The role of oxidative stress in paraquat-induced neurotoxicity in rats: protection by non peptidyl superoxide dismutase mimetic

Proximity to residential and workplace pesticides application and the risk of progression of Parkinson's diseases in Central California

BACKGROUND

Pesticide exposure has consistently been associated with Parkinson's disease (PD) onset. Yet, fewer epidemiologic studies have examined whether pesticides influence PD motor and non-motor symptom progression.

OBJECTIVES

Using a geographic information system tool that integrates agricultural pesticide use reports and land use records to derive ambient exposures at residences and workplaces, we assessed associations between specific pesticides previously related to PD onset with PD symptom progression in two PD patient cohorts living in agricultural regions of California.

METHODS

We calculated the pounds of pesticide applied agriculturally near each participant's residential or occupational addresses from 1974 to the year of PD diagnosis, using a geographic information system tool that links the California Pesticide Use Reports database to land use data. We examined 53 pesticides selected a priori as they have previously been associated with PD onset. We longitudinally followed two PD patient cohorts (PEG1 N = 242, PEG2 N = 259) for an average of 5.0 years (SD ± 3.5) and 2.7 years (SD ± 1.6) respectively and assessed PD symptoms using the movement disorder specialist-administered Unified Parkinson's disease Rating Scale part III (UPDRS), Mini-Mental State Examination (MMSE), and Geriatric Depression Scale (GDS). Weighted time-to-event regression models were implemented to estimate effects.

RESULTS

Ten agricultural pesticides, including copper sulfate (pentahydrate), 2-methyl-4-chlorophenoxyacetic acid (MCPA) dimethylamine salt, tribufos, sodium cacodylate, methamidophos, ethephon, propargite, bromoxynil octanoate, monosodium methanearsonate (MSMA), and dicamba, were associated with faster symptom progression. Among these pesticides, residential or workplace proximity to higher amounts of copper sulfate (pentahydrate) and MCPA (dimethylamine salt) was associated with all three progression endpoints (copper sulfate: HRs = 1.22-1.36, 95 % CIs = 1.03-1.73; MCPA: HRs = 1.27-1.35, 95 % CIs = 1.02-1.70).

CONCLUSIONS

Our findings suggest that pesticide exposure may not only be relevant for PD onset but also PD progression phenotypes. We have implicated ten specific pesticide active ingredients in faster PD motor and non-motor decline.

Potentiation of paraquat toxicity by inhibition of the antioxidant defenses and protective effect of the natural antioxidant, 4-hydroxyisopthalic acid in Drosophila melanogaster

Exposure to pesticides such as paraquat (PQ) is known to induce oxidative stress-mediated damage, which is implicated in neurodegenerative diseases. The antioxidant enzymes are part of the endogenous defense mechanisms capable of protecting against oxidative damage, and down-regulation of these enzymes results in elevated oxidative stress. In this study, we have evaluated the protective action of 4-hydroxyisophthalic acid (DHA-I), a novel bioactive molecule from the roots of D. hamiltonii, against PQ toxicity and demonstrated the protective role of endogenous antioxidant enzymes under the condition of oxidative stress using Drosophila model. The activity of the major antioxidant enzymes, superoxide dismutase 1 (SOD1) and catalase, was suppressed either by RNAi-mediated post transcriptional gene silencing or chemical inhibition. With the decreased in vivo activity of either SOD1 or catalase, Drosophila exhibited hypersensitivity to PQ toxicity, demonstrating the essential role of antioxidant enzymes in the mechanism of defense against PQ-induced oxidative stress. Dietary supplementation of DHA-I increased the resistance of Drosophila depleted in either SOD1 or catalase to PQ toxicity. Enhanced survival of flies against PQ toxicity indicates the protective role of DHA-I against oxidative stress-mediated damage under the condition of compromised antioxidant defenses.

Neurotoxicological Profiling of Paraquat in Zebrafish Model

Paraquat is a polar herbicide protecting plant products against invasive species, it requires careful manipulation and restricted usage because of its harmful potentials. Exposure to paraquat triggers oxidative damage in dopaminergic neurons and subsequently causes a behavioral defect in vivo. Thereby, persistent exposure to paraquat is known to increase Parkinson's disease risk by dysregulating dopaminergic systems in humans. Therefore, most studies have focused on the dopaminergic systems to elucidate the neurotoxicological mechanism of paraquat poisoning, and more comprehensive neurochemistry including histaminergic, serotonergic, cholinergic, and GABAergic systems has remained unclear. Therefore, in this study, we investigated the toxicological potential of paraquat poisoning using a variety of approaches such as toxicokinetic profiles, behavioral effects, neural activity, and broad-spectrum neurochemistry in zebrafish larvae after short-term exposure to paraquat and we performed the molecular modeling approach. Our results showed that paraquat was slowly absorbed in the brain of zebrafish after oral administration of paraquat. In addition, paraquat toxicity resulted in behavioral impairments, namely, reduced motor activity and led to abnormal neural activities in zebrafish larvae. This locomotor deficit came with a dysregulation of dopamine synthesis induced by the inhibition of tyrosine hydroxylase activity, which was also indirectly confirmed by molecular modeling studies. Furthermore, short-term exposure to paraquat also caused simultaneous dysregulation of other neurochemistry including cholinergic and serotonergic systems in zebrafish larvae. The present study suggests that this neurotoxicological profiling could be a useful tool for understanding the brain neurochemistry of neurotoxic agents that might be a potential risk to human and environmental health.

Paraquat initially damages cochlear support cells leading to anoikis-like hair cell death

Paraquat (PQ), one of the most widely used herbicides, is extremely dangerous because it generates the highly toxic superoxide radical. When paraquat was applied to cochlear organotypic cultures, it not only damaged the outer hair cells (OHCs) and inner hair cells (IHCs), but also caused dislocation of the hair cell rows. We hypothesized that the dislocation arose from damage to the support cells (SCs) that anchors hair cells within the epithelium. To test this hypothesis, rat postnatal cochlear cultures were treated with PQ. Shortly after PQ treatment, the rows of OHCs separated from one another and migrated radially away from IHCs suggesting loss of cell-cell adhesion that hold the hair cells in proper alignment. Hair cells dislocation was associated with extensive loss of SCs in the organ of Corti, loss of tympanic border cells (TBCs) beneath the basilar membrane, the early appearance of superoxide staining and caspase-8 labeling in SCs below the OHCs and disintegration of E-cadherin and β-catenin in the organ of Corti. Damage to the TBCs and SCs occurred prior to loss of OHC or IHC loss suggesting a form of detachment-induced apoptosis referred to as anoikis.

