Acteoside protects against 6-OHDA-induced dopaminergic neuron damage via Nrf2-ARE signaling pathway
Acteoside has been reported to have antioxidant and neuroprotective effect, which is a promising therapeutic way in prevention and treatment of Parkinson's disease. The present study was aimed to understand the neuroprotective effect of acteoside and to elucidate its underlying mechanism. 6-hydroxydopamine (6-OHDA)-induced neural damage in zebrafish model was used to study the protective effect of acteoside on Parkinson's disease (PD). Locomotion behavioral test showed that acteoside could prevent 6-OHDA-stimulated movement disorders. Anti-tyrosine hydroxylase (TH) whole-mount immunostaining analysis showed that acteoside could prevent 6-OHDA-induced dopaminergic neuron death. In addition, pretreatment with acteoside could upregulate antioxidative enzymes by activating the Nrf2/ARE signaling pathway in zebrafish. Meanwhile, acteoside was found to be distributed in the brain after intraperitoneal injection into the adult zebrafish, indicating that this compound could penetrate the blood-brain-barrier (BBB). This study demonstrated that acteoside could penetrate BBB and have potential therapeutic value for PD by activating the Nrf2/ARE signaling pathway and attenuating the oxidative stress.
Luteolin protects microglia against rotenone-induced toxicity in a hormetic manner through targeting oxidative stress response, genes associated with Parkinson's disease and inflammatory pathways
Rotenone, an environmental toxin, triggers Parkinson's disease (PD)-like pathology through microglia-mediated neuronal death. The effects and molecular mechanisms of flavonoid luteolin against rotenone-induced toxicity was assessed in microglial BV2 cells. Cells were pretreated with luteolin (1-50 µM) for 12 h and then was co-treated with 20 µM of rotenone for an additional 12 h in the presence of luteolin. The viability (MTT), IL-1β and TNF-α levels and lactate dehydrogenase (LDH) release (ELISA), and Park2, Lrrk2, Pink1, Nrf2 and Trx1 mRNA levels (qRT-PCR) were measured. In rotenone exposed microglia, luteolin increased viability significantly at lower concentrations (1-5 µM) compared to higher concentrations (25-50 µM). Rotenone increased LDH release and IL-1β levels in a dose-dependent manner (1-20 µM). Luteolin inhibited rotenone-induced LDH release, however the activity decreased in concentration-dependent manner Neither rotenone nor luteolin altered TNF-α levels, but luteolin reduced IL-1β levels in a concentration dependent manner in rotenone exposed cells. The mRNA levels of Nrf2 and Trx1, which are the master regulators of redox state, were increased by rotenone, as well as by luteolin, which exhibited an inverse relationship between its concentration and effect (1-20 µM). Park2 mRNA levels increased by luteolin, but decreased by rotenone. Pink1 mRNA levels was not altered by rotenone or luteolin. Lrrk2 mRNA levels reduced by luteolin, while it was increased by rotenone. Results suggest that luteolin have favorable effects on regulation of oxidative stress response, genes associated with PD and inflammatory pathways, hence protects microglia against rotenone toxicity in a hormetic manner.
Pinostrobin Exerts Neuroprotective Actions in Neurotoxin-Induced Parkinson's Disease Models through Nrf2 Induction
The aim of the present study was to assess the neuroprotective effects of pinostrobin (PSB), a dietary bioflavonoid, and its underlying mechanisms in neurotoxin-induced Parkinson's disease (PD) models. First, PSB could attenuate 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-induced loss of dopaminergic neurons and improve behavior deficiency in zebrafish, supporting its potential neuroprotective actions in vivo. Next, PSB could decreased apoptosis and death in the 1-methyl-4-phenylpyridinium (MPP)-intoxicated SH-SY5Y cells, evidenced by MTT, LDH, Annexin V-FITC/PI, and DNA fragmentation assay. PSB also blocked MPP-induced apoptotic cascades, including loss of mitochondrial membrane potential, activation of caspase 3, and reduced ratio of Bcl-2/Bax. In addition, PSB suppressed MPP-induced oxidative stress but increased antioxidant enzymes, evidenced by decrease of reactive oxygen species generation and lipid peroxidation and up-regulation of GSH-Px, SOD, CAT, GSH/GSSG, and NAD/NADH. Further investigations showed that PSB significantly enhanced Nrf2 expression and nuclear accumulation, improved ARE promoter activity and up-regulated expression of HO-1 and GCLC. Furthermore, Nrf2 knockdown via specific Nrf2 siRNA abolished PSB-induced antioxidative and antiapoptotic effects against MPP insults. Interestingly, we then found that PSB promoted phosphorylation of PI3K/AKT and ERK, and pharmacological inhibition of PI3K/AKT or ERK signaling diminished PSB-induced Nrf2/ARE activation and protective actions. In summary, PSB confers neuroprotection against MPTP/MPP-induced neurotoxicity in PD models. Promoting activation of Nrf2/ARE signaling contributes to PSB-mediated antioxidative and neuroprotective actions, which, in part, is mediated by PI3K/AKT and ERK.
