Compartmentalized oxidative stress in dopaminergic cell death induced by pesticides and complex I inhibitors: distinct roles of superoxide anion and superoxide dismutases

Metformin and Trehalose-Modulated Autophagy Exerts a Neurotherapeutic Effect on Parkinson's Disease

Since the number of aged people will increase in the next years, neurodegenerative diseases, including Parkinson's Disease (PD), will also rise. Recently, we demonstrated that autophagy stimulation with rapamycin decreases dopaminergic neuronal death mediated by oxidative stress in the paraquat (PQ)-induced PD model. Assessing the neurotherapeutic efficacy of autophagy-inducing molecules is critical for preventing or delaying neurodegeneration. Therefore, we evaluated the autophagy inducers metformin and trehalose effect in a PD model. Autophagy induced by both molecules was confirmed in the SH-SY5Y dopaminergic cells by detecting increased LC3-II marker and autophagosome number compared to the control by western blot and transmission electron microscopy. Both autophagy inducers showed an antioxidant effect, improved mitochondrial activity, and decreased dopaminergic cell death induced by PQ. Next, we evaluated the effect of both inducers in vivo. C57BL6 mice were pretreated with metformin or trehalose before PQ administration. Cognitive and motor deteriorated functions in the PD model were evaluated through the nest building and the gait tests and were prevented by metformin and trehalose. Both autophagy inducers significantly reduced the dopaminergic neuronal loss, astrocytosis, and microgliosis induced by PQ. Also, cell death mediated by PQ was prevented by metformin and trehalose, assessed by TUNEL assay. Metformin and trehalose induced autophagy through AMPK phosphorylation and decreased α-synuclein accumulation. Therefore, metformin and trehalose are promising neurotherapeutic autophagy inducers with great potential for treating neurodegenerative diseases such as PD.

Astaxanthin ameliorates dopaminergic neuron damage in paraquat-induced SH-SY5Y cells and mouse models of Parkinson's disease

Parkinson's disease (PD) is the second largest neurodegenerative disorder caused by the decreased number of dopaminergic (DAc) neurons in the substantia nigra pars compacta (SNpc). There is evidence that oxidative stress can contribute degeneration of DAc neurons in SNpc which is mainly caused by apoptotic cell death. Thus, suppressing oxidative stress and apoptosis of DAc neurons is an effective strategy to mitigate the progress of PD. Astaxanthin (AST) is a carotenoid, which mainly exists in marine organisms and is a powerful biological antioxidant. In this study, we aimed to determine the neuroprotective effect of AST on paraquat (PQ) -induced models of PD in vitro and in vivo. Here, we showed that AST significantly enhanced cell survival of SH-SY5Y cells against PQ toxicity by suppressing apoptotic cell death and oxidative stress. Moreover, we found that AST significantly ameliorated PQ-induced behavioral disorders associated with PD in C57BL/6 J mice and the damage to DAc neurons in the SNpc of mice. Lastly, we found that the neuroprotective effects of AST were conducted through inhibiting PQ-induced activation of MAPK signaling. In conclusion, our study indicates that AST had a strong protective effect on PQ-induced oxidative stress and antagonized apoptotic cell death in SH-SY5Y cells and PQ-induced mice PD model, which might provide new insights of AST for PD treatment.

Peroxiredoxin 5 overexpression decreases oxidative stress and dopaminergic cell death mediated by paraquat

Peroxiredoxins (Prdxs) are thiol-dependent enzymes that scavenge peroxides. Previously, we found that Prdxs were hyperoxidized in a Parkinson's disease model induced by paraquat (PQ), which led to their inactivation, perpetuating reactive oxygen species (ROS) formation. Herein, we evaluated the redox state of the typical 2-Cys-Prx subgroup. We found that PQ induces ROS compartmentalization in different organelles, reflected by the 2-Cys-Prdx hyperoxidation pattern detected by redox eastern blotting. 2-Cys Prdxs are most vulnerable to hyperoxidation, while atypical 2-Cys Peroxiredoxin 5 (Prdx5) is resistant and is expressed in multiple organelles, such as mitochondria, peroxisomes, and cytoplasm. Therefore, we overexpressed human Prdx5 in the dopaminergic SHSY-5Y cell line using the adenoviral vector Ad-hPrdx5. Prdx5 overexpression was confirmed by western blotting and immunofluorescence (IF) and effectively decreased PQ-mediated mitochondrial and cytoplasmic ROS assessed with a mitochondrial superoxide indicator and DHE through IF or flow cytometry. Decreased ROS mediated by Prdx5 in the main subcellular compartments led to overall cell protection against PQ-induced cell death, which was demonstrated by flow cytometry using Annexin V labeling and 7-AAD. Therefore, Prdx5 is an attractive therapeutic target for PD, as its overexpression protects dopaminergic cells from ROS and death, which warrants further experimental animal studies for its subsequent application in clinical trials.

Redox Regulation and Metabolic Dependency of Zika Virus Replication: Inhibition by Nrf2-Antioxidant Response and NAD(H) Antimetabolites

Viral infections alter host cell metabolism and homeostasis; however, the mechanisms that regulate these processes have only begun to be elucidated. We report here that Zika virus (ZIKV) infection activates the antioxidant nuclear factor erythroid 2-related factor 2 (Nrf2), which precedes oxidative stress. Downregulation of Nrf2 or inhibition of glutathione (GSH) synthesis resulted in significantly increased viral replication. Interestingly, 6-amino-nicotinamide (6-AN), a nicotinamide analog commonly used as an inhibitor of the pentose phosphate pathway (PPP), decreased viral replication by over 1,000-fold. This inhibition was neither recapitulated by the knockdown of PPP enzymes, glucose 6-phosphate dehydrogenase (G6PD), or 6-phosphogluconate dehydrogenase (6PGD), nor prevented by supplementation with ribose 5-phosphate. Instead, our metabolomics and metabolic phenotype studies support a mechanism in which 6-AN depletes cells of NAD(H) and impairs NAD(H)-dependent glycolytic steps resulting in inhibition of viral replication. The inhibitory effect of 6-AN was rescued with precursors of the salvage pathway but not with those of other NAD⁺ biosynthesis pathways. Inhibition of glycolysis reduced viral protein levels, which were recovered transiently. This transient recovery in viral protein synthesis was prevented when oxidative metabolism was inhibited by blockage of the mitochondrial pyruvate carrier, fatty acid oxidation, or glutaminolysis, demonstrating a compensatory role of mitochondrial metabolism in ZIKV replication. These results establish an antagonistic role for the host cell Nrf2/GSH/NADPH-dependent antioxidant response against ZIKV and demonstrate the dependency of ZIKV replication on NAD(H). Importantly, our work suggests the potential use of NAD(H) antimetabolite therapy against the viral infection. IMPORTANCE Zika virus (ZIKV) is a major public health concern of international proportions. While the incidence of ZIKV infections has declined substantially in recent years, the potential for the reemergence or reintroduction remains high. Although viral infection alters host cell metabolism and homeostasis to promote its replication, deciphering the mechanism(s) involved in these processes is important for identifying therapeutic targets. The present work reveals the complexities of host cell redox regulation and metabolic dependency of ZIKV replication. An antagonistic effect of the Nrf2/GSH/NADP(H)-dependent antioxidant response against ZIKV infection and an essential role of NAD(H) metabolism and glycolysis for viral replication are established for the first time. These findings highlight the potential use of NAD(H) antimetabolites to counter ZIKV infection and pathogenesis.

DJ-1 and SOD1 Act Independently in the Protection against Anoxia in Drosophila melanogaster

Redox homeostasis is a vital process the maintenance of which is assured by the presence of numerous antioxidant small molecules and enzymes and the alteration of which is involved in many pathologies, including several neurodegenerative disorders. Among the different enzymes involved in the antioxidant response, SOD1 and DJ-1 have both been associated with the pathogenesis of amyotrophic lateral sclerosis and Parkinson’s disease, suggesting a possible interplay in their mechanism of action. Copper deficiency in the SOD1-active site has been proposed as a central determinant in SOD1-related neurodegeneration. SOD1 maturation mainly relies on the presence of the protein copper chaperone for SOD1 (CCS), but a CCS-independent alternative pathway also exists and functions under anaerobic conditions. To explore the possible involvement of DJ-1 in such a pathway in vivo, we exposed Drosophila melanogaster to anoxia and evaluated the effect of DJ-1 on fly survival and SOD1 levels, in the presence or absence of CCS. Loss of DJ-1 negatively affects the fly response to the anoxic treatment, but our data indicate that the protective activity of DJ-1 is independent of SOD1 in Drosophila, indicating that the two proteins may act in different pathways.

