Thiol-mediated inhibition of FAS and CD2 apoptotic signaling in activated human peripheral T cells

Fas and CD2 receptors can transduce apoptotic signals through two independent biochemical pathways. In this study, we first evaluated the role of intracellular GSH in these signaling pathways by inducing variations in the GSH pool of activated peripheral T lymphocytes. Increasing the concentration of intracellular GSH by means of N-acetyl- L-cysteine (NAC) and GSH ethyl ester (OEt) resulted in total protection against cell death, while inhibiting GSH synthesis with buthionine sulfoximine (BSO) greatly enhanced cell sensitivity to Fas and CD2 apoptotic signaling. The protection exerted by NAC and GSH OEt was essentially based on their capacity to establish an intracellular reducing environment as it still occurred in BSO-treated cells. Thiol- containing compounds (cysteine, captopril, D-penicillamine and 2- mercaptoethanol) inhibited apoptosis while a series of non-thiol antioxidants (including catalase and vitamin E) failed to do so, suggesting that protection was secondary to thiols/disulfides exchange reactions at the level of cysteine residues in proteins and not to detoxification of reactive oxygen intermediates. This conclusion was further supported by the finding that no enhanced generation of O.-2 and H2O2 could be detected in cells experiencing early stages of apoptosis such as a decreased concentration of intracellular GSH and cell shrinkage. Also, protection occurred in the presence of protein synthesis inhibitors, indicating that it was due to post-translational sulfhydryl redox regulation of critical molecules involved in the apoptotic cascade. These data suggest that GSH, the most abundant intracellular thiol antioxidant, may be important in counteracting Fas- and CD2-mediated apoptosis of T lymphocytes.      

Pyrogallol as a glutathione depletor induces apoptosis in HeLa cells

Pyrogallol, a polyphenol, is known to be a superoxide anion (O2(.-)) generator. We investigated the involvement of glutathione (GSH) and reactive oxygen species (ROS) in pyrogallol-induced HeLa cell death. We measured the changes of ROS levels, GSH levels, sub-G1 cells, annexin V/PI staining cells and mitochondria membrane potential (DeltaPsi m) in HeLa cells treated with pyrogallol and/or ROS scavenger. The intracellular ROS levels were decreased or increased depending on the concentration of pyrogallol. The level of O2(.-) was significantly increased and superoxide dismutase (SOD) activity was down-regulated by pyrogallol. Pyrogallol reduced intracellular GSH content in HeLa cells. The ROS scavengers, Tempol, Tiron, Trimetazidine and N-acetylcysteine (NAC), did not down-regulate the production of O2(.-). However, treatment with NAC showed the recovery of GSH depletion and significantly rescued cells from pyrogallol-induced apoptosis. In addition, the recovery of GSH depletion by SOD and catalase was accompanied by the decrease of apoptosis levels. Furthermore, NAC and SOD significantly inhibited CMF-negative (GSH-depleted) and PI-positive cells induced by pyrogallol. Taken together, pyrogallol potently increased intracellular O2(.-) levels and decreased GSH content in HeLa cells, and NAC, SOD and catalase significantly rescued HeLa cells from pyrogallol-induced apoptosis accompanied by the recovery of GSH depletion.     

Fas-mediated apoptosis is modulated by intracellular glutathione in human T cells

Fas antigen is a member of the tumor necrosis factor receptor family that transduces a lethal signal to the Fas-sensitive cells. We previously established the Fas-resistant variant cell lines LAC2D1R and JKT2D1R from the parental Fas-sensitive cell lines, SUPT13 and Jurkat, respectively. Recently, we isolated the Fas-resistant variant CEM2D1R from CCRF-CEM. All of the variants were Fas⁺ but resistant to Fas-mediated apoptosis. Further biochemical analysis revealed that the intracellular gluthathione (GSH) content of the Fas-resistant variants was higher than in the original cells. When the Fas-resistant variants were incubated with buthionine sulfoximine (BSO) or in GSH-free/cysteine-free medium to deplete GSH, Fas resistance was reversed. Incubation of the cells with cycloheximide also decreased intracellular GSH and reversed the Fas resistance. Furthermore, incubation of activated peripheral blood lymphocytes with BSO enhanced Fas-mediated apoptosis. When the Fas-sensitive cells were incubated with N-acetylcysteine (NAC), intracellular GSH was increased and Fas-mediated apoptosis was blocked. In contrast, Fas-resistant variants, as well as Fas-sensitive cells pre-treated with NAC remained susceptible to allogeneic lymphokine-activated killer cells, most likely due to perforin-dependent killing. The results suggest that Fas-mediated apoptosis, but not perforin-dependent killing, is modulated by intracellular GSH in human T lymphocytes.     

