The role of NADPH oxidase 1-derived reactive oxygen species in paraquat-mediated dopaminergic cell death

The role of β-adrenergic blockers in Parkinson's disease: possible genetic and cell-signaling mechanisms

Genetic studies have identified numerous factors linking β-adrenergic blockade to Parkinson's disease (PD), including human leukocyte antigen genes, the renin-angiotensin system, poly(adenosine diphosphate-ribose) polymerase 1, nerve growth factor, vascular endothelial growth factor, and the reduced form of nicotinamide adenine dinucleotide phosphate. β-Adrenergic blockade has also been implicated in PD via its effects on matrix metalloproteinases, mitogen-activated protein kinase pathways, prostaglandins, cyclooxygenase 2, and nitric oxide synthase. β-Adrenergic blockade may have a significant role in PD; therefore, the characterization of β-adrenergic blockade in patients with PD is needed.

Diapocynin prevents early Parkinson's disease symptoms in the leucine-rich repeat kinase 2 (LRRK2R¹⁴⁴¹G) transgenic mouse

The most prominent mechanism proposed for death of dopaminergic neurons in Parkinson's disease (PD) is elevated generation of reactive oxygen/nitrogen species (ROS/RNS). Recent studies suggest that ROS produced during PD pathogenesis may contribute to cytotoxicity in cell culture models of PD. We hypothesized that inhibition of ROS production would prevent PD symptoms in the LRRK2(R1441G) transgenic (tg) mouse model of PD. These mice overexpress a mutant form of leucine-rich repeat kinase 2 (LRRK2) and are reported to develop PD-like symptoms at approximately 10 months of age. Despite similar expression of the transgene, our colony did not recapitulate the same type of motor dysfunction originally reported. However, tests of motor coordination (pole test, Rotor-Rod) revealed a significant defect in LRRK2(R1441G) mice by 16 months of age. LRRK2(R1441G) tg mice, or wild type littermates, were given diapocynin (200mg/kg, a proposed NADPH oxidase inhibitor) three times per week by oral gavage starting at 12 weeks of age. Decreased performance on the pole test and Rotor-Rod in the LRRK2(R1441G) mice was prevented with diapocynin treatment. No loss in open field movement or rearing was found. As expected, tyrosine hydroxylase staining was similar in both the substantia nigra and striatum in all treatment groups. Together these data demonstrate that diapocynin is a viable agent for protection of neurobehavioral function.

Vitamin E ameliorates the decremental effect of paraquat on cardiomyocyte contractility in rats

Background

Exposure to pesticides and industrial toxins are implicated in cardiovascular disease. Paraquat (PAR) is a toxic chemical widely used as an herbicide in developing countries and described as a major suicide agent. The hypothesis tested here is that PAR induced myocardial dysfunction may be attributed to altered mechanisms of Ca²⁺ transport which are in turn possibly linked to oxidative stress. The mechanisms of PAR induced myocardial dysfunction and the impact of antioxidant protection was investigated in rat ventricular myocytes.

Methodology

Forty adult male Wistar rats were divided into 4 groups receiving the following daily intraperitoneal injections for 3 weeks: Group 1 PAR (10 mg/kg), Control Group 2 saline, Group 3 vitamin E (100 mg/kg) and Group 4 PAR (10 mg/kg) and vitamin E (100 mg/kg). Ventricular action potentials were measured in isolated perfused heart, shortening and intracellular Ca²⁺ in electrically stimulated ventricular myocytes by video edge detection and fluorescence photometry techniques, and superoxide dismutase (SOD) and catalase (CAT) levels in heart tissue.

Principal Findings

Spontaneous heart rate, resting cell length, time to peak (TPK) and time to half (THALF) relaxation of myocyte shortening were unaltered. Amplitude of shortening was significantly reduced in PAR treated rats (4.99±0.26%) and was normalized by vitamin E (7.46±0.44%) compared to controls (7.87±0.52%). PAR significantly increased myocytes resting intracellular Ca²⁺ whilst TPK and THALF decay and amplitude of the Ca²⁺ transient were unaltered. The fura-2–cell length trajectory during the relaxation of the twitch contraction was significantly altered in myocytes from PAR treated rats compared to controls suggesting altered myofilament sensitivity to Ca²⁺ as it was normalized by vitamin E treatment. A significant increase in SOD and CAT activities was observed in both PAR and vitamin E plus PAR groups.

