL/6 mice

In current work, we investigated the in-vitro efficacy of Caffeic acid Phenethyl Ester (CAPE) as an anti-melanoma agent in five melanoma cell lines B16-F0, B16F10, SK-MEL-28, SK-MEL-5, and MeWo and in-vivo efficacy study in skin B16-F0 melanoma tumor model in C57BL/6 mice. The IC(50) (48 h) of CAPE in above five melanoma cell lines was 15 µM. CAPE (20-200 µM) led to intracellular GSH depletion of 16-54%, and 10-25 fold increase in Reactive Oxygen Species (ROS) formation in B16-F0 cells. CAPE (15-30 µM) caused 5-7 fold increase in apoptosis in B16-F0 cells. CAPE (10, 20 and 30 mg/Kg/day) led to tumor size growth inhibition by 39 ± 33%, 54 ± 36%, and 57 ± 18%, respectively. The respective therapies led to plasma Alanine Amino Transferase (ALT) levels corresponding to 85 ± 18, 107 ± 26, 154 ± 35 IU/L in comparison to controls 66 ± 14 IU/L. At corresponding doses, the lipid peroxidation levels as measured by malondialdehyde (MDA) formation in liver homogenates were 255 ± 8 μM, 304 ± 21 μM, and 342 ± 14 μM in comparison to 208 ± 6 μM in controls. The level of MDA in kidney homogenates was 263 ± 21 μM, 282 ± 18 μM, and 350 ± 28 μM, respectively, in comparison to 212 ± 8 μM in controls. Administration of CAPE (10, 20, 30 mg/Kg/day) diminished free thiol contents in liver for 21 ± 15%, 40 ± 17%, and 44 ± 19% and in kidney homogenates for 25 ± 15%, 37 ± 18%, and 40 ± 22%, respectively, as compared to controls. Our study suggests that CAPE at 10 mg/Kg/day has significant anti-melanoma efficacy with minimal toxicity.

Liv.52 protects HepG2 cells from oxidative damage induced by tert-butyl hydroperoxide

Oxidative stress induced by toxicants is known to cause various complications in the liver. Herbal drug such as Liv.52 is found to have hepatoprotective effect. However, the biochemical mechanism involved in the Liv.52 mediated protection against toxicity is not well elucidated using suitable in vitro models. Hence, in the present study, the hepatoprotective effect of Liv.52 against oxidative damage induced by tert-butyl hydroperoxide (t-BHP) in HepG2 cells was evaluated in order to relate in vitro antioxidant activity with cytoprotective effects. Cytotoxicity was measured by MTT assay. Antioxidant effect of Liv.52 was determined by 2,2-diphenyl-1-picrylhydrazyl (DPPH) assay, ferric-reducing antioxidant power (FRAP) assay, and lipid peroxidation and measurement of non-enzymic and antioxidant enzymes in HepG2 cells exposed to t-BHP over a period of 24 h. The results obtained indicate that t-BHP induced cell damage in HepG2 cells as shown by significant increase in lipid peroxidation as well as decreased levels of reduced glutathione (GSH). Liv.52 significantly decreased toxicity induced by t-BHP in HepG2 cells. Liv.52 was also significantly decreased lipid peroxidation and prevented GSH depletion in HepG2 cells induced by t-BHP. Therefore, Liv.52 appeared to be important for cell survival when exposed to t-BHP. The protective effect of Liv.52 against cell death evoked by t-BHP was probably achieved by preventing intracellular GSH depletion and lipid peroxidation. The results showed protective effect of Liv.52 against oxidative damage induced in HepG2 cells. Hence, taken together, these findings derived from the present study suggest the beneficial effect of Liv.52 in regulating oxidative stress induced in liver by toxicants.