Paraquat and MPTP induce alteration in the expression profile of long noncoding RNAs in the substantia nigra of mice: Role of the transcription factor Nrf2
Parkinson's disease (PD) is a common age-related degenerative disease of the central nervous system caused mainly by hereditary, pesticides, metals, and polychlorinated biphenyls. Paraquat (PQ), a widely used herbicide, causes PD. Long noncoding RNAs (lncRNAs) are nonprotein-coding transcripts, expressed in the brain and play irreplaceable roles in neurodegenerative diseases. NF-E2-related factor-2 (Nrf2) is an important genetic transcription regulator in oxidative stress. We aimed to discover novel PQ or 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-Nrf2-related lncRNAs and explore their association with PD. 17157 lncRNAs and 13707 mRNAs (fold change ≥2, P < 0.05) were identified by Microarray. And the expressions of six lncRNAs were confirmed by using qRT-PCR and two by FISH. Coding-noncoding analysis and qRT-PCR were applied to discover the functions of lncRNAs and predict the targeted genes. In mice, PQ and MPTP exposure caused alteration of the lncRNA expression profile, suggesting lncRNAs may be involved in PQ- and MPTP-induced neurotoxicity. The changes in their lncRNA expression were distinct but related. PQ caused lncRNA expression profiling alteration in the substantia nigra (SN) through an interaction with Nrf2, thus changing the NR_027648/Zc3h14/Cybb and NR_030777/Zfp326/Cpne5 mRNA pathways. Similarly, MPTP caused lncRNA expression profiling alteration in SN through an interaction with Nrf2. Nrf2 may be involved in the development of neurodegeneration induced by PQ and MPTP via interaction with lncRNAs as the molecular mechanism. Our findings indicate the potential roles of lncRNAs in the development of PD by PQ or MPTP and provide positive insights into future mechanism studies.
In vivo imaging of early signs of dopaminergic neuronal death in an animal model of Parkinson's disease
The Parkinson's disease (PD) evolves over an extended period of time with the onset occurring long before clinical signs begin to manifest. Characterization of the molecular events underlying the PD onset is instrumental for the development of diagnostic markers and preventive treatments, progress in this field is hindered by technical limitations. We applied an imaging approach to demonstrate the activation of Nrf2 transcription factor as a hallmark of neurodegeneration in neurotoxin-driven models of PD. In dopaminergic SK-N-BE neuroblastoma cells, Nrf2 activation was detected in cells committed to die as proven by time lapse microscopy; in the substantia nigra pars compacta area of the mouse brain, the Nrf2 activation preceded dopaminergic neurodegeneration as demonstrated by in vivo and ex vivo optical imaging, a finding confirmed by co-localization experiments carried out by immunohistochemistry. Collectively, our results identify the Nrf2 signaling as an early marker of neurodegeneration, anticipating dopaminergic neurodegeneration and motor deficits.
Astroglial DJ-1 over-expression up-regulates proteins involved in redox regulation and is neuroprotective in vivo
DJ-1, a Parkinson's disease-associated protein, is strongly up-regulated in reactive astrocytes in Parkinson's disease. This is proposed to represent a neuronal protective response, although the mechanism has not yet been identified. We have generated a transgenic zebrafish line with increased astroglial DJ-1 expression driven by regulatory elements from the zebrafish GFAP gene. Larvae from this transgenic line are protected from oxidative stress-induced injuries as caused by MPP, a mitochondrial complex I inhibitor shown to induce dopaminergic cells death. In a global label-free proteomics analysis of wild type and transgenic larvae exposed to MPP, 3418 proteins were identified, in which 366 proteins were differentially regulated. In particular, we identified enzymes belonging to primary metabolism to be among proteins affected by MPP in wild type animals, but not affected in the transgenic line. Moreover, by performing protein profiling on isolated astrocytes we showed that an increase in astrocytic DJ-1 expression up-regulated a large group of proteins associated with redox regulation, inflammation and mitochondrial respiration. The majority of these proteins have also been shown to be regulated by Nrf2. These findings provide a mechanistic insight into the protective role of astroglial up-regulation of DJ-1 and show that our transgenic zebrafish line with astrocytic DJ-1 over-expression can serve as a useful animal model to understand astrocyte-regulated neuroprotection associated with oxidative stress-related neurodegenerative disease.