Conclusions

PAR exposure compromised rats heart function and ameliorated by vitamin E treatment.

Entamoeba histolytica induces cell death of HT29 colonic epithelial cells via NOX1-derived ROS

Entamoeba histolytica, which causes amoebic colitis and occasionally liver abscess in humans, is able to induce host cell death. However, signaling mechanisms of colon cell death induced by E. histolytica are not fully elucidated. In this study, we investigated the signaling role of NOX in cell death of HT29 colonic epithelial cells induced by E. histolytica. Incubation of HT29 cells with amoebic trophozoites resulted in DNA fragmentation that is a hallmark of apoptotic cell death. In addition, E. histolytica generate intracellular reactive oxygen species (ROS) in a contact-dependent manner. Inhibition of intracellular ROS level with treatment with DPI, an inhibitor of NADPH oxidases (NOXs), decreased Entamoeba-induced ROS generation and cell death in HT29 cells. However, pan-caspase inhibitor did not affect E. histolytica-induced HT29 cell death. In HT29 cells, catalytic subunit NOX1 and regulatory subunit Rac1 for NOX1 activation were highly expressed. We next investigated whether NADPH oxidase 1 (NOX1)-derived ROS is closely associated with HT29 cell death induced by E. histolytica. Suppression of Rac1 by siRNA significantly inhibited Entamoeba-induced cell death. Moreover, knockdown of NOX1 by siRNA, effectively inhibited E. histolytica-triggered DNA fragmentation in HT29 cells. These results suggest that NOX1-derived ROS is required for apoptotic cell death in HT29 colon epithelial cells induced by E. histolytica.

NADPH oxidase 1 mediates α-synucleinopathy in Parkinson's disease

Accumulation of misfolded α-synuclein is the pathological hallmark of Parkinson's disease (PD). Nevertheless, little is known about the mechanism contributing to α-synuclein aggregation and its further toxicity to dopaminergic neurons. Since oxidative stress can increase the expression and aggregation levels of α-synuclein, NADPH oxidases (Noxs), which are responsible for reactive oxygen species generation, could be major players in α-synucleinopathy. Previously, we demonstrated that Nox1 is expressed in dopaminergic neurons of the PD animal models as well as postmortem brain tissue of PD patients, and is responsible for oxidative stress and subsequent neuronal degeneration. Here, using paraquat (PQ)-based in vitro and in vivo PD models, we show that Nox1 has a crucial role in modulating the behavior of α-synuclein expression and aggregation in dopaminergic neurons. We observed in differentiated human dopaminergic cells that Nox1 and α-synuclein expressions are increased under PQ exposure. Nox1 knockdown significantly reduced both α-synuclein expression and aggregation, supporting the role of Nox1 in this process. Furthermore, in rats exposed to PQ, the selective knockdown of Nox1 in the substantia nigra, using adeno-associated virus encoding Nox1-specific shRNA, largely attenuated the PQ-mediated increase of α-synuclein and ubiquitin expression levels as well as α-synuclein aggregates (proteinase K resistant) and A11 oligomers. Significant reductions in oxidative stress level and dopaminergic neuronal loss were also observed. Our data reveal a new mechanism by which α-synuclein becomes a neuropathologic protein through Nox1-mediated oxidative stress. This finding may be used to generate new therapeutic interventions that slower the rate of α-synuclein aggregation and the progression of PD pathogenesis.

Thiol-redox signaling, dopaminergic cell death, and Parkinson's disease

SIGNIFICANCE

Parkinson's disease (PD) is characterized by the selective loss of dopaminergic neurons of the substantia nigra pars compacta, which has been widely associated with oxidative stress. However, the mechanisms by which redox signaling regulates cell death progression remain elusive.