Intracellular oxidative stress and cadmium ions release induce cytotoxicity of unmodified cadmium sulfide quantum dots

Objective To fully understand the cytotoxicity of after-degradation QDs, we synthesized CdS QDs and investigated its toxicity mechanism. Methods Biomimetic method was proposed to synthesize cadmium sulfide (CdS) QDs. Thereafter MTT (3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyl tetrazolium bromide) assay was conducted to evaluate their cytotoxicity. To investigate the toxicity mechanism, we subsequently conducted intracellular reactive oxygen species (ROS) measurement with DCFH-DA, glutathione (GSH) measurement with DTNB, and cellular cadmium assay using atomic absorption spectrometer. Microsized CdS were simultaneously tested as a comparison. Results MTT assay results indicated that CdS QDs are more toxic than microsized CdS especially at concentrations below 40 μg/ml. While microsized CdS did not trigger ROS elevation, CdS QDs increase ROS by 20–30% over control levels. However, they both deplete cellular GSH significantly at the medium concentration of 20 μg/ml. In the presence of NAC, cells are partially protected from CdS QDs, but not from microsized particles. Additionally, nearly 20% of cadmium was released from CdS nanoparticles within 24 h, which also accounts for QDs’ toxicity. Conclusion Intracellular ROS production, GSH depletion, and cadmium ions (Cd 2+) release are possible mechanisms for CdS QDs’ cytotoxicity. We also suggested that with QD concentration increasing, the principal toxicity mechanism changes from intracellular oxidative stress to Cd 2+ release.

Sulfasalazine inhibits the growth of primary brain tumors independent of nuclear factor-kappaB.

Nuclear factor-kappaB (NF-kappaB) is a pleiotropic transcription factor that generally enhances cellular resistance to apoptotic cell death. It has been shown to be constitutively active in some cancers and is being pursued as potential anticancer target. Sulfasalazine which is used clinically to treat Crohn's disease has emerged as a potential inhibitor of NF-kappaB and has shown promising results in two pre-clinical studies to target primary brain tumors, gliomas. Once digested, sulfasalazine is cleaved into sulfapyridine and 5-aminosalicylic acid (5-ASA; mesalamine) by colonic bacteria, and the latter, too, is reported to suppress NF-kappaB activity. We now show that glioma cells obtained from patient biopsies or glioma cell lines do not show significant constitutive NF-kappaB activation, unless exposed to inflammatory cytokines. This does not change when gliomas are implanted into the cerebrum of severe combined immun-deficient mice. Nevertheless, sulfasalazine but not its cleaved form 5-ASA caused a dose-dependent inhibition of glioma growth. This effect was entirely attributable to the inhibition of cystine uptake via the system x(c)(-) cystine-glutamate transporter. It could be mimicked by S-4-carboxy-phenylglycine (S-4-CPG) a more specific system x(c)(-) inhibitor, and lentiviral expression of a constitutively active form of IkappaB kinase b was unable to overcome the growth retarding effects of sulfasalazine or S-4-CPG. Both drugs inhibited cystine uptake causing a chronic depletion of intracellular GSH and consequently compromised cellular redox defense which stymied tumor growth. This data suggests that system x(c)(-) is a promising therapeutic target in gliomas and possibly other cancers and that it can be pharmacologically inhibited by Sulfasalazine, an FDA-approved drug.

Efficacy of acetaminophen in skin B16-F0 melanoma tumor-bearing C57BL/6 mice

Previously, we reported that acetaminophen (APAP) showed selective toxicity towards melanoma cell lines. In the current study, we investigated further the role of tyrosinase in APAP toxicity in SK-MEL-28 melanoma cells in the presence of a short hairpin RNA (shRNA) plasmid, silencing tyrosinase gene. Results from tyrosinase shRNA experiments showed that APAP led to negligible toxicity in shRNA plasmid-treated cells. It was also found that APAP selectively caused escalation in reactive oxygen species (ROS) formation and intracellular GSH (ICG) depletion in melanocytic human SK-MEL-28 and murine B16-F0 melanoma cells that express functional tyrosinase whereas it lacked significant effects on ROS formation and ICG in amelanotic C32 melanoma cells that do not express functional tyrosinase. These findings suggest that tyrosinase plays a major role in APAP selective induced toxicity in melanocytic melanoma cell lines. Furthermore, the in vivo efficacy and toxicity of APAP in the skin melanoma tumor model in mice was investigated. Mice receiving APAP at 60, 80, 100 and 300 mg/kg/day, day 7 through 13 post melanoma cell inoculation demonstrated tumor size growth inhibition by 7+/-14, 30+/-17, 45+/-11 and 57+/-3%, respectively. Mice receiving APAP day 1 through 13 post melanoma cell inoculation showed tumor size growth inhibition by 11+/-7, 33+/-9, 36+/-20 and 44+/-28%, respectively.

