Iron accelerates the conversion of dopamine-oxidized intermediates into melanin and provides protection in SH-SY5Y cells

Parkinson's disease (PD) is characterized by the selective loss of dopaminergic neurons in the substantia nigra (SN), and it has been suggested that dopamine is one of the main endogenous toxins in the genesis of PD. We demonstrated that thiol antioxidants (the reduced form of glutathione, N-acetyl-L-cysteine, and L-cysteine), which conjugate with one dopamine oxidation intermediate, o-quinone, provided almost complete protection from dopamine-mediated toxicity in SH-SY5Y, a human neuroblastoma cell line. In contrast, catalase partially provided protection against cell death caused by dopamine. These data suggest that the generation of dopamine oxidation intermediates, rather than hydrogen peroxide, plays a pivotal role in dopamine-induced toxicity. Iron accumulated in the SN of patients with PD can cause dopaminergic neuronal degeneration by enhancing oxidative stress. However, we found that iron reduced the total amounts of dopamine oxidation intermediates and enhanced the formation of melanin, a final product of dopamine oxidation. Also, addition of iron inhibited dopamine-induced cytotoxicity. These results suggest that iron can provide protection when it accelerates the conversion of dopamine oxidation intermediates.     

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.     

RA410/Sly1 suppresses MPP+ and 6-hydroxydopamine-induced cell death in SH-SY5Y cells

Parkinson's disease is characterized by selective loss of dopaminergic neurons in the substantia nigra. However, its associated cell death mechanism remains unknown. 1-Methyl-4-phenil-pyridinium (MPP+) and 6-hydroxydopamine (6-OHDA) cause dopaminergic neuronal cell death. Both are widely used to model PD. We investigated the role of a vesicle-transport-related protein, RA410/Sly1, in SH-SY5Y cells to clarify the mechanism of cellular adaptation to MPP+ and 6-OHDA-induced stress. Antisense RA410/Sly1 transformants treated with these toxins displayed reduced viability in comparison with viability of wild-type or RA410/Sly1 sense transformants. Electron microscopy analysis indicated that the ER in MPP+-treated antisense RA410/Sly1 transformants was rapidly disrupted in comparison to wild-type or sense RNA transformants. Cell death induced by MPP+ and 6-OHDA was suppressed in RA410/Sly1 sense transformants through suppression of caspase-2, -3 and -9 activation. These results suggest that RA410/Sly1 plays an important cytoprotective role in MPP+ and 6-OHDA-induced cellular perturbation.     

β-Ecdysterone Protects SH-SY5Y Cells Against 6-Hydroxydopamine-Induced Apoptosis via Mitochondria-Dependent Mechanism: Involvement of p38<Superscript>MAPK</Superscript>–p53 Signaling Pathway

Parkinson’s disease (PD) is a neurological disorder pathologically characterized by loss of dopaminergic neurons in the substantia nigra. No curative therapy is available for PD. We recently found that phytoestrogen β-ecdysterone (β-Ecd) is able to reduce MPP⁺-induced apoptosis in PC12 cells. This study investigated the potential of β-Ecd to protect against SH-SY5Y cell apoptosis induced by the PD-related neurotoxin 6-hydroxydopamine (6-OHDA) and the underlying mechanism for this cytoprotection. In the present study, pretreatment with β-Ecd significantly reduced 6-OHDA-induced apoptosis of SH-SY5Y cells by a mitochondria-dependent pathway, as indicated by downregulation of Bax and PUMA (p53 upregulated modulator of apoptosis) expression, suppressing ΔΨm loss, inhibiting cytochrome c release, and attenuating caspase-9 activation. Furthermore, we showed that the inhibition of p38 mitogen-activated protein kinase (p38^MAPK)-dependent p53 promoter activity contributed to the protection of SH-SY5Y cells from apoptosis, which was validated by the use of SB203580 or p38β dominant negative (DN) mutants. Additionally, knock-down apoptosis signal-regulating kinase 1 (ASK1) by specific shRNA and blockade reactive oxygen species (ROS) by pharmacological inhibitor competently prevented β-Ecd-mediated inhibition of p38^MAPK and ASK1 phosphorylation, respectively. These data provide the first evidence that β-Ecd protects SH-SY5Y cells against 6-OHDA-induced apoptosis, possibly through mitochondria protection and p53 modulation via ROS-dependent ASK1–p38^MAPK pathways. The neuroprotective effects of β-Ecd make it a promising candidate as a therapeutic agent for PD.     

