Extracellular toxicity of 6-hydroxydopamine on PC12 cells

Protective Effect of Amber Extract on Human Dopaminergic Cells against 6-Hydroxydopamine-Induced Neurotoxicity

Parkinson’s disease (PD) is the second most common progressive neurodegenerative disease, after Alzheimer’s disease. In our previous study, we found that amber—a fossilized plant resin—can protect cells from apoptosis by decreasing the generation of reactive oxygen species (ROS). In this study, we focused on the effect of amber on 6-hydroxydopamine-induced cell apoptosis in the human neuroblastoma cell line SHSY5Y (one model for PD). Initially, we determined the protective effect of amber on the PD model. We found that amber extract has a protective effect against 6-hydroxydopamine-induced cell apoptosis. The decrease in ROS, cleaved caspase-3, pERK, and extracellular signal-regulated kinase (ERK) protein levels confirmed that amber extract decreases apoptosis via the ROS-mediated ERK signaling pathway. Furthermore, we determined the effects of amber extract on autophagy. The results showed that amber extract increased the levels of LC3II and Beclin-1, suggesting that amber extract can protect neuronal cells against 6-hydroxydopamine-induced cell apoptosis by promoting autophagy.

Misregulation of Wnt Signaling Pathways at the Plasma Membrane in Brain and Metabolic Diseases

Wnt signaling pathways constitute a group of signal transduction pathways that direct many physiological processes, such as development, growth, and differentiation. Dysregulation of these pathways is thus associated with many pathological processes, including neurodegenerative diseases, metabolic disorders, and cancer. At the same time, alterations are observed in plasma membrane compositions, lipid organizations, and ordered membrane domains in brain and metabolic diseases that are associated with Wnt signaling pathway activation. Here, we discuss the relationships between plasma membrane components-specifically ligands, (co) receptors, and extracellular or membrane-associated modulators-to activate Wnt pathways in several brain and metabolic diseases. Thus, the Wnt-receptor complex can be targeted based on the composition and organization of the plasma membrane, in order to develop effective targeted therapy drugs.

Neuroprotective effects of Shende'an tablet in the Parkinson's disease model

BACKGROUND

Shende'an tablet (SDA) is a newly capsuled Chinese herbal formula derived from the Chinese traditional medicine Zhengan Xifeng Decoction which is approved for the treatment of neurasthenia and insomnia in China. This study aimed to investigate the neuroprotective effects of SDA against Parkinson's disease (PD) in vitro and in vivo.

METHODS

In the present work, the neuroprotective effects and mechanism of SDA were evaluated in the cellular PD model. Male C57BL/6J mice were subject to a partial MPTP lesion alongside treatment with SDA. Behavioural test and tyrosine-hydroxylase immunohistochemistry were used to evaluate nigrostriatal tract integrity. HPLC analysis and Western blotting were used to assess the effect of SDA on dopamine metabolism and the expression of HO-1, PGC-1α and Nrf2, respectively.

RESULTS

Our results demonstrated that SDA had neuroprotective effect in dopaminergic PC12 cells with 6-OHDA lesion. It had also displayed efficient dopaminergic neuronal protection and motor behavior alleviation properties in MPTP-induced PD mice. In the PC12 cells and MPTP-induced Parkinson's disease animal models, SDA was highly efficacious in α-synuclein clearance associated with the activation of PGC-1α/Nrf2 signal pathway.

CONCLUSIONS

SDA demonstrated potential as a future therapeutic modality in PD through protecting dopamine neurons and alleviating the motor symptoms, mediated by the activation of PGC-1α/Nrf2 signal pathway.

Sesaminol prevents Parkinson's disease by activating the Nrf2-ARE signaling pathway

Parkinson's disease (PD) is a neurodegenerative disease caused by the degeneration of substantia nigra neurons due to oxidative stress. Sesaminol has strong antioxidant and anti-cancer effects. We investigated the preventive effect on PD as a new physiological action of sesaminol produced from sesaminol glycoside using in vitro and in vivo PD models. To prepare an in vitro PD model, 6-hydroxydopamine (6-OHDA) was added to human neuroblastoma (SH-SY5Y cells). The viability of SH-SY5Y cells decreased dose-dependently following 6-OHDA treatment, but the addition of sesaminol restored viability to the control level. 6-OHDA increased intracellular reactive oxygen species production, and the addition of sesaminol significantly suppressed this increase. No Nrf2 expression in the nucleus was observed in the control group, but a slight increase was observed in the 6-OHDA group. The sesaminol group showed strong expression of Nrf2 in the cytoplasm and nucleus. NAD(P)H: quinone oxidoreductase (NQO1) activity was enhanced in the 6-OHDA group and further enhanced in the sesaminol group. Furthermore, the neurotoxine rotenone was orally administrated to mice to prepare an in vivo PD model. The motor function of rotenone-treated mice was shorter than that of the control group, but a small amount of sesaminol restored it to the control level. The intestinal motility in the rotenone group was significantly lower than that in the control group, but it remained at the control level in the sesaminol group. The expression of α-synuclein in the substantia nigra increased in the rotenone group but decreased in the sesaminol group. The rotenone group exhibited shortening and damage to the colonic mucosa, but these abnormalities of the colonic mucosa were scarcely observed in the sesaminol group. These results suggest that sesaminol has a preventative effect on PD.

Nitroxide Radical-Containing Redox Nanoparticles Protect Neuroblastoma SH-SY5Y Cells against 6-Hydroxydopamine Toxicity