Biochemical Mechanism of Acetaminophen (APAP) Induced Toxicity in Melanoma Cell Lines

In this work, we investigated the biochemical mechanism of acetaminophen (APAP) induced toxicity in SK-MEL-28 melanoma cells using tyrosinase enzyme as a molecular cancer therapeutic target. Our results showed that APAP was metabolized 87% by tyrosinase at 2 h incubation. AA and NADH, quinone reducing agents, were significantly depleted during APAP oxidation by tyrosinase. The IC(50) (48 h) of APAP towards SK-MEL-28, MeWo, SK-MEL-5, B16-F0, and B16-F10 melanoma cells was 100 microM whereas it showed no significant toxicity towards BJ, Saos-2, SW-620, and PC-3 nonmelanoma cells, demonstrating selective toxicity towards melanoma cells. Dicoumarol, a diaphorase inhibitor, and 1-bromoheptane, a GSH depleting agent, enhanced APAP toxicity towards SK-MEL-28 cells. AA and GSH were effective in preventing APAP induced melanoma cell toxicity. Trifluoperazine and cyclosporin A, inhibitors of permeability transition pore in mitochondria, significantly prevented APAP melanoma cell toxicity. APAP caused time and dose-dependent decline in intracellular GSH content in SK-MEL-28, which preceded cell toxicity. APAP led to ROS formation in SK-MEL-28 cells which was exacerbated by dicoumarol and 1-bromoheptane whereas cyslosporin A and trifluoperazine prevented it. Our investigation suggests that APAP is a tyrosinase substrate, and that intracellular GSH depletion, ROS formation and induced mitochondrial toxicity contributed towards APAP's selective toxicity in SK-MEL-28 cells.

Oxidation of melatonin by AAPH-derived peroxyl radicals: Evidence of a pro-oxidant effect of melatonin

Background Melatonin is well-established as a powerful reducing agent of oxidant generated in the cell medium. We aimed to investigate how readily melatonin is oxidized by peroxyl radicals ROO⋅ generated by the thermolysis of 2,2′-azobis(2-amidinopropane) hydrochloride (AAPH) and the role of glutathione (GSH) during the reaction course. Methods Chromatographic, mass spectroscopy, and UV–visible spectrometric techniques were used to study the oxidation of melatonin by ROO⋅ or horseradish peroxidase (HRP)/H 2O 2. Our focus was the characterization of products and the study of features of the reaction. Results We found that N 1-acetyl- N 2-formyl-5-methoxykynuramine (AFMK) and a monohydroxylated derivative of melatonin were the main products of the reaction between melatonin and ROO⋅. Higher pH or saturation of the medium with molecular oxygen increased the yield of AFMK but did not affect the reaction rate. Melatonin increased the depletion of intracellular GSH mediated by AAPH. Using the HRP/H 2O 2 as the oxidant system, the addition of melatonin promoted the oxidation of GSH to GSSG. Conclusions These results show, for the first time, that melatonin radical is able to oxidize GSH. General significance We propose that this new property of melatonin could explain or be related to the recently reported pro-oxidant activities of melatonin.