Chronic low-dose pro-oxidant treatment stimulates transcriptional activity of telomeric retroelements and increases telomere length in Drosophila

It has been proposed that oxidative stress, elicited by high levels of reactive oxygen species, accelerates telomere shortening by erosion of telomeric DNA repeats. While most eukaryotes counteract telomere shortening by telomerase-driven addition of these repeats, telomeric loss in Drosophila is compensated by retrotransposition of the telomeric retroelements HeT-A, TART and TAHRE to chromosome ends. In this study we tested the effect of chronic exposure of flies to non-/sub-lethal doses of paraquat, which is a redox cycling compound widely used to induce oxidative stress in various experimental paradigms including telomere length analyses. Indeed, chronic paraquat exposure for five generations resulted in elevated transcriptional activity of both telomeric and non-telomeric transposable elements, and extended telomeric length in the tested fly lines. We propose that low oxidative stress leads to increased telomere length within Drosophila populations. For a mechanistic understanding of the observed phenomenon we discuss two scenarios: adaption, acting through a direct stimulation of telomere extension, or positive selection favoring individuals with longer telomeres within the population.

Antioxidant activity of oleuropein and semisynthetic acetyl-derivatives determined by measuring malondialdehyde in rat brain

OBJECTIVES

The purpose of this study was the evaluation of the antioxidant activity of natural and semisynthetic polyphenol derivatives from Olea europea L., by assessing malondialdehyde (MDA), an important marker of oxidative stress.

METHODS

Polyphenol as hydroxytyrosol, oleuropein, oleuropein aglycone as mix of four tautomeric forms and their respective acetyl-derivatives were obtained from olive leaves using semisynthetic protocols. These compounds were administered intraperitoneally to Wistar rats treated with paraquat, an herbicide which is able to cause oxidative stress after central administration. Malondialdehyde was derivatized with 2,4-dinitrophenylhydrazine to produce hydrazone that was purified by solid-phase extraction. Using high-performance liquid chromatography coupled with a diode array, free and total MDA was measured on homogenate rat brain as marker of lipid peroxidation. The analytical method was fully validated and showed linearity in the tested concentration range, with detection limit of 5 ng/ml. Recovery ranged from 94.1 to 105.8%.

KEY FINDINGS

Both natural and semisynthetic polyphenol derivatives from a natural source as olive leaves were able to reduce MDA detection. The more lipophilic acetyl-derivatives showed an antioxidant activity greater than parent compounds. This potency seems to put in evidence a strict correlation between lipophilicity and bioavailability.

Mitochondrial Dysfunction in Parkinson’s Disease

Parkinson’s disease (PD) is one of the most common neurodegenerative disorders where oxidative stress and mitochondrial dysfunction have been implicated as etiological factors. Mitochondria are the major producers of reactive oxygen species (ROS) that can have damaging effects to cellular macromolecules leading to neurodegeneration. The most compelling evidence for the role of mitochondria in the pathogenesis of PD has been derived from toxicant-induced models of parkinsonism. Over the years, epidemiological studies have suggested a link between exposure to environmental toxins such as pesticides and the risk of developing PD. Data from human and experimental studies involving the use of chemical agents like paraquat, diquat, 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine, rotenone and maneb have provided valuable insight into the underlying mitochondrial mechanisms contributing to PD and associated neurodegeneration. In this review, we have discussed the role of mitochondrial ROS and dysfunction in the pathogenesis of PD with a special focus on environmental agent-induced parkinsonism. We have described the various mitochondrial mechanisms by which such chemicals exert neurotoxicity, highlighting some landmark epidemiological and experimental studies that support the role of mitochondrial ROS and oxidative stress in contributing to these effects. Finally, we have discussed the significance of these studies in understanding the mechanistic underpinnings of PD-related dopaminergic neurodegeneration.

A drastic superoxide-dependent oxidative stress is prerequisite for the down-regulation of IRP1: Insights from studies on SOD1-deficient mice and macrophages treated with paraquat

Iron regulatory protein 1 (IRP1) is a cytosolic bifunctional [4Fe-4S] protein which exhibits aconitase activity or binds iron responsive elements (IREs) in untranslated regions of specific mRNA encoding proteins involved in cellular iron metabolism. Superoxide radical (O₂^.-) converts IRP1 from a [4Fe-4S] aconitase to a [3Fe-4S] „null” form possessing neither aconitase nor trans-regulatory activity. Genetic ablation of superoxide dismutase 1 (SOD1), an antioxidant enzyme that acts to reduce O₂^.- concentration, revealed a new O₂^.--dependent regulation of IRP1 leading to the reduction of IRP1 protein level and in consequence to the diminution of IRP1 enzymatic and IRE-binding activities. Here, we attempted to establish whether developmental changes in SOD1 activity occurring in the mouse liver, impact IRP1 expression. We show no correlation between hepatic SOD1 activity and IRP1 protein level neither in pre- nor postnatal period probably because the magnitude of developmental fluctuations in SOD1 activity is relatively small. The comparison of SOD1 activity in regards to IRP1 protein level in the liver of threeSOD1 genotypes (Sod1^+/+, Sod1^+/- and Sod1^-/-) demonstrates that only drastic SOD1 deficiency leads to the reduction of IRP1 protein level. Importantly, we found that in the liver of fetuses lacking SOD1, IRP1 is not down-regulated. To investigate O₂^.--dependent regulation of IRP1 in a cellular model, we exposed murine RAW 264.7 and bone marrow-derived macrophages to paraquat, widely used as a redox cycler to stimulate O₂^.-production in cells. We showed that IRP1 protein level as well as aconitase and IRE-binding activities are strongly reduced in macrophages treated with paraquat. The analysis of the expression of IRP1-target genes revealed the increase in L-ferritin protein level resulting from the enhanced transcriptional regulation of the LFt gene and diminished translational repression of L-ferritin mRNA by IRP1. We propose that O₂^.--dependent up-regulation of this cellular protectant in paraquat-treated macrophages may counterbalance iron-related toxic effects of O₂^.-.

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.