Parkinson's disease (PD) patients can benefit from antioxidant supplementation, and new efficient antioxidants are needed. The aim of this study was to evaluate the protective effect of selected nitroxide-containing redox nanoparticles (NRNPs) in a cellular model of PD. Antioxidant properties of NRNPs were studied in cell-free systems by protection of dihydrorhodamine 123 against oxidation by 3-morpholino-sydnonimine and protection of fluorescein against bleaching by 2,2-azobis(2-amidinopropane) hydrochloride and sodium hypochlorite. Model blood-brain barrier penetration was studied using hCMEC/D3 cells. Human neuroblastoma SH-SY5Y cells, exposed to 6-hydroxydopamine (6-OHDA), were used as an in vitro model of PD. Cells were preexposed to NRNPs or free nitroxides (TEMPO or 4-amino-TEMPO) for 2 h and treated with 6-OHDA for 1 h and 24 h. The reactive oxygen species (ROS) level was estimated with dihydroethidine 123 and Fluorimetric Mitochondrial Superoxide Activity Assay Kit. Glutathione level (GSH) was measured with ortho-phtalaldehyde, ATP by luminometry, changes in mitochondrial membrane potential with JC-1, and mitochondrial mass with 10-Nonyl-Acridine Orange. NRNP1, TEMPO, and 4-amino-TEMPO (25-150 μM) protected SH-SY5Y cells from 6-OHDA-induced viability loss; the protection was much higher for NRNP1 than for free nitroxides. NRNP1 were better antioxidants in vitro and permeated better the model BBB than free nitroxides. Exposure to 6-OHDA decreased the GSH level after 1 h and increased it considerably after 24 h (apparently a compensatory overresponse); NRNPs and free nitroxides prevented this increase. NRNP1 and free nitroxides prevented the decrease in ATP level after 1 h and increased it after 24 h. 6-OHDA increased the intracellular ROS level and mitochondrial superoxide level. Studied antioxidants mostly decreased ROS and superoxide levels. 6-OHDA decreased the mitochondrial potential and mitochondrial mass; both effects were prevented by NRNP1 and nitroxides. These results suggest that the mitochondria are the main site of 6-OHDA-induced cellular damage and demonstrate a protective effect of NRNP1 in a cellular model of PD.

Allopregnanolone Modulates GABAAR-Dependent CaMKIIδ3 and BDNF to Protect SH-SY5Y Cells Against 6-OHDA-Induced Damage

Allopregnanolone (APα), as a functional neurosteroid, exhibits the neuroprotective effect on neurodegenerative diseases such as Parkinson’s disease (PD) through γ-aminobutyric acid A receptor (GABAAR), but it has not been completely understood about its molecular mechanisms. In order to investigate the neuroprotective effect of APα, as well as to clarify its possible molecular mechanisms, SH-SY5Y neuronal cell lines were incubated with 6-hydroxydopamine (6-OHDA), which has been widely used as an in vitro model for PD, along with APα alone or in combination with GABAAR antagonist (bicuculline, Bic), intracellular Ca²⁺ chelator (EGTA) and voltage-gated L-type Ca²⁺ channel blocker (Nifedipine). The viability, proliferation, and differentiation of SH-SY5Y cells, the expression levels of calmodulin (CaM), Ca²⁺/calmodulin-dependent protein kinase II δ3 (CaMKIIδ3), cyclin-dependent kinase-1 (CDK1) and brain-derived neurotrophic factor (BDNF), as well as the interaction between CaMKIIδ3 and CDK1 or BDNF, were detected by morphological and molecular biological methodology. Our results found that the cell viability and the number of tyrosine hydroxylase (TH), bromodeoxyuridine (BrdU) and TH/BrdU-positive cells in 6-OHDA-treated SH-SY5Y cells were significantly decreased with the concomitant reduction in the expression levels of aforementioned proteins, which were ameliorated following APα administration. In addition, Bic could further increase the number of TH or BrdU-positive cells as well as the expression levels of aforementioned proteins except for TH/BrdU-double positive cells, while EGTA and Nifedipine could attenuate the expression levels of CaM, CaMKIIδ3 and BDNF. Moreover, there existed a direct interaction between CaMKIIδ3 and CDK1 or BDNF. As a result, APα-induced an increase in the number of TH-positive SH-SY5Y cells might be mediated through GABAAR via Ca²⁺/CaM/CaMKIIδ3/BDNF (CDK1) signaling pathway, which would ultimately facilitate to elucidate PD pathogenesis and hold a promise as an alternative therapeutic target for PD.

Wnt1 Promotes EAAT2 Expression and Mediates the Protective Effects of Astrocytes on Dopaminergic Cells in Parkinson's Disease

Background

Wnt/β-catenin signaling has been reported to exert cytoprotective effects in a cellular model of Parkinson's disease (PD). Glutamate excitotoxicity has been suggested to contribute to the pathogenesis of PD, and excitatory amino acid transporters (EAATs) play a predominant role in clearing excessive glutamate. EAAT2 is mainly expressed in astrocytes, which are an important source of Wnt signaling in the brain.

Methods

Wnt1-overexpressing U251 astrocytes were indirectly cocultured with dopaminergic SH-SY5Y cells treated with 6-hydroxydopamine (6-OHDA). Cell toxicity was determined by cell viability and flow cytometric detection. Glutamate level in the culture medium was determined by enzyme-linked immunosorbent assay (ELISA). Western blot analysis was used to detect the expression of Wnt1, β-catenin, and EAAT2. Immunofluorescence was used to display the expression and translocation of NF-κB p65.

Results

6-OHDA treatment significantly decreased cell viability in both U251 cells and SH-SY5Y cells, inhibited the expression of Wnt1, β-catenin, and EAAT2 in U251 cells, and increased the glutamate level in the culture medium. Coculture with Wnt1-overexpressing U251 cells attenuated 6-OHDA-induced apoptosis in SH-SY5Y cells. Overexpression of Wnt1 decreased the glutamate level in the culture media, upregulated β-catenin, EAAT2, and NF-κB levels, and promoted the translocation of NF-κB from the cytoplasm to the nucleus in U251 cells.

Conclusion

Wnt1 promoted EAAT2 expression and mediated the cytoprotective effects of astrocytes on dopaminergic cells. NF-κB might be involved in the regulation of EAAT2 by Wnt1.

Design, Synthesis, and Pharmacological Characterization of Carbazole Based Dopamine Agonists as Potential Symptomatic and Neuroprotective Therapeutic Agents for Parkinson's Disease

We have developed a series of carbazole-derived compounds based on our hybrid D₂/D₃ agonist template to design multifunctional compounds for the symptomatic and disease-modifying treatment of Parkinson's disease (PD). The lead molecules (-)-11b (D-636), (-)-15a (D-653), and (-)-15c (D-656) exhibited high affinity for both D₂ and D₃ receptors and in GTPγS functional assay, the compounds showed potent agonist activity at both D₂ and D₃ receptors (EC₅₀ (GTPγS); D₂ = 48.7 nM, D₃ = 0.96 nM for 11b, D₂ = 0.87 nM, D₃ = 0.23 nM for 15a and D₂ = 2.29 nM, D₃ = 0.22 nM for 15c). In an animal model of PD, the test compounds exhibited potent in vivo activity in reversing hypolocomotion in reserpinized rats with a long duration of action compared to the reference drug ropinirole. In a cellular antioxidant assay, compounds (-)-11b, (-)-15a, and (-)-15c exhibited potent activity in reducing oxidative stress induced by neurotoxin 6-hydroxydopamine (6-OHDA). Also, in a cell-based PD neuroprotection model, these lead compounds significantly increased cell survival from toxicity of 6-OHDA, thereby producing a neuroprotective effect. Additionally, compounds (-)-11b and (-)-15a inhibited aggregation and reduced toxicity of recombinant alpha synuclein protein in a cell based in vitro assay. These observations suggest that the lead carbazole-based dopamine agonists may be promising multifunctional molecules for a viable symptomatic and disease-modifying therapy of PD and should be further investigated.

