Mitochondria are a major source of paraquat-induced reactive oxygen species production in the brain

Chronic Treatment with Paraquat Induces Brain Injury, Changes in Antioxidant Defenses System, and Modulates Behavioral Functions in Zebrafish

Paraquat (PQ) administration consists in a chemical model that mimics phenotypes observed in Parkinson's disease (PD), due to its ability to induce changes in dopaminergic system and oxidative stress. The aim of this study was to evaluate the actions of PQ in behavioral functions of adult zebrafish and its influence on oxidative stress biomarkers in brain samples. PQ (20 mg/kg) was administered intraperitoneally with six injections for 16 days (one injection every 3 days). PQ-treated group showed a significant decrease in the time spent in the bottom section and a shorter latency to enter the top area in the novel tank test. Moreover, PQ-exposed fish showed a significant decrease in the number and duration of risk assessment episodes in the light-dark test, as well as an increase in the agonistic behavior in the mirror-induced aggression (MIA) test. PQ induced brain damage by decreasing mitochondrial viability. Concerning the antioxidant defense system, PQ increased catalase (CAT) and glutathione peroxidase (GPx) activities, as well as the non-protein sulfhydryl content (NPSH), but did not change ROS formation and decreased lipid peroxidation. We demonstrate, for the first time, that PQ induces an increase in aggressive behavior, alters non-motor patterns associated to defensive behaviors, and changes redox parameters in zebrafish brain. Overall, our findings may serve as useful tools to investigate the interaction between behavioral and neurochemical impairments triggered by PQ administration in zebrafish.

Ablation of the mitochondrial complex IV assembly protein Surf1 leads to increased expression of the UPR(MT) and increased resistance to oxidative stress in primary cultures of fibroblasts

Mice deficient in the electron transport chain (ETC) complex IV assembly protein SURF1 have reduced assembly and activity of cytochrome c oxidase that is associated with an upregulation of components of the mitochondrial unfolded protein response (UPR^MT) and increased mitochondrial number. We hypothesized that the upregulation of proteins associated with the UPR^MT in response to reduced cytochrome c oxidase activity in Surf1^−/− mice might contribute to increased stress resistance. To test this hypothesis we asked whether primary cultures of fibroblasts from Surf1^−/− mice exhibit enhanced resistance to stressors compared to wild-type fibroblasts. Here we show that primary dermal fibroblasts isolated from Surf1^−/− mice have increased expression of UPR^MT components ClpP and Hsp60, and increased expression of Lon protease. Fibroblasts from Surf1^−/− mice are significantly more resistant to cell death caused by oxidative stress induced by paraquat or tert-Butyl hydroperoxide compared to cells from wild-type mice. In contrast, Surf1^−/− fibroblasts show no difference in sensitivity to hydrogen peroxide stress. The enhanced cell survival in response to paraquat or tert-Butyl hydroperoxide in Surf1^−/− fibroblasts compared to wild-type fibroblasts is associated with induced expression of Lon, ClpP, and Hsp60, increased maximal respiration, and increased reserve capacity as measured using the Seahorse Extracellular Flux Analyzer. Overall these data support a protective role for the activation of the UPR^MT in cell survival.

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Surf1^−/− mice fibroblasts exhibit upregulation of proteins involved in the UPR^MT.

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Mitochondrial specific oxidative stressors induce UPR^MT in mammalian fibroblasts.

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Surf1^−/− fibroblasts exhibit enhanced mitochondrial specific stress resistance.

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Surf1^−/− fibroblasts have increased maximal respiration and respiratory reserve.

Multifactorial theory applied to the neurotoxicity of paraquat and paraquat-induced mechanisms of developing Parkinson's disease

Laboratory studies involving repeated exposure to paraquat (PQ) in different animal models can induce many of the pathological features of Parkinson's disease (PD), such as the loss of dopaminergic neurons in the nigrostriatal dopamine system. Epidemiological studies identify an increased risk of developing PD in human populations living in areas where PQ exposure is likely to occur and among workers lacking appropriate protective equipment. The mechanisms involved in developing PD may not be due to any single cause, but rather a multifactorial situation may exist where PQ exposure may cause PD in some circumstances. Multifactorial theory is adopted into this review that includes a number of sub-cellular mechanisms to explain the pathogenesis of PD. The theory is placed into an environmental context of chronic low-dose exposure to PQ that consequently acts as an oxidative stress inducer. Oxidative stress and the metabolic processes of PQ-inducing excitotoxicity, α-synuclein aggregate formation, autophagy, alteration of dopamine catabolism, and inactivation of tyrosine hydroxylase are positioned as causes for the loss of dopaminergic cells. The environmental context and biochemistry of PQ in soils, water, and organisms is also reviewed to identify potential routes that can lead to chronic rates of low-dose exposure that would replicate the type of response that is observed in animal models, epidemiological studies, and other types of laboratory investigations involving PQ exposure. The purpose of this review is to synthesize key relations and summarize hypotheses linking PD to PQ exposure by using the multifactorial approach. Recommendations are given to integrate laboratory methods to the environmental context as a means to improve on experimental design. The multifactorial approach is necessary for conducting valid tests of causal relations, for understanding of potential relations between PD and PQ exposure, and may prevent further delay in solving what has proven to be an evasive etiological problem.

Parkinsonian toxin-induced oxidative stress inhibits basal autophagy in astrocytes via NQO2/quinone oxidoreductase 2: Implications for neuroprotection

Oxidative stress (OS) stimulates autophagy in different cellular systems, but it remains controversial if this rule can be generalized. We have analyzed the effect of chronic OS induced by the parkinsonian toxin paraquat (PQ) on autophagy in astrocytoma cells and primary astrocytes, which represent the first cellular target of neurotoxins in the brain. PQ decreased the basal levels of LC3-II and LC3-positive vesicles, and its colocalization with lysosomal markers, both in the absence and presence of chloroquine. This was paralleled by increased number and size of SQSTM1/p62 aggregates. Downregulation of autophagy was also observed in cells chronically exposed to hydrogen peroxide or nonlethal concentrations of PQ, and it was associated with a reduced astrocyte capability to protect dopaminergic cells from OS in co-cultures. Surprisingly, PQ treatment led to inhibition of MTOR, activation of MAPK8/JNK1 and MAPK1/ERK2-MAPK3/ERK1 and upregulation of BECN1/Beclin 1 expression, all signals typically correlating with induction of autophagy. Reduction of OS by NMDPEF, a specific NQO2 inhibitor, but not by N-acetylcysteine, abrogated the inhibitory effect of PQ and restored autophagic flux. Activation of NQO2 by PQ or menadione and genetic manipulation of its expression confirmed the role of this enzyme in the inhibitory action of PQ on autophagy. PQ did not induce NFE2L2/NRF2, but when it was co-administered with NMDPEF NFE2L2 activity was enhanced in a SQSTM1-independent fashion. Thus, a prolonged OS in astrocytes inhibits LC3 lipidation and impairs autophagosome formation and autophagic flux, in spite of concomitant activation of several pro-autophagic signals. These findings outline an unanticipated neuroprotective role of astrocyte autophagy and identify in NQO2 a novel pharmacological target for its positive modulation.

Repurposing an orally available drug for the treatment of geographic atrophy

PURPOSE

Chronic oxidative stress and subacute inflammation have been implicated as causes of age-related macular degeneration (AMD). In this study, we tested whether an orally available 5-OH-tryptamine (5HT) 1a receptor agonist, xaliproden, could protect against retinal pigment epithelium (RPE) cell damage in culture and in a mouse model of geographic atrophy.