Divalent metal transporter 1 up-regulation is involved in the 6-hydroxydopamine-induced ferrous iron influx

The reasons underlying the high iron content found in the substantia nigra (SN) of Parkinson's disease (PD) are largely unknown. We suppose, based on our previous studies, that the newly discovered iron transporter divalent metal transporter 1 (DMT1) might be involved in this SN iron accumulation process. To investigate this, we first observed the cellular expression of DMT1 in rat SN, both with the iron response element (+IRE) and without the IRE (-IRE) forms. The results showed that both forms of DMT1 were expressed on neurons, astrocytes, and microglia but not on oligodendrocytes. We further observed the relationship between the increased iron influx and DMT1 expression in 6-hydroxydopamine (6-OHDA)-treated C6 cells. 6-OHDA (10 micromol/liter) caused a significant increase in ferrous iron influx, with the increased expression of DMT1+IRE, both in protein and in mRNA levels, whereas no change was observed for DMT1-IRE. To clarify further that the increased expression of DMT1 was not due to the increased intracellular iron content, C6 cells were overloaded with ferric ammonium citrate (100 microg/ml). Decreased expression of both forms of DMT1 was observed. Our data suggest that DMT1 is highly expressed in rat SN in a cell-specific manner. Increased DMT1+IRE expression is the mechanism behind ferrous iron influx induced by 6-OHDA treatment in C6 cells. This may give some evidence for the involvement of DMT1 in the iron accumulation in PD.     

Lateromedial Gradient of the Susceptibility of Midbrain Dopaminergic Neurons to Neonatal 6-Hydroxydopamine Toxicity

The topography-dependent vulnerability of midbrain dopaminergic neurons to neonatal intracranial exposure to 6-hydroxydopamine (6-OHDA) was investigated at adult age by the quantitative analysis of cell counts of tyrosine hydroxylase-immunopositive neurons. In all cases of intracisternal 6-OHDA treatment, A9 dopaminergic neurons in the substantia nigra (SN) were much more vulnerable to death than more medially located A10 dopaminergic neurons. Moreover, within each cell group, there were also lateromedial topographic gradients. In the A9 neuronal group, cells located in the pars lateralis of the SN and the lateral part of the pars compacta of the SN were more susceptible to 6-OHDA toxicity than those located more medially. In the A10 neuronal group, cells located in the medial part of the ventral tegmental area were more resistant to toxicity than those located more laterally, and dopaminergic cells in the midline midbrain areas (interfascicular nucleus and rostral linear nucleus of raphe) were completely spared from 6-OHDA toxicity. These findings revealed that 6-OHDA is not equally toxic to all midbrain dopaminergic neurons in neonates and that the lateromedial vulnerability pattern shows similarities to those reported in Parkinson's disease.     

RA Differentiation Enhances Dopaminergic Features,Changes Redox Parameters,and Increases Dopamine Transporter Dependency in 6-Hydroxydopamine-Induced Neurotoxicity in SH-SY5Y Cells