RECENT ADVANCES

Early studies demonstrated that depletion of glutathione (GSH), the most abundant low-molecular-weight thiol and major antioxidant defense in cells, is one of the earliest biochemical events associated with PD, prompting researchers to determine the role of oxidative stress in dopaminergic cell death. Since then, the concept of oxidative stress has evolved into redox signaling, and its complexity is highlighted by the discovery of a variety of thiol-based redox-dependent processes regulating not only oxidative damage, but also the activation of a myriad of signaling/enzymatic mechanisms.

CRITICAL ISSUES

GSH and GSH-based antioxidant systems are important regulators of neurodegeneration associated with PD. In addition, thiol-based redox systems, such as peroxiredoxins, thioredoxins, metallothioneins, methionine sulfoxide reductases, transcription factors, as well as oxidative modifications in protein thiols (cysteines), including cysteine hydroxylation, glutathionylation, and nitrosylation, have been demonstrated to regulate dopaminergic cell loss.

FUTURE DIRECTIONS

In this review, we summarize major advances in the understanding of the role of thiol-redox signaling in dopaminergic cell death in experimental PD. Future research is still required to clearly understand how integrated thiol-redox signaling regulates the activation of the cell death machinery, and the knowledge generated should open new avenues for the design of novel therapeutic approaches against PD.

Targeting NOX enzymes in the central nervous system: therapeutic opportunities

Among the pathogenic mechanisms underlying central nervous system (CNS) diseases, oxidative stress is almost invariably described. For this reason, numerous attempts have been made to decrease reactive oxygen species (ROS) with the administration of antioxidants as potential therapies for CNS disorders. However, such treatments have always failed in clinical trials. Targeting specific sources of reactive oxygen species in the CNS (e.g. NOX enzymes) represents an alternative promising option. Indeed, NOX enzymes are major generators of ROS, which regulate progression of CNS disorders as diverse as amyotrophic lateral sclerosis, schizophrenia, Alzheimer disease, Parkinson disease, and stroke. On the other hand, in autoimmune demyelinating diseases, ROS generated by NOX enzymes are protective, presumably by dampening the specific immune response. In this review, we discuss the possibility of developing therapeutics targeting NADPH oxidase (NOX) enzymes for the treatment of different CNS pathologies. Specific compounds able to modulate the activation of NOX enzymes, and the consequent production of ROS, could fill the need for disease-modifying drugs for many incurable CNS pathologies.

Altered manganese homeostasis: implications for BLI-3-dependent dopaminergic neurodegeneration and SKN-1 protection in C. elegans

The role of environmental factors in the etiology of neurodegenerative disorders, such as in Parkinson's disease (PD), has become increasingly imperative for examination, as genetics can only partially account for most cases. The heavy metal manganese (Mn) falls into this category of environmental contributors, as it is both essential but also neurotoxic upon overexposure and produces Parkinsonian symptomatology. In order to understand its toxicity, this review focuses on the various aspects of improper Mn homeostasis and its consequences using the genetically amenable Caenorhabditis elegans model. Namely, the roles of Mn transporter homologs for the divalent metal transporter 1 (DMT1) will be discussed, as Mn homeostasis is initially governed by proper cellular transport. Mn dyshomeostasis can result in enhanced oxidative stress through synergistic actions of dopamine oxidation that is dependent on the C. elegans dual oxidase BLI-3. Finally, neuroprotection conferred by the antioxidant transcription factor Nrf2 (C. elegans SKN-1) may signify a potential therapeutic approach against Mn toxicity.

NADPH oxidase 1-mediated oxidative stress leads to dopamine neuron death in Parkinson's disease

AIM

Oxidative stress has long been considered as a major contributing factor in the pathogenesis of Parkinson's disease. However, molecular sources for reactive oxygen species in Parkinson's disease have not been clearly elucidated. Herein, we sought to investigate whether a superoxide-producing NADPH oxidases (NOXs) are implicated in oxidative stress-mediated dopaminergic neuronal degeneration.

RESULTS

Expression of various Nox isoforms and cytoplasmic components were investigated in N27, rat dopaminergic cells. While most of Nox isoforms were constitutively expressed, Nox1 expression was significantly increased after treatment with 6-hydroxydopamine. Rac1, a key regulator in the Nox1 system, was also activated. Striatal injection of 6-hydroxydopamine increased Nox1 expression in dopaminergic neurons in the rat substantia nigra. Interestingly, it was localized into the nucleus, and immunostaining for DNA oxidative stress marker, 8-oxo-dG, was increased. Nox1 expression was also found in the nucleus of dopaminergic neurons in the substantia nigra of Parkinson's disease patients. Adeno-associated virus-mediated Nox1 knockdown or Rac1 inhibition reduced 6-hydroxydopamine-induced oxidative DNA damage and dopaminergic neuronal degeneration significantly.