METHODS

Paraquat was used to create mitochondrial oxidative stress in ARPE-19 cells, and tumor necrosis factor-α (TNF-α) was used to stimulate the production of inflammatory cytokines in these cells. The production of antioxidant proteins, metallothionein, and inflammatory cytokines was assayed with quantitative real-time PCR. Cell survival was analyzed with microscopy and a cell titer assay. Integrity of the RPE monolayer was determined by measuring the transepithelial electrical resistance (TEER) and with immunocytochemistry with zona occludens protein 1 (ZO-1) antibody. RPE atrophy was studied in mice deleted for Sod2 (the gene for mitochondrial superoxide dismutase) specifically in the RPE. The mice were treated orally with daily doses of xaliproden at 0.5 and 3 mg/kg for 4 months. The retinal structure was analyzed with spectral domain optical coherence tomography (SD-OCT) and with light and electron microscopy. Retinal function was assessed with full-field electroretinography (ERG) and with optokinetic measurements.

RESULTS

Xaliproden led to a dose-dependent increase in cell survival following treatment with paraquat. Synthesis of the antioxidant response genes NqO1, GSTM1, CAT, HO-1, and Nrf2 was increased in response to the drug, as was the zinc chaperone metallothionein. Treatment of cells with TNF-α led to increased production of IL-1β, IL-6, chemokine (C-C motif) ligand 20 (CCL20), and vascular endothelial growth factor (VEGF) by ARPE-19 cells, and this response was attenuated by treatment with xaliproden. TNF-α also led to a decrease in the TEER that was prevented by treatment with the 5HT1a agonist. Daily gavage with xaliproden at either dose induced the production of protective enzymes in the mouse retina, and treatment of the Sod2-deleted mice with the drug showed improved thickness of the outer nuclear layer and improved visual acuity relative to the control-treated mice. There was no significant difference in full-field scotopic ERG among the treatment groups, however. Vacuolization of the RPE and disorganization of the photoreceptor outer segments were reduced at both dose levels of xaliproden.

CONCLUSIONS

Xaliproden protected RPE cells from oxidative and inflammatory insults and protected the mouse RPE and retina from RPE atrophy in the face of excess mitochondrial oxidative stress. These results suggest that this drug, which had a reasonable safety profile in clinical trials, may be used to prevent the progression of geographic atrophy in humans.

A role for Mfb1p in region-specific anchorage of high-functioning mitochondria and lifespan in Saccharomyces cerevisiae

Previous studies indicate that replicative lifespan in daughter cells of Sacchraromyces cerevisiae depends on the preferential inheritance of young, high-functioning mitochondria. We report here that mitochondria are functionally segregated even within single mother cells in S. cerevisiae. A high-functioning population of mitochondria accumulates at the tip of the mother cell distal to the bud. We find that the mitochondrial F-box protein (Mfb1p) localizes to mitochondria in the mother tip and is required for mitochondrial anchorage at that site, independent of the previously identified anchorage protein Num1p. Deletion of MFB1 results in loss of the mother-tip-localized mitochondrial population, defects in mitochondrial function and premature replicative ageing. Inhibiting mitochondrial inheritance to buds, by deletion of MMR1, in mfb1Δ cells restores mitochondrial distribution, promotes mitochondrial function and extends replicative lifespan. Our results identify a mechanism that retains a reservoir of high-functioning mitochondria in mother cells and thereby preserves maternal reproductive capacity.

Mitochondria are asymmetrically inherited during cell division, a process that can affect cell fate and lifespan. Here the authors describe a mechanism for mitochondrial quality control in yeast that maintains a reservoir of high-functioning mitochondria in mother cells and preserves maternal reproductive capacity.

Methyl viologen induces neural differentiation on murine P19 cells

Methyl viologen is a highly effective contact herbicide, a neurotoxic compound and an inducer of reactive oxygen species, which generate oxidative stress in cells. Reactive oxygen species has been known to function as an important messenger in cell differentiation. In this study, we investigated the effect of methyl viologen on neural cell differentiation using pluripotent mouse embryonal carcinoma P19 cells, which reportedly differentiate into neural cells upon exposure to retinoic acid. Methyl viologen, an inducer of intracellular reactive oxygen species, induced the differentiation of P19 cells into neural cells in the presence of neurofilament. Reduced glutathione, an eliminator of reactive oxygen species, also induced neural differentiation in P19 cells. These results suggest that P19 cells differentiate into neural cells, conceivably independent of intracellular reactive oxygen species.

SIRT6 safeguards human mesenchymal stem cells from oxidative stress by coactivating NRF2

SIRT6 belongs to the mammalian homologs of Sir2 histone NAD(+)-dependent deacylase family. In rodents, SIRT6 deficiency leads to aging-associated degeneration of mesodermal tissues. It remains unknown whether human SIRT6 has a direct role in maintaining the homeostasis of mesodermal tissues. To this end, we generated SIRT6 knockout human mesenchymal stem cells (hMSCs) by targeted gene editing. SIRT6-deficient hMSCs exhibited accelerated functional decay, a feature distinct from typical premature cellular senescence. Rather than compromised chromosomal stability, SIRT6-null hMSCs were predominately characterized by dysregulated redox metabolism and increased sensitivity to the oxidative stress. In addition, we found SIRT6 in a protein complex with both nuclear factor erythroid 2-related factor 2 (NRF2) and RNA polymerase II, which was required for the transactivation of NRF2-regulated antioxidant genes, including heme oxygenase 1 (HO-1). Overexpression of HO-1 in SIRT6-null hMSCs rescued premature cellular attrition. Our study uncovers a novel function of SIRT6 in maintaining hMSC homeostasis by serving as a NRF2 coactivator, which represents a new layer of regulation of oxidative stress-associated stem cell decay.

Antioxidant activity in vitro and in vivo of the polysaccharides from different varieties of Auricularia auricula

In this study, five different kinds of polysaccharides (AAP1, AAP2, AAP3, AAP4, and AAP5) were extracted from different varieties ofAuricularia auriculathrough an alkali extraction process.

Cu/Zn-superoxide dismutase and glutathione are involved in response to oxidative stress induced by protein denaturing effect of alachlor in Saccharomyces cerevisiae

Alachlor is a widely used pre-emergent chloroacetanilide herbicide which has been shown to have many harmful ecological and environmental effects. However, the mechanism of alachlor-induced oxidative stress is poorly understood. We found that, in Saccharomyces cerevisiae, the intracellular levels of reactive oxygen species (ROS) including superoxide anions were increased only after long-term exposure to alachlor, suggesting that alachlor is not a pro-oxidant. It is likely that alachlor-induced oxidative stress may result from protein denaturation because alachlor rapidly induced an increased protein aggregation, leading to upregulation of SSA4 and HSP82 genes encoding heat shock proteins (Hsp) of Hsp70 and Hsp90 family, respectively. Although only SOD1 encoding Cu/Zn-superoxide dismutase (SOD), but not SOD2 encoding Mn-SOD, is essential for alachlor tolerance, both SODs play a crucial role in reducing alachlor-induced ROS. We found that, after alachlor exposure, glutathione production was inhibited while its utilization was increased, suggesting the role of glutathione in protecting cells against alachlor, which becomes more important when lacking Cu/Zn-SOD. Based on our results, it seems that alachlor primarily causes damages to cellular macromolecules such as proteins, leading to an induction of endogenous oxidative stress, of which intracellular antioxidant defense systems are required for elimination.

Artificial sweetener neohesperidin dihydrochalcone showed antioxidative, anti-inflammatory and anti-apoptosis effects against paraquat-induced liver injury in mice

The present study evaluated the protective effect of artificial sweetener neohesperidin dihydrochalcone (NHDC) against paraquat (PQ)-induced acute liver injury in mice. A single dose of PQ (75mg/kg body weight, i.p.) induced acute liver toxicity with the evidences of increased liver damage biomarkers, aspartate transaminase (AST) and alanine transaminase (ALT) activities in serum. Consistently, PQ decreased the antioxidant capacity by reducing glutathione peroxidase (GP-X), glutathione-S-transferase (GST) and catalase (CAT) activities, glutathione (GSH) level and total antioxidant capacity (T-AOC), as well as increasing reactive oxygen species (ROS) and thiobarbituric acid reactive substances (TBARS) levels. Histopathological examination revealed that PQ induced numerous changes in the liver tissues. Immunochemical staining assay indicated the upregulation of cyclooxygenase-2 (COX-2) and inducible nitric oxide synthase (iNOS) expressions. However, NHDC ameliorates PQ-induced hepatic toxicity in mice by reversing these parameters. Additionally, NHDC significantly inhibited PQ-induced nuclear factor-kappa B (NF-κB) expression and mitochondrial-driven apoptotic signaling. TUNEL assay confirmed that PQ-induced apoptosis was relieved by NHDC. In conclusion, these findings suggested that NHDC showed potent antioxidant, anti-inflammatory and anti-apoptotic effects against PQ-induced acute liver damage.