Kynurenic Acid Restores Nrf2 Levels and Prevents Quinolinic Acid-Induced Toxicity in Rat Striatal Slices
Kynurenic acid (KYNA) and quinolinic acid (QUIN) are metabolites produced in the degradation of tryptophan and have important neurological activities. KYNA/QUIN ratio changes are known to be associated with central nervous system disorders, such Alzheimer, Parkinson, and Huntington diseases. In the present study, we investigate the ability of KYNA in prevent the first events preceding QUIN-induced neurodegeneration in striatal slices of rat. We evaluated the protective effect of KYNA on oxidative status (reactive oxygen species production, antioxidant enzymes activities, lipid peroxidation, nitrite levels, protein and DNA damage, and iNOS immunocontent), mitochondrial function (mitochondrial mass, membrane potential, and respiratory chain enzymes), and Na,K-ATPase in striatal slices of rats treated with QUIN. Since QUIN alters the levels of Nrf2, we evaluated the influence of KYNA protection on this parameter. Striatal slices from 30-day-old Wistar rats were preincubated with KYNA (100 μM) for 15 min, followed by incubation with 100-μM QUIN for 30 min. Results showed that KYNA prevented the increase of ROS production caused by QUIN and restored antioxidant enzyme activities and the protein and lipid damage, as well as the Nrf2 levels. KYNA also prevented the effects of QUIN on mitochondrial mass and mitochondrial membrane potential, as well as the decrease in the activities of complex II, SDH, and Na,K-ATPase. We suggest that KYNA prevents changes in Nrf2 levels, oxidative imbalance, and mitochondrial dysfunction caused by QUIN in striatal slices. This study elucidates some of the protective effects of KYNA against the damage caused by QUIN toxicity.
Neuroprotective effect of an Nrf2-ARE activator identified from a chemical library on dopaminergic neurons
The nuclear factor erythroid 2-related factor 2 (Nrf2)-antioxidant response element (ARE) pathway, which induces the production of antioxidant enzymes, is a possible therapeutic target for treating diseases related to oxidative stress. Nrf2 activators often exhibit cytotoxicity due to nonspecific electrophilic reactions with thiol groups. We screened a chemical library to explore Nrf2 activators with a wide safety margin. In at least in vitro experiments, TPNA10168, identified from the library, showed a higher efficacy in Nrf2 activation and a lower cytotoxicity than sulforaphane, a well-known Nrf2 activator. The present study demonstrated the protective effect of TPNA10168 against 6-hydroxydopamine-induced cytotoxicity. In PC12 cells, NAD(P)H:quinone oxidoreductase 1 was upregulated by TPNA10168 and participated in the protective effect. In primary mesencephalic cultures, heme oxygenase-1, upregulated by TPNA10168 in astrocytes, provided protection of dopaminergic neurons via a guanylate cyclase/protein kinase G signaling pathway via carbon monoxide. These results suggest that the compound identified from the chemical library may be suitable as a neuroprotective agent with the ability to induce antioxidant enzymes.
Activation of the Nrf2 signaling pathway and neuroprotection of nigral dopaminergic neurons by a novel synthetic compound KMS99220
The transcription factor Nrf2 is known to induce gene expression of antioxidant enzymes and proteasome subunits. Because both oxidative stress and protein aggregation have damaging effects on neurons, activation of the Nrf2 signaling should be beneficial against neurodegeneration. In this study, we report a novel synthetic morpholine-containing chalcone KMS99220 that confers neuroprotection. It showed high binding affinity to the Nrf2 inhibitory protein Keap-1 and increased nuclear translocation of Nrf2 and gene expression of the antioxidant enzymes heme oxygenase-1, NAD(P)H:quinone oxidoreductase-1, and the catalytic and modifier subunits of glutamate-cysteine ligase in dopaminergic CATH.a cells. KMS99220 also increased expression of the proteasome subunits PSMB5, PSMB7, PSMB8 and PSMA1, and the respective chymotrypsin and trypsin-like proteasomal enzyme activities, and reduced α-synuclein aggregate in GFP-α-syn A53T-overexpressing cells. KMS99220 exhibited a favorable pharmacokinetic profile with excellent bioavailability and metabolic stability, did not interfere with activities of the cytochrome p450 isotypes, and showed no apparent in vivo toxicity when administered up to 2000 mg/kg. In 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine-treated mice, oral administration of KMS99220 prevented degeneration of the nigral dopaminergic neurons, induced the Nrf2 target genes, and effectively prevented the associated motor deficits. These results suggest KMS99220 as a potential candidate for therapy against Parkinson's disease.
