Paraquat-induced Cell Death Research Articles

Comparison of the effects of the superoxide dismutase mimetics EUK-134 and tempol on paraquat-induced nephrotoxicity

Paraquat-induced nephrotoxicity involves severe renal cell damage caused by reactive oxygen species (ROS), specifically via increasing concentrations of superoxide anions in the kidney. Recently, superoxide dismutase (SOD) mimetics (SODm) have been developed that display safe SOD activities but which also possess additional antioxidant enzyme (e.g., catalase) or ROS-scavenging activities. The aim of this study was to compare the effects of two such SODm, specifically, EUK-134, a SODm with catalase activity, and tempol, a SODm with ROS-scavenging properties, on paraquat-induced nephrotoxicity of renal NRK-52E cells. Incubation with paraquat (1 mM) for 24 h reduced cell viability and increased necrosis significantly. Paraquat also generated significant quantities of superoxide anions and hydroxyl radicals. Both EUK-134 (10–300 μM) and tempol (0.3–1.0 mM) were able to improve cell viability and reduced paraquat-induced cell death significantly via dismutation or scavenging of superoxide anions and reduced hydroxyl radical generation. The data presented here suggest that SODm such as EUK-134 and tempol, which possess additional catalase and/or ROS-scavenging activities, can significantly reduce renal cell damage caused by paraquat. These effects were evident at concentrations which avoid the pro-oxidant activities associated with higher concentrations of SOD. Such SODm could therefore prove to be beneficial as therapies for paraquat nephrotoxicity.

Hypoxia protects human corneal endothelium from tertiary butyl hydroperoxide and paraquat-induced cell death in vitro.

To develop new and safe approaches to protect and preserve the function of the human corneal endothelium (HCE), we have established an in vitro model of cell loss using an HCE cell line and have examined the potential for hypoxia conditioning to protect HCE from death induced by two ROS generating cytotoxins (tertiary butyl hydroperoxide [tBHP] and paraquat [PQ]). Cell death was assessed by flow cytometric analysis of Annexin-V (An) and propidium iodide (PI) double staining and oligonucleosome production. Mitochondrial membrane potential (MMP) was measured with JC-1 fluorescent dye to determine possible associations between MMP preservation and cell survival. PQ and tBHP both induced HCE cell death in a dose-dependent manner, with 48% and 32% of An(+) cells observed with 60 microM tBHP and 500 microM PQ, respectively. In addition, this level of tBHP and PQ resulted in 66% and 49% decreases in MMP, respectively. Hypoxia (0.6% +/- 0.1% oxygen) pretreatment (8 hrs) significantly reduced An(+) cells caused by 60 microM tBHP to 15%, whereas hypoxia had no effect on the decreased MMP. Hypoxia pretreatments (24 hrs) slightly reduced An(+) cells caused by 500 microM PQ to 25% and completely prevented the induced MMP reduction. Conversely, hypoxia posttreatment (24 hrs) resulted in a greater inhibition of cell death than pretreatment and yet failed to prevent the PQ-induced MMP collapse. In conclusion, these results suggest that hypoxia can sufficiently protect HCE cells against cell death caused by tBHP and PQ, although no direct link between hypoxia cell protection and MMP preservation was observed.

Yeast NDI1 improves oxidative phosphorylation capacity and increases protection against oxidative stress and cell death in cells carrying a Leber's hereditary optic neuropathy mutation