NLRP3 inflammasome activation by mitochondrial reactive oxygen species plays a key role in long-term cognitive impairment induced by paraquat exposure

Exposure to environmental toxins such as pesticides is implicated in increasing Alzheimer's disease risk. In this study, we investigated the long-term effects of paraquat exposure on cognition of Alzheimer's disease animal model APP/PS1 mice and wild-type (WT) mice. Our results showed that APP/PS1 mice had exacerbated cognition impairment and elevated Aβ levels at 5 months after paraquat exposure, and that WT mice had cognition impairment at 5 and 16 months after paraquat exposure. In addition, increased mitochondrial oxidative stress and augmented brain inflammation were observed in both paraquat-exposed APP/PS1 mice and WT mice. Interestingly, activation of NLRP3 inflammasome, which triggers inflammation in response to mitochondrial stress, was enhanced in paraquat-exposed mice. Moreover, transgenic mice overexpressing Prdx3, a key enzyme in detoxifying mitochondrial H2O2, had suppressed NLRP3 inflammasome activation, reduced brain inflammation, and attenuated cognition impairment after paraquat exposure. Together, our results indicate that NLRP3 inflammasome activation induced by mitochondrial reactive oxygen species plays a key role in mediating paraquat-induced long-term cognition decline by elevating brain inflammation.

Paraquat Induces Apoptosis through a Mitochondria-Dependent Pathway in RAW264.7 Cells

Paraquat dichloride (N,N-dimethyl-4-4′-bipiridinium, PQ) is an extremely toxic chemical that is widely used in herbicides. PQ generates reactive oxygen species (ROS) and causes multiple organ failure. In particular, PQ has been reported to be an immunotoxic agrochemical compound. PQ was shown to decrease the number of macrophages in rats and suppress monocyte phagocytic activity in mice. However, the effect of PQ on macrophage cell viability remains unclear. In this study, we evaluated the cytotoxic effect of PQ on the mouse macrophage cell line, RAW264.7 and its possible mechanism of action. RAW264.7 cells were treated with PQ (0, 75, and 150 μM), and cellular apoptosis, mitochondrial membrane potential (MMP), and intracellular ROS levels were determined. Morphological changes to the cell nucleus and cellular apoptosis were also evaluated by DAPI and Annexin V staining, respectively. In this study, PQ induced apoptotic cell death by dose-dependently decreasing MMP. Additionally, PQ increased the cleaved form of caspase-3, an apoptotic marker. In conclusion, PQ induces apoptosis in RAW264.7 cells through a ROS-mediated mitochondrial pathway. Thus, our study improves our knowledge of PQ-induced toxicity, and may give us a greater understanding of how PQ affects the immune system.

NADPH oxidase mediated maneb- and paraquat-induced oxidative stress in rat polymorphs: Crosstalk with mitochondrial dysfunction

Oxidative stress is a key factor in Parkinson's disease (PD) pathogenesis. Nicotinamide adenine dinucleotide phosphate (NADPH) oxidase and impaired mitochondrion regulate oxidative stress-mediated maneb (MB)- and paraquat (PQ)-induced Parkinsonism. However, their contribution in the MB- and PQ-induced toxicity in polymorphonuclear leukocytes (PMNs) is still elusive. The study investigated the role of NADPH oxidase and mitochondria in MB- and/or PQ-induced oxidative stress in the PMNs and the crossing point between the two. Animals were treated with MB and/or PQ for 1-3 weeks along with respective controls. In a few sets of experiments, rats were treated with/without NADPH oxidase inhibitor, apocynin, an hour prior to MB and/or PQ treatment. PMNs of MB and/or PQ treated animals were also treated with/without carbonyl cyanide 3-chlorophenylhydrazone (CCCP) to assess the role of the mitochondria in superoxide and total free radical productions. MB and/or PQ were found to increase the level of total reactive oxygen species (ROS), superoxide radicals, catalytic activity and expression of NADPH oxidase and superoxide dismutase (SOD1/2) and mitochondrial ROS content in a time dependent manner. Conversely, catalase activity and mitochondrial membrane potential were attenuated. Apocynin alleviated MB- and/or PQ-induced changes in total ROS, superoxide radicals, expression/catalytic activity of NADPH oxidase and SOD1/2 along with the mitochondrial ROS and membrane potential. CCCP also inhibited ROS and superoxide levels in the PMNs of MB and/or PQ-treated animals. The results demonstrate the involvement of NADPH oxidase and mitochondrial dysfunction in MB and PQ-induced oxidative stress in PMNs and a plausible crosstalk between them.

Systemic treatment with a 5HT1a agonist induces anti-oxidant protection and preserves the retina from mitochondrial oxidative stress

Chronic oxidative stress contributes to age related diseases including age related macular degeneration (AMD). Earlier work showed that the 5-hydroxy-tryptamine 1a (5HT1a) receptor agonist 8-hydroxy-2-(di-n-propylamino)-tetralin (8-OH-DPAT) protects retinal pigment epithelium (RPE) cells from hydrogen peroxide treatment and mouse retinas from oxidative insults including light injury. In our current experiments, RPE derived cells subjected to mitochondrial oxidative stress were protected from cell death by the up-regulation of anti-oxidant enzymes and of the metal ion chaperone metallothionein. Differentiated RPE cells were resistant to oxidative stress, and the expression of genes for protective proteins was highly increased by oxidative stress plus drug treatment. In mice treated with 8-OH-DPAT, the same genes (MT1, HO1, NqO1, Cat, Sod1) were induced in the neural retina, but the drug did not affect the expression of Sod2, the gene for manganese superoxide dismutase. We used a mouse strain deleted for Sod2 in the RPE to accelerate age-related oxidative stress in the retina and to test the impact of 8-OH-DPAT on the photoreceptor and RPE degeneration developed in these mice. Treatment of mice with daily injections of the drug led to increased electroretinogram (ERG) amplitudes in dark-adapted mice and to a slight improvement in visual acuity. Most strikingly, in mice treated with a high dose of the drug (5 mg/kg) the structure of the RPE and Bruch's membrane and the normal architecture of photoreceptor outer segments were preserved. These results suggest that systemic treatment with this class of drugs may be useful in preventing geographic atrophy, the advanced form of dry AMD, which is characterized by RPE degeneration.

Heme Signaling Impacts Global Gene Expression, Immunity and Dengue Virus Infectivity in Aedes aegypti

Blood-feeding mosquitoes are exposed to high levels of heme, the product of hemoglobin degradation. Heme is a pro-oxidant that influences a variety of cellular processes. We performed a global analysis of heme-regulated Aedes aegypti (yellow fever mosquito) transcriptional changes to better understand influence on mosquito physiology at the molecular level. We observed an iron- and reactive oxygen species (ROS)-independent signaling induced by heme that comprised genes related to redox metabolism. By modulating the abundance of these transcripts, heme possibly acts as a danger signaling molecule. Furthermore, heme triggered critical changes in the expression of energy metabolism and immune response genes, altering the susceptibility towards bacteria and dengue virus. These findings seem to have implications on the adaptation of mosquitoes to hematophagy and consequently on their ability to transmit diseases. Altogether, these results may also contribute to the understanding of heme cell biology in eukaryotic cells.