TRPM2 channel protective properties of N-acetylcysteine on cytosolic glutathione depletion dependent oxidative stress and Ca2+ influx in rat dorsal root ganglion

N-acetylcysteine (NAC) is a thiol-containing (sulphydryl donor) antioxidant, which contributes to regeneration of glutathione (GSH) and also acts through a direct reaction with free radicals. Thiol depletion has been implicated in the neurobiology of sensory neurons and pain. We reported recently an activator role of intracellular GSH depletion on calcium influx through transient receptor potential melastatin-like 2 (TRPM2) channels in rat dorsal root ganglion (DRG). NAC may have a protective role on calcium influx through regulation of TRPM2 channels in the neurons. Therefore, we tested the effects of NAC on TRPM2 channel currents in cytosolic GSH depleted DRG in rats. DRG neurons were freshly isolated from rats and the neurons were incubated for 24 h with buthionine sulfoximine (BSO). In whole-cell patch clamp experiments, TRPM2 currents in the DRG incubated with BSO were gated by H(2)O(2). TRPM2 channels current densities, cytosolic free Ca(2+) content, and lipid peroxidation values in the neurons were higher in H(2)O(2) and BSO + H(2)O(2) group than in controls; however GSH and GSH peroxidase (GSH-Px) values were decreased. BSO + H(2)O(2)-induced TRPM2 channel gating was totally inhibited by extracellular NAC and partially inhibited by 2-aminoethyl diphenylborinate. GSH-Px activity, lipid peroxidation and GSH levels in the DRG neurons were also modulated by NAC. In conclusion, we observed a modulator role of NAC on Ca(2+) influx through a TRPM2 channel in intracellular GSH depleted DRG neurons. NAC incubation before BSO exposure appears to be more protective than NAC incubation after BSO exposure. Since cytosolic thiol group depletion is a common feature of neuropathic pain, our findings are relevant to the etiology and treatment of pain neuropathology in DRG neurons.     

Intracellular glutathione levels are involved in carbonyl cyanide p-(trifluoromethoxy) phenylhydrazone-induced apoptosis in As4.1 juxtaglomerular cells

Carbonyl cyanide p-(trifluoromethoxy) phenylhydrazone (FCCP) is an uncoupler of mitochondrial oxidative phosphorylation in eukaryotic cells. In the present study, we investigated the involvement of reactive oxygen species (ROS) and glutathione (GSH) in FCCP-induced As4.1 juxtaglomerular cell death. Intracellular ROS levels were decreased by FCCP at the early time points (10-150 min) and increased at 48 h. FCCP inhibited the activity of Mn-superoxide dismutase (Mn-SOD) via down-regulating its protein expression. Ebselen (an antioxidant) significantly attenuated ROS levels in FCCP-treated cells, but did not prevent FCCP-induced cell death. Moreover, intracellular GSH content was rapidly diminished within 10 min of FCCP treatment, which was accompanied by a reduction of the mitochondrial membrane potential [MMP (?ψm)]. L-buthionine sulfoximine (BSO, a GSH synthesis inhibitor) significantly augmented As4.1 cell death by FCCP. However, N-acetylcysteine (NAC, a GSH precursor and antioxidant) attenuated GSH depletion, MMP (?ψm) loss and cell death in FCCP-treated As4.1 cells. In addition, NAC increased Mn-SOD activity and decreased ROS levels in FCCP-treated As4.1 cells. In conclusion, these results suggest that compared to ROS levels, intracellular GSH levels are more closely linked to FCCP-induced apoptosis in As4.1 juxtaglomerular cells.     