G11778A in the subunit ND4 gene of NADH dehydrogenase complex is the most common primary mutation found in Leber's hereditary optic neuropathy (LHON) patients. The NDI1 gene, which encodes the internal NADH–quinone oxidoreductase in Saccharomyces cerevisiae, was introduced into the nuclear genome of a mitochondrial defective human cell line, Le1.3.1, carrying the G11778A mutation. In transformant cell lines, LeNDI1-1 and -2, total and complex I-dependent respiration were fully restored and largely resistant to complex I inhibitor, rotenone, indicating a dominant role of NDI1 in the transfer of electrons in the host cells. Whereas the original mutant Le1.3.1 cell grows poorly in medium containing galactose, the transformants have a fully restored growth capacity in galactose medium, although the ATP production was not totally recovered. Furthermore, the increased oxidative stress in the cells carrying the G11778A mutation was alleviated in transformants, demonstrated by a decreased reactive oxygen species (ROS) level. Finally, transformants were also shown to be desensitized to induction to apoptosis and also exhibit greater resistance to paraquat-induced cell death. It is concluded that the yeast NDI1 enzyme can improve the oxidative phosphorylation capacity in cells carrying the G11778A mutation and protect the cells from oxidative stress and cell death.

Transduced Tat-α-Synuclein Protects against Oxidative Stress In vitro and In vivo

Parkinson's disease (PD) is a common neurodegenerative disorder and is characterized by the progressive loss of dopaminergic neurons in the substantia nigra. Although many studies showed that the aggregation of alpha-synuclein might be involved in the pathogenesis of PD, its protective properties against oxidative stress remain to be elucidated. In this study, human wild type and mutant alpha-synuclein genes were fused with a gene fragment encoding the nine amino acid transactivator of transcription (Tat) protein transduction domain of HIV-1 in a bacterial expression vector to produce a genetic in-frame WT Tat-alpha-synuclein (wild type) and mutant Tat-alpha-synucleins (mutants; A30P and A53T), respectively, and we investigated the protective effects of wild type and mutant Tat-alpha-synucleins in vitro and in vivo. WT Tat-alpha-synuclein rapidly transduced into an astrocyte cells and protected the cells against paraquat induced cell death. However, mutant Tat-alpha-synucleins did not protect at all. In the mice models exposed to the herbicide paraquat, the WT Tat-alpha-synuclein completely protected against dopaminergic neuronal cell death, whereas mutants failed in protecting against oxidative stress. We found that these protective effects were characterized by increasing the expression level of heat shock protein 70 (HSP70) in the neuronal cells and this expression level was dependent on the concentration of transduced WT Tat-alpha-synuclein. These results suggest that transduced Tat-alpha-synuclein might protect cell death from oxidative stress by increasing the expression level of HSP70 in vitro and in vivo and this may be of potential therapeutic benefit in the pathogenesis of PD.

Low Concentrations of Paraquat Induces Early Activation of Extracellular Signal-Regulated Kinase 1/2, Protein Kinase B, and c-Jun N-terminal Kinase 1/2 Pathways: Role of c-Jun N-Terminal Kinase in Paraquat-Induced Cell Death

Paraquat is a herbicide with a potential risk to induce parkinsonism due to its demonstrated neurotoxicity and its strong structural similarity to 1-methyl-4-phenylpyridinium (MPP(+)), a well-known neurotoxin which causes a clinical syndrome similar to Parkinson's disease (PD). However, at present very little is known about the signaling pathways activated by paraquat in any cell system. In this study, we have investigated the effect of paraquat on extracellular signal-regulated kinases 1 and 2 (ERK1/2), c-Jun N-terminal kinase (JNK), and protein kinase B (PKB) activation in E18 cells. Low concentrations of paraquat stimulated very early increases in ERK1/2, JNK1/2, and PKB phosphorylation. The phosphatidylinositol 3-kinase (PI-3K) inhibitors wortmannin and LY 294002 (2-(4-morpholinyl)-8-phenyl-4H-1-benzopyran-4-one) inhibited early paraquat-induced increases in PKB phosphorylation. Furthermore, early paraquat-mediated increases in ERK1/2 activation were sensitive to the mitogen-activated protein kinase kinase 1 (MEK1) inhibitor PD 98059 (2'-amino-3'-methoxyflavone), whereas JNK1/2 responses were blocked by the JNK1/2 inhibitor SP 600125 (anthra[1-9-cd]pyrazol-6(2H)-one). Pretreatment with wortmannin, LY 294002, or PD 98059 had no effect on paraquat cell death in E18 cells. In contrast, SP 600125 significantly decreased paraquat-induced cell death in E18 cells. In conclusion, we have shown that low concentrations of paraquat stimulate robust very early increases in ERK1/2, JNK1/2, and PKB phosphorylation in E18 cells. Furthermore, the data presented clearly suggest that inhibition of the JNK1/2 pathway protects E18 cells from paraquat-induced cell death and support the fact that inhibition of early activation of JNK1/2 can constitute a potential strategy in PD treatment.