Synergistic Effect of L-Carnosine and Hyaluronic Acid in Their Covalent Conjugates on the Antioxidant Abilities and the Mutual Defense against Enzymatic Degradation

Hyaluronic acid (Hy) is a natural linear polymer that is widely distributed in different organisms, especially in the articular cartilage and the synovial fluid. During tissue injury due to oxidative stress, Hy plays an important protective role. All the beneficial properties of Hy make the polymer attractive for many biomedical uses; however, the low stability and short biological half-life limit Hy application. To overcome these problems, the addition of small antioxidant molecules to Hy solution has been employed to protect the molecular integrity of Hy or delay its degradation. Carnosine (β-alanyl-L-histidine, Car) protects cells from the damage due to the reactive species derived from oxygen (ROS), nitrogen (RNS) or carbonyl groups (RCS). Car inhibits the degradation of hyaluronan induced by free radical processes in vitro but, like Hy, the potential protective action of Car is drastically hampered by the enzymatic hydrolysis in vivo. Recently, we conjugated Hy to Car and the derivatives (HyCar) showed protective effects in experimental models of osteoarthritis and rheumatoid arthritis in vivo. Here we report the antioxidant activity exerted by HyCar against ROS, RNS and RCS. Moreover, we tested if the covalent conjugation between Hy and Car inhibits the enzymatic hydrolysis of the polymer and the dipeptide backbone. We found that the antioxidant properties and the resistance to the enzymatic hydrolysis of Hy and Car are greatly improved by the conjugation.

Calycosin Alleviates Paraquat-Induced Neurodegeneration by Improving Mitochondrial Functions and Regulating Autophagy in a Drosophila Model of Parkinson's Disease

Parkinson's disease (PD) is the second most common age-related neurodegenerative disorder with limited clinical treatments. The occurrence of PD includes both genetic and environmental toxins, such as the pesticides paraquat (PQ), as major contributors to PD pathology in both invertebrate and mammalian models. Calycosin, an isoflavone phytoestrogen, has multiple pharmacological properties, including neuroprotective activity. However, the paucity of information regarding the neuroprotective potential of calycosin on PQ-induced neurodegeneration led us to explore whether calycosin can mitigate PD-like phenotypes and the underlying molecular mechanisms. We used a PQ-induced PD model in Drosophila as a cost-effective in vivo screening platform to investigate the neuroprotective efficacy of natural compounds on PD. We reported that calycosin shows a protective role in preventing dopaminergic (DA) neuronal cell death in PQ-exposed Canton S flies. Calycosin-fed PQ-exposed flies exhibit significant resistance against PQ-induced mortality and locomotor deficits in terms of reduced oxidative stress, loss of DA neurons, the depletion of dopamine content, and phosphorylated JNK-caspase-3 levels. Additionally, mechanistic studies show that calycosin administration improves PQ-induced mitochondrial dysfunction and stimulates mitophagy and general autophagy with reduced pS6K and p4EBP1 levels, suggestive of a maintained energy balance between anabolic and catabolic processes, resulting in the inhibition of neuronal cell death. Collectively, this study substantiates the protective effect of calycosin against PQ-induced neurodegeneration by improving DA neurons' survival and reducing apoptosis, likely via autophagy induction, and it is implicated as a novel therapeutic application against toxin-induced PD pathogenesis.

A Common Feature of Pesticides: Oxidative Stress-The Role of Oxidative Stress in Pesticide-Induced Toxicity

Pesticides are important chemicals or biological agents that deter or kill pests. The use of pesticides has continued to increase as it is still considered the most effective method to reduce pests and increase crop growth. However, pesticides have other consequences, including potential toxicity to humans and wildlife. Pesticides have been associated with increased risk of cardiovascular disease, cancer, and birth defects. Labels on pesticides also suggest limiting exposure to these hazardous chemicals. Based on experimental evidence, various types of pesticides all seem to have a common effect, the induction of oxidative stress in different cell types and animal models. Pesticide-induced oxidative stress is caused by both reactive oxygen species (ROS) and reactive nitrogen species (RNS), which are associated with several diseases including cancer, inflammation, and cardiovascular and neurodegenerative diseases. ROS and RNS can activate at least five independent signaling pathways including mitochondrial-induced apoptosis. Limited in vitro studies also suggest that exogenous antioxidants can reduce or prevent the deleterious effects of pesticides.

Systematic Review of Calcium Channels and Intracellular Calcium Signaling: Relevance to Pesticide Neurotoxicity

Pesticides of different chemical classes exert their toxic effects on the nervous system by acting on the different regulatory mechanisms of calcium (Ca²⁺) homeostasis. Pesticides have been shown to alter Ca²⁺ homeostasis, mainly by increasing its intracellular concentration above physiological levels. The pesticide-induced Ca²⁺ overload occurs through two main mechanisms: the entry of Ca²⁺ from the extracellular medium through the different types of Ca²⁺ channels present in the plasma membrane or its release into the cytoplasm from intracellular stocks, mainly from the endoplasmic reticulum. It has also been observed that intracellular increases in the Ca²⁺ concentrations are maintained over time, because pesticides inhibit the enzymes involved in reducing its levels. Thus, the alteration of Ca²⁺ levels can lead to the activation of various signaling pathways that generate oxidative stress, neuroinflammation and, finally, neuronal death. In this review, we also discuss some proposed strategies to counteract the detrimental effects of pesticides on Ca²⁺ homeostasis.

Environmental factors in Parkinson's disease: New insights into the molecular mechanisms

Parkinson's disease is a chronic, progressive neurodegenerative disorder affecting 2-3% of the population ≥65 years. It has long been characterized by motor impairment, autonomic dysfunction, and psychological and cognitive changes. The pathological hallmarks are intracellular inclusions containing α-synuclein aggregates and the loss of dopaminergic neurons in the substantia nigra. Parkinson's disease is thought to be caused by a combination of various pathogenic factors, including genetic factors, environmental factors, and lifestyles. Although much research has focused on the genetic causes of PD, environmental risk factors also play a crucial role in the development of the disease. Here, we summarize the environmental risk factors that may increase the occurrence of PD, as well as the underlying molecular mechanisms.

Oxidative Stress and Cognitive Decline: The Neuroprotective Role of Natural Antioxidants

Free- radicals (Oxygen and Nitrogen species) are formed in mitochondria during the oxidative phosphorylation. Their high reactivity, due to not-engaged electrons, leads to an increase of the oxidative stress. This condition affects above all the brain, that usually needs a large oxygen amount and in which there is the major possibility to accumulate "Reacting Species." Antioxidant molecules are fundamental in limiting free-radical damage, in particular in the central nervous system: the oxidative stress, in fact, seems to worsen the course of neurodegenerative diseases. The aim of this review is to sum up natural antioxidant molecules with the greatest neuroprotective properties against free radical genesis, understanding their relationship with the Central Nervous System.

Molecular and functional characaterization of the novel odorant-binding protein gene AccOBP10 from Apis cerana cerana

Odorant-binding proteins (OBPs) play an important role in odour perception and transport in insects. However, little is known about whether OBPs perform other functions in insects, particularly in Apis cerana cerana. Within this study, an OBP gene (AccOBP10) was isolated and identified from A. c. cerana. Both homology and phylogenetic relationship analyses indicated that the amino acid sequence of AccOBP10 had a high degree of sequence identity with other members of the gene family. Analysis of quantitative real-time PCR (qRT-PCR) showed that AccOBP10 mRNA was expressed at higher levels in the venom gland than in other tissues. The mRNA transcript expression of AccOBP10 was upregulated by low temperature (4°C), hydrogen peroxide (H2O2), pyridaben, methomyl and imidacloprid but downregulated by heat (42°C), ultraviolet light, vitamin C, mercuric chloride, cadmium chloride, paraquat and phoxim. Expression of AccOBP10 under abiotic stress was analysed by western blotting, and the results were consistent with those of qRT-PCR. And as a further study of AccOBP10 function, we demonstrated that knockdown of AccOBP10 by RNA interference could slightly increase the expression levels of some stress-related genes. Collectively, these results suggest that AccOBP10 is mainly involved in the response to stress conditions.