Antioxidant and Anti-Apoptotic Activity of Octadecaneuropeptide Against 6-OHDA Toxicity in Cultured Rat Astrocytes

Oxidative stress, associated with various neurodegenerative diseases, promotes ROS generation, impairs cellular antioxidant defenses, and finally, triggers both neurons and astroglial cell death by apoptosis. Astrocytes specifically synthesize and release endozepines, a family of regulatory peptides, including the octadecaneuropeptide (ODN). We have previously reported that ODN acts as a potent neuroprotective agent that prevents 6-OHDA-induced apoptotic neuronal death. The purpose of the present study was to investigate the potential glioprotective effect of ODN on 6-OHDA-induced oxidative stress and cell death in cultured rat astrocytes. Incubation of astrocytes with graded concentrations of ODN (10^-14 to 10^-8 M) inhibited 6-OHDA-evoked cell death in a concentration- and time-dependent manner. In addition, ODN prevented the decrease of mitochondrial activity and caspase-3 activation induced by 6-OHDA. 6-OHDA-treated cells also exhibited enhanced levels of ROS associated with a generation of H₂O₂ and O₂^°-, and a reduction of both superoxide dismutase (SOD) and catalase (CAT) activities. Co-treatment of astrocytes with low concentrations of ODN dose-dependently blocked 6-OHDA-evoked production of ROS and inhibition of antioxidant enzyme activities. Concomitantly, ODN stimulated Mn-SOD, CAT, glutathione peroxidase-1, and sulfiredoxin-1 gene transcription and rescued 6-OHDA-associated reduced expression of endogenous antioxidant enzymes. Taken together, these data indicate that, in rat astrocytes, ODN exerts anti-apoptotic and anti-oxidative activities, and hence prevents 6-OHDA-induced oxidative assault and cell death. ODN is thus a potential candidate to delay neuronal damages in various pathological conditions involving oxidative neurodegeneration.

Isolation and Characterization of NP-POL Nonapeptide for Possible Therapeutic Use in Parkinson's Disease

Colostrum and milk are the initial mammalian nourishment and rich reservoir of essential nutrients for newborn development. Bioactive peptides isolated from natural sources, such as colostrum, serve as endogenous regulators and can be used as alternative therapeutic agents in the treatment of neurodegenerative diseases. One example is the previously unknown NP-POL nonapeptide isolated from Colostrinin. In the present study, we investigated a method of NP-POL nonapeptide isolation using Bio-Gel P2 molecular sieve chromatography. We showed the protective effect of NP-POL on 6-hydroxydopamine- (6-OHDA-) induced neurotoxicity using rat adrenal pheochromocytoma (PC12 Tet On) cells. Treatment of PC12 cells with NP-POL nonapeptide reduced 6-OHDA-induced apoptosis and caused transient phosphorylation of extracellular signal-regulated kinases (ERK 1/2), which were shown to promote cell survival. NP-POL nonapeptide also protected neuronal cells against oxidative injury induced by 6-OHDA. These results showed a potential use of NP-POL in the therapy of Parkinson's disease.

Chromaffin cells as a model to evaluate mechanisms of cell death and neuroprotective compounds

In this review, we show how chromaffin cells have contributed to evaluate neuroprotective compounds with diverse mechanisms of action. Chromaffin cells are considered paraneurons, as they share many common features with neurons: (i) they synthesize, store, and release neurotransmitters upon stimulation and (ii) they express voltage-dependent calcium, sodium, and potassium channels, in addition to a wide variety of receptors. All these characteristics, together with the fact that primary cultures from bovine adrenal glands or chromaffin cells from the tumor pheochromocytoma cell line PC12 are easy to culture, make them an ideal model to study neurotoxic mechanisms and neuroprotective drugs. In the first part of this review, we will analyze the different cytotoxicity models related to calcium dyshomeostasis and neurodegenerative disorders like Alzheimer's or Parkinson's. Along the second part of the review, we describe how different classes of drugs have been evaluated in chromaffin cells to determine their neuroprotective profile in different neurodegenerative-related models.

Mitochondrial Dysfunction in Parkinson’s Disease

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

A novel iron (II) preferring dopamine agonist chelator D-607 significantly suppresses α-syn- and MPTP-induced toxicities in vivo

Here, we report the characterization of a novel hybrid D₂/D₃ agonist and iron (II) specific chelator, D-607, as a multi-target-directed ligand against Parkinson's disease (PD). In our previously published report, we showed that D-607 is a potent agonist of dopamine (DA) D₂/D₃ receptors, exhibits efficacy in a reserpinized PD animal model and preferentially chelates to iron (II). As further evidence of its potential as a neuroprotective agent in PD, the present study reveals D-607 to be protective in neuronal PC12 cells against 6-OHDA toxicity. In an in vivo Drosophila melanogaster model expressing a disease-causing variant of α-synuclein (α-Syn) protein in fly eyes, the compound was found to significantly suppress toxicity compared to controls, concomitant with reduced levels of aggregated α-Syn. Furthermore, D-607 was able to rescue DAergic neurons from MPTP toxicity in mice, a well-known PD neurotoxicity model, following both sub-chronic and chronic MPTP administration. Mechanistic studies indicated that possible protection of mitochondria, up-regulation of hypoxia-inducible factor, reduction in formation of α-Syn aggregates and antioxidant activity may underlie the observed neuroprotection effects. These observations strongly suggest that D-607 has potential as a promising multifunctional lead molecule for viable symptomatic and disease-modifying therapy for PD.