Effect of low doses of herbicide paraquat on antioxidant defense in Drosophila

Despite a high toxicity, paraquat is one of the most widely used herbicides in the world. Our study evaluated the effect of paraquat exposure on antioxidant response and locomotion activity in Drosophila melanogaster. We examined the enzymatic activity of superoxide dismutase (SOD) and catalase, and the transcript levels of both enzymes. Flies were exposed to a wide range of paraquat concentrations (0.25 μM to 25 mM) for 12 h. SOD, at both transcript and enzymatic levels, revealed a biphasic dose-response curve with the peak at 2.5 μM paraquat. A similar dose-response curve was observed at transcript levels of catalase. Males revealed higher susceptibility to paraquat exposure, displaying higher lethality, increased levels of SOD activity, and increased peroxide levels than in females. We found that the exposure of females to 2.5 μM paraquat leads to an increase in locomotion activity. Because susceptibility to paraquat was enhanced by mating, the study supports the hypothesis of elevation of stress sensitivity as a physiological cost of reproduction.

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.

Hydrogen peroxide responsive miR153 targets Nrf2/ARE cytoprotection in paraquat induced dopaminergic neurotoxicity

Epidemiological and animal studies suggest that environmental toxins including paraquat (PQ) increase the risk of developing Parkinson's disease (PD) by damaging nigrostriatal dopaminergic neurons. We previously showed that overexpression of a group of microRNAs (miRs) affects the antioxidant promoting factor, Nrf2 and related glutathione-redox homeostasis in SH-SY5Y dopaminergic neurons. Although, dysregulation of redox balance by PQ is well documented, the role for miRs and their impact have not been elucidated. In the current study we investigated whether PQ impairs Nrf2 and its related cytoprotective machinery by misexpression of specific fine tune miRs in SH-SY5Y neurons. Real time PCR analysis revealed that PQ significantly (p<0.05) increased the expression of brain enriched miR153 with an associated decrease in Nrf2 and its function as revealed by decrease in 4× ARE activity and expression of GCLC and NQO1. Also, PQ and H2O2-induced decrease in Nrf2 3' UTR activity was restored on miR153 site mutation suggesting a 3' UTR interacting role. Overexpression of either anti-miR153 or Nrf2 cDNA devoid of 3' UTR prevented PQ and H2O2-induced loss in Nrf2 activity confirming that PQ could cause miR153 to bind to and target Nrf2 3' UTR thereby weakening the cellular antioxidant defense. Adenovirus mediated overexpression of cytoplasmic catalase (Ad cCAT) confirmed that PQ induced miR153 is hydrogen peroxide (H2O2) dependent. In addition, Ad cCAT significantly (p<0.05) negated the PQ induced dysregulation of Nrf2 and function along with minimizing ROS, caspase 3/7 activation and neuronal death. Altogether, these results suggest a critical role for oxidant mediated miR153-Nrf2/ARE pathway interaction in paraquat neurotoxicity. This novel finding facilitates the understanding of molecular mechanisms and to develop appropriate management alternatives to counteract PQ-induced neuronal pathogenesis.

Region specific mitochondrial impairment in mice with widespread overexpression of alpha-synuclein

Parkinson's disease (PD) is characterized by the progressive degeneration of nigrostriatal dopaminergic neurons leading to motor deficits. The mechanisms underlying the preferential vulnerability of nigrostriatal dopaminergic neurons in PD remain poorly understood. Recent evidence supports a role for mitochondrial dysfunction and increased oxidative stress in PD pathogenesis. Genetic and pathological studies also point to alpha-synuclein as a critical factor in both familial and sporadic forms of the disease; alpha-synuclein pathology affects mitochondrial function but is widespread in PD brain, raising the question of its role in the greater vulnerability of nigrostriatal neurons in PD. We have examined mitochondrial function and oxidative damage in mice overexpressing human wild type alpha-synuclein broadly throughout the nervous system under the Thy1 promoter (Thy1-aSyn mice) between 4 and 8months of age. Similar levels of alpha-synuclein accumulation in mitochondria were detected in the ventral midbrain, striatum and cortex of Thy1-aSyn mice. However, analysis of mitochondrial respiration using Seahorse XF analyzer showed defects in mitochondrial respiratory complexes I, II, IV and V specifically in the midbrain, and IV and V in the striatum, of Thy1-aSyn mice compared to wild type littermates; mitochondrial complex I activity assay by ELISA confirmed a 40% inhibition specifically in the ventral midbrain. Mitochondrial dysfunction can contribute to oxidative stress and we observed a 40% increase in 4-hydroxynenal and 2-fold increase in malondialdehyde levels, indicative of a high level of lipid peroxidation, specifically in the ventral midbrain of Thy1-aSyn mice. The levels of peroxiredoxin 2, a neuronal antioxidant enzyme that is involved in removal of H2O2 and other toxic peroxides were decreased in the midbrain whereas its oxidized form increased 4-fold, suggesting that antioxidant defenses were compromised in this region. In contrast, peroxiredoxin 2 increased in the striatum and cortex, which may contribute to their protection in the presence of high levels of alpha-synuclein. Thus, in mice over-expressing alpha-synuclein, mitochondrial dysfunction occurred preferentially in nigrostriatal dopaminergic neurons many months before striatal dopamine loss occurs at 14months of age. This may contribute to a higher level of oxidative stress that overwhelms antioxidant defense in these neurons, leading to their increased vulnerability in PD.

Developmental expression of GPR3 in rodent cerebellar granule neurons is associated with cell survival and protects neurons from various apoptotic stimuli