Research on Parkinson’s disease (PD) and drug development is hampered by the lack of suitable human in vitro models that simply and accurately recreate the disease conditions. To counteract this, many attempts to differentiate cell lines, such as the human SH-SY5Y neuroblastoma, into dopaminergic neurons have been undertaken since they are easier to cultivate when compared with other cellular models. Here, we characterized neuronal features discriminating undifferentiated and retinoic acid (RA)-differentiated SH-SYSY cells and described significant differences between these cell models in 6-hydroxydopamine (6-OHDA) cytotoxicity. In contrast to undifferentiated cells, RA-differentiated SH-SY5Y cells demonstrated low proliferative rate and a pronounced neuronal morphology with high expression of genes related to synapse vesicle cycle, dopamine synthesis/degradation, and of dopamine transporter (DAT). Significant differences between undifferentiated and RA-differentiated SH-SY5Y cells in the overall capacity of antioxidant defenses were found; although RA-differentiated SH-SY5Y cells presented a higher basal antioxidant capacity with high resistance against H₂O₂ insult, they were twofold more sensitive to 6-OHDA. DAT inhibition by 3α-bis-4-fluorophenyl-methoxytropane and dithiothreitol (a cell-permeable thiol-reducing agent) protected RA-differentiated, but not undifferentiated, SH-SY5Y cells from oxidative damage and cell death caused by 6-OHDA. Here, we demonstrate that undifferentiated and RA-differentiated SH-SY5Y cells are two unique phenotypes and also have dissimilar mechanisms in 6-OHDA cytotoxicity. Hence, our data support the use of RA-differentiated SH-SY5Y cells as an in vitro model of PD. This study may impact our understanding of the pathological mechanisms of PD and the development of new therapies and drugs for the management of the disease.     

Neuroprotective effect of citicoline in 6-hydroxydopamine-lesioned rats and in 6-hydroxydopamine-treated SH-SY5Y human neuroblastoma cells

Citicoline (CDP-choline or cytidine 5'-diphosphocholine) has been used as a therapeutic agent in combination with levodopa in the treatment of Parkinson's disease (PD). The present study examines the effects of citicoline by using validated in vivo and in vitro models. Citicoline reduces the cytotoxic effect of 6-hydroxydopamine (6-OHDA)-treated human dopaminergic SH-SY5Y neuroblastoma cells as measured cellular redox activity with 3-[4.5-dimethylthiazol-2-yl]-2.5-diphenyltetrazolium bromide (MTT) and increases the levels of reduced glutathione (GSH), a major antioxidant agent. Moreover, citicoline (500 mg/kg i.p.) administered for 7 days ameliorates functional behaviour by significantly reducing the number of apomorphine-induced contralateral rotations in 6-OHDA rats. Finally, citicoline significantly attenuates substantia nigra (SN) dopaminergic cell dropout and tyrosine hydroxylase immunoreactivity in the ipsilateral striatum in rats injected intrastriatally with 6-hydroxydopamine (6-OHDA).     

重组人促红细胞生成素预处理对黑质多巴胺能神经元凋亡的影响

目的研究重组人促红细胞生成素(rhEPO)对离体帕金森病模型中黑质多巴胺神经元凋亡的影响。方法以6-羟基多巴胺(6-OHDA)为毁损剂建立大鼠离体帕金森病(PD)模型。用6u/mlrhEPO预处理黑质多巴胺神经元,然后用免疫组化方法观察黑质中酪氨酸羟化酶(TH)免疫反应阳性细胞数和半胱天冬酶-3(Caspase-3)免疫反应阳性细胞数的变化,TUNEL法观察黑质中多巴胺神经元的凋亡情况。结果与6-OHDA组(44.2±5.0)相比,rhEPO预处理组TH免疫反应阳性细胞(63.8±6.2,P<0.01)增多;与6-OHDA组(22.3±2.8)相比,rhEPO预处理组多巴胺神经元中Caspase-3表达减少,Caspase-3免疫反应阳性细胞染色较淡,数量减少(13.7±1.8,P<0.01);与6-OHDA组(20.3±3.1)相比,rhEPO预处理组TUNEL阳性细胞染色较淡,数量减少(10.7±1.5,P<0.01)。结论rhEPO预处理可以减轻6-OHDA对离体帕金森病模型中多巴胺神经元的损伤,其机制可能与rhEPO抑制黑质多巴胺神经元凋亡有关。     