Tetramethylpyrazine Analogue CXC195 Protects Against Dopaminergic Neuronal Apoptosis via Activation of PI3K/Akt/GSK3β Signaling Pathway in 6-OHDA-Induced Parkinson's Disease Mice

Parkinson's disease (PD) is a progressive neurodegenerative disorder and characterized by motor system disorders resulting in loss of dopaminergic (DA) neurons. CXC195, a novel tetramethylpyrazine derivative, has been shown strongest neuroprotective effects due to its anti-apoptotic activity. However, whether CXC195 protects against DA neuronal damage in PD and the mechanisms underlying its beneficial effects are unknown. The purpose of our study was to investigate the potential neuroprotective role of CXC195 and to elucidate its mechanism of action against 6-hydroxydopamine (6-OHDA)-induced mouse model of PD. CXC195 administration improved DA neurodegeneration in PD mice induced by 6-OHDA. Our further findings confirmed treatment of CXC195 at the dose of 10 mg/kg significantly inhibited the apoptosis by decreasing the level of cleaved caspase-3 and Bax, and increasing the level of Bcl-2 in 6-OHDA-lesioned mice. Meanwhile, 6-OHDA also decreased the amount of phosphorylated Akt while increased GSK-3β activity (the amount of phosphorylated GSK-3β at Ser9 was decreased) which was prevented by CXC195. Wortmannin, a specific PI3K inhibitor, dramatically abolished the changes induced by CXC195. Our study firstly demonstrated that CXC195 protected against DA neurodegeneration in 6-OHDA-induced PD model by its anti-apoptotic properties and PI3K/Akt/GSK3β signaling pathway was involved in it.

Novel multifunctional dopamine D2/D3 receptors agonists with potential neuroprotection and anti-alpha synuclein protein aggregation properties

Our ongoing drug development endeavor to design compounds for symptomatic and neuroprotective treatment of Parkinson's disease (PD) led us to carry out a structure activity relationship study based on dopamine agonists pramipexole and 5-OHDPAT. Our goal was to incorporate structural elements in these agonists in a way to preserve their agonist activity while producing inhibitory activity against aggregation of α-synuclein protein. In our design we appended various catechol and related phenol derivatives to the parent agonists via different linker lengths. Structural optimization led to development of several potent agonists among which (-)-8a, (-)-14 and (-)-20 exhibited potent neuroprotective properties in a cellular PD model involving neurotoxin 6-OHDA. The lead compounds (-)-8a and (-)-14 were able to modulate aggregation of α-synuclein protein efficiently. Finally, in an in vivo PD animal model, compound (-)-8a exhibited efficacious anti-parkinsonian effect.

Development of a Highly Potent D2/D3 Agonist and a Partial Agonist from Structure-Activity Relationship Study of N(6)-(2-(4-(1H-Indol-5-yl)piperazin-1-yl)ethyl)-N(6)-propyl-4,5,6,7-tetrahydrobenzo[d]thiazole-2,6-diamine Analogues: Implication in the Treatment of Parkinson's Disease

Our structure-activity relationship studies with N(6)-(2-(4-(1H-indol-5-yl)piperazin-1-yl)ethyl)-N(6)-propyl-4,5,6,7-tetrahydrobenzo[d]thiazole-2,6-diamine derivatives led to development of a lead compound (-)-21a which exhibited very high affinity (Ki, D2 = 16.4 nM, D3 = 1.15 nM) and full agonist activity (EC50 (GTPγS); D2 = 3.23 and D3 = 1.41 nM) at both D2 and D3 receptors. A partial agonist molecule (-)-34 (EC50 (GTPγS); D2 = 21.6 (Emax = 27%) and D3 = 10.9 nM) was also identified. In a Parkinson's disease (PD) animal model, (-)-21a was highly efficacious in reversing hypolocomotion in reserpinized rats with a long duration of action, indicating its potential as an anti-PD drug. Compound (-)-34 was also able to elevate locomotor activity in the above PD animal model significantly, implying its potential application in PD therapy. Furthermore, (-)-21a was shown to be neuroprotective in protecting neuronal PC12 from toxicity of 6-OHDA. This report, therefore, underpins the notion that a multifunctional drug like (-)-21a might have the potential not only to ameliorate motor dysfunction in PD patients but also to modify disease progression by protecting DA neurons from progressive degeneration.

Assessment of Protective Role of Multifunctional Dopamine Agonist D-512 Against Oxidative Stress Produced by Depletion of Glutathione in PC12 Cells: Implication in Neuroprotective Therapy for Parkinson's Disease

Oxidative stress has been strongly implicated in the progression of Parkinson's disease (PD). Depletion of cytoplasmic glutathione levels is one of the indications of oxidative stress, which occur in the substantia nigra of PD patients at an early stage of the disease process. It has been shown that glutathione depletion causes the inhibition of mitochondrial complex I, thus affecting mitochondrial function leading to oxidative stress via production of reactive oxygen species. Studies were carried out to investigate the role of D-512, a potent multifunctional neuroprotective D2/D3 receptor agonist, in protecting dopaminergic PC12 cells treated with buthionine sulfoximine (BSO), an inhibitor of key enzyme in glutathione synthesis and 6-hydroxydopamine (6-OHDA), a widely used neurotoxin. D-512 was able to restore level of glutathione against BSO/6-OHDA-mediated glutathione depletion. D-512 also showed significant neuroprotection in PC12 cells against toxicity induced by combined treatment of BSO and 6-OHDA. Furthermore, D-512 was able to restore both phospho-extracellular signal-regulated kinase and phospho-Jun N-terminal kinase levels upon treatment with 6-OHDA providing an evidence on the possible mechanism of action for neuroprotection by modulating mitogen-activated protein kinases. We have further demonstrated the neuroprotective effects of D-512 against oxidative insult produced by BSO and 6-OHDA in PC12 cells.

Agmatine Protects Against 6-OHDA-Induced Apoptosis, and ERK and Akt/GSK Disruption in SH-SY5Y Cells

6-Hydroxydopamine (6-OHDA), a metabolite of dopamine is known to induce dopaminergic cell toxicity which makes that a suitable agent inducing an experimental model of Parkinson's disease (PD). Agmatine has been shown to protect against some cellular and animal PD models. This study was aimed to assess whether agmatine prevents 6-OHDA-induced SH-SY5Y cell death and if yes, then how it affects Akt/glycogen synthesis kinase-3β (GSK-3β) and extracellular signal-regulated kinases (ERK) signals. The cells were treated with different drugs, and their viability was examined via MTT (3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyl tetrazolium bromide) assay and morphological observation. Western blot studies were done to assess cleaved caspase-3, Akt/GSK-3β, and ERK proteins. 6-OHDA-induced cell death and caspase-3 cleavage, while agmatine prevented those changes. 6-OHDA also decreased the amount of phosphorylated Akt (pAkt)/Akt while increased GSK-3β activity which was prevented by agmatine. Additionally, this toxin increased pERK/ERK ratio which was averted again by agmatine. The PI3/Akt inhibitor, LY294002, impeded the changes induced by agmatine, while ERK inhibitor (PD98059) did not disturb the effects of agmatine, and by itself, it preserved the cells against 6-OHDA toxicity. This study revealed that agmatine is protective in 6-OHDA model of PD and affects Akt/GSK-3β and ERK pathways.