INNOVATION

Nox1/Rac1 could serve as a potential therapeutic target for Parkinson's disease.

CONCLUSION

We provide evidence that dopaminergic neurons are equipped with the Nox1/Rac1 superoxide-generating system. Stress-induced Nox1/Rac1 activation causes oxidative DNA damage and neurodegeneration. Reduced dopaminergic neuronal death achieved by targeting Nox1/Rac1, emphasizes the impact of oxidative stress caused by this system on the pathogenesis and therapy in Parkinson's disease.

siRNA-mediated knock-down of NOX3: therapy for hearing loss?

Cisplatin is a widely used chemotherapeutic agent that causes significant hearing loss. Previous studies have shown that cisplatin exposure is associated with increase in reactive oxygen species (ROS) in the cochlea. The inner ear expresses a unique isoform of NADPH oxidase, NOX3. This enzyme may be the primary source of ROS generation in the cochlea. The knockdown of NOX3 by pretreatment with siRNA prevented cisplatin ototoxicity, as demonstrated by preservation of hearing thresholds and inner ear sensory cells. Trans-tympanic NOX3 siRNA reduced the expression of NOX3 and biomarkers of cochlear damage, including transient receptor vanilloid 1 (TRPV1) channel and kidney injury molecule-1 (KIM-1) in cochlear tissues. In addition, siRNA against NOX3 reduced apoptosis as demonstrated by TUNEL staining, and prevented the increased expression of Bax and abrogated the decrease in Bcl2 expression following cisplatin administration. Trans-tympanic administration of siRNA directed against NOX3 may provide a useful method of attenuating cisplatin ototoxicity. In this paper, we review recent publications dealing with the role of NOX3 in ototoxicity and the effects of siRNA against cisplatin-induced hearing loss.

NADPH oxidases: novel therapeutic targets for neurodegenerative diseases

Oxidative stress is a key pathologic factor in neurodegenerative diseases such as Alzheimer and Parkinson diseases (AD, PD). The failure of free-radical-scavenging antioxidants in clinical trials pinpoints an urgent need to identify and to block major sources of oxidative stress in neurodegenerative diseases. As a major superoxide-producing enzyme complex in activated phagocytes, phagocyte NADPH oxidase (PHOX) is essential for host defense. However, recent preclinical evidence has underscored a pivotal role of overactivated PHOX in chronic neuroinflammation and progressive neurodegeneration. Deficiency in PHOX subunits mitigates neuronal damage induced by diverse insults/stresses relevant to neurodegenerative diseases. More importantly, suppression of PHOX activity correlates with reduced neuronal impairment in models of neurodegenerative diseases. The discovery of PHOX and non-phagocyte NADPH oxidases in astroglia and neurons further reinforces the crucial role of NADPH oxidases in oxidative stress-mediated chronic neurodegeneration. Thus, proper modulation of NADPH oxidase activity might hold therapeutic potential for currently incurable neurodegenerative diseases.

Integrating cytosolic phospholipase A₂ with oxidative/nitrosative signaling pathways in neurons: a novel therapeutic strategy for AD