G-protein coupled receptor 3 (GPR3), GPR6, and GPR12 belong to a family of constitutively active Gs-coupled receptors that activate 3'-5'-cyclic adenosine monophosphate (cAMP) and are highly expressed in the brain. Among these receptors, the endogenous expression of GPR3 in cerebellar granule neurons (CGNs) is increased following development. GPR3 is important for neurite outgrowth and neural maturation; however, the physiological functions of GPR3 remain to be fully elucidated. Here, we investigated the survival and antiapoptotic functions of GPR3 under normal and apoptosis-inducing culture conditions. Under normal culture conditions, CGNs from GPR3-knockout mice demonstrated lower survival than did CGNs from wild-type or GPR3-heterozygous mice. Cerebellar sections from GPR3-/- mice at P7, P14, and P21 revealed more caspase-3-positive neurons in the internal granular layer than in cerebellar sections from wild-type mice. Conversely, in a potassium-deprivation model of apoptosis, increased expression of these three receptors promoted neuronal survival. The antiapoptotic effect of GPR3 was also observed under hypoxic (1% O2/5% CO2) and reactive oxygen species (ROS)-induced apoptotic conditions. We further investigated the signaling pathways involved in the GPR3-mediated antiapoptotic effect. The addition of the PKA inhibitor KT5720, the MAP kinase inhibitor U0126, and the PI3 kinase inhibitor LY294002 abrogated the GPR3-mediated antiapoptotic effect in a potassium-deprivation model of apoptosis, whereas the PKC inhibitor Gö6976 did not affect the antiapoptotic function of GPR3. Furthermore, downregulation of endogenous GPR3 expression in CGNs resulted in a marked reduction in the basal levels of ERK and Akt phosphorylation under normal culture conditions. Finally, we used a transient middle cerebral artery occlusion (tMCAO) model in wild-type and GPR3-knockout mice to determine whether GPR3 expression modulates neuronal survival after brain ischemia. After tMCAO, GPR3-knockout mice exhibited a significantly larger infarct area than did wild-type mice. Collectively, these in vitro and in vivo results suggest that the developmental expression of constitutively active Gs-coupled GPR3 activates the ERK and Akt signaling pathways at the basal level, thereby protecting neurons from apoptosis that is induced by various stimuli.

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.

Mitochondrial dysfunction and oxidative stress in Parkinson's disease

Parkinson's disease (PD) is a movement disorder that is characterized by the progressive degeneration of dopaminergic neurons in substantia nigra pars compacta resulting in dopamine deficiency in the striatum. Although majority of the PD cases are sporadic several genetic mutations have also been linked to the disease thus providing new opportunities to study the pathology of the illness. Studies in humans and various animal models of PD reveal that mitochondrial dysfunction might be a defect that occurs early in PD pathogenesis and appears to be a widespread feature in both sporadic and monogenic forms of PD. The general mitochondrial abnormalities linked with the disease include mitochondrial electron transport chain impairment, alterations in mitochondrial morphology and dynamics, mitochondrial DNA mutations and anomaly in calcium homeostasis. Mitochondria are vital organelles with multiple functions and their dysfunction can lead to a decline in energy production, generation of reactive oxygen species and induction of stress-induced apoptosis. In this review, we give an outline of mitochondrial functions that are affected in the pathogenesis of sporadic and familial PD, and hence provide insights that might be valuable for focused future research to exploit possible mitochondrial targets for neuroprotective interventions in PD.

Defective autophagy in Parkinson's disease: role of oxidative stress

Parkinson's disease (PD) is a paradigmatic example of neurodegenerative disorder with a critical role of oxidative stress in its etiopathogenesis. Genetic susceptibility factors of PD, such as mutations in Parkin, PTEN-induced kinase 1, and DJ-1 as well as the exposure to pesticides and heavy metals, both contribute to altered redox balance and degeneration of dopaminergic neurons in the substantia nigra. Dysregulation of autophagy, a lysosomal-driven process of self degradation of cellular organelles and protein aggregates, is also implicated in PD and PD-related mutations, and environmental toxins deregulate autophagy. However, experimental evidence suggests a complex and ambiguous role of autophagy in PD since either impaired or abnormally upregulated autophagic flux has been shown to cause neuronal loss. Finally, it is generally believed that oxidative stress is a strong proautophagic stimulus. However, some evidence coming from neurobiology as well as from other fields indicate an inhibitory role of reactive oxygen species and reactive nitrogen species on the autophagic machinery. This review examines the scientific evidence supporting different concepts on how autophagy is dysregulated in PD and attempts to reconcile apparently contradictory views on the role of oxidative stress in autophagy regulation. The complex relationship between autophagy and oxidative stress is also considered in the context of the ongoing search for a novel PD therapy.

Systems biology of antioxidants

Understanding the role of oxidative injury will allow for therapy with agents that scavenge ROS (reactive oxygen species) and antioxidants in the management of several diseases related to free radical damage. The majority of free radicals are generated by mitochondria as a consequence of the mitochondrial cycle, whereas free radical accumulation is limited by the action of a variety of antioxidant processes that reside in every cell. In the present review, we provide an overview of the mitochondrial generation of ROS and discuss the role of ROS in the regulation of endothelial and adipocyte function. Moreover, we also discuss recent findings on the role of ROS in sepsis, cerebral ataxia and stroke. These results provide avenues for the therapeutic potential of antioxidants in a variety of diseases.

Toxin models of mitochondrial dysfunction in Parkinson's disease

SIGNIFICANCE

Parkinson's disease (PD) is a neurodegenerative disorder characterized, in part, by the progressive and selective loss of dopaminergic neuron cell bodies within the substantia nigra pars compacta (SNpc) and the associated deficiency of the neurotransmitter dopamine (DA) in the striatum, which gives rise to the typical motor symptoms of PD. The mechanisms that contribute to the induction and progressive cell death of dopaminergic neurons in PD are multi-faceted and remain incompletely understood. Data from epidemiological studies in humans and molecular studies in genetic, as well as toxin-induced animal models of parkinsonism, indicate that mitochondrial dysfunction occurs early in the pathogenesis of both familial and idiopathic PD. In this review, we provide an overview of toxin models of mitochondrial dysfunction in experimental Parkinson's disease and discuss mitochondrial mechanisms of neurotoxicity.

RECENT ADVANCES

A new toxin model using the mitochondrial toxin trichloroethylene was recently described and novel methods, such as intranasal exposure to toxins, have been explored. Additionally, recent research conducted in toxin models of parkinsonism provides an emerging emphasis on extranigral aspects of PD pathology.

CRITICAL ISSUES

Unfortunately, none of the existing animal models of experimental PD completely mimics the etiology, progression, and pathology of human PD.

FUTURE DIRECTIONS

Continued efforts to optimize established animal models of parkinsonism, as well as the development and characterization of new animal models are essential, as there still remains a disconnect in terms of translating mechanistic observations in animal models of experimental PD into bona fide disease-modifying therapeutics for human PD patients.