PGE(2) receptor EP1 renders dopaminergic neurons selectively vulnerable to low-level oxidative stress and direct PGE(2) neurotoxicity

Oxidative stress and increased cyclooxygenase-2 (COX-2) activity are both implicated in the loss of dopaminergic neurons from the substantia nigra (SN) in idiopathic Parkinson's disease (PD). Prostaglandin E(2) (PGE(2)) is one of the key products of COX-2 activity and PGE(2) production is increased in PD. However, little is known about its role in the selective death of dopaminergic neurons. Previously, we showed that oxidative stress evoked by low concentrations of 6-hydroxydopamine (6-OHDA) was selective for dopaminergic neurons in culture and fully dependent on COX-2 activity. We postulated that this loss was mediated by PGE(2) acting through its receptors, EP1, EP2, EP3, and EP4. Using double-label immunohistochemistry for specific EP receptors and tyrosine hydroxylase (TH), we identified EP1 and EP2 receptors on dopaminergic neurons in rat SN. EP2 receptors were also found in non-dopaminergic neurons of this nucleus, as were EP3 receptors, whereas the EP4 receptor was absent. PGE(2), 16-phenyl tetranor PGE(2) (a stable synthetic analogue), and 17-phenyl trinor PGE(2) (an EP1 receptor-selective agonist) were significantly toxic to dopaminergic cells at nanomolar concentrations; EP2- and EP3-selective agonists were not. We challenged dopaminergic neurons in embryonic rat mesencephalic primary neuronal cultures and tested whether these receptors mediate selective 6-OHDA toxicity. The nonselective EP1-3 receptor antagonist AH-6809 and two selective EP1 antagonists, SC-19220 and SC-51089, completely prevented the 40%-50% loss of dopaminergic neurons caused by exposure to 5 muM 6-OHDA. Together, these results strongly implicate PGE(2) activation of EP1 receptors as a mediator of selective toxicity in this model of dopaminergic cell loss.     

6-Hydroxydopamine toxicity towards human SH-SY5Y dopaminergic neuroblastoma cells: independent of mitochondrial energy metabolism

Summary. 6-Hydroxydopamine (6-OHDA) is widely used to generate animal models of Parkinson's disease. However, little is known about the intracellular events leading to cell death of dopaminergic neurones. Here we correlate indices of energy production and cell viability in human dopaminergic neuroblastoma SH-SY5Y cells after exposure to 6-OHDA. The toxin induces a time and dose-dependent decrease in cell survival with an IC₅₀ value of 25 μM after 24 h. In contrast to the mitochondrial complex I inhibitor 1-methyl-4-phenylpyridinium (MPP⁺), 6-OHDA-induced reduction of cell viability is not associated with a decrease of intracellular ATP content, intracellular ATP/ADP ratio or NAD⁺ content. In addition, preventing or forcing glycolysis do not alter 6-OHDA toxicity. The antioxidant D-α-tocopherol can attenuate cell death induced by 6-OHDA. These results suggest that cell death induced by 6-OHDA is not due to an inhibition of mitochondrial energy supply, but probably involves production of free radicals. Received February 10, 1999; accepted August 18, 1999     

Delivery of a GDNF gene into the substantia nigra after a progressive 6-OHDA lesion maintains functional nigrostriatal connections