The pathophysiology of Alzheimer's disease (AD) is comprised of complex metabolic abnormalities in different cell types in the brain. To date, there are not yet effective drugs that can completely inhibit the pathophysiological event, and efforts have been devoted to prevent or minimize the progression of this disease. Much attention has focused on studies to understand aberrant functions of the ionotropic glutamate receptors, perturbation of calcium homeostasis, and toxic effects of oligomeric amyloid beta peptides (Aβ) which results in production of reactive oxygen and nitrogen species and signaling pathways, leading to mitochondrial dysfunction and synaptic impairments. Aberrant phospholipase A(2) (PLA(2)) activity has been implicated to play a role in the pathogenesis of many neurodegenerative diseases, including AD. However, mechanisms for their modes of action and their roles in the oxidative and nitrosative signaling pathways have not been firmly established. In this article, we review recent studies providing a metabolic link between cytosolic PLA(2) (cPLA(2)) and neuronal excitation due to stimulation of ionotropic glutamate receptors and toxic Aβ peptides. The requirements for Ca(2+) binding together with its posttranslational modifications by protein kinases and possible by the redox-based S-nitrosylation, provide strong support for a dynamic role of cPLA(2) in serving multiple functions to neurons and glial cells under abnormal physiological and pathological conditions. Therefore, understanding mechanisms for cPLA(2) in the oxidative and nitrosative pathways in neurons will allow the development of novel therapeutic targets to mitigate the detrimental effects of AD.

The neuroprotective effects of apocynin

The recognition of health benefits of phytomedicines and herbal supplements lead to an increased interest to understand the cellular and molecular basis of their biological activities. Apocynin (4-hydroxy-3-methoxy-acetophenone) is a constituent of the Himalayan medicinal herb Picrorhiza kurroa which is regarded as an inhibitor of nicotinamide adenine dinucleotide phosphate (NADPH)-oxidase, a superoxide-producing enzyme. NADPH oxidase appears to be especially important in the modulation of redox-sensitive signaling pathways and also has been implicated in neuronal dysfunction and degeneration, and neuroinflammmation in diseases ranging from stroke, Alzheimer's and Parkinson's diseases to psychiatric disorders. In this review, we aim to give an overview of current literature on the neuroprotective effects of apocynin in the prevention and treatment of neurodegenerative disorders. Particular attention is given to in vivo studies.

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 neurotoxicity is mediated by the dopamine transporter and organic cation transporter-3

The herbicide paraquat (PQ) has increasingly been reported in epidemiological studies to enhance the risk of developing Parkinson's disease (PD). Furthermore, case-control studies report that individuals with genetic variants in the dopamine transporter (DAT, SLC6A) have a higher PD risk when exposed to PQ. However, it remains a topic of debate whether PQ can enter dopamine (DA) neurons through DAT. We report here a mechanism by which PQ is transported by DAT: In its native divalent cation state, PQ(2+) is not a substrate for DAT; however, when converted to the monovalent cation PQ(+) by either a reducing agent or NADPH oxidase on microglia, it becomes a substrate for DAT and is accumulated in DA neurons, where it induces oxidative stress and cytotoxicity. Impaired DAT function in cultured cells and mutant mice significantly attenuated neurotoxicity induced by PQ(+). In addition to DAT, PQ(+) is also a substrate for the organic cation transporter 3 (Oct3, Slc22a3), which is abundantly expressed in non-DA cells in the nigrostriatal regions. In mice with Oct3 deficiency, enhanced striatal damage was detected after PQ treatment. This increased sensitivity likely results from reduced buffering capacity by non-DA cells, leading to more PQ(+) being available for uptake by DA neurons. This study provides a mechanism by which DAT and Oct3 modulate nigrostriatal damage induced by PQ(2+)/PQ(+) redox cycling.

Deficiency of multidrug and toxin extrusion 1 enhances renal accumulation of paraquat and deteriorates kidney injury in mice

Multidrug and toxin extrusion 1 (MATE1/solute carrier 47A1) mediates cellular transport of a variety of structurally diverse compounds. Paraquat (PQ), which has been characterized in vitro as a MATE1 substrate, is a widely used herbicide and can cause severe toxicity to humans after exposure. However, the contribution of MATE1 to PQ disposition in vivo has not been determined. In the present study, we generated Mate1-deficient (Mate1–/–) mice and performed toxicokinetic analyses of PQ in Mate1–/– and wild-type (Mate1+/+) mice. After a single intravenous administration of PQ (50 mg/kg), Mate1–/– mice exhibited significantly higher plasma PQ concentrations than Mate1+/+ mice. The renal PQ concentration was markedly increased in Mate1–/– mice compared with Mate1+/+ mice. The subsequent nephrotoxicity of PQ were examined in these mice. Three days after intraperitoneal administration of PQ (20 mg/kg), the transcript levels of N-acetyl-β-d-glucosaminidase (Lcn2) and kidney injury molecule-1 (Kim-1) in the kidney were remarkably enhanced in the Mate1–/– mice. This was accompanied by apparent difference in renal histology between Mate1–/– and Mate1+/+ mice. In conclusion, we demonstrated that Mate1 is responsible for renal elimination of PQ in vivo and the deficiency of Mate1 function confers deteriorated kidney injury caused by PQ in mice.