Identification of a mitogen-activated protein kinase kinase (AccMKK4) from Apis cerana cerana and its involvement in various stress responses

The mitogen-activated protein kinase (MAPK) cascade pathway is a ubiquitous signal transduction pathway in eukaryotes that regulates a variety of immune responses. This study accomplished the first isolation of an AccMKK4 gene from Apis cerana cerana and explored its function. Yeast two-hybrid experiments proved that AccMKK4 can interact with Accp38b, and the silencing of AccMKK4 in honeybees downregulated the expression level of Accp38b, which suggests that AccMKK4 might participate in the oxidative stress response through the p38 MAPK pathway. Tissue-specific expression levels of AccMKK4 analysis showed that AccMKK4 in the thorax, particularly muscle tissue, was higher than that in other tissues. The qRT-PCR results from different conditions demonstrated that AccMKK4 responds to various environmental stresses. After AccMKK4 silencing, the transcription level of some antioxidant genes and the activity of antioxidant-related enzymes are reduced, which indicated that AccMKK4 plays an important role in resistance against oxidative stress caused by external stimuli. In summary, our findings indicate that AccMKK4 probably plays an indispensable role in the response of honeybees to environmental stress and might aid for further research on the role of the MAPK cascade pathway in the antioxidant defence mechanisms of insects.

Natural products as pharmacological modulators of mitochondrial dysfunctions for the treatments of Alzheimer's disease: A comprehensive review

Alzheimer's disease (AD) is the most common progressive neurodegenerative disorder characterized by neuronal loss and cognitive impairment that harshly affect the elderly individuals. Currently, the available anti-AD pharmacological approaches are purely symptomatic to alleviate AD symptoms, and the curative effects of novel anti-AD drugs focused on Aβ target are disappointing. Hence, there is a tremendous need to adjust AD therapeutic targets and discover novel anti-AD agents. In AD, mitochondrial dysfunction gradually triggers neuronal death from different aspects and worsens the occurrence and progress of AD. Consequently, it has been proposed that the intervention of impaired mitochondria represents an attractive breakthrough point for AD treatments. Due to chemical diversity, poly-pharmacological activities, few adverse effects and multiple targeting, natural products (NPs) have been identified as a valuable treasure for drug discovery and development. Multiple lines of studies have scientifically proven that NPs display ameliorative benefits in AD treatment in relation to mitochondrial dysfunction. This review surveys the complicated implications for mitochondrial dysregulation and AD, and then summarizes the potentials of NPs and their underlying molecular mechanisms against AD via reducing or improving mitochondrial dysfunction. It is expected that this work may open the window to speed up the development of innovative anti-AD drugs originated from NPs and improve upcoming AD therapeutics.

Early low-dose ghrelin intervention via miniosmotic pumps could protect against the progressive dopaminergic neuron loss in Parkinson's disease mice

Ghrelin has been identified as a multifunctional peptide that has a potential application for treating Parkinson's disease (PD). The objective of this study was to assess the effects of subcutaneous administration of low-dose ghrelin via miniosmotic pumps on PD progression. The decreased levels of total and active ghrelin in plasma were rescued by ghrelin administration in PD mice. Interestingly, ghrelin did not affect weight gain in wild-type mice but improved weight loss in PD mice. We observed the attenuation of dopaminergic neuron loss in substantia nigra and a low level of dopamine content in the striatum in PD mice with ghrelin treatment. Ghrelin administration could improve the microenvironment of dopaminergic neurons by inhibiting microglial proliferation and proinflammatory cytokine expression and could enhance cell survival by upregulating Bcl-2/Bax ratio and superoxide dismutase1 protein level in the substantia nigra of PD mice. Subcutaneous administration of low-dose ghrelin could prevent the onset of the progression of PD and also provide a possible method for ghrelin application to cure PD.

Effects of pyriproxyfen on zebrafish brain mitochondria and acetylcholinesterase

Pyriproxyfen is an insecticide used worldwide that acts as a biomimetic of juvenile hormone. This study investigated metabolic and synaptic impairments triggered by pyriproxyfen using zebrafish acetylcholinesterase (zbAChE) and mitochondria as markers. A brain zbAChE assay was performed in vitro and in vivo covering a range of pyriproxyfen concentrations (0.001-10 μmol/L) to assess inhibition kinetics. Docking simulations were performed to characterize inhibitory interactions. Zebrafish male adults were acutely exposed to 0.001, 0.01 and 0.1 μg/mL pyriproxyfen for 16 h. Mitochondrial respiration of brain tissues was assessed. ROS generation was estimated using H₂DCF-DA and MitoSOX. Calcium transport was monitored by Calcium Green™ 5 N. NO synthesis activity was estimated using DAF-FM-DA. Brain acetylcholinesterase showed an in vivo IC₂₀ of 0.30 μmol/L pyriproxyfen, and an IC₅₀ of 92.5 μmol/L. The inhibitory effect on zbAChE activity was competitive-like. Respiratory control of Complex I/II decreased significantly after insecticide exposure. The MitoSOX test showed that O₂^- generation had a pyriproxyfen dose-dependent effect. Brain tissue lost 50% of Ca²⁺ uptake capacity at 0.1 μg/mL pyriproxyfen. Ca²⁺ release showed a clear mitochondrial impairment at lower pyriproxyfen exposures. Thus, Ca²⁺ transport imbalance caused by pyriproxyfen may be a novel deleterious mechanism of action. Overall, the results showed that pyriproxyfen can compromise multiple and interconnected pathways: (1) zbAChE impairment and (2) the functioning of the electron transport chain, ROS generation and calcium homeostasis in zebrafish brain mitochondria. Considering the many similarities between zebrafish and human, more caution is needed when pyriproxyfen is used in both urban and agricultural pest control.

Celecoxib promotes survival and upregulates the expression of neuroprotective marker genes in two different in vitro models of Parkinson's disease

Parkinson's disease (PD) is the second most common age-related neurodegenerative disorder after Alzheimer's disease. Increasing evidence highlights the role of age-related chronic inflammation, oxidative stress and mitochondrial dysfunction in the pathogenesis of PD. A combination of these factors impairs the crosstalk between mitochondria and lysosomes, resulting in compromised cell homeostasis. Apolipoprotein D (APOD), an ancient and highly conserved anti-inflammatory and antioxidant lipocalin, and the transcription factor EB (TFEB), a master regulator of mitophagy, autophagy and lysosomal biogenesis, play key roles in these processes. Both APOD and TFEB have attracted attention as therapeutic targets for PD. The aim of this study was to investigate if the selective cyclooxygenase-2 inhibitor celecoxib (CXB) exerts a direct neuroprotective effect in 6-hydroxydopamine (6-OHDA) and paraquat (PQ) PD models. We found that CXB rescued SH-SY5Y cells challenged by 6-OHDA- and PQ-induced toxicity. Furthermore, treatment with CXB led to a marked and sustained upregulation of APOD and the two microphthalmia transcription factors TFEB and MITF. In sum, this study highlights the clinically approved drug CXB as a promising neuroprotective therapeutic tool in PD research that has the potential to increase the survival rate of dopaminergic neurons that are still alive at the time of diagnosis.

Saponins of Panax japonicus Confer Neuroprotection against Brain Aging through Mitochondrial Related Oxidative Stress and Autophagy in Rats

BACKGROUND

Oxidative stress and mitochondrial dysfunction play a vital role in the pathogenesis of brain aging. Saponins from Panax japonicus (SPJ) have attracted much attention for their potential to attenuate age-related oxidative stress as the main ingredient in rhizomes of Panax japonicus.