The effects of delivering GDNF via an adenoviral vector (AdGDNF) 1 week after lesioning dopaminergic neurons in the rat substantia nigra (SN) with 6-hydroxydopamine (6-OHDA) were examined. Rats were unilaterally lesioned by injection of 6-OHDA into the striatum, resulting in progressive degeneration of dopaminergic neurons in the SN. One week later, when substantial damage had already occurred, AdGDNF or a control vector harboring beta-galactosidase (AdLacZ) was injected into either the striatum or SN (3.2 x 10(7) PFU/microl in 2 microl). Rats were examined behaviorally with the amphetamine-induced rotation test and for forelimb use for weight-bearing movements. On day 30 postlesion, the extent of nigrostriatal tract degeneration was determined by injecting a retrograde tracer (FluoroGold) bilaterally into the lesioned striatum. Five days later, rats were sacrificed within 2 h of amphetamine injection to examine amphetamine-induced Fos expression in the striatum, a measure of dopaminergic-dependent function in target neurons. AdGDNF injection in the SN rescued dopaminergic neurons in the SN and increased the number of dopaminergic neurons that maintained a connection to the striatum, compared to rats injected with AdLacZ. Further support that these spared SN cells maintained functional connections to the striatum was evidenced by increased Fos expression in striatal target neurons and a decrease in amphetamine-induced rotation. In contrast to the effects observed in rats injected with AdGDNF in the SN, rats injected with AdGDNF in the striatum did not exhibit significant ameliorative effects. This study demonstrates that experimentally increasing levels of GDNF biosynthesis near the dopaminergic neuronal soma is effective in protecting the survival of these neurons and their function even when therapy is begun after 6-OHDA-induced degeneration has commenced. Thus, GDNF gene therapy may ameliorate the consequences of Parkinson's disease through rescuing compromised dopaminergic neurons.     

Gene expression profiling in the midbrain of striatal 6-hydroxydopamine-injected mice

In order to clarify mechanisms underlying dopaminergic neuronal death in Parkinson's disease (PD), a gene expression profiling study was performed in a rodent model of PD. In this model, mice are intrastriatally injected with 6-hydroxydopamine (6-OHDA) and dopaminergic neurons in the substantia nigra (SN) gradually die by retrograde degeneration. The SN were removed 2 h, 24 h, or 14 days after 6-OHDA administration. Levels of mRNAs related to cell death or survival were quantified using adaptor-tagged competitive PCR (ATAC-PCR). The cyclin D1 gene showed an immediate increase in mRNA expression. After 24 h, when dopaminergic neurons were under intense degeneration, levels of caspase 8 mRNA and p53 apoptosis effecter related to pmp 22 (PERP) mRNA increased and, conversely, FAS mRNA decreased. After 14 days, when the degeneration was attenuated, levels of PERP mRNA and serum- and glucocorticoid-regulated kinase (SGK) mRNA still increased. SGK has a similarity to AKT, which is an important molecule involved in nerve growth factor signal transduction. AKT mRNA levels are low in dopaminergic neurons. These results suggest that an increase in cyclin D1 mRNA triggers dopaminergic neurons to enter an abnormal cell cycle, which leads to neuronal degeneration and cell death, possibly induced by PERP and caspase 8. In addition to cell death-related genes, several survival-related genes are activated. SGK might function as a key enzyme for the survival of dopaminergic neurons.     

Iron,melanin and dopamine interaction: relevance to parkinson's disease

1. Interaction between iron and melanin may provide a reasonable explanation for the vulnerability of the melanin containing dopaminergic neurons in the substantia nigra (SN) to neurodegeneration in Parkinson's disease (PD).2. Scatchard analysis of the binding of iron to synthetic dopamine melanin revealed a high-affinity (K_D = 13 nM) and a lower affinity (K_D = 200 nM) binding sites.3. The binding of iron to melanin is dependent on the concentration of melanin and on pH.4. Iron chelators, U74500A, desferrioxamine and to a lesser extent 1,10-phenanthroline and chlorpromazine could displace iron from melanin. In contrast, 1-methyl-4-phenyl-1,2,3,6-tetrahdropyridine (MPTP) and its metabolite 1-methyl-4-phenyl-pyridinium (MPP+), which cause Parkinsonism, were unable to displace iron.5. Melanin alone reduced lipid peroxidation in rat cortical membrane preparations. However, iron induced lipid peroxidation, which could he inhibited by desferrioxamine, was potentiated by melanin.6. Iron bound to neuromelanin in melanized dopamine neurons was detected only in parkinsonian brains and not in controls. The interaction of iron with neuromelanin as identified by x-ray defraction technique was identical to iron interaction with synthetic dopamine melanin.7. In the absence of an identified exogenous or endogenous neurotoxin in idiopathic Parkinson's disease, iron-melanin interaction in the SN may serve as a candidate for the oxygen-radical induced neurodegeneration of the melanin containing dopaminergic neurons.     