Pyrogallol inhibits the growth of human pulmonary adenocarcinoma A549 cells by arresting cell cycle and triggering apoptosis

Pyrogallol (PG) is a polyphenol compound and has been known to be an O(2)(*-) generator. We evaluated the effects of PG on the growth of human pulmonary A549 cells in relation to the cell cycle and apoptosis. Treatment with 50 or 100 microM PG significantly inhibited the cell growth of A549 for 72 h. DNA flow cytometric analysis indicated that PG slightly induced a G1 phase arrest of the cell cycle at 24 or 48 h, but did not induce the specific cell cycle arrest at 72 h. Intracellular GSH depletion was observed in PG-treated cells. PG induced apoptosis in A549 cells, as evidenced by sub-G1 cells, annexin V staining cells, and the loss of mitochondrial membrane potential (DeltaPsi(m)). The intracellular ROS (reactive oxygen species) level including O(2)(*-) increased in PG-treated A549 cells at 24 and 48 h, and persisted at 72 h. The changes in GSH as well as ROS levels by PG affected the cell viability in A549 cells. In conclusion, PG inhibited the growth of human pulmonary A549 cells by inducing cell cycle arrest as well as triggering apoptosis.

Multidrug-resistance-associated protein plays a protective role in menadione-induced oxidative stress in endothelial cells

Aims Menadione, a redox-cycling quinone known to cause oxidative stress, binds to reduced glutathione (GSH) to form glutathione S-conjugate. Glutathione S-conjugates efflux is often mediated by multidrug-resistance-associated protein (MRP). We investigated the effect of a transporter inhibitor, MK571 (3-[[3-[2-(7-chloroquinolin-2-yl)vinyl]phenyl]-(2-dimethylcarbamoylethylsulfanyl)methylsulfanyl] propionic acid), on menadione-induced oxidative stress in bovine aortic endothelial cells (BAECs). Main methods BAECs were treated with menadione and MK571, and cell viability was measured. Modulation of intracellular GSH levels was performed with buthionine sulfoximine and GSH ethyl ester treatments. Intracellular superoxide was estimated by dihydroethidium oxidation using fluorescence microscopy or flow cytometry. Expression of MRP was determined by flow cytometry using phycoerythrin-conjugated anti-MRP monoclonal antibody. Key findings Intracellular GSH depletion by buthionine sulfoximine promoted the loss of viability of BAECs exposed to menadione. Exogenous GSH, which does not permeate the cell membrane, or GSH ethyl ester protected BAECs against the loss of viability induced by menadione. The results suggest that GSH binds to menadione outside the cells as well as inside. Pretreatment of BAECs with MK571 dramatically increased intracellular levels of superoxide generated from menadione, indicating that menadione may accumulate in the intracellular milieu. Finally, we found that MK571 aggravated menadione-induced toxicity in BAECs and that MRP levels were increased in menadione-treated cells. Significance We conclude that MRP plays a vital role in protecting BAECs against menadione-induced oxidative stress, presumably due to its ability to transport glutathione S-conjugate.

Biochemical mechanism of acetylsalicylic acid (Aspirin) selective toxicity toward melanoma cell lines

In the current work, we investigated the biochemical toxicity of acetylsalicylic acid (ASA; Aspirin) in human melanoma cell lines using tyrosinase enzyme as a molecular cancer therapeutic target. At 2 h, ASA was oxidized 88% by tyrosinase. Ascorbic acid and NADH, quinone reducing agents, were significantly depleted during the enzymatic oxidation of ASA by tyrosinase to quinone. The 50% inhibitory concentration (48 h) of ASA and salicylic acid toward SK-MEL-28 cells were 100 micromol/l and 5.2 mmol/l, respectively. ASA at 100 micromol/l was selectively toxic toward human melanocytic SK-MEL-28, MeWo, and SK-MEL-5 and murine melanocytic B16-F0 and B16-F10 melanoma cell lines. However, ASA was not significantly toxic to human amelanotic C32 melanoma cell line, which does not express tyrosinase enzyme, and human nonmelanoma BJ, SW-620, Saos, and PC-3 cells. Dicoumarol, a diaphorase inhibitor, and 1-bromoheptane, a GSH depleting agent, increased ASA toxicity toward SK-MEL-28 cells indicating quinone formation and intracellular GSH depletion played important mechanistic roles in ASA-induced melanoma toxicity. Ascorbic acid, a quinone reducing agent, and GSH, an antioxidant and quinone trap substrate, prevented ASA cell toxicity. Trifluoperazine, inhibitor of permeability transition pore in mitochondria, prevented ASA toxicity. ASA led to significant intracellular GSH depletion in melanocytic SK-MEL-28 melanoma cells but not in amelanotic C32 melanoma cells. ASA also led to significant reactive oxygen species (ROS) formation in melanocytic SK-MEL-28 melanoma cells but not in amelanotic C32 melanoma cells. ROS formation was exacerbated by dicoumarol and 1-bromoheptane in SK-MEL-28. Our investigation suggests that quinone species, intracellular GSH depletion, ROS formation, and mitochondrial toxicity significantly contributed toward ASA selective toxicity in melanocytic SK-MEL-28 melanoma cells.