Comparison of Adaptive Neuroprotective Mechanisms of Sulforaphane and its Interconversion Product Erucin in in Vitro and in Vivo Models of Parkinson's Disease
Several studies suggest that an increase of glutathione (GSH) through activation of the transcriptional nuclear factor (erythroid-derived 2)-like 2 (Nrf2) in the dopaminergic neurons may be a promising neuroprotective strategy in Parkinson's disease (PD). Among Nrf2 activators, isothiocyanate sulforaphane (SFN), derived from precursor glucosinolate present in Brassica vegetables, has gained attention as a potential neuroprotective compound. Bioavailability studies also suggest the contribution of SFN metabolites, including erucin (ERN), to the neuroprotective effects of SFN. Therefore, we compared the in vitro neuroprotective effects of SFN and ERN at the same dose level (5 μM) and oxidative treatment with 6-hydroxydopamine (6-OHDA) in SH-SY5Y cells. The pretreatment of SH-SY5Y cells with SFN recorded a higher (p < 0.05) active nuclear Nrf2 protein (12.0 ± 0.4 vs 8.0 ± 0.2 fold increase), mRNA Nrf2 (2.0 ± 0.3 vs 1.4 ± 0.1 fold increase), total GSH (384.0 ± 9.0 vs 256.0 ± 8.0 μM) levels, and resistance to neuronal apoptosis elicited by 6-OHDA compared to ERN. By contrast, the simultaneous treatment of SH-SY5Y cells with either SFN or ERN and 6-OHDA recorded similar neuroprotective effects with both the isothiocyanates (Nrf2 protein 2.2 ± 0.2 vs 2.1 ± 0.1 and mRNA Nrf2 2.1 ± 0.3 vs 1.9 ± 0.2 fold increase; total GSH 384.0 ± 4.8 vs 352.0 ± 6.4 μM). Finally, in vitro finding was confirmed in a 6-OHDA-PD mouse model. The metabolic oxidation of ERN to SFN could account for their similar neuroprotective effects in vivo, raising the possibility of using vegetables containing a precursor of ERN for systemic antioxidant benefits in a similar manner to SFN.
Uric acid demonstrates neuroprotective effect on Parkinson's disease mice through Nrf2-ARE signaling pathway
Uric acid has neuroprotective effect on Parkinson's disease (PD) by inhibiting oxidative damage and neuronal cell death. Our previous study has shown that uric acid protected dopaminergic cell line damage through inhibiting accumulation of NF-E2-related factor 2 (Nrf2). This study aimed to investigate its in vivo neuroprotective effect. PD was induced by MPTP intraperitoneally injection for 7 d in male C57BL/6 mice. Mice were treated with either uric acid (intraperitoneally injection 250 mg/kg) or saline for a total of 13 d. We showed that uric acid improved behavioral performances and cognition of PD mice, increased TH-positive dopaminergic neurons and decreased GFAP-positive astrocytes in substantia nigra (SN). Uric acid increased mRNA and protein expressions of Nrf2 and three Nrf2-responsive genes, including γ-glutamate-cysteine ligase catalytic subunit (γ-GCLC), heme oxygenase-1 (HO-1) and NQO1. Uric acid significantly increased superoxide dismutase (SOD), CAT, glutathione (GSH) levels and decreased malondialdehyde (MDA) level in SN regions of MPTP-treated mice. Uric acid inhibited the hippocampal expression of IL-1β and decreased serum and hippocampus levels of interleukin-1β (IL-1β), IL-6 and tumor necrosis factor-α (TNF-α). In conclusion, uric acid demonstrates neuroprotective properties for dopaminergic neurons in PD mice through modulation of neuroinflammation and oxidative stress.