OBJECTIVE

This study aimed to investigate the neuroprotective effects of SPJ on natural aging rats as well as the underlying mechanisms regarding oxidative stress and mitochondrial pathway.

METHODS

Sprague-Dawley rats were divided into control groups (3-, 9-, 15- and 24-month old groups) and SPJ-treated groups. For SPJ-treated groups, SPJ were orally administrated to 18-month old rats at doses of 10 mg/kg, 30 mg/kg and 60 mg/kg once daily. Control groups were given the same volume of saline. After the treatment with SPJ or saline for six months, the cortex and hippocampus were rapidly harvested and deposited at -80°C after the rats were decapitated under anesthesia. The neuroprotective effects of SPJ were estimated by histopathological observation, TUNEL detection, biochemical determination and western blotting.

RESULTS

SPJ improved pathomorphological changes in neuronal cells and decreased apoptosis in the cortex and hippocampus of aging rats, increased the activities of superoxide dismutase (SOD), glutathione peroxidase (GSH-Px), Na+/K+-ATPase, Ca2+-ATPase and Ca2+/Mg2+-ATPase whereas, decreased malondialdehyde (MDA) contents in the cortex of aging rats. Furthermore, the SPJ increased silent mating type information regulation 2 homolog-1 (SIRT1) protein expression, decreased acetylated level of peroxisome proliferator-activated receptor-γ coactivator-1α (PGC-1α) in the cortex and hippocampus of aging rats, and reversed the aging-induced decline of Forkhead box O3 (Foxo3a), Superoxide Dismutase 2 (SOD2), microtubule-associated protein light chain 3 (LC3II) and Beclin1 levels in the cortex and hippocampus.

CONCLUSION

Our data showed that SPJ conferred neuroprotection partly through the regulation of oxidative stress and mitochondria-related pathways in aging rats.

Neuroprotection of GLP-1/GIP receptor agonist via inhibition of mitochondrial stress by AKT/JNK pathway in a Parkinson's disease model

OBJECTIVES

To investigate the effect of glucagon-like peptide-1 (GLP-1) receptor and glucose dependent insulinotrophic polypeptide (GIP) receptor dual agonist DA-JC4 on alleviating Parkinson's disease (PD) and unveil related cellular mechanisms.

METHODS

Rotenone was injected to generate a rat PD model, on which the effect of DA-JC4 on motor functions was evaluated by rotational behavioral assay and open field test. The survival of dopaminergic neurons was analyzed, in addition to assays for mitochondrial stress and quantification of neurotransmitter levels using high performance liquid chromatography (HPLC). In cultured hippocampal neurons, the effect of DA-JC4 on mitochondrial stress and related cellular mechanism was analyzed by Flow cytometry, western blotting and reactive oxygen species (ROS).

RESULTS

DA-JC4 significantly improved motor functions in PD rats, and elevated levels of major neurotransmitters. By histological analysis, DA-JC4 protected dopaminergic neurons from rotenone-induced cell death, which was associated with reduced mitochondrial stress. Experiments in cultured rat hippocampal neurons validated the neuroprotective role of DA-JC4 against cell apoptosis and mitochondrial stress induced by rotenone. The protective effect of DA-JC4 was later found to be dependent on AKT/JNK signal pathway, as treatment using AKT inhibitor or JNK activator abolished such effects.

CONCLUSION

Our results showed that the dual agonist of GLP-1/GIP receptor could ameliorate motor dysfunctions of PD by protecting dopaminergic neurons which was mediated by relieved mitochondrial stress and apoptosis via AKT/JNK signal pathway.

Survival Mechanisms and Xenobiotic Susceptibility of Keratinocytes Exposed to Metal-Derived Nanoparticles

Metal-derived nanoparticles (Mt-NPs) are increasingly used in cosmetology due to their ultraviolet shielding (titanium dioxide [TiO₂]), antioxidant (cerium dioxide [CeO₂]), and biocidal (silver [Ag]) properties. In the absence of overt toxicity (i.e., cell death), Mt-NPs are considered safe for cosmetic applications. However, there is little understanding about the mechanisms involved in the survival of keratinocytes exposed to subtoxic levels of Mt-NPs. Human keratinocytes (HaCaT) were exposed subacutely to subtoxic concentrations (≤30 μg/mL, 48-72 h) of rutile (r) TiO₂ (cylindrical), CeO₂ (cubic) and Ag (spherical) with a core/hydrodynamic size of <50/<100 nm and >98% purity. Mt-NP uptake was indirectly quantified by changes in the light side scatter, where the kinetics (time/dose-response) suggested that the three types of Mt-NPs were similarly uptaken by keratinocytes. rTiO₂ and CeO₂, but not Ag-NPs, increased autophagy, whose inhibition prompted cell death. No increase in the steady-state levels of reactive oxygen species (ROS) was induced by exposure to any of the Mt-NPs tested. Interestingly, intracellular Ag-NP aggregates observed an increased far-red autofluorescence (≥740 nm em), which has been ascribed to their binding to thiol molecules such as glutathione (GSH). Accordingly, inhibition of GSH synthesis, but not the impairment of oxidized GSH recycling, sensitized keratinocytes to Ag-NPs suggesting that GSH homeostasis, and its direct scavenging of Ag-NPs, but not ROS, is essential for keratinocyte survival upon exposure to Ag-NP. rTiO₂ and Ag, but not CeO₂-NPs, compromised metabolic flux (glycolysis and respiration), but ATP levels were unaltered. Finally, we also observed that exposure to Mt-NPs sensitized keratinocytes to non-UV xenobiotic exposure (arsenite and paraquat). Our results demonstrate the differential contribution of autophagy and GSH homeostasis to the survival of human keratinocytes exposed to subtoxic concentrations of Mt-NPs and highlight the increased susceptibility of keratinocytes exposed to Mt-NPs to a second xenobiotic insult.

Oxidative Stress in Neurodegenerative Diseases: From a Mitochondrial Point of View

Age is the main risk factor for a number of human diseases, including neurodegenerative disorders such as Alzheimer's disease, Parkinson's disease, and amyotrophic lateral sclerosis, which increasing numbers of elderly individuals suffer. These pathological conditions are characterized by progressive loss of neuron cells, compromised motor or cognitive functions, and accumulation of abnormally aggregated proteins. Mitochondrial dysfunction is one of the main features of the aging process, particularly in organs requiring a high-energy source such as the heart, muscles, brain, or liver. Neurons rely almost exclusively on the mitochondria, which produce the energy required for most of the cellular processes, including synaptic plasticity and neurotransmitter synthesis. The brain is particularly vulnerable to oxidative stress and damage, because of its high oxygen consumption, low antioxidant defenses, and high content of polyunsaturated fats very prone to be oxidized. Thus, it is not surprising the importance of protecting systems, including antioxidant defenses, to maintain neuronal integrity and survival. Here, we review the role of mitochondrial oxidative stress in the aging process, with a specific focus on neurodegenerative diseases. Understanding the molecular mechanisms involving mitochondria and oxidative stress in the aging and neurodegeneration may help to identify new strategies for improving the health and extending lifespan.

Redox Mechanisms in Neurodegeneration: From Disease Outcomes to Therapeutic Opportunities

SIGNIFICANCE

Once considered to be mere by-products of metabolism, reactive oxygen, nitrogen and sulfur species are now recognized to play important roles in diverse cellular processes such as response to pathogens and regulation of cellular differentiation. It is becoming increasingly evident that redox imbalance can impact several signaling pathways. For instance, disturbances of redox regulation in the brain mediate neurodegeneration and alter normal cytoprotective responses to stress. Very often small disturbances in redox signaling processes, which are reversible, precede damage in neurodegeneration. Recent Advances: The identification of redox-regulated processes, such as regulation of biochemical pathways involved in the maintenance of redox homeostasis in the brain has provided deeper insights into mechanisms of neuroprotection and neurodegeneration. Recent studies have also identified several post-translational modifications involving reactive cysteine residues, such as nitrosylation and sulfhydration, which fine-tune redox regulation. Thus, the study of mechanisms via which cell death occurs in several neurodegenerative disorders, reveal several similarities and dissimilarities. Here, we review redox regulated events that are disrupted in neurodegenerative disorders and whose modulation affords therapeutic opportunities.