Wnt3a protects SH-SY5Y cells against 6-hydroxydopamine toxicity by restoration of mitochondria function

Background

Wnt/β-catenin signal has been reported to exert cytoprotective effects in cellular models of several diseases, including Parkinson’s disease (PD). This study aimed to investigate the neuroprotective effects of actived Wnt/β-catenin signal by Wnt3a on SH-SY5Y cells treated with 6-hydroxydopamine (6-OHDA).

Methods

Wnt3a-conditioned medium (Wnt3a-CM) was used to intervene dopaminegic SH-SY5Y cells treated with 6-OHDA. Cell toxicity was determined by cell viability and lactate dehydrogenase leakage (LDH) assay. The mitochondria function was measured by the mitochondrial membrane potential, while oxidative stress was monitored with intracellular reactive oxygen species (ROS). Western blot analysis was used to detect the expression of GSK3β, β-catenin as well as Akt.

Results

Our results showed that 100 μM 6-OHDA treated for 24 h significantly decreased cell viability and mitochondrial transmembrane potential, reduced the level of β-catenin and p-Akt, increased LDH leakage, ROS production and the ratio of p-GSK3β (Tyr216) to p-GSK3β (Ser9). However, Wnt3a-conditioned medium reversing SH-SY5Y cells against 6-OHDA-induced neurotoxicity by reversing these changes.

Conclusions

Activating of Wnt/β-catenin pathway by Wnt3a-CM attenuated 6-OHDA-induced neurotoxicity significantly, which related to the inhibition of oxidative stress and maintenance of normal mitochondrial function.

The high-affinity D2/D3 agonist D512 protects PC12 cells from 6-OHDA-induced apoptotic cell death and rescues dopaminergic neurons in the MPTP mouse model of Parkinson's disease

In this study, in vitro and in vivo experiments were carried out with the high-affinity multifunctional D2/D3 agonist D-512 to explore its potential neuroprotective effects in models of Parkinson's disease and the potential mechanism(s) underlying such properties. Pre-treatment with D-512 in vitro was found to rescue rat adrenal Pheochromocytoma PC12 cells from toxicity induced by 6-hydroxydopamine administration in a dose-dependent manner. Neuroprotection was found to coincide with reductions in intracellular reactive oxygen species, lipid peroxidation, and DNA damage. In vivo, pre-treatment with 0.5 mg/kg D-512 was protective against neurodegenerative phenotypes associated with systemic administration of MPTP, including losses in striatal dopamine, reductions in numbers of DAergic neurons in the substantia nigra (SN), and locomotor dysfunction. These observations strongly suggest that the multifunctional drug D-512 may constitute a novel viable therapy for Parkinson's disease.

Luteolin modulates 6-hydroxydopamine-induced transcriptional changes of stress response pathways in PC12 cells

The neurotoxin 6-hydroxydopamine (6-OHDA), which causes transcriptional changes associated with oxidative and proteotoxic stress, has been widely used to generate an experimental model of Parkinson's disease. The food-derived compound luteolin has multi-target actions including antioxidant, anti-inflammatory and neurotrophic activities. The aim of this study is to investigate how luteolin affects 6-OHDA-mediated stress response pathways. The results showed that when PC12 cells were pre-treated with luteolin (20 µM) 30 min prior to 6-OHDA (100 µM) exposure, 6-OHDA-induced ROS overproduction, cytotoxicity, caspase-3 activation, and mRNA expression of BIM, TRB3 and GADD34 were significantly attenuated. Moreover, 6-OHDA-mediated cell cycle arrest and transcription of p53 target genes, p21, GADD45α and PUMA, were reduced by luteolin. Luteolin also significantly down-regulated 6-OHDA-mediated unfolded protein response (UPR), leading to decreases in phospho-eIF2α, ATF4, GRP78 and CHOP. In addition, luteolin attenuated 6-OHDA-induced Nrf2-mediated HO-1 and GCLC. Taken together, these results suggest that diminishing intracellular ROS formation and down-regulation of p53, UPR and Nrf2-ARE pathways may be involved in the neuroprotective effect of luteolin.

Dopamine down-regulation of protein L-isoaspartyl methyltransferase is dependent on reactive oxygen species in SH-SY5Y cells

Parkinson's disease (PD) is a chronic and progressive neurological disorder that is characterized by the loss of dopaminergic neurons in the substantia nigra. Dopamine, via the oxidative stress that it generates in the cytosol, could contribute to the selective loss of neurons observed in PD. Protein L-isoaspartyl methyltransferase (PIMT) is an enzyme that repairs L-isoaspartyl-containing proteins and possesses anti-apoptotic properties. PIMT expression has been shown to decrease with age. Together, these observations prompted us to investigate whether dopamine can regulate PIMT expression in SH-SY5Y neuroblastoma cells. Here, we report that dopamine down-regulated PIMT at both gene and protein levels. The same inhibition of PIMT protein level was caused by the electron transport chain inhibitor, rotenone, which was accompanied, in both cases, by an increase in cell death and reactive oxygen species (ROS) production. In fact, pre-treatment with the antioxidant N-acetyl cysteine blocked PIMT dopamine-associated down-regulation. PCMT1 promoter mapping experiments allowed the identification of two regions that showed different sensitivity to DA action. A first region localized between 61 and 94bp upstream of transcription start site was very sensitive to dopamine inhibition while a second region between 41 and 61bp appeared more resistant to dopamine inhibitory effect. The inhibition of PCMT1 promoter activity was mediated by dopamine-induced ROS since it was prevented by the hydroxyl radical scavenger N,N'-dimethylthiourea. Conversely, H2O2 inhibited in a dose-dependent manner the transcriptional activity of PCMT1 promoter. Therefore, our findings identified new molecular mechanisms, cytosolic dopamine and its resulting ROS, as inhibitors of PIMT expression. This suggests that ROS generated from cytosolic dopamine could reduce both the PCMT1 gene promoter activity and the PIMT protein level thus decreasing its capacity to repair proteins involved in apoptosis and could contribute to neuronal cell death observed in PD.