Role of histone acetylation in activation of nuclear factor erythroid 2-related factor 2/heme oxygenase 1 pathway by manganese chloride
Manganese neurotoxicity is characterized by Parkinson-like symptoms with degeneration of dopaminergic neurons in the basal ganglia as the principal pathological feature. Manganese neurotoxicity studies may contribute to a good understanding of the mechanism of Parkinson's disease (PD). In this study, we first confirmed that MnCl can promote the expression of nuclear factor erythroid 2-related factor 2 (Nrf2) protein in the nucleus or cytoplasm while increasing the binding activity of Nrf2 and antioxidant response elements, further promoting the expression of downstream target gene heme oxygenase 1 (HO-1) and leading to increase levels of reactive oxygen species (ROS) and reduce the levels of reduced glutathione (GSH). Second, we investigated the role of histone acetylation in the activation of Nrf2/HO-1 pathway by manganese chloride in rat adrenal pheochromocytoma (PC12) cells. Histone acetyltransferase inhibitor (anacardic acid) and histone deacetylase inhibitor (trichostatin A, TSA) were used as pretreatment reagents to adjust the level of histone acetylation. Here, we show that downregulation of histone acetylation can inhibit Mn-induced Nrf2 nuclear translocation and further inhibits the Mn-activated Nrf2/HO-1 pathway. This downregulation also promotes manganese-induced increase of ROS and decrease of GSH in neurons. These results suggest that the downregulation of histone acetylation may play an important role in the neurotoxicity caused by manganese and that TSA may provide new ideas and targets in treating manganese-induced Parkinson's syndrome and PD.
Glaucocalyxin B Alleviates Lipopolysaccharide-Induced Parkinson's Disease by Inhibiting TLR/NF-κB and Activating Nrf2/HO-1 Pathway
Parkinson's disease (PD) is a common neurodegenerative disease in the old population, characterized by dopaminergic neuron loss, inflammation and oxidative stress injury in the substantia nigra. Glaucocalyxin B (GLB), an ent-kauranoid diterpenoid isolated from Rabdosia japonica, has anti-inflammation and anti-tumor effects. However, its effects on PD remain unclear.
Piperlongumine restores the balance of autophagy and apoptosis by increasing BCL2 phosphorylation in rotenone-induced Parkinson disease models
Parkinson disease (PD) is the second most common neurodegenerative disorder after Alzheimer disease and is caused by genetics, environmental factors and aging, with few treatments currently available. Apoptosis and macroautophagy/autophagy play critical roles in PD pathogenesis; as such, modulating their balance is a potential treatment strategy. BCL2 (B cell leukemia/lymphoma 2) is a key molecule regulating this balance. Piperlongumine (PLG) is an alkaloid extracted from Piper longum L. that has antiinflammatory and anticancer effects. The present study investigated the protective effects of PLG in rotenone-induced PD cell and mouse models. We found that PLG administration (2 and 4 mg/kg) for 4 wk attenuated motor deficits in mice and prevented the loss of dopaminergic neurons in the substantia nigra induced by oral administration of rotenone (10 mg/kg) for 6 wk. PLG improved cell viability and enhanced mitochondrial function in primary neurons and SK-N-SH cells. These protective effects were exerted via inhibition of apoptosis and induction of autophagy through enhancement of BCL2 phosphorylation at Ser70. These results demonstrate that PLG exerts therapeutic effects in a rotenone-induced PD models by restoring the balance between apoptosis and autophagy.
Neuroprotective Role of Astroglia in Parkinson Disease by Reducing Oxidative Stress Through Dopamine-Induced Activation of Pentose-Phosphate Pathway
Oxidative stress plays an important role in the onset and progression of Parkinson disease. Although released dopamine at the synaptic terminal is mostly reabsorbed by dopaminergic neurons, some dopamine is presumably taken up by astroglia. This study examined the dopamine-induced astroglial protective function through the activation of the pentose-phosphate pathway (PPP) to reduce reactive oxygen species (ROS). In vitro experiments were performed using striatal neurons and cortical or striatal astroglia prepared from Sprague-Dawley rats or C57BL/6 mice. The rates of glucose phosphorylation in astroglia were evaluated using the [C]deoxyglucose method. PPP activity was measured using [1-C]glucose and [6-C]glucose after acute (60 min) or chronic (15 hr) exposure to dopamine. ROS production was measured using 2',7'-dichlorodihydrofluorescein diacetate. The involvement of the Kelch-like ECH-associated protein 1 (Keap1) or nuclear factor-erythroid-2-related factor 2 (Nrf2) system was evaluated using Nrf2 gene knockout mice, immunohistochemistry, and quantitative reverse transcription polymerase chain reaction analysis for heme oxygenase-1. Acute exposure to dopamine elicited increases in astroglial glucose consumption with lactate release. PPP activity in astroglia was robustly enhanced independently of Na-dependent monoamine transporters. In contrast, chronic exposure to dopamine induced moderate increases in PPP activity via the Keap1/Nrf2 system. ROS production from dopamine increased gradually over 12 hr. Dopamine induced neuronal cell damage that was prevented by coculturing with astroglia but not with Nrf2-deficient astroglia. Dopamine-enhanced astroglial PPP activity in both acute and chronic manners may possibly reduce neuronal oxidative stress.