CRITICAL ISSUES

Although accumulating evidence suggests that redox imbalance plays a significant role in progression of several neurodegenerative diseases, precise understanding of redox regulated events is lacking. Probes and methodologies that can precisely detect and quantify in vivo levels of reactive oxygen, nitrogen and sulfur species are not available.

FUTURE DIRECTIONS

Due to the importance of redox control in physiologic processes, organisms have evolved multiple pathways to counteract redox imbalance and maintain homeostasis. Cells and tissues address stress by harnessing an array of both endogenous and exogenous redox active substances. Targeting these pathways can help mitigate symptoms associated with neurodegeneration and may provide avenues for novel therapeutics. Antioxid. Redox Signal. 30, 1450-1499.

Oxidative stress and pesticide disease: a challenge for toxicology

Introducción. En los últimos decenios, la síntesis de compuestos químicos ha producido un alto número de sustancias utilizadas para proteger los cultivos y las cosechas de las plagas. La mayoría de pesticidas han sido usados en grandes cantidades para fines agrícolas y la exposición tóxica a estos compuestos es un problema de gran envergadura para la toxicología, pues tiene impacto en la salud pública por su importante morbilidad y discapacidad. Así, las intoxicaciones agudas y crónicas pueden ser comunes entre trabajadores agrícolas y población general. Estos compuestos desencadenan mecanismos moleculares relacionados con la peroxidación lipídica, donde las especies reactivas de oxigeno pueden incrementar procesos oxidativos intracelulares.Objetivo. Realizar una revisión de la literatura científica relacionada con enfermedades por estrés oxidativo producido por pesticidas.Materiales y métodos. Revisión de artículos que utilizó las palabras clave Estrés oxidativo; Pesticidas; Peroxidación de lípido; Toxicidad. Se eligieron los artículos relacionados con las enfermedades por estrés oxidativo producido por pesticidas.Resultados. Se encontró que algunas enfermedades hematológicas, neurológicas, metabólicas y genotóxicas pueden estar relacionadas con la peroxidación lipídica que producen los pesticidas.Conclusión. Se presenta una revisión de la literatura científica sobre el estrés oxidativo, la peroxidación lipídica inducida por pesticidas y las diferentes enfermedades que pueden afectar a la población en general.

Redox-sensitive GFP to monitor oxidative stress in neurodegenerative diseases

Redox processes are key events in the degenerative cascade of many adult-onset neurodegenerative diseases (NDs), but the biological relevance of a single redox change is often dependent on the redox couple involved and on its subcellular origin. The biosensors based on engineered fluorescent proteins (redox-sensitive GFP [roGFP]) offer a unique opportunity to monitor redox changes in both physiological and pathological contexts in living animals and plants. Here, we review the use of roGFPs to monitor oxidative stress in different three adult-onset NDs: Alzheimer's disease (AD), Parkinson's disease (PD), and amyotrophic lateral sclerosis (ALS). Despite the many differences spanning from incidence to onset, the hypotheses on biological processes underlying both sporadic and familiar ND forms in humans outline a model in which noncompeting mechanisms are likely to converge in various unsuccessful patterns to mediate the selective degeneration of a specific neuronal population. roGFPs, targeted to different cell compartments, are successfully used as specific markers of cell toxicity, induced by expression of causative genes linked to a determined ND. We also report the use of roGFP to monitor oxidative stress induced by the expression of the ALS-causative gene SOD1.

The Analgesic Acetaminophen and the Antipsychotic Clozapine Can Each Redox-Cycle with Melanin

Melanins are ubiquitous but their complexity and insolubility has hindered characterization of their structures and functions. We are developing electrochemical reverse engineering methodologies that focus on properties and especially on redox properties. Previous studies have shown that melanins (i) are redox-active and can rapidly and repeatedly exchange electrons with diffusible oxidants and reductants, and (ii) have redox potentials in midregion of the physiological range. These properties suggest the functional activities of melanins will depend on their redox context. The brain has a complex redox context with steep local gradients in O₂ that can promote redox-cycling between melanin and diffusible redox-active chemical species. Here, we performed in vitro reverse engineering studies and report that melanins can redox-cycle with two common redox-active drugs. Experimentally, we used two melanin models: a convenient natural melanin derived from cuttlefish (Sepia melanin) and a synthetic cysteinyldopamine-dopamine core-shell model of neuromelanin. One drug, acetaminophen (APAP), has been used clinically for over a century, and recent studies suggest that low doses of APAP can protect the brain from oxidative-stress-induced toxicity and neurodegeneration, while higher doses can have toxic effects in the brain. The second drug, clozapine (CLZ), is a second generation antipsychotic with polypharmacological activities that remain incompletely understood. These in vitro observations suggest that the redox activities of drugs may be relevant to their modes-of-action, and that melanins may interact with drugs in ways that affect their activities, metabolism, and toxicities.

Purinergic receptor P2Y6 contributes to 1-methyl-4-phenylpyridinium-induced oxidative stress and cell death in neuronal SH-SY5Y cells

Oxidative stress and neural degeneration have been shown to be involved in the pathogenesis of Parkinson's disease (PD). The P2Y6 purinergic receptor (P2Y6R) has been shown to participate in the activation of microglia and the production of pro-inflammatory factors induced by lipopolysaccharide to cause neuronal loss. However, the function of P2Y6R during oxidative stress in neurons is unclear. In the present study, 1-methyl-4-phenylpyridinium (MPP⁺ ) treatment increased the level of UDP/P2Y6R on neuronal SH-SY5Y cells. Importantly, pharmacological inhibition of P2Y6R or knockdown of P2Y6R using a siRNA exerted an increased protective effect by preventing MPP⁺ -induced increases in the levels of reactive oxygen species (ROS), superoxide anion, inducible nitric oxide synthase (iNOS), and malondialdehyde (MDA) and down-regulation of superoxide dismutase 1 (SOD1) expression. UDP, an agonist of P2Y6R, enhanced the effects of MPP⁺ , which was also inhibited by apyrase or MRS2578. Additionally, P2Y6R knockdown also significantly reversed both the loss of cell viability and the increase in the levels of phosphorylated extracellular signal-regulated protein kinase (p-ERK1/2) and p38 (p-p38) caused by MPP⁺ stimulation. However, the inhibition of the ERK1/2 and p38 kinase signaling pathways had no effect on P2Y6R expression. Taken together, these results support the hypothesis that P2Y6R expressed on neuronal SH-SY5Y cell is associated with the progression of oxidative stress and cell death induced by MPP⁺ , suggesting that P2Y6R may play an important role in the pathogenesis of PD.

The impact of pesticides on oxidative stress level in human organism and their activity as an endocrine disruptor

Pesticides cause serious environmental and health problems both to humans and animals. The aim of this review is to discuss selected herbicides and fungicides regarding their mode of action and their influence on basic oxidative stress parameters and endocrine disruption properties tested in selected cell cultures in vitro. Because of numerous difficulties which animal studies are subject to, cell cultures are an excellent experimental model reflecting human exposure to different pesticides through all relevant routes. This experimental model can be used to monitor aggregate and cumulative pesticide exposures.

Metabolic Dysfunction in Parkinson's Disease: Bioenergetics, Redox Homeostasis and Central Carbon Metabolism

The loss of dopaminergic neurons in the substantia nigra pars compacta (SNpc) and the accumulation of protein inclusions (Lewy bodies) are the pathological hallmarks of Parkinson's disease (PD). PD is triggered by genetic alterations, environmental/occupational exposures and aging. However, the exact molecular mechanisms linking these PD risk factors to neuronal dysfunction are still unclear. Alterations in redox homeostasis and bioenergetics (energy failure) are thought to be central components of neurodegeneration that contribute to the impairment of important homeostatic processes in dopaminergic cells such as protein quality control mechanisms, neurotransmitter release/metabolism, axonal transport of vesicles and cell survival. Importantly, both bioenergetics and redox homeostasis are coupled to neuro-glial central carbon metabolism. We and others have recently established a link between the alterations in central carbon metabolism induced by PD risk factors, redox homeostasis and bioenergetics and their contribution to the survival/death of dopaminergic cells. In this review, we focus on the link between metabolic dysfunction, energy failure and redox imbalance in PD, making an emphasis in the contribution of central carbon (glucose) metabolism. The evidence summarized here strongly supports the consideration of PD as a disorder of cell metabolism.