Different cytoprotective effect of antioxidants and change in the iron regulatory system in rodent cells exposed to paraquat or formaldehyde

To study the mechanism of toxicity of paraquat and formaldehyde, the response of oxidant-exposed cultured NIH3T3 cells to antioxidants or an iron chelator was investigated. Paraquat-induced cell death was reduced by treatment with 10 microM pyrrolidine dithiocarbamate (PDTC) and 10 microM desferrioxamine (DFO), but not with N-acetyl-L-cysteine (NAC). Cells were protected from formaldehyde-induced cytotoxicity by 1 mM NAC, but not by PDTC or DFO. Moreover, paraquat modulated the cellular iron regulatory system. Paraquat induced a time-dependent increase in the binding of iron regulatory protein 1 (IRP1) to iron-responsive element (IRE), and the enhanced IRP1 activity continued over 24 h. On the other hand, no induction of increased IRP1 binding to IRE was observed in rodent cells exposed to formaldehyde. Previously, we observed stimulation of EpRE-mediated ferritin mRNA expression in the cells exposed to hydrogen peroxide. However, paraquat did not induce any transcriptional activation of ferritin genes. These results suggest that intracellular iron may be involved in paraquat-mediated cytotoxicity and the influence of paraquat on iron metabolism differs from that of hydrogen peroxide.

Paraquat-induced apoptotic cell death in cerebellar granule cells

Paraquat-induced apoptotic cell death in cerebellar granule cells

Serofendic acid, a sulfur-containing diterpenoid derived from fetal calf serum, attenuates reactive oxygen species-induced oxidative stress in cultured striatal neurons.

We previously identified a novel endogenous substance, serofendic acid, from a lipophilic extract of fetal calf serum. Serofendic acid protects cultured cortical neurons against the cytotoxicity of glutamate and nitric oxide. Here, we reported the protective effect of serofendic acid on reactive oxygen species-induced oxidative stress using primary rat striatal cultures. In addition, we compared the neuroprotective effect and the radical-scavenging activity of serofendic acid with those of dimethyl sulfoxide (DMSO), because serofendic acid possesses a DMSO structure. Paraquat caused neuronal death, which was inhibited by a cell-permeable superoxide dismutase (SOD) mimetic, Mn(III)tetrakis(4-benzoic acid)porphyrin chloride (Mn-TBAP); a cell-permeable SOD/catalase mimetic, EUK-134 [manganese 3-methoxy N,N'-bis(salicylidene)ethylenediamine chloride]; and a ferrous ion chelator, 2,2'-dipyridyl, in rat striatal cultures. Serofendic acid (10-100 microM) suppressed the neurotoxicity of paraquat, whereas DMSO (10-100 microM) did not. By contrast, higher concentrations (30-300 mM) of DMSO ameliorated the paraquat-induced cell death. Furthermore, H(2)O(2) induced neurotoxicity, which was prevented by EUK-134 and 2,2'-dipyridyl. Serofendic acid (10-100 microM) also protected striatal neurons against the H(2)O(2)-induced toxicity. Higher concentrations (30-300 mM) of DMSO ameliorated H(2)O(2)-induced neuronal death, whereas lower concentrations (10-100 microM) did not. Electron spin resonance spectrometry with a spin-trapping technique revealed that serofendic acid and DMSO had approximately the same ability to inhibit the formation of the hydroxyl radical (.OH). These results suggest that the.OH-scavenging activity of serofendic acid is attributable to its DMSO structure and that the remaining components such as the atisane structure play an important role in eliciting neuroprotection at a concentration range of 10 to 100 microM.