The potential of synthetic thiourea compound to reduce the cytotoxic and genotoxic effects of paraquat in Hordeum vulgare and cultured human lymphocytes

This work evaluated the ability of one synthetic compound 1-(4-fluorophenylthiocarbamoyl)-4-methyl-piperazine (FTMP), thiourea derivative to reduce cytotoxic and genotoxic effects of free radical inducer paraquat (PQ) in two different test systems Hordeum vulgare and human lymphocytes in vitro. The mitotic index was used as a marker for cytotoxicity. To indicate genotoxicity, chromosome aberrations test and micronucleus induction test were used. FTMP manifested a weak genotoxic effect in both test systems. Clear evidence was obtained that conditioning treatment with FTMP (10(-6) , 5 × 10(-6) , and 10(-5) mol/l) could decrease chromosome aberrations and micronuclei induced by PQ in both test systems. "Aberration hot spots" in heterochromatin containing segments were reduced. The present data show that the thiourea synthetic compound FTMP provides genome protection against the harmful action of oxidative stress inductor PQ. Human lymphocytes were found to be more sensitive to the cytotoxic and clastogenic effects of FTMP conditioning treatment than Hordeum vulgare. Revealing the protective action of newly synthesized compounds could contribute to the improvement of our present knowledge of the mechanisms of mutagenesis and antimutagenesis.

Astrocyte mediated protection of fetal cerebral cortical neurons from rotenone and paraquat

Primary cultures of fetal rat cortical neurons and astrocytes were used to test the hypothesis that astrocyte-mediated control of neuronal glutathione (GSH) is a potent factor in neuroprotection against rotenone and paraquat. In neurons, rotenone (0.025-1 μM) for 4 and 24 h decreased viability as did paraquat (2-100 μM). Rotenone (30 nM) decreased neuronal viability and GSH by 24% and 30%, while ROS were increased by 56%. Paraquat (30 μM) decreased neuronal viability and GSH by 36% and 70%, while ROS were increased by 23%. When neurons were co-cultured with astrocytes, their GSH increased 1.5 fold and 5 fold at 12 and 24 h. Co-culturing with astrocytes blocked neuronal death and damage by rotenone and paraquat. Astrocyte-mediated neuroprotection was dependent on the activity of components of the γ-glutamyl cycle. These studies illustrate the importance of astrocyte-mediated glutathione homeostasis for protection of neurons from rotenone and paraquat and the role of the γ-glutamyl cycle in this neuroprotection.

Edaravone attenuates paraquat-induced lung injury by inhibiting oxidative stress in human type II alveolar epithelial cells

BACKGROUND

Edaravone (3-methyl-1-penyl-2-pyrazolin-5-one) is a potent free-radical scavenger and has the antioxidant ability to inhibit lipid peroxidation. The study aimed to examine the effect of edaravone on protecting the acute injury of human type II alveolar epithelial cells (A549 cells) induced by paraquat (PQ) and the change of production of reactive oxygen species (ROS), malondialdehyde (MDA), superoxide dismutase (SOD).

METHODS

A549 cells were cultured and divided into PQ group (group P), edaravone-treated group (group E) and normal control group (group C). The cells in group P were exposed to paraquat (600 μmol/L), and the cells in group E were treated with edaravone (100 μmol/L) additionally, and no drug intervention was given to the cells in group C. Real-time monitoring by LSCM was used to detect the cell response and the intracellular dynamic change of ROS level in A549 cells after administration of PQ and edaravone. And the levels of SOD and MDA were detected respectively by biochemistry colorimetry. Data were expressed as mean ± standard error of the mean. Statistical analysis was carried out with the soft SPSS 16.0.

RESULTS

The concentration of intracellular ROS significantly increased when PQ was given to A549 cells. But after administration of edaravone, the concentration of intracellular ROS was decreased. Compared to the PQ group, the levels of SOD in the edaravone group were significantly increased while the levels of MDA were markedly decreased.

CONCLUSIONS

Paraquat can increase the oxidative stress, and induce the lipid peroxidation of A549 cells. Edaravone has the effect to scavenge reactive oxygen species, and to protect against the PQ-induced lung toxicity.

Involvement of NADPH oxidase and glutathione in zinc-induced dopaminergic neurodegeneration in rats: similarity with paraquat neurotoxicity

An association between excessive zinc (Zn) accumulation in brain and incidences of Parkinson's disease (PD) has been shown in several epidemiological and experimental investigations. The involvement of nicotinamide adenine dinucleotide phosphate (NADPH) oxidase and glutathione (GSH) in the pathogenesis of PD has also been proposed in a few studies. Despite the implicated role of oxidative stress in PD, the entire mechanism of Zn-induced dopaminergic neurodegeneration has not yet been clearly understood. The present study aimed to investigate the involvement of NADPH oxidase and GSH in Zn-induced dopaminergic neurodegeneration and also to assess its similarity with paraquat (PQ)-induced rat model of PD. Male Wistar rats were treated either with Zn (20 mg/kg; i.p.) or PQ (5 mg/kg; i.p.) in the presence and absence of NADPH oxidase inhibitor, apocynin (10 mg/kg; i.p.) and a GSH precursor, N-acetyl cysteine (NAC; 200 mg/kg; i.p.) either alone or in combination along with the respective controls. Apocynin and/or NAC pre-treatment significantly alleviated Zn- and PQ-induced changes in neurobehavioral deficits, number of dopaminergic neurons and contents of the striatal dopamine and its metabolites. Apocynin and/or NAC also mitigated Zn- and PQ-induced alterations in oxidative stress, NADPH oxidase activation and cytochrome c release, caspases-9 and -3 activation and CD11b expression. The results obtained thus suggest that Zn induces oxidative stress via the activation of NADPH oxidase and depletion of GSH, which in turn activate the apoptotic machinery leading to dopaminergic neurodegeneration similar to PQ.

Paraquat- and rotenone-induced models of Parkinson's disease

Parkinson's disease (PD) is a neurodegenerative disorder mainly characterized by a loss of dopaminergic (DA) neurons in the substantia nigra pars compacta. In recent years, several new genes and environmental factors have been implicated in PD, and their impact on DA neuronal cell death is slowly emerging. However, PD etiology remains unknown, whereas its pathogenesis begins to be clarified as a multifactorial cascade of deleterious factors. Recent epidemiological studies have linked exposure to environmental agents, including pesticides, with an increased risk of developing the disease. As a result, over the last two decades the "environmental hypothesis" of PD has gained considerable interest. This speculates that agricultural chemicals in the environment, by producing selective dopaminergic cell death, can contribute to the development of the disease. However, a causal role for pesticides in the etiology of PD has yet to be definitively established. Importantly, most insights into PD pathogenesis came from investigations performed in experimental models of PD, especially those produced by neurotoxins. This review presents data obtained in our laboratories along with current views on the neurotoxic actions induced by the two most popular parkinsonian pesticide neurotoxins, namely paraquat and rotenone. Although confined to these two chemicals, mechanistic studies underlying dopaminergic cell death are of the utmost importance to identify new drug targets for the treatment of PD.