Glycyrrhizic acid modulates t-BHP induced apoptosis in primary rat hepatocytes

Glycyrrhizic acid (GA) is the main bioactive ingredient of licorice ( Glycyrrhiza glabra). The object of this study was to evaluate the protective effects of GA on tert-butyl hydroperoxide (t-BHP) induced oxidative injury leading to apoptosis in cultured primary rat hepatocytes. Throughout the study silymarin was used as positive control. Molecular mechanisms involved in apoptotic pathways induced in hepatocytes by t-BHP at 250 μM were explored in detail. DNA fragmentation, activation of caspases and cytochrome c release were demonstrated. In addition, changes in the mitochondrial membrane potential and ROS generation were detected confirming involvement of mitochondrial pathway. Pre-treatment with GA (4 μg) protected the hepatocytes against t-BHP induced oxidative injury and the results were comparable to the pre-treatment with positive control, i.e. silymarin. The protective potential against cell death was achieved mainly by preventing intracellular GSH depletion, decrease in ROS formation as well as inhibition of mitochondrial membrane depolarization. GA was found to modulate critical end points of oxidative stress induced apoptosis and could be beneficial against liver diseases where oxidative stress is known to play a crucial role.

Role of Xanthine Oxidase Activation and Reduced Glutathione Depletion in Rhinovirus Induction of Inflammation in Respiratory Epithelial Cells

Rhinoviruses are the major cause of the common cold and acute exacerbations of asthma and chronic obstructive pulmonary disease. We previously reported rapid rhinovirus induction of intracellular superoxide anion, resulting in NF-kappaB activation and pro-inflammatory molecule production. The mechanisms of rhinovirus superoxide induction are poorly understood. Here we found that the proteolytic activation of the xanthine dehydrogenase/xanthine oxidase (XD/XO) system was required because pretreatment with serine protease inhibitors abolished rhinovirus-induced superoxide generation in primary bronchial and A549 respiratory epithelial cells. These findings were confirmed by Western blotting analysis and by silencing experiments. Rhinovirus infection induced intracellular depletion of reduced glutathione (GSH) that was abolished by pretreatment with either XO inhibitor oxypurinol or serine protease inhibitors. Increasing intracellular GSH with exogenous H2S or GSH prevented both rhinovirus-mediated intracellular GSH depletion and rhinovirus-induced superoxide production. We propose that rhinovirus infection proteolytically activates XO initiating a pro-inflammatory vicious circle driven by virus-induced depletion of intracellular reducing power. Inhibition of these pathways has therapeutic potential.

Manipulation of oxidative stress to induce cell death in Ewing’s sarcoma family of tumours

Ewing’s sarcoma family of tumours (ESFT) are childhood cancers whose aggressive behaviour and propensity to relapse prompts the need for new treatment approaches. In this study, the role of cellular antioxidants in determining the sensitivity of ESFT cell lines to the cytotoxicity of the antineoplasic agent fenretinide was investigated with a view to identifying targets for the development of new treatment strategies. ESFT cell lines differentially express cellular antioxidants, although cellular glutathione (GSH) was identified as the major determinant of sensitivity to fenretinide. The importance of GSH in ESFT physiology was demonstrated by the depletion of intracellular GSH using l-buthionine ( S, R) sulphoximine (BSO), which decreased cell viability. Furthermore, pre-treatment of ESFT cells with BSO sensitised them to fenretinide-induced death. Overall, these results demonstrate that ESFT cells are sensitive to changes in intracellular redox environment, and that targeting specific cellular antioxidants might be a viable strategy in treating ESFT.