Synergy between sulforaphane and selenium in the induction of thioredoxin reductase 1 requires both transcriptional and translational modulation.

Thioredoxin reductases (TrxRs) catalyse the NADPH-dependent reduction of thioredoxin and play an important role in multiple cellular events related to carcinogenesis including cell proliferation, apoptosis and cell signaling. We have used human hepatoma HepG2 cells to examine the regulation of TrxRs by isothiocyanate (sulforaphane) and selenium (Se). We show that TrxR1 mRNA, but not TrxR2 mRNA, is induced up to 4-fold by sulforaphane, and this increase was abolished by actinomycin D, a transcription inhibitor. Se, in the form of sodium selenite, induced TrxR1 at the translational level, as shown by an increase in protein (2.1-fold) and activity (4.8-fold), but not mRNA. In combination, sulforaphane and Se synergistically induced TrxR1 protein (5.5-fold), activity (13-fold) and mRNA (6.5-fold). Although Se does not induce TrxR1 mRNA, Se can delay the degradation of sulforaphane-induced TrxR1 mRNA. Modulation of TrxR1 mRNA by sulforaphane was glutathione and protein kinase C-dependent, as L-buthionine-S,R-sulfoximine (a specific inhibitor of glutathione synthesis), and the protein kinase C inhibitor 1-(5-isoquinolinesulfonyl)-2-methyl-piperazine, significantly reduced the induction. The combination of sulforaphane and Se also efficiently protected HepG2 cells from paraquat-induced cell death, whereas sulforaphane-only and Se-only treatments showed very little if any protective effect. These results demonstrate that synergy can result from a combination of induction at the levels of transcription and translation.

Paraquat-induced cell death in PC12 cells.

Paraquat was taken up by PC12 cells in a carrier-mediated, saturable manner. When PC12 cells were permeabilized with digitonin (50 microg/ml) lipid peroxidation was observed after paraquat treatment in the presence of NADPH and chelated iron. The fact that lipid peroxidation preceded the appearance of LDH release provides positive evidence that lipid peroxidation may be one of the important factors leading to cytotoxicity of cells. Furthermore, the fact that addition of superoxide dismutase, catalase and promethazine efficiently blocked the malondialdehyde formation and attenuated the cell death indicated the involvement of reactive oxygen radicals in mediating the cytotoxicity induced by paraquat. Taken together the results present in vitro evidence that neurotoxicity of paraquat may be a consequence of cellular lipid peroxidation, which leads to cell death and may have great implications in assessing the risk of exposure to paraquat in Parkinson's disease.

Paraquat poisoning: the rationale for current treatment regimes.

The critical events leading to death from the ingestion of paraquat are absorption from the gastrointestinal tract, active accumulation in the lung almost certainly preceded by acute renal failure and redox cycling in the lung which initiates certain, as yet unidentified, biochemical events leading to cell death with subsequent destruction of the lung and death from anoxia. Present evidence suggests that absorption of paraquat is rapid and the use of absorbents more than 6 hours after ingestion is likely to be ineffective. Further work is needed to characterize the mechanism of absorption and to identify an innocuous chemical which could be added to formulations of paraquat to inhibit absorption; this approach may be the best solution to the problem of paraquat poisoning. Steps to actively remove paraquat from the systemic circulation will probably only succeed in a small number of patients taking moderate doses and developing early renal failure. The 'window' for such treatment may be as narrow as 6-18 h after ingestion. This 'window' would also operate for chemicals designed to inhibit the pulmonary uptake of paraquat. The biochemical events leading to paraquat-induced cell death are not sufficiently defined to permit the design of treatments to prevent or reverse these processes.