Glucose Metabolism and AMPK Signaling Regulate Dopaminergic Cell Death Induced by Gene (α-Synuclein)-Environment (Paraquat) Interactions

While environmental exposures are not the single cause of Parkinson's disease (PD), their interaction with genetic alterations is thought to contribute to neuronal dopaminergic degeneration. However, the mechanisms involved in dopaminergic cell death induced by gene-environment interactions remain unclear. In this work, we have revealed for the first time the role of central carbon metabolism and metabolic dysfunction in dopaminergic cell death induced by the paraquat (PQ)-α-synuclein interaction. The toxicity of PQ in dopaminergic N27 cells was significantly reduced by glucose deprivation, inhibition of hexokinase with 2-deoxy-D-glucose (2-DG), or equimolar substitution of glucose with galactose, which evidenced the contribution of glucose metabolism to PQ-induced cell death. PQ also stimulated an increase in glucose uptake, and in the levels of glucose transporter type 4 (GLUT4) and Na⁺-glucose transporters isoform 1 (SGLT1) proteins, but only inhibition of GLUT-like transport with STF-31 or ascorbic acid reduced PQ-induced cell death. Importantly, while autophagy protein 5 (ATG5)/unc-51 like autophagy activating kinase 1 (ULK1)-dependent autophagy protected against PQ toxicity, the inhibitory effect of glucose deprivation on cell death progression was largely independent of autophagy or mammalian target of rapamycin (mTOR) signaling. PQ selectively induced metabolomic alterations and adenosine monophosphate-activated protein kinase (AMPK) activation in the midbrain and striatum of mice chronically treated with PQ. Inhibition of AMPK signaling led to metabolic dysfunction and an enhanced sensitivity of dopaminergic cells to PQ. In addition, activation of AMPK by PQ was prevented by inhibition of the inducible nitric oxide syntase (iNOS) with 1400W, but PQ had no effect on iNOS levels. Overexpression of wild type or A53T mutant α-synuclein stimulated glucose accumulation and PQ toxicity, and this toxic synergism was reduced by inhibition of glucose metabolism/transport and the pentose phosphate pathway (6-aminonicotinamide). These results demonstrate that glucose metabolism and AMPK regulate dopaminergic cell death induced by gene (α-synuclein)-environment (PQ) interactions.

Mitochondrially targeted fluorescent redox sensors

The balance of oxidants and antioxidants within the cell is crucial for maintaining health, and regulating physiological processes such as signalling. Consequently, imbalances between oxidants and antioxidants are now understood to lead to oxidative stress, a physiological feature that underlies many diseases. These processes have spurred the field of chemical biology to develop a plethora of sensors, both small-molecule and fluorescent protein-based, for the detection of specific oxidizing species and general redox balances within cells. The mitochondrion, in particular, is the site of many vital redox reactions. There is therefore a need to target redox sensors to this particular organelle. It has been well established that targeting mitochondria can be achieved by the use of a lipophilic cation-targeting group, or by utilizing natural peptidic mitochondrial localization sequences. Here, we review how these two approaches have been used by a number of researchers to develop mitochondrially localized fluorescent redox sensors that are already proving useful in providing insights into the roles of reactive oxygen species in the mitochondria.

Differential Effects of CORM-2 and CORM-401 in Murine Intestinal Epithelial MODE-K Cells under Oxidative Stress

Carbon monoxide (CO)-releasing molecules (CO-RMs) are intensively studied to provide cytoprotective and anti-inflammatory effects of CO in inflammatory conditions including intestinal inflammation. The water-soluble CORM-A1 reduced apoptosis and NADPH oxidase (NOX)-derived reactive oxygen species (ROS) induced by tumor necrosis factor (TNF)-α/cycloheximide (CHX) in mouse MODE-K intestinal epithelial cells (IECs), without influencing TNF-α/CHX-induced mitochondrial superoxide anion (O2•–). The aim of the present study in the same model was to comparatively investigate the influence of lipid-soluble CORM-2 and water-soluble CORM-401, shown in vitro to release more CO under oxidative conditions. CORM-2 abolished TNF-α/CHX-induced total cellular ROS whereas CORM-401 partially reduced it, both partially reducing TNF-α/CHX-induced cell death. Only CORM-2 increased mitochondrial O2•– production after 2 h of incubation. CORM-2 reduced TNF-α/CHX-, rotenone- and antimycin-A-induced mitochondrial O2•– production; CORM-401 only reduced the effect of antimycin-A. Co-treatment with CORM-401 during 1 h exposure to H₂O₂ reduced H₂O₂ (7.5 mM)-induced ROS production and cell death, whereas CORM-2 did not. The study illustrates the importance of the chemical characteristics of different CO-RMs. The lipid solubility of CORM-2 might contribute to its interference with TNF-α/CHX-induced mitochondrial ROS signaling, at least in mouse IECs. CORM-401 is more effective than other CO-RMs under H₂O₂-induced oxidative stress conditions.

Neuroprotective Effect of a New 7,8-Dihydroxycoumarin-Based Fe2+/Cu2+ Chelator in Cell and Animal Models of Parkinson's Disease

Disturbed iron homeostasis, often coupled to mitochondrial dysfunction, plays an important role in the progression of common neurodegenerative diseases such as Parkinson's disease (PD). Recent studies have underlined the relevance of iron chelation therapy for the treatment of these diseases. Here we describe the synthesis, chemical, and biological characterization of the multifunctional chelator 7,8-dihydroxy-4-((methylamino)methyl)-2H-chromen-2-one (DHC12). Metal selectivity of DHC12 was Cu²⁺ ∼ Fe²⁺ > Zn²⁺ > Fe³⁺. No binding capacity was detected for Hg²⁺, Co²⁺, Ca²⁺, Mn²⁺, Mg²⁺, Ni²⁺, Pb²⁺, or Cd²⁺. DHC12 accessed cells colocalizing with Mitotracker Orange, an indication of mitochondrial targeting. In addition, DHC12 chelated mitochondrial and cytoplasmic labile iron. Upon mitochondrial complex I inhibition, DHC12 protected plasma membrane and mitochondria against lipid peroxidation, as detected by the reduced formation of 4-hydroxynonenal adducts and oxidation of C11-BODIPY^581/591. DHC12 also blocked the decrease in mitochondrial membrane potential, detected by tetramethylrhodamine distribution. DHC12 inhibited MAO-A and MAO-B activity. Oral administration of DHC12 to mice (0.25 mg/kg body weight) protected substantia nigra pars compacta (SNpc) neurons against MPTP-induced death. Taken together, our results support the concept that DHC12 is a mitochondrial-targeted neuroprotective iron-copper chelator and MAO-B inhibitor with potent antioxidant and mitochondria protective activities. Oral administration of low doses of DHC12 is a promising therapeutic strategy for the treatment of diseases with a mitochondrial iron accumulation component, such as PD.