Molecular mechanisms of pesticide-induced neurotoxicity: Relevance to Parkinson's disease

Pesticides are widely used in agricultural and other settings, resulting in continued human exposure. Pesticide toxicity has been clearly demonstrated to alter a variety of neurological functions. Particularly, there is strong evidence suggesting that pesticide exposure predisposes to neurodegenerative diseases. Epidemiological data have suggested a relationship between pesticide exposure and brain neurodegeneration. However, an increasing debate has aroused regarding this issue. Paraquat is a highly toxic quaternary nitrogen herbicide which has been largely studied as a model for Parkinson's disease providing valuable insight into the molecular mechanisms involved in the toxic effects of pesticides and their role in the progression of neurodegenerative diseases. In this work, we review the molecular mechanisms involved in the neurotoxic action of pesticides, with emphasis on the mechanisms associated with the induction of neuronal cell death by paraquat as a model for Parkinsonian neurodegeneration.

Maneb and paraquat-induced modulation of toxicant responsive genes in the rat liver: comparison with polymorphonuclear leukocytes

Experimental studies have shown that toxicant responsive genes, cytochrome P450s (CYPs) and glutathione S-transferases (GSTs) play a critical role in pesticide-induced toxicity. CYPs play pro-oxidant role and GSTs offer protection in maneb (MB) and paraquat (PQ)-induced brain and lung toxicities. The present study aimed to investigate the effect of repeated exposures of MB and/or PQ on lipid peroxidation (LPO), glutathione content (GSH) and toxicant responsive genes, i.e., CYP1A1, 1A2, 2E1, GSTA4-4, GSTA1-1 and GSTA3-3 in the liver and to correlate the same with polymorphonuclear leukocytes (PMNs). A significant augmentation in LPO and reduction in GSH content was observed in a time of exposure dependent manner in the liver and PMNs of MB and/or PQ treated animals. The expression and catalytic activity of CYP2E1 and GSTA4-4 were significantly increased following MB and/or PQ exposure both in the liver and PMNs. Although the expression of GSTA3-3 was increased, the expression of GSTA1-1 was unaltered after MB and/or PQ treatment in both the liver and PMNs. MB augmented the expression and catalytic activity of CYP1A1 in the liver, however, CYP1A2 was unaffected. PQ, on the other hand, significantly increased hepatic CYP1A2 expression and catalytic activity. MB and/or PQ did not produce any significant changes in CYP1A1 and CYP1A2 in PMNs. The results of the study thus demonstrate that MB and PQ differentially regulate hepatic CYP1A1 and CYP1A2 while LPO, GSH, CYP2E1, GSTA4-4 and GSTA3-3 are modulated in the similar fashions both in the liver and PMNs.

Cytotoxic and genotoxic effects of paraquat in Hordeum vulgare and human lymphocytes in vitro

Two phylogenetically distant types of test-systems-root tip meristems of barley (Hordeum vulgare) and human lymphocytes in vitro were used to detect genotoxicity and cytotoxicity induced by the herbicide paraquat (PQ) in the concentration range (10(-6) to 5 x 10(-4) mol/l). As an endpoint for cytotoxicity the mitotic index (MI) was evaluated. The frequency of chromosome aberrations (CA) and the frequency of micronuclei (MN) were used as endpoints for genotoxicity. A dose-dependent increase of CA and MN was observed in both test systems, although the values for PQ-induced MN were somewhat lower. The increase of the genotoxic effect corresponds to a decrease of mitotic activity. The structurally reconstructed barley karyotype MK14/2034 allowed the allocation of the PQ-specific features of aberration distribution patterns and gave information about which chromosome segments in different chromosomal positions were involved in induced aberrations. Paraquat produced preferably isochromatid breaks and "aberration hot spots" in a restricted number of heterochromatin-containing segments. The comparative analysis of susceptibility in the used test-systems to PQ with respect to its cytotoxic and clastogenic effect showed that the human lymphocytes were more sensitive than Hordeum vulgare.

Chemistry and antihypertensive effects of tempol and other nitroxides

Nitroxides can undergo one- or two-electron reduction reactions to hydroxylamines or oxammonium cations, respectively, which themselves are interconvertible, thereby providing redox metabolic actions. 4-Hydroxy-2,2,6,6-tetramethylpiperidine-N-oxyl (tempol) is the most extensively studied nitroxide. It is a cell membrane-permeable amphilite that dismutates superoxide catalytically, facilitates hydrogen peroxide metabolism by catalase-like actions, and limits formation of toxic hydroxyl radicals produced by Fenton reactions. It is broadly effective in detoxifying these reactive oxygen species in cell and animal studies. When administered intravenously to hypertensive rodent models, tempol caused rapid and reversible dose-dependent reductions in blood pressure in 22 of 26 studies. This was accompanied by vasodilation, increased nitric oxide activity, reduced sympathetic nervous system activity at central and peripheral sites, and enhanced potassium channel conductance in blood vessels and neurons. When administered orally or by infusion over days or weeks to hypertensive rodent models, it reduced blood pressure in 59 of 68 studies. This was accompanied by correction of salt sensitivity and endothelial dysfunction and reduced agonist-evoked oxidative stress and contractility of blood vessels, reduced renal vascular resistance, and increased renal tissue oxygen tension. Thus, tempol is broadly effective in reducing blood pressure, whether given by acute intravenous injection or by prolonged administration, in a wide range of rodent models of hypertension.

Chapter 21 Paraquat-induced production of reactive oxygen species in brain mitochondria

Paraquat (PQ) is a prototypical redox cycling agent commonly used experimentally to generate reactive oxygen species and oxidative stress. Recently, PQ has also come under investigation as a potential environmental neurotoxin associated with increased risk for neurodegenerative disease developing after chronic exposure. The interactions of PQ with mitochondria remain an important aspect of its toxicity, particularly in the brain, although the underlying mechanisms are relatively uncharacterized. Here, we describe the basic measurement of PQ-induced hydrogen peroxide (H(2)O(2)) production in isolated brain mitochondria by use of two independent methods, polarography and fluorometry. The advantages of the use of these two independent methods include the capability to validate results and overcoming limitations in the use of either method exclusively. These simplified in vitro techniques for measurement of mitochondrial-generated H(2)O(2) can be easily applied to other tissues and models.