Differential effects of ifosfamide on dendritic cell-mediated stimulation of T cell interleukin-2 production, natural killer cell cytotoxicity and interferon-γ production

Ifosfamide is a DNA-alkylating agent used frequently in chemotherapy of human malignancies. Ifosfamide and its major decomposition products deplete intracellular glutathione (GSH). Glutathione is the major intracellular thiol reductant that protects cells against oxidative injury. Ifosfamide depletion of intracellular GSH in human dendritic cells (DC), T cells and natural killer (NK) cells impairs their functional activity which can be restored by reconstituting GSH. Here we assessed the effect of ifosfamide on DC-mediated stimulation of NK cell proliferation via T cells and on direct DC stimulation of NK cell cytotoxicity and interferon (IFN)-gamma production. Indirect DC stimulation of NK cell proliferation via T cells and T cell-derived interleukin (IL)-2 were reduced by ifosfamide treatment of DC and reconstitution of GSH in DC restored both responses. When DC and NK cells were treated with ifosfamide, DC could overcome the negative effect of ifosfamide on NK cytotoxic function whereas NK cell IFN-gamma production was less efficiently restored. The ability of IL-2 activated NK cells to kill autologous immature DC or to induce DC maturation was reduced moderately by treatment of both cell types with ifosfamide. Overall, our results suggest that DC may stimulate anti-tumour effector cells in patients even if they had received treatment with chemotherapeutic agents such as ifosfamide.

Theaflavin‐3‐Gallate and Theaflavin‐3′‐Gallate, Polyphenols in Black Tea with Prooxidant Properties

This study compared the in vitro responses of human gingival fibroblasts and of carcinoma cells derived from the tongue to theaflavin-3-gallate (TF-2A) and theaflavin-3'-gallate (TF-2B), polyphenols in black tea. The antiproliferative and cytotoxic effects of the theaflavin monomers were more pronounced to the carcinoma, than to the normal, cells. In phosphate buffer at pH 7.4, the theaflavins generated hydrogen peroxide and the superoxide anion, suggesting that their mode of toxicity may be due, in part, to the induction of oxidative stress. In a cell-free assay, TF-2A and TF-2B reacted directly with reduced glutathione (GSH), in a time- and concentration-dependent manner. Intracellular storages of GSH were depleted on treatment of the cells with the theaflavin monomers. Depletion of intracellular GSH was more extensive with TF-2A than with TF-2B and was more pronounced in the carcinoma, than in the normal, cells. The toxicities of the theaflavins were potentiated when the cells were cotreated with the GSH depleter, d,l-buthionine-[S,R]-sulfoximine. In the presence of catalase, pyruvate and divalent cobalt, all scavengers of reactive oxygen species, the cytotoxicities of the theaflavins were lessened. TF-2A and TF-2B induced lipid peroxidation in the carcinoma cells, whereas in the fibroblasts, peroxidation was evident upon exposure to TF-2A, but not to TF-2B. These studies demonstrated that the black tea theaflavin monomers, TF-2A and TF-2B, act as prooxidants and induce oxidative stress, with carcinoma cells more sensitive than normal fibroblasts.