Regulation of LPS induced IL-12 production by IFN-gamma and IL-4 through intracellular glutathione status in human alveolar macrophages.

Interleukin-12 (IL-12) is secreted from monocytes and macrophages; it exerts pleiotropic effects on T cells and natural killer (NK) cells, and stimulates interferon-gamma (IFN-gamma) secretion. Glutathione tripeptide regulates the intracellular redox status and other aspects of cell physiology. We examined whether IFN-gamma and IL-4 affect the balance between intracellular reduced glutathione (GSH) and oxidized (GSSG) glutathione, as this may affect IL-12 production in human alveolar macrophages (AM). We used both AM from healthy non-smokers obtained by bronchoalveolar lavage and the monocytic THP-1 cell line in this study. Incubation of AM for 2 h with the GSH precursor N-acetylcysteine (NAC) increased the intracellular GSH/GSSG ratio, and enhanced lipopolysaccharide (LPS)-induced IL-12 secretion by AM. In THP-1 cells, NAC increased the GSH/GSSG ratio and the expression of LPS-induced IL-12 mRNA, whereas L-buthionine-[S,R]-sulphoximine (BSO) decreased these. NAC and BSO offset their own effects on the intracellular GSH/GSSG ratio and the expression of LPS-induced IL-12 mRNA. Furthermore, exposure of AM to the helper T cell type 1 (Th1) cytokine IFN-gamma or the helper T cell type 2 (Th2) cytokine IL-4 for 72 h increased and decreased the GSH/GSSG ratio, respectively. Lipopolysaccharide (LPS)-induced secretion of IL-12 in AM was enhanced by IFN-gamma but inhibited by IL-4. These results suggest that IFN-gamma and IL-4 oppositely affect the GSH/GSSG balance, which may regulate IL-12 secretion from AM in response to LPS.     

Protective effects of the glutathione redox cycle and vitamin E on cultured fibroblasts infected by Mycoplasma pneumoniae.

The role of the glutathione (GSH) redox cycle and vitamin E as antioxidant defense systems was studied in normal human cultured skin fibroblasts infected by virulent Mycoplasma pneumoniae. In cells infected for 20 h, catalase activity was inhibited by 75% and the intracellular GSH decreased to 32% of its normal values. GSH peroxidase and oxidized glutathione (reductase activities in the infected cells were unaffected.) GSSG glutathione in the medium of the infected cells rose in accordance with the intracellular GSH decrease. The observed elevation in GSSG/GSH ratio was attributed to the increase in intracellular H2O2 content in M. pneumoniae-infected cells due to the marked inhibition in their catalase activity. The protective effect of the GSH redox cycle in infected cells was studied by depletion of cellular GSH, prior to their infection with M. pneumoniae, using buthionine sulfoximine (BSO), a selective inhibitor of gamma-glutamyl cysteine synthetase. After 16 h of incubation with BSO, the GSH levels were reduced to 38% of their normal value and recovered to 55% during 24 h after removal of the inhibitor. BSO had no effect on GSH peroxidase and catalase activities in either infected or noninfected cells. The level of malonyldialdehyde (an indicator of membrane lipid peroxidation) in BSO-treated cells infected by M. pneumoniae was 1.8 times higher than in infected controls. Cells enriched with 0.25 and 2.25 micrograms of vitamin E per mg of protein prior to their infection by M. pneumoniae revealed the following: a lesser degree of catalase inhibition, 46 and 30%, respectively, versus 64% in infected control cells that were not supplemented with vitamin E; lower levels of malonyldialdehyde, 55 and 20% increments, respectively, versus a 140% increment in infected controls; higher residual activity of lactate dehydrogenase, 76 and 96%, respectively, versus 58% in infected controls. Our data indicate that the oxidative damage induced in M. pneumoniae-infected cells due to the increase in intracellular levels of H2O2 and O2- is limited by the host cell GSH redox cycle and by supplementation with vitamin E.     