预热激对6-OHDA诱导SH-SY5Y细胞神经毒性损伤的保护作用

目的探讨预热激对6-羟多巴胺(6-OHDA)诱导人神经母细胞瘤细胞(SH-SY5Y)神经毒性损伤的保护作用及其机制。方法对实验组SH-SY5Y细胞进行预热激(42±0.5)℃处理,再通过6-OHDA对其进行神经毒性诱导,未行预热激处理细胞作为对照组。逆转录酶-聚合酶链式反应(RT-PCR)检测不同热激时间(15 min、30 min、60 min)SH-SY5Y细胞内葡萄糖调节蛋白(GRP78、GRP94)的表达水平;显微镜下观察细胞形态学变化,并用四甲基偶氮唑蓝(MTT)比色法检测SH-SY5Y细胞活性情况。结果 6-OHDA对SH-SY5Y细胞的神经毒性损伤呈剂量依赖性及时间依赖性关系,实验组SH-SY5Y细胞较对照组所受的神经毒性损伤轻(P<0.05),且实验组间差异也具有统计学意义(P<0.05);SH-SY5Y细胞中GRP78和GRP94 mRNA表达水平与热应激时间正相关(P<0.05)。结论预热激可降低6-OHDA诱导SH-SY5Y细胞的神经毒性损伤作用,且热激过程中SH-SY5Y细胞中GRP78和GRP94表达上调。     

重组人促红细胞生成素预处理对帕金森病大鼠胶质细胞源性炎症因子表达的影响

目的探讨重组人促红细胞生成素(rhEPO)预处理对帕金森病(PD)大鼠胶质细胞源性炎症因子表达的影响。方法 40只SD大鼠随机分为4组,A组:右侧纹状体内注射rhEPO 24 h后,同侧黑质内注射6-羟基多巴胺(6-OHDA);B组:右侧纹状体内立体定向注射与rhEPO等量的生理盐水,24 h后同侧黑质内立体定向注射6-OHDA;C组:右侧黑质内立体定向注射6-OHDA;D组:右侧黑质内立体定向注射与6-OHDA等量的生理盐水。4周后采用酶联免疫吸附法检测血清诱导型一氧化氮合酶(iNOS)和肿瘤坏死因子(TNF)-α含量;逆转录(RT)-PCR法检测黑质iNOS和TNF-αmRNA的表达。结果与D组比较,A、B、C组大鼠血清iNOS、TNF-α含量增多,黑质iNOS、TNF-αmRNA表达增高(均P<0.05);与B组和C组比较,A组大鼠血清iNOS、TNF-α含量显著减少,黑质iNOS、TNF-αmRNA表达显著降低(均P<0.05)。结论 rhEPO可能通过抑制黑质TNF-α、iNOS表达,减轻6-OHDA对多巴胺能神经元的毒性损害,具有神经保护作用。     

Effects of GDNF on 6-OHDA-induced death in a dopaminergic cell line: modulation by inhibitors of PI3 kinase and MEK

Parkinson's disease is a neurodegenerative disorder associated with the selective death of dopaminergic neurons. Glial cell line-derived neurotrophic factor (GDNF) can protect dopaminergic neurons in several parkinsonian models. We used the dopaminergic cell line MN9D to explore the mechanisms underlying GDNF-mediated protection against the neurotoxin 6-hydroxydopamine (6-OHDA). MN9D cell viability was decreased 24 hr after a 15-min exposure to 6-OHDA (50-1000 microM) as revealed by staining with Hoechst reagent and Trypan blue. The addition of GDNF (10 ng/ml) before, during, and after exposure to 6-OHDA significantly increased the number of viable cells as assessed by Hoechst staining. In contrast, 6-OHDA-induced cell membrane damage was unaffected as measured by Trypan blue exclusion. The PI3K specific inhibitor LY294002 (10-50 microM) blocked GDNF-mediated protection against nuclear condensation, as did the MAPK kinase (MEK) inhibitor U0126 (5- 20 microM). These studies suggest that GDNF can protect dopaminergic cells against some but not all aspects of 6-OHDA-induced toxicity by acting through both PI3K and MAPK signaling pathways.     