Salvicine triggers DNA double-strand breaks and apoptosis by GSH-depletion-driven H 2O 2 generation and topoisomerase II inhibition

Glutathione (GSH), as the major small-molecule antioxidant in cells, has been implicated in the regulation of cell proliferation and apoptosis. Salvicine (SAL), a novel diterpenoid quinone compound, exhibits potent antitumor activities both in vitro and in vivo by poisoning topoisomerase II (Topo II) and has entered Phase II clinical trials for cancer therapy. Herein, we provide further evidence that SAL-induced DNA double-strand breaks (DSBs) and apoptosis by GSH depletion drives H 2O 2 generation and Topo II inhibition. Our data reveal that treatment with SAL results in a pronounced increase in intracellular H 2O 2 and is accompanied by the occurrence of DNA DSBs and apoptosis in epithelial HeLa cells. Furthermore, SAL was also noted to trigger a dramatic depletion of intracellular GSH via its direct reaction with GSH. Importantly, the introduction of GSH and overexpression of catalase antagonized SAL-mediated DNA DSBs and apoptosis, and the GSH synthesis inhibitor dl-buthionine-[ S,R]-sulfoximine reduced SAL-mediated H 2O 2 generation, indicating that SAL-mediated H 2O 2 generation is derived from intracellular GSH depletion. Notably, SAL-mediated Topo II inhibition was also concentration-dependently reversed by GSH. Furthermore, we found that Topo II-defective HL-60/MX2 cells were almost completely resistant to SAL-induced DNA DSBs, suggesting that, in addition to its direct inhibitory effect on Topo II, SAL-mediated H 2O 2 generation may also trigger DNA DSBs via poisoning of Topo II. All these findings together suggest that GSH-depletion-driven H 2O 2 generation and Topo II inhibition are both critical for SAL-induced DNA DSBs and apoptosis.

Muscle Disuse: Adaptation of Antioxidant Systems Is Age Dependent

This study investigated the age effect on antioxidant adaptation to muscle disuse. Adult and old rats were randomized into 4 groups: weight bearing (control), 3 days of hind-limb unloading (HU), 7 days of HU, and 14 days of HU. Activities of Cu-Zn superoxide dismutase (SOD), catalase, and glutathione (GSH), as well as GSH peroxidase levels were measured in the soleus. Neither disuse nor aging changed the activity of Cu-Zn SOD. The old rats had greater GSH peroxidase activity, whereas the activity of catalase had a compensatory increase with disuse, independent of age. Reduced GSH level and total glutathione (tGSH) level had age-related change with disuse. In old rats, the GSH and tGSH levels were lower with disuse, whereas the levels remained stable with disuse in adult rats. The depletion of intracellular GSH and tGSH levels of muscles from aged animals with disuse may make aged muscles more susceptible to oxidative damage.

Metabolic Bioactivation and Toxicity of Ethyl 4-Hydroxybenzoate in Human SK-MEL-28 Melanoma Cells

The metabolism and toxicity of ethyl 4-hydroxybenzoate (4-HEB) were investigated in vitro using tyrosinase enzyme, a melanoma molecular target, and CYP2E1 induced rat liver microsomes, and in human SK-MEL-28 melanoma cells. The results were compared to 4-hydroxyanisole (4-HA). At 90 min, 4-HEB was metabolized 48% by tyrosinase and 26% by liver microsomes while the extent of 4-HA metabolism was 196% and 88%, respectively. The IC50 (day 2) of 4-HEB and 4-HA towards SK-MEL-28 cells were 75 and 50 µM, respectively. Dicoumarol, a diaphorase inhibitor, and 1-bromoheptane, a GSH depleting agent, increased 4-HEB toxicity towards SK-MEL-28 cells indicating o-quinone formation played an important role in 4-HEB induced cell toxicity. Addition of ascorbic acid and GSH to the media was effective in preventing 4-HEB cell toxicity. Cyclosporin A and trifluoperazine, inhibitors of permeability transition pore in mitochondria, were significantly potent in inhibiting 4-HEB cell toxicity. 4-HEB caused time-dependent decline in intracellular GSH concentration which preceded cell death. 4-HEB also led to reactive oxygen species (ROS) formation in melanoma cells which exacerbated by dicoumarol and 1-bromoheptane whereas cyclosporin A and trifluoperazine prevented it. Our findings suggest that the mechanisms of 4-HEB toxicity in SK-MEL-28 were o-quinone formation, intracellular GSH depletion, ROS formation and mitochondrial toxicity.