Effect of N-acetyl-L-cysteine on ROS production and cell death caused by HEMA in human primary gingival fibroblasts

Previous investigations have shown that 2-hydroxyethyl methacrylate (HEMA) causes reactive oxygen species (ROS) production, which in turn affects cell survival and cell death. The purpose of this study was to evaluate the effects of the antioxidant N-acetyl-L-cysteine (NAC) on HEMA-induced toxicity in human primary gingival fibroblasts (HGF). HGF were treated with various concentrations of HEMA (0-12 mm) in the absence and presence of NAC (1, 5, and 10 mm). The 3-(4,5 dimethyiazol-2-1)-2-5-diphenyl tetrazolium bromide (MTT) assay was used to evaluate the mitochondrial dehydrogenase activity after HEMA exposure. Viability and cell death were determined by flow cytometry using Annexin V and PI staining. ROS production was detected by the increasing fluorescence of the oxidation-sensitive dye 2',7'-dichlorofluorescein diacetate (DCFH-DA) after HEMA treatment. After a 24h incubation period, HEMA concentrations higher then 10mm caused a decrease of cell viability, mitochondrial activity, and an increase of cell death. HEMA concentrations of 4-12 mm markedly increased ROS levels in a dose-dependent manner. High NAC concentrations (5 and 10 mm) significantly reduced cell death, and restored the mitochondrial activity after a 24 h co-treatment, but 1 mm NAC increased HEMA toxicity (p<0.05). All NAC concentrations significantly reduced ROS levels induced by HEMA after a 2 h exposure (p<0.05), but no such reduction was observed after a 4 h treatment. Furthermore, treatment with 10 mm HEMA and 1 mm NAC for 6h caused an increase in ROS levels compared to 10 mm HEMA alone (p<0.05). In conclusion, our results suggest that high NAC concentrations protect HGF against HEMA cytotoxicity by reducing the induced ROS levels.     

The effect of N-acetylcysteine on ifosfamide-induced nephrotoxicity: in vitro studies in renal tubular cells

Ifosfamide (IF) nephrotoxicity is a serious adverse effect in children undergoing chemotherapy. Previous studies have shown that, in addition to the renal production of chloroacetaldehyde, a toxic metabolite of IF, lower levels of glutathione (GSH) may predispose the kidney to damage. The antioxidant N-acetylcysteine (NAC) is used extensively as an antidote for acetaminophen poisoning in children by replenishing GSH levels. As it has been safely and effectively used clinically, the objective of this study was to test whether the reversal of ifosfamide-induced nephrotoxicity can be achieved by administering NAC. Supplementation with NAC may reduce or prevent the degree of cellular cytotoxicity induced by IF. Porcine renal proximal tubular (LLCPK-1) cells were treated with NAC (0.4 mM or 2.5 mM) concurrently with 1 mM IF and 50 microM L-buthionine sulfoximine (BSO). Cellular viability was assessed by alamarBlue assay at 96 h. Intracellular GSH and oxidized GSH (GSSG) levels were determined using a GSH/GSSG colorimetric detection kit. A significant 60% decrease in cellular viability occurred when cells were treated daily with BSO and IF for 96 h. This decrease was significantly reduced when cells were concurrently treated with NAC in a concentration-dependent manner. Intracellular and total GSH levels in cells receiving concurrent treatment of NAC were significantly higher than those without NAC treatment. NAC protects renal tubular cells from IF-induced cytotoxicity. It is likely that NAC is protecting the cells by partially acting as a precursor for GSH synthesis. This mode of therapy may allow for protecting children from life-threatening nephrotoxicity induced by IF.     