Prevention of 1-methyl-4-phenylpyridinium- and 6-hydroxydopamine-induced nitration of tyrosine hydroxylase and neurotoxicity by EUK-134, a superoxide dismutase and catalase mimetic, in cultured dopaminergic neurons

Oxidative stress has been implicated in the selective degeneration of dopaminergic (DAergic) neurons in Parkinson's disease (PD). In this study, we tested the efficacy of EUK-134, a superoxide dismutase (SOD) and catalase mimetic, on the nitration of tyrosine hydroxylase (TH), a marker of oxidative stress, and neurotoxicity produced by 1-methyl-4-phenylpyridinium (MPP(+)) and 6-hydroxydopamine (6-OHDA) in primary DAergic neuron cultures. Exposure of cultures to 10 microM MPP(+) reduced dopamine (DA) uptake and the number of tyrosine hydroxylase immunoreactive (THir) neurons to 56 and 52% of control, while exposure to 30 microM 6-OHDA reduced DA uptake and the number of THir neurons to 58 and 59% of control, respectively. Pretreatment of cultures with 0.5 microM EUK-134 completely protected DAergic neurons against MPP(+)- and 6-OHDA-induced neurotoxicity. Exposure of primary neuron cultures to either MPP(+) or 6-OHDA produced nitration of tyrosine residues in TH. Pretreatment of cultures with 0.5 microM EUK-134 completely prevented MPP(+)- or 6-OHDA-induced nitration of tyrosine residues in TH. Taken together, these results support the idea that reactive oxygen species (ROS) are critically involved in MPP(+)- and 6-OHDA-induced neurotoxicity and suggest a potential therapeutic role for synthetic catalytic scavengers of ROS, such as EUK-134, in the treatment of PD.     

A tetracycline-regulated adenovirus encoding dominant-negative caspase-9 is regulated in rat brain and protects against neurotoxin-induced cell death in vitro, but not in vivo

Caspase-9 is a critical downstream effector molecule involved in apoptosis, a cell death process thought to be involved in the demise of dopamine (DA) neurons in the substantia nigra (SN) affected by Parkinson's disease (PD). In this study, we determined that a tetracycline-regulated adenovirus harboring a dominant-negative form of caspase-9 (Casp9DN) and the marker gene, enhanced green fluorescent protein (EGFP), under the control of a bidirectional promoter could each be regulated in vitro and in vivo by doxycycline. We next observed that Casp9DN gene delivery significantly protected against TNFalpha and cycloheximide-induced chromatin condensation in HeLa cells and prevented chromatin condensation and the appearance of the early apoptotic marker annexin V in 6-hydroxydopamine (6-OHDA) treated MN9D cells, a dopaminergic cell line. Effects of Casp9DN on DA neurons in vivo were also assessed. DA neurons were retrogradely labeled with fluorogold (FG) and transduced with Casp9DN and EGFP or EGFP alone. A progressive lesion of DA neurons was induced by striatal injection of 6-OHDA 1 week later. At 2 weeks post-lesion, a morphometric analysis of FG+ neurons in the SN revealed that the mean cell diameter of FG labeled neurons in the Casp9DN group was 8% and 21% larger than the EGFP and PBS groups, respectively (P <0.05). However, there was no difference among the treatment groups in the number of neurons remaining in the lesioned SN. These results suggest that while inhibiting apoptosis at the level of caspase-9 is protective in vitro, it is not protective against 6-OHDA-induced cell death in vivo.