Traditional chinese medicine Xuebijing treatment is associated with decreased mortality risk of patients with moderate paraquat poisoning

Paraquat poisoning causes multiple organ injury and high mortality due to severe toxicity and lack of effective treatment. Xuebijing (XBJ) injection, a traditional Chinese medicine preparation of five Chinese herbs (Radix Salviae Miltiorrhiae, Rhizoma Chuanxiong, Flos Carthami, Angelica Sinensis and Radix Paeoniae Rubra), has an anti-inflammatory effect and is widely used in the treatment of sepsis. This retrospective study was designed to evaluate the effects of XBJ combined with conventional therapy on mortality risk of patients with acute paraquat poisoning. Out of 68 patients, 27 were treated with conventional therapy (control group) and 41 were treated with intravenous administration of XBJ (100 ml, twice a day, up to 7 days) plus conventional therapy (XBJ group). Vital organ function, survival time within 28 days and adverse events during the treatment were reviewed. Results indicated that XBJ treatment significantly increased median survival time among patients ingesting 10-30 ml of paraquat (P=0.02) compared with the control group. After adjustment for covariates, XBJ treatment was associated significantly with a lower mortality risk (adjusted HR 0.242, 95% CI 0.113 to 0.516, P=0.001) compared with the control group. Additionally, compared with Day 1, on Day 3 the value of PaO2/FiO2 was significantly decreased, and the values of serum alanine aminotransferase, creatinine and troponin T were significantly increased in the control group (all P<0.05), but these values were significant improved in the XBJ group (all P<0.05). Only one patient had skin rash with itch within 30 minutes after injection and no severe adverse events were found in the XBJ group. In conclusion, XBJ treatment is associated with decreased mortality risk of patients with moderate paraquat poisoning, which may be attributed to improved function of vital organs with no severe adverse events.

Environmental pollutants as risk factors for neurodegenerative disorders: Alzheimer and Parkinson diseases

Neurodegenerative diseases including Alzheimer (AD) and Parkinson (PD) have attracted attention in last decades due to their high incidence worldwide. The etiology of these diseases is still unclear; however the role of the environment as a putative risk factor has gained importance. More worryingly is the evidence that pre- and post-natal exposures to environmental factors predispose to the onset of neurodegenerative diseases in later life. Neurotoxic metals such as lead, mercury, aluminum, cadmium and arsenic, as well as some pesticides and metal-based nanoparticles have been involved in AD due to their ability to increase beta-amyloid (Aβ) peptide and the phosphorylation of Tau protein (P-Tau), causing senile/amyloid plaques and neurofibrillary tangles (NFTs) characteristic of AD. The exposure to lead, manganese, solvents and some pesticides has been related to hallmarks of PD such as mitochondrial dysfunction, alterations in metal homeostasis and aggregation of proteins such as α-synuclein (α-syn), which is a key constituent of Lewy bodies (LB), a crucial factor in PD pathogenesis. Common mechanisms of environmental pollutants to increase Aβ, P-Tau, α-syn and neuronal death have been reported, including the oxidative stress mainly involved in the increase of Aβ and α-syn, and the reduced activity/protein levels of Aβ degrading enzyme (IDE)s such as neprilysin or insulin IDE. In addition, epigenetic mechanisms by maternal nutrient supplementation and exposure to heavy metals and pesticides have been proposed to lead phenotypic diversity and susceptibility to neurodegenerative diseases. This review discusses data from epidemiological and experimental studies about the role of environmental factors in the development of idiopathic AD and PD, and their mechanisms of action.

Mitochondrial-derived reactive oxygen species play a vital role in the salicylic acid signaling pathway in Arabidopsis thaliana

Plant mitochondria constitute a major source of ROS and are proposed to act as signaling organelles in the orchestration of defense response. At present, the signals generated and then integrated by mitochondria are still limited. Here, fluorescence techniques were used to monitor the events of mitochondria in vivo, as well as the induction of mitochondrial signaling by a natural defensive signal chemical salicylic acid (SA). An inhibition of respiration was observed in isolated mitochondria subjected to SA. The cytochrome reductase activity analysis in isolated mitochondria demonstrated that SA might act directly on the complex III in the respiration chain by inhibiting the activity. With this alteration, a quick burst of mitochondrial ROS (mtROS) was stimulated. SA-induced mtROS caused mitochondrial morphology transition in leaf tissue or protoplasts expressing mitochondria-GFP (43C5) and depolarization of membrane potential. However, the application of AsA, an H2O2 scavenger, significantly prevented both events, indicating that both of them are attributable to ROS accumulation. In parallel, SA-induced mtROS up-regulated AOX1a transcript abundance and this induction was correlated with the disease resistance, whereas AsA-pretreatment interdicted this effect. It is concluded that mitochondria play an essential role in the signaling pathway of SA-induced ROS generation, which possibly provided new insight into the SA-mediated biological processes, including plant defense response.

Mitochondrial mechanisms of redox cycling agents implicated in Parkinson's disease

Environmental agents have been implicated in Parkinson's disease (PD) based on epidemiological studies and the ability of toxicants to replicate features of PD. However, the precise mechanisms by which toxicants induce dopaminergic toxicity observed in the idiopathic form of PD remain to be fully understood. The roles of ROS and mitochondria are strongly suggested in the mechanisms by which these toxicants exert dopaminergic toxicity. There are marked differences and similarities shared by the toxicants in increasing steady-state levels of mitochondrial ROS. Furthermore, toxicants increase steady-state mitochondrial ROS levels by stimulating the production, inhibiting the antioxidant pathways of both. This review will focus on the role of mitochondria and ROS in PD associated with environmental exposures to redox-based toxicants.

DNaseI protects against Paraquat-induced acute lung injury and pulmonary fibrosis mediated by mitochondrial DNA

BACKGROUND

Paraquat (PQ) poisoning is a lethal toxicological challenge that served as a disease model of acute lung injury and pulmonary fibrosis, but the mechanism is undetermined and no effective treatment has been discovered.

METHODS AND FINDINGS

We demonstrated that PQ injures mitochondria and leads to mtDNA release. The mtDNA mediated PBMC recruitment and stimulated the alveolar epithelial cell production of TGF-β1 in vitro. The levels of mtDNA in circulation and bronchial alveolar lavage fluid (BALF) were elevated in a mouse of PQ-induced lung injury. DNaseI could protect PQ-induced lung injury and significantly improved survival. Acute lung injury markers, such as TNFα, IL-1β, and IL-6, and marker of fibrosis, collagen I, were downregulated in parallel with the elimination of mtDNA by DNaseI. These data indicate a possible mechanism for PQ-induced, mtDNA-mediated lung injury, which may be shared by other causes of lung injury, as suggested by the same protective effect of DNaseI in bleomycin-induced lung injury model. Interestingly, increased mtDNA in the BALF of patients with amyopathic dermatomyositis-interstitial lung disease can be appreciated.

CONCLUSIONS

DNaseI targeting mtDNA may be a promising approach for the treatment of PQ-induced acute lung injury and pulmonary fibrosis that merits fast tracking through clinical trials.

Docosahexaenoic acid prevents paraquat-induced reactive oxygen species production in dopaminergic neurons via enhancement of glutathione homeostasis

Omega-3 polyunsaturated fatty acid levels are reduced in the substantia nigra area in Parkinson's disease patients and animal models, implicating docosahexaenoic acid (DHA) as a potential treatment for preventing Parkinson's disease and suggesting the need for investigations into how DHA might protect against neurotoxin-induced dopaminergic neuron loss. The herbicide paraquat (PQ) induces dopaminergic neuron loss through the excessive production of reactive oxygen species (ROS). We found that treatment of dopaminergic SN4741 cells with PQ reduced cell viability in a dose-dependent manner, but pretreatment with DHA ameliorated the toxic effect of PQ. To determine the toxic mechanism of PQ, we measured intracellular ROS content in different organelles with specific dyes. As expected, all types of ROS were increased by PQ treatment, but DHA pretreatment selectively decreased cytosolic hydrogen peroxide content. Furthermore, DHA treatment-induced increases in glutathione reductase and glutamate cysteine ligase modifier subunit (GCLm) mRNA expression were positively correlated with glutathione (GSH) content. Consistent with this increase in GCLm mRNA levels, Western blot analysis revealed that DHA pretreatment increased nuclear factor-erythroid 2 related factor 2 (Nrf2) protein levels. These findings indicate that DHA prevents PQ-induced neuronal cell loss by enhancing Nrf2-regulated GSH homeostasis.