Protective effect of NAC on formaldehyde-containing-ZOE-based root-canal-sealers-induced cyclooxygenase-2 expression and cytotoxicity in human osteoblastic cells

Cyclooxygenase-2 (COX-2) is an inducible enzyme believed to be responsible for prostaglandin synthesis at site of inflammation. Recently, the activation of COX-2 expression may be one of the important pathogenesis of root-canal-sealers-induced periapical inflammation. However, little is known about whether chemical interaction can modulate the COX-2 expression and cytotoxicity induced by formaldehyde-containing-ZOE-based root canal sealers. The aim of this study was to investigate the effects of antioxidants such as catalase, superoxide dismutase (SOD), and N-acetyl-L-cysteine (NAC) on N2- and endomethasone-induced COX-2 mRNA gene and cytotoxicity in human osteoblastic cell line U2OS cells. Our data demonstrated that both formaldehyde-containing-ZOE-based root canal sealers were found to induce COX-2 mRNA gene expression in U2OS cells. The addition of glutathione (GSH) precursor NAC led to decrease the induction of COX-2 mRNA gene expression and cytotoxicity by both N2 and Endomethasone (p < 0.05). However, catalase and SOD lacked the ability to prevent cytotoxicity and COX-2 mRNA gene expression induced by N2 and Endomethasone (p > 0.05). The data presented here demonstrated that the activation of COX-2 mRNA gene expression may be one of the pathogenesis of formaldehyde-containing-ZOE-based root-canal-sealers-induced periapical inflammation. In addition, GSH depletion, but not the attack of oxygen free radicals, could be the mechanism for cytotoxicity and COX-2 mRNA gene expression induced by formaldehyde-containing-ZOE-based root canal sealers. NAC appears as a useful agent in protecting cell damage mediated by formaldehyde-containing-ZOE-based root canal sealers.     

Effects of N-acetylcysteine on TEGDMA- and HEMA-induced suppression of osteogenic differentiation of human osteosarcoma MG63 cells

Triethyleneglycol dimethacrylate (TEGDMA) and 2-hydroxyethyl methacrylate (HEMA) are major resinous components of dental restorative materials and dentin bonding adhesives. Resin monomers are known to cause cytotoxicity in mammalian cells via oxidative stress and inhibit differentiation of dental pulp cells and osteoblasts. This study was aimed to investigate whether oxidative stress was involved in the inhibition of TEGDMA- and HEMA-induced differentiation. TEGDMA and HEMA reduced alkaline phosphatase (ALP) activity and the mRNA expression of the osteopontin (OPN) gene in MG63 cells at noncytotoxic concentrations. On the other hand, N-acetylcysteine (NAC) did not affect ALP activity at concentrations below 10 mM. Reduced ALP activity and OPN mRNA expression by TEGDMA were partially recovered via cotreatment with NAC. However, NAC did not exhibit significant effects in HEMA-treated cells. Glutathione (GSH) levels were also down-regulated by both TEGDMA and HEMA. The addition of NAC induced the partial recovery of GSH in cells treated with 0.5 mM TEGDMA. On the other hand, the levels of GSH in HEMA-treated cells were not affected by NAC. These results suggest that oxidative stress is involved in the suppression of differentiation by TEGDMA. Translocation of Nrf2 from the cytoplasm to the nucleus has been known to play a role in the suppression of osteogenic differentiation by oxidative stress. However, Nrf2 did not move into the nucleus in resin monomer-treated MG63 cells, suggesting the contribution of other signaling pathways to the suppressive effects of resin monomers.     

Thiols decrease cytokine levels and down-regulate the expression of CD30 on human allergen-specific T helper (Th) 0 and Th2 cells

The thiol antioxidant N-acetyl- L-cysteine (NAC), known as a precursor of glutathione (GSH), is used in AIDS treatment trials, as a chemoprotectant in cancer chemotherapy and in treatment of chronic bronchitis. In vitro, GSH and NAC are known to enhance T cell proliferation, production of IL-2 and up-regulation of the IL-2 receptor. The 120-kD CD30 surface antigen belongs to the tumour necrosis factor (TNF) receptor superfamily. It is expressed by activated T helper (Th) cells and its expression is sustained in Th2 cells. We have analysed the effect of GSH and NAC on the cytokine profile and CD30 expression on human allergen-specific T cell clones (TCC). TCC were stimulated with anti-CD3 antibodies in the presence of different concentrations of GSH and NAC. Both thiols caused a dose dependent down-regulation of IL-4, IL-5 and IFN-gamma levels in Th0 and Th2 clones, with the most pronounced decrease of IL-4. Furthermore, they down-regulated the surface expression of CD30, and the levels of soluble CD30 (sCD30) in the culture supernatants were decreased. In contrast, the surface expression of CD28 or CD40 ligand (CD40L) was not significantly changed after treatment with 20 m M NAC. These results indicate that GSH and NAC favour a Th1 response by a preferential down-regulation of IL-4. In addition, the expression of CD30 was down regulated by GSH and NAC, suggesting that CD30 expression is dependent on IL-4, or modified by NAC. In the likely event that CD30 and its soluble counterpart prove to contribute to the pathogenesis in Th2 related diseases such as allergy, NAC may be considered as a future therapeutic agent in the treatment of these diseases.     