Generation of reactive oxygen species in 1-methyl-4-phenylpyridinium (MPP+) treated dopaminergic neurons occurs as an NADPH oxidase-dependent two-wave cascade

BACKGROUND

Reactive oxygen species (ROS), superoxide and hydrogen peroxide (H2O2), are necessary for appropriate responses to immune challenges. In the brain, excess superoxide production predicts neuronal cell loss, suggesting that Parkinson's disease (PD) with its wholesale death of dopaminergic neurons in substantia nigra pars compacta (nigra) may be a case in point. Although microglial NADPH oxidase-produced superoxide contributes to dopaminergic neuron death in an MPTP mouse model of PD, this is secondary to an initial die off of such neurons, suggesting that the initial MPTP-induced death of neurons may be via activation of NADPH oxidase in neurons themselves, thus providing an early therapeutic target.

METHODS

NADPH oxidase subunits were visualized in adult mouse nigra neurons and in N27 rat dopaminergic cells by immunofluorescence. NADPH oxidase subunits in N27 cell cultures were detected by immunoblots and RT-PCR. Superoxide was measured by flow cytometric detection of H2O2-induced carboxy-H2-DCFDA fluorescence. Cells were treated with MPP+ (MPTP metabolite) following siRNA silencing of the Nox2-stabilizing subunit p22phox, or simultaneously with NADPH oxidase pharmacological inhibitors or with losartan to antagonize angiotensin II type 1 receptor-induced NADPH oxidase activation.

RESULTS

Nigral dopaminergic neurons in situ expressed three subunits necessary for NADPH oxidase activation, and these as well as several other NADPH oxidase subunits and their encoding mRNAs were detected in unstimulated N27 cells. Overnight MPP+ treatment of N27 cells induced Nox2 protein and superoxide generation, which was counteracted by NADPH oxidase inhibitors, by siRNA silencing of p22phox, or losartan. A two-wave ROS cascade was identified: 1) as a first wave, mitochondrial H2O2 production was first noted at three hours of MPP+ treatment; and 2) as a second wave, H2O2 levels were further increased by 24 hours. This second wave was eliminated by pharmacological inhibitors and a blocker of protein synthesis.

CONCLUSIONS

A two-wave cascade of ROS production is active in nigral dopaminergic neurons in response to neurotoxicity-induced superoxide. Our findings allow us to conclude that superoxide generated by NADPH oxidase present in nigral neurons contributes to the loss of such neurons in PD. Losartan suppression of nigral-cell superoxide production suggests that angiotensin receptor blockers have potential as PD preventatives.

Oxidative toxicity in neurodegenerative diseases: role of mitochondrial dysfunction and therapeutic strategies

Besides fluorine, oxygen is the most electronegative element with the highest reduction potential in biological systems. Metabolic pathways in mammalian cells utilize oxygen as the ultimate oxidizing agent to harvest free energy. They are very efficient, but not without risk of generating various oxygen radicals. These cells have good antioxidative defense mechanisms to neutralize these radicals and prevent oxidative stress. However, increased oxidative stress results in oxidative modifications in lipid, protein, and nucleic acids, leading to mitochondrial dysfunction and cell death. Oxidative stress and mitochondrial dysfunction have been implicated in many neurodegenerative disorders including Alzheimer's disease, Parkinson's disease, and stroke-related brain damage. Research has indicated mitochondria play a central role in cell suicide. An increase in oxidative stress causes mitochondrial dysfunction, leading to more production of reactive oxygen species and eventually mitochondrial membrane permeabilization. Once the mitochondria are destabilized, cells are destined to commit suicide. Therefore, antioxidative agents alone are not sufficient to protect neuronal loss in many neurodegenerative diseases. Combinatorial treatment with antioxidative agents could stabilize mitochondria and may be the most suitable strategy to prevent neuronal loss. This review discusses recent work related to oxidative toxicity in the central nervous system and strategies to treat neurodegenerative diseases.