How Parkinsonian toxins dysregulate the autophagy machinery

Since their discovery, Parkinsonian toxins (6-hydroxydopamine, MPP+, paraquat, and rotenone) have been widely employed as in vivo and in vitro chemical models of Parkinson's disease (PD). Alterations in mitochondrial homeostasis, protein quality control pathways, and more recently, autophagy/mitophagy have been implicated in neurotoxin models of PD. Here, we highlight the molecular mechanisms by which different PD toxins dysregulate autophagy/mitophagy and how alterations of these pathways play beneficial or detrimental roles in dopamine neurons. The convergent and divergent effects of PD toxins on mitochondrial function and autophagy/mitophagy are also discussed in this review. Furthermore, we propose new diagnostic tools and discuss how pharmacological modulators of autophagy/mitophagy can be developed as disease-modifying treatments for PD. Finally, we discuss the critical need to identify endogenous and synthetic forms of PD toxins and develop efficient health preventive programs to mitigate the risk of developing PD.

Activation of Wnt/β-catenin pathway by exogenous Wnt1 protects SH-SY5Y cells against 6-hydroxydopamine toxicity

Wnt1, initially described as a modulator of embryonic development, has recently been discovered to exert cytoprotective effects in cellular models of several diseases, including Parkinson's disease (PD). We, therefore, examined the neuroprotective effects of exogenous Wnt1 on dopaminergic SH-SY5Y cells treated with 6-hydroxydopamine (6-OHDA). Here, we show that 10-500 μM 6-OHDA treatment decreased cell viability and increased lactate dehydrogenase (LDH) leakage. SH-SY5Y cells treated with 100 μM 6-OHDA for 24 h showed reduced Wnt/β-catenin activity, decreased mitochondrial transmembrane potential, elevated levels of reactive oxidative species (ROS) and phosphatidylserine (PS) extraversion, increased levels of Chop and Bip/GRP78 and reduced level of p-Akt (Ser473). In contrast, exogenous Wnt1 attenuated 6-OHDA-induced changes. These results suggest that activation of the Wnt/β-catenin pathway by exogenous Wnt1 protects against 6-OHDA-induced changes by restoring mitochondria and endoplasmic reticulum (ER) function.

Differential toxicity of 6-hydroxydopamine in SH-SY5Y human neuroblastoma cells and rat brain mitochondria: protective role of catalase and superoxide dismutase

Oxidative stress and mitochondrial dysfunction are two pathophysiological factors often associated with the neurodegenerative process involved in Parkinson's disease (PD). Although, 6-hydroxydopamine (6-OHDA) is able to cause dopaminergic neurodegeneration in experimental models of PD by an oxidative stress-mediated process, the underlying molecular mechanism remains unclear. It has been established that some antioxidant enzymes such as catalase (CAT) and superoxide dismutase (SOD) are often altered in PD, which suggests a potential role of these enzymes in the onset and/or development of this multifactorial syndrome. In this study we have used high-resolution respirometry to evaluate the effect of 6-OHDA on mitochondrial respiration of isolated rat brain mitochondria and the lactate dehydrogenase cytotoxicity assay to assess the percentage of cell death induced by 6-OHDA in human neuroblastoma cell line SH-SY5Y. Our results show that 6-OHDA affects mitochondrial respiration by causing a reduction in both respiratory control ratio (IC(50) = 200 ± 15 nM) and state 3 respiration (IC(50) = 192 ± 17 nM), with no significant effects on state 4(o). An inhibition in the activity of both complex I and V was also observed. 6-OHDA also caused cellular death in human neuroblastoma SH-SY5Y cells (IC(50) = 100 ± 9 μM). Both SOD and CAT have been shown to protect against the toxic effects caused by 6-OHDA on mitochondrial respiration. However, whereas SOD protects against 6-OHDA-induced cellular death, CAT enhances its cytotoxicity. The here reported data suggest that both superoxide anion and hydroperoxyl radical could account for 6-OHDA toxicity. Furthermore, factors reducing the rate of 6-OHDA autoxidation to its p-quinone appear to enhance its cytotoxicity.

Neuroprotective effects of ginsenosides Rh1 and Rg2 on neuronal cells

Background

The present study investigates the effects of ginsenosides Rh₁ and Rg₂ against 6-hydroxydopamine (6-OHDA), a neurotoxin on SH-SY5Y cells and PC-12 cells. The effects of these two ginsenosides on neuronal differentiation are also examined.

Methods

LDH assay was used to measure cell viability after exposure to 6-OHDA and ginsenosides. Neuronal differentiation was evaluated by changes in cell morphology and density of neurite outgrowths. Western blotting was used to determine the ginsenosides' effects on activation of extracellular signal-regulated protein kinases (ERKs).

Results

Rh₁ and Rg₂ attenuated 6-OHDA toxicity in SH-SY5Y cells and induced neurite outgrowths in PC-12 cells. 6-OHDA-induced ERK phosphorylation was decreased by Rh₁ and Rg₂. 20(R)-form and 20(S)-form of the ginsenosides exerted similar effects in inducing neurite outgrowths in PC-12 cells.

Conclusion

The present study demonstrates neuroprotective effects of ginsenosides Rh₁ and Rg₂ on neuronal cell lines. These results suggest potential Chinese medicine treatment for neurodegenerative disorders (eg Parkinson's disease).

6-OHDA generated ROS induces DNA damage and p53- and PUMA-dependent cell death

BACKGROUND

Parkinson's disease (PD) is characterized by the selective loss of dopaminergic neurons in the substantia nigra (SN), resulting in tremor, rigidity, and bradykinesia. Although the etiology is unknown, insight into the disease process comes from the dopamine (DA) derivative, 6-hydroxydopamine (6-OHDA), which produces PD-like symptoms. Studies show that 6-OHDA activates stress pathways, such as the unfolded protein response (UPR), triggers mitochondrial release of cytochrome-c, and activates caspases, such as caspase-3. Because the BH3-only protein, Puma (p53-upregulated mediator of apoptosis), is activated in response to UPR, it is thought to be a link between cell stress and apoptosis.

RESULTS

To test the hypothesis that Puma serves such a role in 6-OHDA-mediated cell death, we compared the response of dopaminergic neurons from wild-type and Puma-null mice to 6-OHDA. Results indicate that Puma is required for 6-OHDA-induced cell death, in primary dissociated midbrain cultures as well as in vivo. In these cultures, 6-OHDA-induced DNA damage and p53 were required for 6-OHDA-induced cell death. In contrast, while 6-OHDA led to upregulation of UPR markers, loss of ATF3 did not protect against 6-OHDA.

CONCLUSIONS

Together, our results indicate that 6-OHDA-induced upregulation of Puma and cell death are independent of UPR. Instead, p53 and DNA damage repair pathways mediate 6-OHDA-induced toxicity.