The involvement of nitric oxide in maneb- and paraquat-induced oxidative stress in rat polymorphonuclear leukocytes

Oxidative stress plays a crucial role in the manifestations of maneb (MB) and paraquat (PQ)-induced toxicity including MB+PQ-induced Parkinson's disease (PD). Polymorphonuclear leukocytes (PMNs) actively participate in the oxidative stress-mediated inflammation and organ toxicity. The present study was undertaken to investigate the MB- and/or PQ-induced alterations in the indices of oxidative stress in rat PMNs. Animals were treated with or without MB and/or PQ in an exposure time dependent manner. In some sets of experiments, the animals were pre-treated with NOS inhibitors N(G)-nitro-L-arginine methyl ester (L-NAME) and aminoguanidine (AG) along with respective controls. A significant increase in myeloperoxidase (MPO), superoxide dismutase (SOD), nitric oxide, iNOS expression and lipid peroxidation (LPO) was observed in PMNs of MB- and/or PQ-treated animals, while catalase and glutathione S-transferase (GST) activities were attenuated. L-NAME and AG significantly reduced the augmented nitrite content, iNOS expression and MPO activity to control level in MB and PQ exposed animals. Although the augmented LPO was also reduced significantly in L-NAME and AG treated rat PMNs, the level was still higher as compared with controls. Alterations induced in SOD and GST activities were not affected by NOS inhibitors. The results thus suggest that MB and/or PQ induce iNOS-mediated nitric oxide production, which in turn increases MPO activity and lipid peroxidation, thereby oxidative stress.

Role of reactive oxygen species in the neurotoxicity of environmental agents implicated in Parkinson's disease

Among age-related neurodegenerative diseases, Parkinson's disease (PD) represents the best example for which oxidative stress has been strongly implicated. The etiology of PD remains unknown, yet recent epidemiological studies have linked exposure to environmental agents, including pesticides, with an increased risk of developing the disease. As a result, the environmental hypothesis of PD has developed, which speculates that chemical agents in the environment are capable of producing selective dopaminergic cell death, thus contributing to disease development. The use of environmental agents such as 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine, rotenone, paraquat, dieldrin, and maneb in toxicant-based models of PD has become increasingly popular and provided valuable insight into the neurodegenerative process. Understanding the unique and shared mechanisms by which these environmental agents act as selective dopaminergic toxicants is critical in identifying pathways involved in PD pathogenesis. In this review, we discuss the neurotoxic properties of these compounds with specific focus on the induction of oxidative stress. We highlight landmark studies along with recent advances that support the role of reactive oxygen and reactive nitrogen species from a variety of cellular sources as potent contributors to the neurotoxicity of these environmental agents. Finally, human risk and the implications of these studies in our understanding of PD-related neurodegeneration are discussed.

Reduction of paraquat-induced renal cytotoxicity by manganese and copper complexes of EGTA and EHPG

Superoxide anion generation plays an important role in the development of paraquat toxicity. Although superoxide dismutase mimetics (SODm) have provided protection against organ injury involving generation of superoxide anions, they often suffer problems, e.g., regarding their bioavailability or potential pro-oxidant activity. The aim here was to investigate and compare the therapeutic potential of two novel SODm, manganese(II) and copper(II) complexes of the calcium chelator ethylenebis(oxyethylenenitrilo)tetraacetic acid (EGTA) and of the contrast agent ethylenebis(hydroxyphenylglycine) (EHPG), against paraquat-induced renal toxicity in vitro. Incubation of renal NRK-52E cells with paraquat (1 mM) for 24 h produced submaximal, yet significant, reduction in cellular viability and cell death and produced significant increases in superoxide anion and hydroxyl radical generation. Manganese and copper complexes of EGTA (10-100 microM) and EHPG (30-100 microM) reduced paraquat-induced renal cell toxicity and reduced superoxide anion and hydroxyl radical generation significantly. Manganese complexes displayed greater efficacy than copper complexes and, at equivalent concentrations, manganese complexed with EHPG provided the greatest protection. Furthermore, these metal complexes did not interfere with the uptake of [methyl-(14)C]paraquat into NRK-52E cells, suggesting that they provided protection against paraquat cytotoxicity via intracellular mechanisms. These complexes did not display cytotoxicity at the concentrations examined. Together, these results suggest that manganese and copper complexes of EGTA and EHPG, and especially the manganese-EHPG complex, could provide benefit against paraquat nephrotoxicity.

Protective effects of a new metalloporphyrin on paraquat-induced oxidative stress and apoptosis in N27 cells

Paraquat (PQ, 1,1'-dimethyl-4,4'-bipyridinium), a widely-used herbicide, has been suggested as a potential etiologic factor for the development of Parkinson's disease. In recent years, many studies have focused on the mechanism(s) of PQ neurotoxicity. In this study, we examined the neuroprotective effect of manganese (III) meso-tetrakis (N,N'-diethylimidazolium) porphyrin (MnTDM), a superoxide dismutase/catalase mimetic, on PQ-induced oxidative stress and apoptosis in 1RB3AN27 (N27) cells, a dopaminergic neuronal cell line. The results indicated that MnTDM significantly attenuated PQ-induced loss of cell viability, glutathione depletion, and reactive oxygen species production. MnTDM also ameliorated PQ-induced morphological nuclear changes of apoptosis and increased rates of apoptosis. In addition, our data provide direct evidence that MnTDM suppressed PQ-induced caspase-3 cleavage, possibly a key event of PQ neurotoxicity. These observations suggested that oxidative stress and apoptosis are implicated in PQ-induced neurotoxicity and this toxicity could be prevented by MnTDM. These findings also proposed a novel therapeutic approach for Parkinson's disease and other disorders associated with oxidative stress.

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 microM) 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.

Pesticide exposure on southwestern Taiwanese with MnSOD and NQO1 polymorphisms is associated with increased risk of Parkinson's disease

BACKGROUND

Hypothetic mechanism of the individual vulnerability to oxidative stress through metabolism of environmental xenobiotics and genotypic polymorphisms has been considered to promote the development of Parkinson's disease (PD). In this case-control study, we determined the role of manganese-containing superoxide dismutase (MnSOD) and NAD(P)H: quinone oxidoreductase 1 (NQO1) genes in PD risk in a population with high prevalence of pesticide exposure.