Mitochondrial aconitase knockdown attenuates paraquat-induced dopaminergic cell death via decreased cellular metabolism and release of iron and H₂O₂

Mitochondrial oxidative stress is a contributing factor in the etiology of numerous neuronal disorders. However, the precise mechanism(s) by which mitochondrial reactive oxygen species modify cellular targets to induce neurotoxicity remains unknown. In this study, we determined the role of mitochondrial aconitase (m-aconitase) in neurotoxicity by decreasing its expression. Incubation of the rat dopaminergic cell line, N27, with paraquat (PQ(2+) ) resulted in aconitase inactivation, increased hydrogen peroxide (H(2) O(2) ) and increased ferrous iron (Fe(2+) ) at times preceding cell death. To confirm the role of m-aconitase in dopaminergic cell death, we knocked down m-aconitase expression via RNA interference. Incubation of m-aconitase knockdown N27 cells with PQ(2+) resulted in decreased H(2) O(2) production, Fe(2+) accumulation, and cell death compared with cells expressing basal levels of m-aconitase. To determine the metabolic role of m-aconitase in mediating neuroprotection, we conducted a complete bioenergetic profile. m-Aconitase knockdown N27 cells showed a global decrease in metabolism (glycolysis and oxygen consumption rates) which blocked PQ(2+) -induced H(+) leak and respiratory capacity deficiency. These findings suggest that dopaminergic cells are protected from death by decreasing release of H(2) O(2) and Fe(2+) in addition to decreased cellular metabolism.

NOX1 participates in ROS-dependent cell death of colon epithelial Caco2 cells induced by Entamoeba histolytica

Entamoeba histolytica, which causes amebic colitis and occasional liver abscesses in humans, can induce host cell death through apoptosis and necrosis. Recently, we have demonstrated that E. histolytica can induce cell death in neutrophils via diphenyleneiodonium-sensitive NADPH oxidase (NOX)-derived reactive oxygen species (ROS). Although there are enzyme systems similar to the phagocyte NADPH oxidase system in many non-phagocytic cell types, the signaling role of NOX-derived ROS in cell death of human colon epithelial cells induced by E. histolytica remains obscure. Incubation of colon epithelial Caco2 tumor cell lines with amebic trophozoites resulted in intracellular ROS generation and cell death in a caspase-independent manner. Pretreatment with DPI, an inhibitor of NOX, strongly decreased E. histolytica-induced cell death in Caco2 cells. As identified by RT-PCR, NOX1 transcripts were highly expressed in Caco2 cells. siRNA-mediated suppression of NOX1 protein significantly inhibited E. histolytica-induced cell death and ROS response in Caco2 cells. These results suggest that NOX1 participates in the ROS-dependent cell death of colon epithelial cells induced by amebic adhesion during the early phase of intestinal amebiasis.

The endoplasmic reticulum-associated degradation is necessary for plant salt tolerance

Eukaryotic organisms have quality-control mechanisms that allow misfolded or unassembled proteins to be retained in the endoplasmic reticulum (ER) and subsequently degraded by ER-associated degradation (ERAD). The ERAD pathway is well studied in yeast and mammals; however, the biological functions of plant ERAD have not been reported. Through molecular and cellular biological approaches, we found that ERAD is necessary for plants to overcome salt stress. Upon salt treatment ubiquitinated proteins increased in plant cells, especially unfolded proteins that quickly accumulated in the ER and subsequently induced ER stress responses. Defect in HRD3A of the HRD1/HRD3 complex of the ERAD pathway resulted in alteration of the unfolded protein response (UPR), increased plant sensitivity to salt, and retention of ERAD substrates in plant cells. Furthermore, we demonstrated that Ca(2+) release from the ER is involved in the elevation of UPR and reactive oxygen species (ROS) participates the ERAD-related plant salt response pathway.