Paraquat reduces natural killer cell activity via metallothionein induction

Paraquat (PQ), one of the most widely used herbicides, has been used for several decades in agriculture. Some studies suggest that PQ has effects on the immune system. Moreover, previous studies have shown that PQ imparted some immunosuppressive effects. In the present study, cytotoxicity assays using splenic NK cells from mice treated for 28 days with PQ (at 0.2, 1, and 5 mg/kg) were performed to determine whether PQ altered the function of NK cells. Given that PQ was expected to induce an immunosuppressive effect, it was hypothesized that a gene involved in cellular metal ion homeostasis, metallothionein-1 (MT-1), could play an important role in this outcome. This belief was based on the fact that MT1 encodes a protein responsible for zinc ion homeostasis, and that a reduction in free zinc ion levels impairs NK cell function. The results showed that PQ treatments led to increased MT expression in several organs (liver, kidneys, testes) and in splenocytes, caused a reduction of both free zinc ions in sera and in free intracellular zinc, and reduced the expression of GATA-3, a zinc-finger transcription factor important for maturation and activity of T-cells and NK cells. These results provide a basis for a new molecular mechanism to describe potential immunosuppressive effects of PQ in vivo.

Inhibition of JNK aggravates the recovery of rat hearts after global ischemia: the role of mitochondrial JNK

c-Jun N-terminal kinase (JNK), a stress-activated MAPK, is activated during cardiac ischemia-reperfusion (IR). The role of JNK inhibitors in cardioprotection against IR still remains controversial, in part, due to spill-over effects of non-specific inhibitors. In the present study, we sought to examine whether inhibition of JNK by SU3327, a specific JNK inhibitor that inhibits upstream JNK signaling rather than the kinase activity of JNK, improves cardiac function and reduces heart damage during IR. Hearts of male Sprague-Dawley rats perfused by Langendorff were subjected to 25 min of global ischemia followed by 30 min reperfusion in the presence or absence of SU3327. Cardiac function was monitored throughout the perfusion period. Myocardial damage was extrapolated from LDH activity in the coronary effluent. At the end of reperfusion, mitochondria were isolated and used to measure respiration rates and mitochondrial permeability transition pore opening. Protein analysis of mitochondria predictably revealed that SU3327 inhibited JNK phosphorylation. Although SU3327 significantly reduced cell damage during the first minutes of reperfusion, it did not improve cardiac function and, furthermore, reduced the mitochondrial respiratory control index. Interestingly, SU3327 activated the other stress-related MAPK, p38, and greatly increased its translocation to mitochondria. Mitochondrial P-JNK and P-p38 were co-immunoprecipitated with complex III of the electron transfer chain. Thus, JNK plays an essential role in cardiac signaling under both physiological and pathological conditions. Its inhibition by SU3327 during IR aggravates cardiac function. The detrimental effects of JNK inhibition are associated with reciprocal p38 activation and mitochondrial dysfunction.

Mitochondrial dysfunction induces Sarm1-dependent cell death in sensory neurons

Mitochondrial dysfunction is the underlying cause of many neurological disorders, including peripheral neuropathies. Mitochondria rely on a proton gradient to generate ATP and interfering with electron transport chain function can lead to the deleterious accumulation of reactive oxygen species (ROS). Notably, loss of mitochondrial potential precedes cellular demise in several programmed cell destruction pathways, including axons undergoing Wallerian degeneration. Here, we demonstrate that mitochondrial depolarization triggers axon degeneration and cell death in primary mouse sensory neurons. These degenerative events are not blocked by inhibitors of canonical programmed cell death pathways such as apoptosis, necroptosis, and parthanatos. Instead, the axodestructive factor Sarm1 is required for this axon degeneration and cell death. In the absence of Sarm1, the mitochondrial poison CCCP still induces depolarization of mitochondria, ATP depletion, calcium influx, and the accumulation of ROS, yet cell death and axon degeneration are blocked. The survival of these neurons despite the accumulation of ROS indicates that Sarm1 acts downstream of ROS generation. Indeed, loss of Sarm1 protects sensory neurons and their axons from prolonged exposure to ROS. Therefore, Sarm1 functions downstream of ROS to induce neuronal cell death and axon degeneration during oxidative stress. These findings highlight the central role for Sarm1 in a novel form of programmed cell destruction that we term sarmoptosis.

Pharmacological inhibition of CXCR2 chemokine receptors modulates paraquat-induced intoxication in rats

Paraquat (PQ) is an agrochemical agent commonly used worldwide, which is allied to potential risks of intoxication. This herbicide induces the formation of reactive oxygen species (ROS) that ends up compromising various organs, particularly the lungs and the brain. This study evaluated the deleterious effects of paraquat on the central nervous system (CNS) and peripherally, with special attempts to assess the putative protective effects of the selective CXCR2 receptor antagonist SB225002 on these parameters. PQ-toxicity was induced in male Wistar rats, in a total dose of 50 mg/kg, and control animals received saline solution at the same schedule of administration. Separate groups of animals were treated with the selective CXCR2 antagonist SB225002 (1 or 3 mg/kg), administered 30 min before each paraquat injection. The major changes found in paraquat-treated animals were: decreased body weight and hypothermia, nociception behavior, impairment of locomotor and gait capabilities, enhanced TNF-α and IL-1β expression in the striatum, and cell migration to the lungs and blood. Some of these parameters were reversed when the antagonist SB225002 was administered, including recovery of physiological parameters, decreased nociception, improvement of gait abnormalities, modulation of striatal TNF-α and IL-1β expression, and decrease of neutrophil migration to the lungs and blood. Taken together, our results demonstrate that damage to the central and peripheral systems elicited by paraquat can be prevented by the pharmacological inhibition of CXCR2 chemokine receptors. The experimental evidence presented herein extends the comprehension on the toxicodynamic aspects of paraquat, and opens new avenues to treat intoxication induced by this herbicide.

Metallothioneins attenuate paraquat-induced acute lung injury in mice through the mechanisms of anti-oxidation and anti-apoptosis

Paraquat (PQ) is a widely used herbicide, and lung is the primary target of PQ poisoning. Metallothionein (MT) is a potent antioxidant and free radical scavenger, and has been shown to play a protective role in lung injury induced by different stressors. This study was undertaken to evaluate the protective potential of MT against PQ-induced acute lung injury using MT-I/II null (MT(-/-)) mice. Wild-type (MT(+/+)) mice and MT(-/-) mice were given one intragastric administration of 50mg/kg PQ for 24h, and it was revealed that MT(-/-) mice were more susceptible to PQ-induced acute lung injury than MT(+/+) mice evidenced by the following findings. As compared with MT(+/+) mice, MT(-/-) mice presented more severe histopathological lesions in the lung, higher pulmonary malondialdehyde content, and more reduced pulmonary antioxidative enzymes activities. PQ also induced more apoptosis in pneumocytes from MT(-/-) mice, and the expressions of apoptosis-related proteins Bax, Bcl-2, cleaved-caspase-3, and the ratio of Bax/Bcl-2 were all more significantly increased in PQ-treated MT(-/-) mice. Our results clearly demonstrate that endogenous MT can attenuate PQ-induced acute lung injury, possibly through the mechanisms of anti-oxidation and anti-apoptosis.