METHODS

From southwestern region of Taiwan, we enrolled 153 patients with idiopathic PD and 155 healthy control subjects matched for age, sex and origin. Detailed questionnaires of face-to-face interviews among these subjects were collected. PCR-based restriction fragment length polymorphism (RFLP) assays were used to determine the genotypes of MnSOD (-9 T>C) and NQO1 (609 C>T) genes.

RESULTS

Exposure to pesticides associated with PD was significant among patients with an increased odds ratio (OR) of 1.69 (95%CI, 1.07-2.65), and this association remained significant after adjustment for age, sex, and cigarette smoking (aOR=1.68, 95%CI, 1.03-2.76, P=0.023). Considering genetic factors, there were no significant differences in frequencies of both genotypes of MnSOD and NQO1 polymorphisms between PD patients and the control subjects (P>0.05). However, this difference in genotype distribution was significant among subjects who had been exposed to pesticide, with aOR of 2.49 (95%CI, 1.18-5.26, P=0.0072) for MnSOD C allele and aOR of 2.42 (95%CI, 1.16-4.76, P=0.0089) for NQO1 T allele, respectively. Moreover, among subjects exposed to pesticide, the combined MnSOD/NQO1 variant genotype was significantly associated with a 4.09-fold increased risk of PD (95%CI, 1.34-10.64, P=0.0052).

CONCLUSION

Susceptible variants of MnSOD and NQO1 genes may interact with occupational pesticide exposure to increase PD risk in southwestern Taiwanese.

Protective effects of Ginkgo biloba extract on paraquat-induced apoptosis of PC12 cells

Previous studies have suggested that Ginkgo biloba extract (EGb761) has a protective potentiality against apoptosis of neurons or neuron-like cells induced by MPTP. In this study, the effects of EGb761 on PC12 cells injured by paraquat (PQ), a neurotoxin, were tested. The results showed that after incubation of PC12 cells with EGb761 prior to PQ exposure, the PQ-induced decrease of cell viability was significantly reversed, the collapse of mitochondrial membrane potential (MMP) was attenuated and the percentage of apoptotic cells was reduced. Moreover, EGb761 pretreatment evidently increased the numbers of tyrosine hydroxylase (TH) positive and bcl-2 positive cells and degraded the number of caspase-3 positive cells in PQ-injured PC12 cells, in comparison to the treatment with PQ alone. This study indicates that EGb761 has a neuroprotective effect on paraquat-induced apoptosis of PC12 cells. The mechanism underlying the protective effects of EGb761 in PQ-injured PC12 cells might be related to the increase of bcl-2 activation, maintenance of MMP stability and decrease of caspase-3 activation through mitochondria-dependent pathway. The results from this study provide an experimental basis for the potential use of EGb761 in treatment of Parkinson's disease.

Protective effect of NADP-isocitrate dehydrogenase on the paraquat-mediated oxidative inactivation of aconitase in heart mitochondria

Protective role of NADP-isocitrate dehydrogenase in the oxidative inactivation of mitochondrial enzymes was analyzed. Administration of paraquat to the rat inactivated liver mitochondrial enzymes: the aconitase activity decreased to one quarter, and citrate synthase and fumarase to half, whereas cytosolic enzymes were not affected. Activities of heart mitochondrial and cytosolic enzymes were not at all changed in the rat treated with paraquat, but paraquat directly inactivated aconitase in the heart mitochondria isolated from the non-treated rats. The paraquat-dependent inactivation of aconitase was prevented by activating NADP-isocitrate dehydrogenase in the presence of oxidized glutathione. NADP-isocitrate dehydrogenase could regenerate glutathione in isolated heart mitochondria, indicating that paraquat-mediated inactivation depends on the glutathione-regenerating activity by enhanced NADPH supply. Lower NADP-isocitrate dehydrogenase activity in liver mitochondria cannot regenerate reduced glutathione for scavenging reactive oxygen species, resulting in the paraquat-induced oxidative inactivation of mitochondrial enzymes. However, higher activity of NADP-isocitrate dehydrogenase participates in the regeneration of reduced glutathione causing stabilization of enzymes in heart mitochondria.

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.

Status of antioxidant defense system and expression of toxicant responsive genes in striatum of maneb- and paraquat-induced Parkinson's disease phenotype in mouse: Mechanism of neurodegeneration

Parkinson's disease (PD) is a progressive neurodegenerative disorder contributed by the combination of age, genetic and environmental factors. Several studies have clearly shown increase in the incidences of PD in the rural environments and hypothesized the involvement of pesticides such as paraquat and maneb in neurodegeneration. These studies have prompted researchers to develop paraquat and maneb models to study the effect of co-treatment of maneb and paraquat on neuronal toxicity; however, the mechanism underlying maneb and paraquat co-treatment induced neuronal toxicity has not yet been clearly understood. The involvement of cytochrome P4502E1 and glutathione S-transferases A4-4 enzymes in the detoxification of several pesticides such as atrazine, fenamirol, organophosphorous insecticide parathion, methoxychlor, diethyl dithiocarbamate and paraquat has been known. The contribution of CYP2E1 and GSTA4-4 in neuronal toxicity has also been reported. The present study was therefore undertaken to investigate the mechanism of maneb- and paraquat-induced neurodegeneration by estimating the level of antioxidant defense enzymes in the striatum and measuring the differential expressions of CYP2E1 and GSTA4-4 genes. Animals were treated with and without maneb (30 mg/kg, i.p.) or paraquat (10 mg/kg, i.p.) either alone or in combination in exposure time-dependent manner. A significant increase in catalase, glutathione S-transferase and lipid peroxidation in the striatum was found following 3, 6 and 9 weeks of co-treatment as compared with individual treatment or controls. Individual treatment of maneb or paraquat did not exhibit any significant alteration in CYP2E1 and GSTA4-4 expression up to 6 weeks; however, an augmentation in CYP2E1 and GSTA4-4 expression was observed in the animals exposed to maneb or paraquat for 9 weeks. Augmentation in the expression of CYP2E1 and GSTA4-4 was more pronounced in the animals treated with maneb and paraquat in combination for nine weeks. A significant reduction in the augmented lipid peroxidation in the striatum was observed when the striatum was pre-administered with CYP2E1 inhibitors; however, glutathione pre-administration induced lipid peroxidation. Results obtained from the present investigation suggest the involvement of CYP2E1 and GSTA4-4 in the augmentation of the lipid peroxidation thereby enhancing neurodegeneration.