Cardiac-specific overexpression of catalase attenuates paraquat-induced myocardial geometric and contractile alteration: role of ER stress

Paraquat, a quaternary nitrogen herbicide, is a highly toxic pro-oxidant that causes multiorgan failure including that of the heart via generation of reactive oxygen species, although the underlying mechanism has not been well elucidated. This study examined the influence of cardiac-specific overexpression of catalase, an antioxidant detoxifying H(2)O(2), on paraquat-induced myocardial geometric and functional alterations, with a focus on ER stress. FVB and catalase transgenic mice were administered paraquat for 48h. Myocardial geometry, contractile function, apoptosis, and ER stress were evaluated using echocardiography, edge detection, caspase-3 activity, and immunoblotting. Our results revealed that paraquat treatment significantly enlarged left ventricular (LV) end diastolic and systolic diameters; increased LV mass and resting myocyte length; reduced fractional shortening, cardiomyocyte peak shortening, and maximal velocity of shortening/relengthening; and prolonged relengthening duration in the FVB group. Whereas the catalase transgene itself did not alter myocardial geometry and function, it mitigated or significantly attenuated paraquat-elicited myocardial geometric and functional changes. Paraquat promoted overt apoptosis and ER stress as evidenced by increased caspase-3 activity, apoptosis, and ER stress markers including Bax, Bcl-2, GADD153, calregulin, and phosphorylated JNK, IRE1α, and eIF2α; all were ablated by the catalase transgene. Paraquat-induced cardiomyocyte dysfunction was mitigated by the ER stress inhibitor tauroursodeoxycholic acid. Moreover, the JNK inhibitor SP600125 reversed paraquat-induced ER stress as evidenced by enhanced GADD153 and IRE1α phosphorylation. Taken together, these data revealed that catalase may rescue paraquat-induced myocardial geometric and functional alteration possibly by alleviating JNK-mediated ER stress.

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.

Nox-4-dependent nuclear H2O2 drives DNA oxidation resulting in 8-OHdG as urinary biomarker and hemangioendothelioma formation

Hemangioendotheliomas are classified as endothelial cell tumors, which are the most common soft tissue tumors in infants. In a murine model of hemangioendothelioma, we previously showed that MCP-1 is required for its development and that the expression of MCP-1 in EOMA cells is redox sensitive. Here, we sought to identify the source of oxidants that drive hemangioendothelioma formation. Seven known isoforms exist of the catalytic subunit gp91. Only the nox-4 isoform of gp91 was present in EOMA cells, in contrast with non-tumor-forming murine endothelial cells that contained multiple forms of nox. Nox-4 knockdown markedly attenuated MCP-1 expression and hemangioendothelioma formation. We report that in EOMA cells, nox-4 is localized such that it delivers H2O2 to the nuclear compartment. Such delivery of H2O2 causes oxidative modification of DNA, which can be detected in the urine of tumor-bearing mice as 8-hydroxy-2-deoxyguanosine. Iron chelation by in vivo administration of deferoxamine improved tumor outcomes. The current state of information connects nox-4 to MCP-1 to form a major axis of control that regulates the fate of hemangioendothelioma development in vivo.

Parkinson's disease: from molecular pathways in disease to therapeutic approaches

Parkinson's disease (PD) is a complex multifactor disease marked by extensive neuropathology in the brain with selective yet prominent and progressive loss of midbrain dopamine neurons. Clinically PD is characterized by motor abnormalities including resting tremor, bradykinesia, altered gait, muscular rigidity, postural instability, together with autonomic dysfunctions. The etiological factors involved in the development of PD are still elusive, but there is considerable evidence that a combination of genetic susceptibilities and environmental factors plays a critical role in disease pathogenesis. The identification of single genes in the past decade linked to heritable forms of PD has challenged the previously held view of a nongenetic etiology for this progressive movement disorder. These genetic breakthroughs have revolutionized the research by providing unique opportunities to pursue novel mechanisms and identified new clues to disease pathogenesis in PD. This forum review provides an update on current hypotheses and recent findings in mitochondrial dysfunction, oxidative damage, innate and adaptive immune systems, protein misfolding and aggregation, and advances in translational approaches to PD. These aspects are reviewed with an aim to promote better understanding of molecular pathways prevalent in parkinsonian brain that will eventually aide in development of promising therapeutic strategies.