Protective effect of hydrogen sulphide against 6-OHDA-induced cell injury in SH-SY5Y cells involves PKC/PI3K/Akt pathway

BACKGROUND AND PURPOSE

Hydrogen sulphide (H(2)S) is a novel neuromodulator. The present study aimed to investigate the protective effect of H(2)S against cell injury induced by 6-hydroxydopamine (6-OHDA), a selective dopaminergic neurotoxin often used to establish a model of Parkinson's disease for studying the underlying mechanisms of this condition.

EXPERIMENTAL APPROACH

Cell viability in SH-SY5Y cells was measured using MTT assay. Western blot analysis and pharmacological manipulation were employed to study the signalling mechanisms.

KEY RESULTS

Treatment of SH-SY5Y cells with 6-OHDA (50-200 microM) for 12 h decreased cell viability. Exogenous application of NaHS (an H(2)S donor, 100-1000 microM) or overexpression of cystathionine beta-synthase (a predominant enzyme to produce endogenous H(2)S in SH-SY5Y cells) protected cells against 6-OHDA-induced cell apoptosis and death. Furthermore, NaHS reversed 6-OHDA-induced loss of tyrosine hydroxylase. Western blot analysis showed that NaHS reversed the down-regulation of PKCalpha, epsilon and Akt and the up-regulation of PKCdelta in 6-OHDA-treated cells. Blockade of PKCalpha with Gö6976 (2 microM), PKCepsilon with EAVSLKPT (200 microM) or PI3K with LY294002 (20 microM) reduced the protective effects of H(2)S. However, inhibition of PKCdelta with rottlerin (5 microM) failed to affect 6-OHDA-induced cell injury. These data suggest that the protective effects of NaHS mainly resulted from activation of PKCalpha, epsilon and PI3K/Akt pathway. In addition, NaHS-induced Akt phosphorylation was significantly attenuated by Gö6976 and EAVSLKPT, suggesting that the activation of Akt by NaHS is PKCalpha, epsilon-dependent.

CONCLUSIONS AND IMPLICATIONS

H(2)S protects SH-SY5Y cells against 6-OHDA-induced cell injury by activating the PKCalpha, epsilon/PI3K/Akt pathway.

Static magnetic field exposure reproduces cellular effects of the Parkinson's disease drug candidate ZM241385

Background

This study was inspired by coalescing evidence that magnetic therapy may be a viable treatment option for certain diseases. This premise is based on the ability of moderate strength fields (i.e., 0.1 to 1 Tesla) to alter the biophysical properties of lipid bilayers and in turn modulate cellular signaling pathways. In particular, previous results from our laboratory (Wang et al., BMC Genomics, 10, 356 (2009)) established that moderate strength static magnetic field (SMF) exposure altered cellular endpoints associated with neuronal function and differentiation. Building on this background, the current paper investigated SMF by focusing on the adenosine A_2A receptor (A_2AR) in the PC12 rat adrenal pheochromocytoma cell line that displays metabolic features of Parkinson's disease (PD).

Methodology and Principal Findings

SMF reproduced several responses elicited by ZM241385, a selective A_2AR antagonist, in PC12 cells including altered calcium flux, increased ATP levels, reduced cAMP levels, reduced nitric oxide production, reduced p44/42 MAPK phosphorylation, inhibited proliferation, and reduced iron uptake. SMF also counteracted several PD-relevant endpoints exacerbated by A_2AR agonist CGS21680 in a manner similar to ZM241385; these include reduction of increased expression of A_2AR, reversal of altered calcium efflux, dampening of increased adenosine production, reduction of enhanced proliferation and associated p44/42 MAPK phosphorylation, and inhibition of neurite outgrowth.

Conclusions and Significance

When measured against multiple endpoints, SMF elicited qualitatively similar responses as ZM241385, a PD drug candidate. Provided that the in vitro results presented in this paper apply in vivo, SMF holds promise as an intriguing non-invasive approach to treat PD and potentially other neurological disorders.

Alpha-synuclein overexpression increases dopamine toxicity in BE2-M17 cells

Background

Oxidative stress has been proposed to be involved in the pathogenesis of Parkinson's disease (PD). A plausible source of oxidative stress in nigral dopaminergic neurons is the redox reactions that specifically involve dopamine and produce various toxic molecules, i.e., free radicals and quinone species. α-Synuclein, a protein found in Lewy bodies characteristic of PD, is also thought to be involved in the pathogenesis of PD and point mutations and multiplications in the gene coding for α-synuclein have been found in familial forms of PD.

Results

We used dopaminergic human neuroblastoma BE(2)-M17 cell lines stably transfected with WT or A30P mutant α-synuclein to characterize the effect of α-synuclein on dopamine toxicity. Cellular toxicity was analyzed by lactate dehydrogenase assay and by fluorescence-activated cell sorter analysis. Increased expression of either wild-type or mutant α-synuclein enhances the cellular toxicity induced by the accumulation of intracellular dopamine or DOPA.

Conclusions

Our results suggest that an interplay between dopamine and α-synuclein can cause cell death in a neuron-like background. The data presented here are compatible with several models of cytotoxicity, including the formation of α-synuclein oligomers and impairment of the lysosomal degradation.

Up-regulation of divalent metal transporter 1 in 6-hydroxydopamine intoxication is IRE/IRP dependent

Iron plays a key role in Parkinson's disease (PD). Increased iron content of the substantia nigra (SN) has been found in PD patients, and divalent metal transporter 1 (DMT1) has been shown to be up-regulated in the SN of both MPTP-induced PD models and PD patients. However, the mechanisms underlying DMT1 up-regulation are largely unknown. In the present study, we observed that in the SN of 6-hydroxydopamine (6-OHDA)-induced PD rats, DMT1 with the iron responsive element (IRE, DMT1+IRE), but not DMT1 without IRE (DMT1-IRE), was up-regulated, suggesting that increased DMT1+IRE expression might account for nigral iron accumulation in PD rats. This possibility was further assessed in an in vitro study using 6-OHDA-treated and DMT1+IRE-over-expressing MES23.5 cells. In 6-OHDA-treated MES23.5 cells, increased iron regulatory protein (IRP) 1 and IRP2 expression was observed, while silencing of IRPs dramatically diminished 6-OHDA-induced DMT1+IRE up-regulation. Pretreatment with N-acetyl-L-cysteine fully suppressed IRPs up-regulation by inhibition of 6-OHDA-induced oxidative stress. Increased DMT1+IRE expression resulted in increased iron influx by MES23.5 cells. Our data provide direct evidence that DMT1+IRE up-regulation can account for IRE/IRP-dependent 6-OHDA-induced iron accumulation initiated by 6-OHDA-induced intracellular oxidative stress and that increased levels of intracellular iron result in aggravated oxidative stress. The results of this study provide novel evidence supporting the use of anti-oxidants in the treatment of PD, with the goal of inhibiting iron accumulation by regulation of DMT1 expression.