Differential Effects of CORM-2 and CORM-401 in Murine Intestinal Epithelial MODE-K Cells under Oxidative Stress

Carbon monoxide (CO)-releasing molecules (CO-RMs) are intensively studied to provide cytoprotective and anti-inflammatory effects of CO in inflammatory conditions including intestinal inflammation. The water-soluble CORM-A1 reduced apoptosis and NADPH oxidase (NOX)-derived reactive oxygen species (ROS) induced by tumor necrosis factor (TNF)-α/cycloheximide (CHX) in mouse MODE-K intestinal epithelial cells (IECs), without influencing TNF-α/CHX-induced mitochondrial superoxide anion ([Formula: see text]). The aim of the present study in the same model was to comparatively investigate the influence of lipid-soluble CORM-2 and water-soluble CORM-401, shown in vitro to release more CO under oxidative conditions. CORM-2 abolished TNF-α/CHX-induced total cellular ROS whereas CORM-401 partially reduced it, both partially reducing TNF-α/CHX-induced cell death. Only CORM-2 increased mitochondrial [Formula: see text] production after 2 h of incubation. CORM-2 reduced TNF-α/CHX-, rotenone- and antimycin-A-induced mitochondrial [Formula: see text] production; CORM-401 only reduced the effect of antimycin-A. Co-treatment with CORM-401 during 1 h exposure to H₂O₂ reduced H₂O₂ (7.5 mM)-induced ROS production and cell death, whereas CORM-2 did not. The study illustrates the importance of the chemical characteristics of different CO-RMs. The lipid solubility of CORM-2 might contribute to its interference with TNF-α/CHX-induced mitochondrial ROS signaling, at least in mouse IECs. CORM-401 is more effective than other CO-RMs under H₂O₂-induced oxidative stress conditions.

Crosstalk between Ca2+ signaling and mitochondrial H2O2 is required for rotenone inhibition of mTOR signaling pathway leading to neuronal apoptosis

Rotenone, a neurotoxic pesticide, induces loss of dopaminergic neurons related to Parkinson's disease. Previous studies have shown that rotenone induces neuronal apoptosis partly by triggering hydrogen peroxide (H₂O₂)-dependent suppression of mTOR pathway. However, the underlying mechanism is not fully understood. Here, we show that rotenone elevates intracellular free calcium ion ([Ca²⁺]_i) level, and activates CaMKII, resulting in inhibition of mTOR signaling and induction of neuronal apoptosis. Chelating [Ca²⁺]_i with BAPTA/AM, preventing extracellular Ca²⁺ influx using EGTA, inhibiting CaMKII with KN93, or silencing CaMKII significantly attenuated rotenone-induced H₂O₂ production, mTOR inhibition, and cell death. Interestingly, using TTFA, antimycin A, catalase or Mito-TEMPO, we found that rotenone-induced mitochondrial H₂O₂ also in turn elevated [Ca²⁺]_i level, thereby stimulating CaMKII, leading to inhibition of mTOR pathway and induction of neuronal apoptosis. Expression of wild type mTOR or constitutively active S6K1, or silencing 4E-BP1 strengthened the inhibitory effects of catalase, Mito-TEMPO, BAPTA/AM or EGTA on rotenone-induced [Ca²⁺]_i elevation, CaMKII phosphorylation and neuronal apoptosis. Together, the results indicate that the crosstalk between Ca²⁺ signaling and mitochondrial H₂O₂ is required for rotenone inhibition of mTOR-mediated S6K1 and 4E-BP1 pathways. Our findings suggest that how to control over-elevation of intracellular Ca²⁺ and overproduction of mitochondrial H₂O₂ may be a new approach to deal with the neurotoxicity of rotenone.

Low-Dose Pesticide Mixture Induces Senescence in Normal Mesenchymal Stem Cells (MSC) and Promotes Tumorigenic Phenotype in Premalignant MSC

Humans are chronically exposed to multiple environmental pollutants such as pesticides with no significant evidence about the safety of such poly-exposures. We exposed mesenchymal stem cells (MSC) to very low doses of mixture of seven pesticides frequently detected in food samples for 21 days in vitro. We observed a permanent phenotype modification with a specific induction of an oxidative stress-related senescence. Pesticide mixture also induced a shift in MSC differentiation towards adipogenesis but did not initiate a tumorigenic transformation. In modified MSC in which a premalignant phenotype was induced, the exposure to pesticide mixture promoted tumorigenic phenotype both in vitro and in vivo after cell implantation, in all nude mice. Our results suggest that a common combination of pesticides can induce a premature ageing of adult MSC, and as such could accelerate age-related diseases. Exposure to pesticide mixture may also promote the tumorigenic transformation in a predisposed stromal environment. Abstract Video Link: https://youtu.be/mfSVPTol-Gk Stem Cells 2017;35:800-811.

Paraquat-Melanin Redox-Cycling: Evidence from Electrochemical Reverse Engineering

Parkinson's disease is a neurodegenerative disorder associated with oxidative stress and the death of melanin-containing neurons of the substantia nigra. Epidemiological evidence links exposure to the pesticide paraquat (PQ) to Parkinson's disease, and this link has been explained by a redox cycling mechanism that induces oxidative stress. Here, we used a novel electrochemistry-based reverse engineering methodology to test the hypothesis that PQ can undergo reductive redox cycling with melanin. In this method, (i) an insoluble natural melanin (from Sepia melanin) and a synthetic model melanin (having a cysteinyldopamine-melanin core and dopamine-melanin shell) were entrapped in a nonconducting hydrogel film adjacent to an electrode, (ii) the film-coated electrode was immersed in solutions containing PQ (putative redox cycling reductant) and a redox cycling oxidant (ferrocene dimethanol), (iii) sequences of input potentials (i.e., voltages) were imposed to the underlying electrode to systematically engage reductive and oxidative redox cycling, and (iv) output response currents were analyzed for signatures of redox cycling. The response characteristics of the PQ-melanin systems to various input potential sequences support the hypothesis that PQ can directly donate electrons to melanin. This observation of PQ-melanin redox interactions demonstrates an association between two components that have been individually linked to oxidative stress and Parkinson's disease. Potentially, melanin's redox activity could be an important component in understanding the etiology of neurological disorders such as Parkinson's disease.

Glucose Metabolism and AMPK Signaling Regulate Dopaminergic Cell Death Induced by Gene (α-Synuclein)-Environment (Paraquat) Interactions

While environmental exposures are not the single cause of Parkinson's disease (PD), their interaction with genetic alterations is thought to contribute to neuronal dopaminergic degeneration. However, the mechanisms involved in dopaminergic cell death induced by gene-environment interactions remain unclear. In this work, we have revealed for the first time the role of central carbon metabolism and metabolic dysfunction in dopaminergic cell death induced by the paraquat (PQ)-α-synuclein interaction. The toxicity of PQ in dopaminergic N27 cells was significantly reduced by glucose deprivation, inhibition of hexokinase with 2-deoxy-D-glucose (2-DG), or equimolar substitution of glucose with galactose, which evidenced the contribution of glucose metabolism to PQ-induced cell death. PQ also stimulated an increase in glucose uptake, and in the levels of glucose transporter type 4 (GLUT4) and Na⁺-glucose transporters isoform 1 (SGLT1) proteins, but only inhibition of GLUT-like transport with STF-31 or ascorbic acid reduced PQ-induced cell death. Importantly, while autophagy protein 5 (ATG5)/unc-51 like autophagy activating kinase 1 (ULK1)-dependent autophagy protected against PQ toxicity, the inhibitory effect of glucose deprivation on cell death progression was largely independent of autophagy or mammalian target of rapamycin (mTOR) signaling. PQ selectively induced metabolomic alterations and adenosine monophosphate-activated protein kinase (AMPK) activation in the midbrain and striatum of mice chronically treated with PQ. Inhibition of AMPK signaling led to metabolic dysfunction and an enhanced sensitivity of dopaminergic cells to PQ. In addition, activation of AMPK by PQ was prevented by inhibition of the inducible nitric oxide syntase (iNOS) with 1400W, but PQ had no effect on iNOS levels. Overexpression of wild type or A53T mutant α-synuclein stimulated glucose accumulation and PQ toxicity, and this toxic synergism was reduced by inhibition of glucose metabolism/transport and the pentose phosphate pathway (6-aminonicotinamide). These results demonstrate that glucose metabolism and AMPK regulate dopaminergic cell death induced by gene (α-synuclein)-environment (PQ) interactions.

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

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

Dissecting Redox Biology Using Fluorescent Protein Sensors

SIGNIFICANCE

Fluorescent protein sensors have revitalized the field of redox biology by revolutionizing the study of redox processes in living cells and organisms.

RECENT ADVANCES

Within one decade, a set of fundamental new insights has been gained, driven by the rapid technical development of in vivo redox sensing. Redox-sensitive yellow and green fluorescent protein variants (rxYFP and roGFPs) have been the central players.