Overexpression of ALTERNATIVE OXIDASE1a alleviates mitochondria-dependent programmed cell death induced by aluminium phytotoxicity in Arabidopsis

Alternative oxidase (AOX) is a terminal oxidase found in all plants, and functions to maintain the electron flux and reduce the production of reactive oxygen species (ROS). Our previous study demonstrated that aluminium (Al) treatment could induce increased expression of the AOX1a gene, but the mechanism of how AOX1a participates in the regulation of Al-induced programmed cell death (PCD) is still not clear. To investigate the possible mechanism, mitochondrial ROS production and the behaviour of mitochondria, as well as caspase-3-like activation were monitored under Al treatment in wild-type (WT), AOX1a-lacking (aox1a), and AOX1a-overexpressing (AOX1a-OE) Arabidopsis. Our results showed that Al treatment increased the expression of AOX1a at both the transcriptional and translational levels. Overexpression of AOX1a reduced mitochondrial ROS production by maintaining the mitochondrial electron flux, and alleviated subsequent mitochondrial dysfunction and caspase-3-like activation in Al-induced PCD. Moreover, it was found that a change in AOX1a level could influence the expression levels of downstream functional genes that play protective roles in Al-induced PCD. Experiments using mutants and inhibitors demonstrated that superoxide anion (O2 (-)) derived from mitochondria was involved in Al-induced upregulation of AOX1a gene expression. Taken together, these results indicated that overexpression of AOX1a alleviated Al-induced PCD by maintaining mitochondrial function and promoting the expression of protective functional genes, providing new insights into the signalling cascades that modulate the Al phytotoxicity mechanism.

Effect of paraquat-induced oxidative stress on gene expression and aging of the filamentous ascomycete Podospora anserina

Aging of biological systems is influenced by various factors, conditions and processes. Among others, processes allowing organisms to deal with various types of stress are of key importance. In particular, oxidative stress as the result of the generation of reactive oxygen species (ROS) at the mitochondrial respiratory chain and the accumulation of ROS-induced molecular damage has been strongly linked to aging. Here we view the impact of ROS from a different angle: their role in the control of gene expression. We report a genome-wide transcriptome analysis of the fungal aging model Podospora anserina grown on medium containing paraquat (PQ). This treatment leads to an increased cellular generation and release of H₂O₂, a reduced growth rate, and a decrease in lifespan. The combined challenge by PQ and copper has a synergistic negative effect on growth and lifespan. The data from the transcriptome analysis of the wild type cultivated under PQ-stress and their comparison to those of a longitudinal aging study as well as of a copper-uptake longevity mutant of P. anserina revealed that PQ-stress leads to the up-regulation of transcripts coding for components involved in mitochondrial remodeling. PQ also affects the expression of copper-regulated genes suggesting an increase of cytoplasmic copper levels as it has been demonstrated earlier to occur during aging of P. anserina and during senescence of human fibroblasts. This effect may result from the induction of the mitochondrial permeability transition pore via PQ-induced ROS, leading to programmed cell death as part of an evolutionary conserved mechanism involved in biological aging and lifespan control.

The relation between oxidative stress, inflammation, and neopterin in the paraquat-induced lung toxicity

Paraquat (PQ) is a well-known quaternary nitrogen herbicide. The major target organ in PQ poisoning is the lung. Reactive oxygen species (ROS) and inflammation play a crucial role in the development of PQ-induced pulmonary injury. Neopterin is synthesized in macrophage by interferon γ and other cytokines. We aimed to evaluate the utility of neopterin as a diagnostic marker in PQ-induced lung toxicity. Sprague Dawley rats were randomly divided into two groups (sham and PQ), administered intraperitoneally 1 mL saline and PQ (15 mg/kg/mL) respectively. Blood samples and lungs were collected for analyses. Lung injury and fibrosis were seen in the PQ group. Serum total antioxidant capacity, lactate dehydrogenase (LDH), and lung transforming growth factor-1β (TGF-1β) levels were significantly higher than the sham group (in all, p < 0.001). In addition, in the PQ group, serum neopterin and lung malondialdehyde (MDA) levels were also significantly higher than the sham group (in all, p = 0.001). Serum neopterin levels were correlated with LDH activities, lung MDA, lung TGF-1β levels, and the degree of lung injury. These findings demonstrated that oxidative stress, reduction of antioxidant capacity, and inflammation play a crucial role in the PQ-induced lung injury. Elevated serum neopterin levels may be a prognostic parameter to determine extends of PQ-induced lung toxicity. Further studies may be performed to clarify the role of neopterin by different doses of PQ.

Celastrol targets proteostasis and acts synergistically with a heat-shock protein 90 inhibitor to kill human glioblastoma cells

Glioblastoma multiforme is a devastating disease of the central nervous system and, at present, no effective therapeutic interventions have been identified. Celastrol, a natural occurring triterpene, exhibits potent anti-tumor activity against gliomas in xenograft mouse models. In this study, we describe the cell death mechanism employed by celastrol and identify secondary targets for effective combination therapy against glioblastoma cell survival. In contrast to the previously proposed reactive oxygen species (ROS)-dependent mechanism, cell death in human glioblastoma cells is shown here to be mediated by alternate signal transduction pathways involving, but not fully dependent on, poly(ADP-ribose) polymerase-1 and caspase-3. Our studies indicate that celastrol promotes proteotoxic stress, supported by two feedback mechanisms: (i) impairment of protein quality control as revealed by accumulation of polyubiquitinated aggregates and the canonical autophagy substrate, p62, and (ii) the induction of heat-shock proteins, HSP72 and HSP90. The Michael adduct of celastrol and N-acetylcysteine, 6-N-acetylcysteinyldihydrocelastrol, had no effect on p62, nor on HSP72 expression, confirming a thiol-dependent mechanism. Restriction of protein folding stress with cycloheximide was protective, while combination with autophagy inhibitors did not sensitize cells to celastrol-mediated cytotoxicity. Collectively, these findings imply that celastrol targets proteostasis by disrupting sulfyhydryl homeostasis, independently of ROS, in human glioblastoma cells. This study further emphasizes that targeting proteotoxic stress responses by inhibiting HSP90 with 17-N-Allylamino-17-demethoxygeldanamycin sensitizes human glioblastoma to celastrol treatment, thereby serving as a novel synergism to overcome drug resistance.

Betanin attenuates paraquat-induced liver toxicity through a mitochondrial pathway

We attempted to determine whether betanin (from natural pigments) that has anti-oxidant properties would be protective against paraquat-induced liver injury in Sprague-Dawley rats. Paraquat was injected intraperitoneally into rats to induce liver toxicity. The rats were randomly divided into four groups: a control group, a paraquat group, and two groups that received betanin at doses of 25 and 100mg/kg/day three days before and two days after they were administered paraquat. We evaluated liver histopathology, serum liver enzymatic activities, oxidative stress, cytochrome P450 (CYP) 3A2 mRNA expression, and mitochondrial damage. The rats that were injected with paraquat incurred liver injury, evidenced by histological changes and elevated serum aspartate aminotransferase and alanine aminotransferase levels; paraquat also led to oxidative stress, an increase of cytochrome P450 3A2 mRNA expression, and mitochondrial damage, indicated by mitochondrial membrane swelling, reduced mitochondrial cytochrome C, and apoptosis-inducing factor protein levels. Pathological damage and all of the above mentioned markers were lesser in the animals treated with betanin than in those who received paraquat alone. Betanin had a protective effect against paraquat-induced liver damage in rats. The mechanism of the protection appears to be the inhibition of CYP 3A2 expression and protection of mitochondria.