Imaging serotonin transporters using [123I]ADAM SPECT in a parkinsonian primate model

Parkinson's disease (PD) affects multiple neurotransmitter systems. The purpose of this study was to investigate differences in the serotonin transport system between normal and parkinsonian monkeys using 2-([2-([di-methylamino]methyl)phenyl]thio)-5-[(123)I] iodophenyl-amine([(123)I]ADAM), a serotonin transporters (SERT) radioligand. The brain single photon emission computed tomography (SPECT) was performed on two normal and one parkinsonian monkey. The parkinsonian monkey was induced by bilateral injection of 6-hydroxydopamine (6-OHDA) into the medial forebrain bundle under magnetic resonance imaging (MRI) guidance. Each monkey underwent two [(99m)Tc] TRODAT-1 (a dopamine transporters imaging agent) and two [(123)I] ADAM brain SPECT scans. After a bolus injection of the radioligand, the SPECT data were acquired over 4h using a dual-head gamma camera equipped with ultra-high resolution fan-beam collimators. The striatal uptake of [(99m)Tc]TRODAT-1 was 46% lower in the parkinsonian monkey than those of normal monkeys at 210-240 min post-injection. [(123)I]ADAM uptake in the midbrain of the parkinsonian monkey was comparable to those of the controls. The uptakes of [(123)I]ADAM in the striatum, thalamus, and frontal cortex of the parkinsonian monkey, were 31%, 31%, and 23% lower than those of normal monkeys at 210-240 min post-injection, respectively. Our results suggest that [(123)I]ADAM SPECT has potential for evaluating the serotonin transporter changes in human PD.

Effects of Ginkgolide B on 6-OHDA-induced apoptosis and calcium over load in cultured PC12

Ginkgolide B, one of the major components of Ginkgo biloba extracts, is a potent platelet-activating factor (PAF) receptor antagonist, which is also regarded as having neuroprotective effects on the CNS. The aim of this research is to observe the effects of Ginkgolide B on the PC12 apoptosis induced by 6-hydroxydopamine (6-OHDA) and to explore whether these effects are related to the changes of intracellular Ca(2+) and Calbindin D28K mRNA in PC12 cells. In the present work, the damage of PC12 cells was induced by 100 microM 6-OHDA. The cells survival rate was examined by MTT assays. The intracellular free calcium concentration in PC12 cells was measured by using the fluorescent Ca(2+) indicator fluo-3/AM. Semi-quantitative reverse transcriptase-polymerase chain reaction (RT-PCR) was employed to determine the expression of Calbindin D28K mRNA in PC12. The data show that the Ginkgolide B inhibited PC12 cells apoptosis induced by 6-OHDA in a dose-dependent manner, and decreased the activity of caspase-3. In addition, Ginkgolide B increased the expression of Calbindin D28K mRNA and inhibited 6-OHDA-induced elevation in the intracellular calcium concentration. Our results showed that the Ginkgolide B inhibited the apoptosis of PC12 induced by 6-OHDA, and the protective effects of Ginkgolide B on PC12 cells are mediated, at least in part, by up-regulating the Calbindin D28K mRNA and by decreasing the intracellular calcium concentration.

6-Hydroxydopamine induces mitochondrial ERK activation

Reactive oxygen species (ROS) are implicated in 6-hydroxydopamine (6-OHDA) injury to catecholaminergic neurons; however, the mechanism(s) are unclear. In addition to ROS generated during autoxidation, 6-OHDA may initiate secondary cellular sources of ROS that contribute to toxicity. Using a neuronal cell line, we found that catalytic metalloporphyrin antioxidants conferred protection if added 1 h after exposure to 6-OHDA, whereas the hydrogen peroxide scavenger catalase failed to protect if added more than 15 min after 6-OHDA. There was a temporal correspondence between loss of protection and loss of the ability of the antioxidant to inhibit 6-OHDA-induced ERK phosphorylation. Time course studies of aconitase inactivation, an indicator of intracellular superoxide, and MitoSOX red, a mitochondria targeted ROS indicator, demonstrate early intracellular ROS followed by a delayed phase of mitochondrial ROS production, associated with phosphorylation of a mitochondrial pool of ERK. Furthermore, on initiation of mitochondrial ROS and ERK activation, 6-OHDA-injured cells became refractory to rescue by metalloporphyrin antioxidants. Together with previous studies showing that inhibition of the ERK pathway confers protection from 6-OHDA toxicity, and that phosphorylated ERK accumulates in mitochondria of degenerating human Parkinson's disease neurons, these studies implicate mitochondrial ERK activation in Parkinsonian oxidative neuronal injury.

Mechanism of 6-hydroxydopamine neurotoxicity: the role of NADPH oxidase and microglial activation in 6-hydroxydopamine-induced degeneration of dopaminergic neurons

Cell death induced by 6-hydroxydopamine (6-OHDA) is thought to be caused by reactive oxygen species (ROS) derived from 6-OHDA autooxidation and by a possible direct effect of 6-OHDA on the mitochondrial respiratory chain. However, the process has not been totally clarified. In rat primary mesencephalic cultures, we observed a significant increase in dopaminergic (DA) cell loss 24 h after administration of 6-OHDA (40 micromol/L) and a significant increase in NADPH subunit expression, microglial activation and superoxide anion/superoxide-derived ROS in DA cells that were decreased by the NADPH inhibitor apocynin. Low doses of 6-OHDA (10 micromol/L) did not induce a significant loss of DA cells or a significant increase in NADPH subunit expression, microglial activation or superoxide-derived ROS. However, treatment with the NADPH complex activator angiotensin II caused a significant increase in all the latter. Forty-eight hours after intrastriatal 6-OHDA injection in rats, there was still no loss of DA neurons although there was an increase in NADPH subunit expression and NADPH oxidase activity. The results suggest that in addition to the autooxidation-derived ROS and the inhibition of the mitochondrial respiratory chain, early microglial activation and NADPH oxidase-derived ROS act synergistically with 6-OHDA and constitute a relevant and early component of the 6-OHDA-induced cell death.