CRITICAL ISSUES

Although widely used as an established standard tool, important questions remain surrounding their meaningful use in vivo. We review the growing range of thiol redox sensor variants and their application in different cells, tissues, and organisms. We highlight five key findings where in vivo sensing has been instrumental in changing our understanding of redox biology, critically assess the interpretation of in vivo redox data, and discuss technical and biological limitations of current redox sensors and sensing approaches.

FUTURE DIRECTIONS

We explore how novel sensor variants may further add to the current momentum toward a novel mechanistic and integrated understanding of redox biology in vivo. Antioxid. Redox Signal. 24, 680-712.

Superoxide Dismutase (SOD)-mimetic M40403 Is Protective in Cell and Fly Models of Paraquat Toxicity: IMPLICATIONS FOR PARKINSON DISEASE

Parkinson disease is a debilitating and incurable neurodegenerative disorder affecting ∼1–2% of people over 65 years of age. Oxidative damage is considered to play a central role in the progression of Parkinson disease and strong evidence links chronic exposure to the pesticide paraquat with the incidence of the disease, most probably through the generation of oxidative damage. In this work, we demonstrated in human SH-SY5Y neuroblastoma cells the beneficial role of superoxide dismutase (SOD) enzymes against paraquat-induced toxicity, as well as the therapeutic potential of the SOD-mimetic compound M40403. Having verified the beneficial effects of superoxide dismutation in cells, we then evaluated the effects using Drosophila melanogaster as an in vivo model. Besides protecting against the oxidative damage induced by paraquat treatment, our data demonstrated that in Drosophila M40403 was able to compensate for the loss of endogenous SOD enzymes, acting both at a cytosolic and mitochondrial level. Because previous clinical trials have indicated that the M40403 molecule is well tolerated in humans, this study may have important implication for the treatment of Parkinson disease.

Acute paraquat exposure impairs colonic motility by selectively attenuating nitrergic signalling in the mouse

Paraquat, a common herbicide, is responsible for large numbers of deaths worldwide through both deliberate and accidental ingestion. Previous studies have eluded that the bioavailability of paraquat increases substantially with increasing dose and that these changes may in part be due to the effects that these high concentrations have on the gastrointestinal tract (GI tract). To date, the actions of acute, high concentrations (20mM for 60 min) of paraquat on the GI tract, particularly the colon which is a major site of paraquat absorption, are unknown. This study examined the effects of acute paraquat administration on colonic motility in the C57BL/6 mouse. Acute paraquat exposure decreased colonic motility and the amplitude of colonic migrating motor complexes (CMMCs), which are major motor patterns involved in faecal pellet propulsion. In isolated segments of distal colon, paraquat increased resting tension and markedly attenuated electrical field stimulation-evoked relaxations. Pharmacological dissection of paraquat's mechanism of action on both the CMMCs and field stimulated tissue using the nitric oxide synthase inhibitor NG-nitro-L-arginine and direct measurement of NO release from the myenteric plexus, demonstrated that paraquat selectively attenuates nitrergic signalling pathways. These changes did not appear to be due to alterations in colonic oxidative stress, inflammation or complex 1 activity, but were most likely caused by paraquat's ability to act as a redox couple. In summary, these data demonstrate that acute paraquat exposure attenuates colonic transit. These changes may facilitate the absorption of paraquat into the circulation and so facilitate its toxicity.

Dieckol, an edible seaweed polyphenol, retards rotenone-induced neurotoxicity and α-synuclein aggregation in human dopaminergic neuronal cells

Dopaminergic neurons are particularly vulnerable to oxidative stress, which may initiate a cascade of intracellular toxic events that lead to protein aggregation and subsequent cell death, causing Parkinson's disease.

Inhibition of Protein Ubiquitination by Paraquat and 1-Methyl-4-Phenylpyridinium Impairs Ubiquitin-Dependent Protein Degradation Pathways

Intracytoplasmic inclusions of protein aggregates in dopaminergic cells (Lewy bodies) are the pathological hallmark of Parkinson's disease (PD). Ubiquitin (Ub), alpha (α)-synuclein, p62/sequestosome 1, and oxidized proteins are the major components of Lewy bodies. However, the mechanisms involved in the impairment of misfolded/oxidized protein degradation pathways in PD are still unclear. PD is linked to mitochondrial dysfunction and environmental pesticide exposure. In this work, we evaluated the effects of the pesticide paraquat (PQ) and the mitochondrial toxin 1-methyl-4-phenylpyridinium (MPP(+)) on Ub-dependent protein degradation pathways. No increase in the accumulation of Ub-bound proteins or aggregates was observed in dopaminergic cells (SK-N-SH) treated with PQ or MPP(+), or in mice chronically exposed to PQ. PQ decreased Ub protein content, but not its mRNA transcription. Protein synthesis inhibition with cycloheximide depleted Ub levels and potentiated PQ-induced cell death. The inhibition of proteasomal activity by PQ was found to be a late event in cell death progression and had neither effect on the toxicity of either MPP(+) or PQ, nor on the accumulation of oxidized sulfenylated, sulfonylated (DJ-1/PARK7 and peroxiredoxins), and carbonylated proteins induced by PQ. PQ- and MPP(+)-induced Ub protein depletion prompted the dimerization/inactivation of the Ub-binding protein p62 that regulates the clearance of ubiquitinated proteins by autophagy. We confirmed that PQ and MPP(+) impaired autophagy flux and that the blockage of autophagy by the overexpression of a dominant-negative form of the autophagy protein 5 (dnAtg5) stimulated their toxicity, but there was no additional effect upon inhibition of the proteasome. PQ induced an increase in the accumulation of α-synuclein in dopaminergic cells and membrane-associated foci in yeast cells. Our results demonstrate that the inhibition of protein ubiquitination by PQ and MPP(+) is involved in the dysfunction of Ub-dependent protein degradation pathways.

Antioxidant potential of CORM-A1 and resveratrol during TNF-α/cycloheximide-induced oxidative stress and apoptosis in murine intestinal epithelial MODE-K cells

Targeting excessive production of reactive oxygen species (ROS) could be an effective therapeutic strategy to prevent oxidative stress-associated gastrointestinal inflammation. NADPH oxidase (NOX) and mitochondrial complexes (I and II) are the major sources of ROS production contributing to TNF-α/cycloheximide (CHX)-induced apoptosis in the mouse intestinal epithelial cell line, MODE-K. In the current study, the influence of a polyphenolic compound (resveratrol) and a water-soluble carbon monoxide (CO)-releasing molecule (CORM-A1) on the different sources of TNF-α/CHX-induced ROS production in MODE-K cells was assessed. This was compared with H2O2-, rotenone- or antimycin-A-induced ROS-generating systems. Intracellular total ROS, mitochondrial-derived ROS and mitochondrial superoxide anion (O2(-)) production levels were assessed. Additionally, the influence on TNF-α/CHX-induced changes in mitochondrial membrane potential (Ψm) and mitochondrial function was studied. In basal conditions, CORM-A1 did not affect intracellular total or mitochondrial ROS levels, while resveratrol increased intracellular total ROS but reduced mitochondrial ROS production. TNF-α/CHX- and H2O2-mediated increase in intracellular total ROS production was reduced by both resveratrol and CORM-A1, whereas only resveratrol attenuated the increase in mitochondrial ROS triggered by TNF-α/CHX. CORM-A1 decreased antimycin-A-induced mitochondrial O2(-) production without any influence on TNF-α/CHX- and rotenone-induced mitochondrial O2(-) levels, while resveratrol abolished all three effects. Finally, resveratrol greatly reduced and abolished TNF-α/CHX-induced mitochondrial depolarization and mitochondrial dysfunction, while CORM-A1 only mildly affected these parameters. These data indicate that the cytoprotective effect of resveratrol is predominantly due to mitigation of mitochondrial ROS, while CORM-A1 acts solely on NOX-derived ROS to protect MODE-K cells from TNF-α/CHX-induced cell death. This might explain the more pronounced cytoprotective effect of resveratrol.