Changes in sensitivity of a human myeloid cell line (U937) to metal toxicity after glutathione depletion.

Glutathione (GSH) concentrations have been determined in the human myeloid cell line U937. The effects of modulating GSH concentration on sensitivity to metal toxicity has also been examined. Intracellular concentrations of GSH increased as the cells entered into the cell cycle, reaching a maximum level after 24 hours of cell culture, after which levels declined. Cell concentration was also observed to influence intracellular GSH concentrations. A reciprocal relationship was observed with higher maximum intracellular GSH concentrations being measured in cultures initiated with smaller cell number. The relative toxicity's determined for five metal chlorides were mercury > cadmium > cobalt > zinc > gold. Treatment of cells with N-acetylcysteine (NAC) increased intracellular GSH but had little effect on the absolute or relative toxicity's of the metals. Treatment of cells with L-buthionine-(S-R)-sulfoximine (BSO) depleted intracellular GSH and resulted in increased sensitivity of the cells to gold, 40 fold, cadmium 8 fold and mercury 3 fold.     

Preventive effect of antioxidants in MPTP-induced mouse model of Parkinson's disease

Oxidative stress to dopaminergic neurons is believed to be one of the causes of neurodegeneration in Parkinson's disease (PD). It was investigated whether N-acetylcysteine (NAC) and l-2-oxothiazolidine-4-carboxylate (OTC) have a preventive effect in an oxidative stress-induced model of PD. We found that NAC and OTC prevent degradation of PARP during auto-oxidized dopamine- or auto-oxidized L-DOPA-induced apoptosis in PC12 cells. In an animal model study, NAC and OTC showed a preventive effect against MPTP-induced loss of tyrosine hydroxylase-positive neurons, and suppressed the nuclear translocation of c-jun N-terminal kinase (JNK), suggesting that NAC and OTC can prevent MPTP-induced apoptosis by suppressing JNK activation. Therefore, these results suggest that NAC and OTC can be used as potential agents to prevent the progression of PD.     

Involvement of oxidative stress in taxol-induced apoptosis in chronic myelogenous leukemia K562 cells

It is now well accepted that taxol exhibits cytotoxicity and antitumor activity in many human tumors through microtubule stabilization and induction of G2/M cell cycle arrest with final extensive cell apoptosis. Since many anti-cancer agents exert their cytotoxic effects through reactive oxygen species (ROS), we were interested to evaluate whether oxidative stress is involved in taxol-induced cytotoxicity among human leukemia K562 cells. Our results showed that induction of apoptosis was associated with generation of ROS and glutathione (GSH) depletion. The increase in ROS production and apoptosis were both suppressed by antioxidant N-acetyl-l-cysteine (NAC). Moreover, taxol caused an increase in c-Jun NH₂-terminal kinase (JNK) and p38 activities, two of the well known mediators of the stress activation pathways. Attenuation of JNK expression in the presence of NAC might indicate the modulation of the level of JNK activity by ROS. Furthermore, our data indicated that Bcl-2α was down-regulated in taxol-treated cells and its expression was modulated by ROS and JNK activity. The activities of caspase-9 and -3 were also increased upon treatment with taxol; however, pre-treatment of cells with NAC or JNK inhibitor (SP600125) impeded taxol-mediated caspase activation and apoptosis in K562 cells, suggesting that JNK acts upstream of the caspases. Taken together, these results indicate that taxol induces apoptosis in chronic myelogenous leukemia cells by inducing intracellular oxidative stress and JNK activation pathway.