Antioxidant gene therapy against neuronal cell death

Oxidative stress is a common hallmark of neuronal cell death associated with neurodegenerative disorders such as Alzheimer's disease, Parkinson's disease, as well as brain stroke/ischemia and traumatic brain injury. Increased accumulation of reactive species of both oxygen (ROS) and nitrogen (RNS) has been implicated in mitochondrial dysfunction, energy impairment, alterations in metal homeostasis and accumulation of aggregated proteins observed in neurodegenerative disorders, which lead to the activation/modulation of cell death mechanisms that include apoptotic, necrotic and autophagic pathways. Thus, the design of novel antioxidant strategies to selectively target oxidative stress and redox imbalance might represent important therapeutic approaches against neurological disorders. This work reviews the evidence demonstrating the ability of genetically encoded antioxidant systems to selectively counteract neuronal cell loss in neurodegenerative diseases and ischemic brain damage. Because gene therapy approaches to treat inherited and acquired disorders offer many unique advantages over conventional therapeutic approaches, we discussed basic research/clinical evidence and the potential of virus-mediated gene delivery techniques for antioxidant gene therapy.

Brain mitochondria from DJ-1 knockout mice show increased respiration-dependent hydrogen peroxide consumption

Mutations in the DJ-1 gene have been shown to cause a rare autosomal-recessive genetic form of Parkinson's disease (PD). The function of DJ-1 and its role in PD development has been linked to multiple pathways, however its exact role in the development of PD has remained elusive. It is thought that DJ-1 may play a role in regulating reactive oxygen species (ROS) formation and overall oxidative stress in cells through directly scavenging ROS itself, or through the regulation of ROS scavenging systems such as glutathione (GSH) or thioredoxin (Trx) or ROS producing complexes such as complex I of the electron transport chain. Previous work in this laboratory has demonstrated that isolated brain mitochondria consume H2O2 predominantly by the Trx/Thioredoxin Reductase (TrxR)/Peroxiredoxin (Prx) system in a respiration dependent manner (Drechsel et al., Journal of Biological Chemistry, 2010). Therefore we wanted to determine if mitochondrial H2O2 consumption was altered in brains from DJ-1 deficient mice (DJ-1(-/-)). Surprisingly, DJ-1(-/-) mice showed an increase in mitochondrial respiration-dependent H2O2 consumption compared to controls. To determine the basis of the increased H2O2 consumption in DJ1(-/-) mice, the activities of Trx, Thioredoxin Reductase (TrxR), GSH, glutathione disulfide (GSSG) and glutathione reductase (GR) were measured. Compared to control mice, brains from DJ-1(-/-) mice showed an increase in (1) mitochondrial Trx activity, (2) GSH and GSSG levels and (3) mitochondrial glutaredoxin (GRX) activity. Brains from DJ-1(-/-) mice showed a decrease in mitochondrial GR activity compared to controls. The increase in the enzymatic activities of mitochondrial Trx and total GSH levels may account for the increased H2O2 consumption observed in the brain mitochondria in DJ-1(-/-) mice perhaps as an adaptive response to chronic DJ-1 deficiency.

Nicotinamide nucleotide transhydrogenase (Nnt) links the substrate requirement in brain mitochondria for hydrogen peroxide removal to the thioredoxin/peroxiredoxin (Trx/Prx) system

Mitochondrial reactive oxygen species are implicated in the etiology of multiple neurodegenerative diseases, including Parkinson disease. Mitochondria are known to be net producers of ROS, but recently we have shown that brain mitochondria can consume mitochondrial hydrogen peroxide (H2O2) in a respiration-dependent manner predominantly by the thioredoxin/peroxiredoxin system. Here, we sought to determine the mechanism linking mitochondrial respiration with H2O2 catabolism in brain mitochondria and dopaminergic cells. We hypothesized that nicotinamide nucleotide transhydrogenase (Nnt), which utilizes the proton gradient to generate NADPH from NADH and NADP(+), provides the link between mitochondrial respiration and H2O2 detoxification through the thioredoxin/peroxiredoxin system. Pharmacological inhibition of Nnt in isolated brain mitochondria significantly decreased their ability to consume H2O2 in the presence, but not absence, of respiration substrates. Nnt inhibition in liver mitochondria, which do not require substrates to detoxify H2O2, had no effect. Pharmacological inhibition or lentiviral knockdown of Nnt in N27 dopaminergic cells (a) decreased H2O2 catabolism, (b) decreased NADPH and increased NADP(+) levels, and (c) decreased basal, spare, and maximal mitochondrial oxygen consumption rates. Nnt-deficient cells possessed higher levels of oxidized mitochondrial Prx, which rendered them more susceptible to steady-state increases in H2O2 and cell death following exposure to subtoxic levels of paraquat. These data implicate Nnt as the critical link between the metabolic and H2O2 antioxidant function in brain mitochondria and suggests Nnt as a potential therapeutic target to improve the redox balance in conditions of oxidative stress associated with neurodegenerative diseases.

New insights into antioxidant strategies against paraquat toxicity

Paraquat (PQ, 1,1'-dimethyl-4-4'-bipyridinium dichloride) is a highly toxic quaternary ammonium herbicide widely used in agriculture, it exerts its toxic effects mainly because of its redox cycle through the production of superoxide anions in organisms, leading to an imbalance in the redox state of the cell causing oxidative damage and finally cell death. The contribution of mitochondrial dysfunction including increased production of reactive oxygen species besides the reduction in oxygen consumption as well as in the activity of some respiratory complexes has emerged as a key component in the mechanisms through which PQ induces cell death. Although several aspects of PQ-mitochondria interaction remain to be clarified, recent advances have been conducted with reproducible results. Currently, there is no treatment for PQ poisoning; however, several studies taking into account oxidative stress as the main mechanism of PQ-induced toxicity suggest an antioxidant therapy as a viable alternative. In fact, it has been shown that the antioxidants naringin, sylimarin, edaravone, Bathysa cuspidata extracts, alpha-lipoic acid, pirfenidone, lysine acetylsalicylate, selenium, quercetin, C-phycocyanin, bacosides, and vitamin C may be useful in the treatment against PQ toxicity. The main mechanisms involved in the protective effect of these antioxidants include the reduction of oxidative stress and inflammation and the induction of antioxidant defenses. Interestingly, recent findings suggest that the induction of nuclear factor erythroid like-2 (Nrf2), a major regulator of the antioxidant response, by some of the above-mentioned antioxidants, has been involved in the protective effect against PQ-induced toxicity.

The antidote effect of quinone oxidoreductase 2 inhibitor against paraquat-induced toxicity in vitro and in vivo

BACKGROUND AND PURPOSE The mechanisms of paraquat (PQ)-induced toxicity are poorly understood and PQ poisoning is often fatal due to a lack of effective antidotes. In this study we report the effects of N-[2-(2-methoxy-6H-dipyrido{2,3-a:3,2-e}pyrrolizin-11-yl)ethyl]-2-furamide (NMDPEF), a melatonin-related inhibitor of quinone oxidoreductase2 (QR2) on the toxicity of PQ in vitro & in vivo. EXPERIMENTAL APPROACH Prevention of PQ-induced toxicity was tested in different cells, including primary pneumocytes and astroglial U373 cells. Cell death and reactive oxygen species (ROS) were analysed by flow cytometry and fluorescent probes. QR2 silencing was achieved by lentiviral shRNAs. PQ (30 mg·kg(-1)) and NMDPEF were administered i.p. to Wistar rats and animals were monitored for 28 days. PQ toxicity in the substantia nigra (SN) was tested by a localized microinfusion and electrocorticography. QR2 activity was measured by fluorimetry of N-benzyldihydronicotinamide oxidation. KEY RESULTS NMDPEF potently antagonized non-apoptotic PQ-induced cell death, ROS generation and inhibited cellular QR2 activity. In contrast, the cytoprotective effect of melatonin and apocynin was limited and transient compared with NMDPEF. Silencing of QR2 attenuated PQ-induced cell death and reduced the efficacy of NMDPEF. Significantly, NMDPEF (4.5 mg·kg(-1)) potently antagonized PQ-induced systemic toxicity and animal mortality. Microinfusion of NMDPEF into SN prevented severe behavioural and electrocortical effects of PQ which correlated with inhibition of malondialdehyde accumulation in cells and tissues. CONCLUSIONS AND IMPLICATIONS NMDPEF protected against PQ-induced toxicity in vitro and in vivo, suggesting a key role for QR2 in the regulation of oxidative stress.

PGC-1α signaling coordinates susceptibility to metabolic and oxidative injury in the inner retina

Retinal ganglion cells (RGCs), used as a common model of central nervous system injury, are particularly vulnerable to metabolic and oxidative damage. However, molecular mechanisms underlying this sensitivity have not been determined in vivo. PGC-1α (encoded by PPARGC1A) regulates adaptive metabolism and oxidative stress responses in a tissue- and cell-specific manner. Aberrant PGC-1α signaling is implicated in neurodegeneration, but the mechanism underlying its role in central nervous system injury remains unclear. We provide evidence from a mouse model that PGC-1α expression and activity are induced in adult retina in response to metabolic and oxidative challenge. Deletion of Ppargc1a dramatically increased RGC loss, in association with dysregulated expression of PGC-1α target metabolic and oxidative stress response genes, including Hmox1 (encoding HO-1), Tfam, and Vegfa. Vehicle-treated and naive Ppargc1a(-/-) mice also showed mild RGC loss, and surprisingly prominent and consistent retinal astrocyte reactivity. These cells critically regulate metabolic homeostasis in the inner retina. We show that PGC-1α signaling (not previously studied in glia) regulates detoxifying astrocyte responses to hypoxic and oxidative stresses. Finally, PGC-1α expression was modulated in the inner retina with age and in a model of chronic optic neuropathy. These data implicate PGC-1α signaling as an important regulator of astrocyte reactivity and RGC homeostasis to coordinate pathogenic susceptibility to metabolic and oxidative injury in the inner retina.

Edaravone decreases paraquat toxicity in a549 cells and lung isolated mitochondria

Edaravone, an antioxidant and radical scavenger, showed protective effects against oxidative stress-like condition. Paraquat (PQ) is toxic herbicide considerable evidence suggests that oxidative stress and mitochondrial dysfunction contribute to PQ toxicity. In this study, protective effect of edaravone against PQ induced toxicity and reactive oxygen species (ROS) generation in A549 cells and lung isolated mitochondria were evaluated. A549 cells and lung isolated mitochondria were divided into control group, PQ group, edaravone group and PQ plus edaravone-pretreated group. Cellular and mitochondrial viability assayed using MTT test and ROS generations in both cellular and mitochondrial fraction were determined by fluorometry using DCFH-DA as indicator. Our results showed that edaravone (5-100 µM) prevented PQ (500 µM) induced cytotoxicity in A549 cells that the best protective effect was observed at concentration of 50 µM of edaravone. In addition, PQ-induced ROS generation in A549 cells significantly inhibited by edaravone. Moreover, PQ decreased mitochondria viability and also increased ROS generation in lung isolated mitochondria that edaravone (25-400 µM) markedly inhibited these toxic effects. In overall, the results of this study suggest that lung mitochondria maintenance is essential for maintaining PQt cytotoxicity and Edaravone is a protective drug against PQ toxicity in-vitro.

ROS detoxification and proinflammatory cytokines are linked by p38 MAPK signaling in a model of mature astrocyte activation

Astrocytes are the most abundant glial cell in the retinal nerve fiber layer (NFL) and optic nerve head (ONH), and perform essential roles in maintaining retinal ganglion cell (RGC) detoxification and homeostasis. Mature astrocytes are relatively quiescent, but rapidly undergo a phenotypic switch in response to insult, characterized by upregulation of intermediate filament proteins, loss of glutamate buffering, secretion of pro-inflammatory cytokines, and increased antioxidant production. These changes result in both positive and negative influences on RGCs. However, the mechanism regulating these responses is still unclear, and pharmacologic strategies to modulate select aspects of this switch have not been thoroughly explored. Here we describe a system for rapid culture of mature astrocytes from the adult rat retina that remain relatively quiescent, but respond robustly when challenged with oxidative damage, a key pathogenic stress associated with inner retinal injury. When primary astrocytes were exposed to reactive oxygen species (ROS) we consistently observed characteristic changes in activation markers, along with increased expression of detoxifying genes, and secretion of proinflammatory cytokines. This in vitro model was then used for a pilot chemical screen to target specific aspects of this switch. Increased activity of p38α and β Mitogen Activated Protein Kinases (MAPKs) were identified as a necessary signal regulating expression of MnSOD, and heme oxygenase 1 (HO-1), with consequent changes in ROS-mediated injury. Additionally, multiplex cytokine profiling detected p38 MAPK-dependent secretion of IL-6, MCP-1, and MIP-2α, which are proinflammatory signals recently implicated in damage to the inner retina. These data provide a mechanism to link increased oxidative stress to proinflammatory signaling by astrocytes, and establish this assay as a useful model to further dissect factors regulating the reactive switch.

Redox-sensitive glycogen synthase kinase 3β-directed control of mitochondrial permeability transition: rheostatic regulation of acute kidney injury

Mitochondrial dysfunction plays a pivotal role in necroapoptotic cell death and in the development of acute kidney injury (AKI). Evidence suggests that glycogen synthase kinase (GSK) 3β resides at the nexus of multiple signaling pathways implicated in the regulation of mitochondrial permeability transition (MPT). In cultured renal tubular epithelial cells, a discrete pool of GSK3β was detected in mitochondria. Coimmunoprecipitation assay confirmed that GSK3β physically interacts with cyclophilin F and voltage-dependent anion channel (VDAC), key MPT regulators that possess multiple GSK3β phosphorylation consensus motifs, suggesting that GSK3β has a direct control of MPT. Upon a strong burst of reactive oxygen species elicited by the pro-oxidant herbicide paraquat, the activity of the redox-sensitive GSK3β was drastically enhanced. This was accompanied by augmented phosphorylation of cyclophilin F and VDAC, associated with MPT and cell death. Inhibition of GSK3β by either the selective inhibitor 4-Benzyl-2-methyl-1,2,4-thiadiazolidine-3,5-dione (TDZD-8) or forced expression of a kinase-dead mutant obliterated paraquat-induced phosphorylation of cyclophilin F and VDAC, prevented MPT, and improved cellular viability. Conversely, ectopic expression of a constitutively active GSK3β amplified the effect of paraquat on cyclophilin F and VDAC phosphorylation and sensitized cells to paraquat-induced MPT and death. In vivo, paraquat injection elicited marked oxidant stress in the kidney and resulted in acute kidney dysfunction and massive tubular apoptosis and necrosis. Consistent with in vitro findings, the activity of GSK3β was augmented in the kidney after paraquat injury, associated with increased phosphorylation of cyclophilin F and VDAC and sensitized MPT. TDZD-8 blocked GSK3β activity in the kidney, intercepted cyclophilin F and VDAC phosphorylation, prevented MPT, attenuated tubular cell death, and ameliorated paraquat-induced AKI. Our data suggest that the redox-sensitive GSK3β regulates renal tubular injury in AKI by controlling the activity of MPT regulators.

Sigma-1 receptor chaperone at the ER-mitochondrion interface mediates the mitochondrion-ER-nucleus signaling for cellular survival

The membrane of the endoplasmic reticulum (ER) of a cell forms contacts directly with mitochondria whereby the contact is referred to as the mitochondrion-associated ER membrane or the MAM. Here we found that the MAM regulates cellular survival via an MAM-residing ER chaperone the sigma-1 receptor (Sig-1R) in that the Sig-1R chaperones the ER stress sensor IRE1 to facilitate inter-organelle signaling for survival. IRE1 is found in this study to be enriched at the MAM in CHO cells. We found that IRE1 is stabilized at the MAM by Sig-1Rs when cells are under ER stress. Sig-1Rs stabilize IRE1 and thus allow for conformationally correct IRE1 to dimerize into the long-lasting, activated endonuclease. The IRE1 at the MAM also responds to reactive oxygen species derived from mitochondria. Therefore, the ER-mitochondrion interface serves as an important subcellular entity in the regulation of cellular survival by enhancing the stress-responding signaling between mitochondria, ER, and nucleus.