Protective effect of sulforaphane against dopaminergic cell death

Parkinson's disease (PD) is a progressive neurodegenerative disorder with a selective loss of dopaminergic neurons in the substantia nigra. Evidence suggests oxidation of dopamine (DA) to DA quinone and consequent oxidative stress as a major factor contributing to this vulnerability. We have previously observed that exposure to or induction of NAD(P)H:quinone reductase (QR1), the enzyme that catalyzes the reduction of quinone, effectively protects DA cells. Sulforaphane (SF) is a drug identified as a potent inducer of QR1 in various non-neuronal cells. In the present study, we show that SF protects against compounds known to induce DA quinone production (6-hydroxydopamine and tetrahydrobiopterin) in DAergic cell lines CATH.a and SK-N-BE(2)C as well as in mesencephalic DAergic neurons. SF leads to attenuation of the increase in protein-bound quinone in tetrahydrobiopterin-treated cells, but this does not occur in cells that have been depleted of DA, suggesting involvement of DA quinone. SF pretreatment prevents membrane damage, DNA fragmentation, and accumulation of reactive oxygen species. SF causes increases in mRNA levels and enzymatic activity of QR1 in a dose-dependent manner. Taken together, these results indicate that SF causes induction of QR1 gene expression, removal of intracellular DA quinone, and protection against toxicity in DAergic cells. Thus, this major isothiocyanate found in cruciferous vegetables may serve as a potential candidate for development of treatment and/or prevention of PD.     

Aldehyde dehydrogenase 1 defines and protects a nigrostriatal dopaminergic neuron subpopulation

Subpopulations of dopaminergic (DA) neurons within the substantia nigra pars compacta (SNpc) display a differential vulnerability to loss in Parkinson’s disease (PD); however, it is not clear why these subsets are preferentially selected in PD-associated neurodegeneration. In rodent SNpc, DA neurons can be divided into two subpopulations based on the expression of aldehyde dehydrogenase 1 (ALDH1A1). Here, we have shown that, in α-synuclein transgenic mice, a murine model of PD-related disease, DA neurodegeneration occurs mainly in a dorsomedial ALDH1A1-negative subpopulation that is also prone to cytotoxic aggregation of α-synuclein. Notably, the topographic ALDH1A1 pattern observed in α-synuclein transgenic mice was conserved in human SNpc. Postmortem evaluation of brains of patients with PD revealed a severe reduction of ALDH1A1 expression and neurodegeneration in the ventral ALDH1A1-positive DA subpopulations. ALDH1A1 expression was also suppressed in α-synuclein transgenic mice. Deletion of Aldh1a1 exacerbated α-synuclein–mediated DA neurodegeneration and α-synuclein aggregation, whereas Aldh1a1-null and control DA neurons were comparably susceptible to 1-methyl-4-phenylpyridinium–, glutamate-, or camptothecin-induced cell death. ALDH1A1 overexpression appeared to preferentially protect against α-synuclein–mediated DA neurodegeneration but did not rescue α-synuclein–induced loss of cortical neurons. Together, our findings suggest that ALDH1A1 protects subpopulations of SNpc DA neurons by preventing the accumulation of dopamine aldehyde intermediates and formation of cytotoxic α-synuclein oligomers.     

The lipopolysaccharide Parkinson's disease animal model: mechanistic studies and drug discovery

Research in the last two decades has unveiled an important role for neuroinflammation in the degeneration of the nigrostriatal dopaminergic (DA) pathway that constitutes the pathological basis of the prevailing movement disorder, Parkinson's disease (PD). Neuroinflammation is characterized by the activation of brain glial cells, primarily microglia and astrocytes that release various soluble factors that include free radicals (reactive oxygen and nitrogen species), cytokines, and lipid metabolites. The majority of these glia-derived factors are proinflammatory and neurotoxic and are particularly deleterious to oxidative damage-vulnerable nigral DA neurons. As a proof of concept, various immunologic stimuli have been employed to directly induce glial activation to model DA neurodegeneration in PD. The bacterial endotoxin, lipopolysaccharide (LPS), has been the most extensively utilized glial activator for the induction of inflammatory DA neurodegeneration. In this review, we will summarize the various in vitro and in vivo LPS PD models. Furthermore, we will highlight the contribution of the LPS PD models to the mechanistic studies of PD pathogenesis and the search for neuroprotective agents for the treatment of PD.     

Cordycepin protects PC12 cells against 6-hydroxydopamine induced neurotoxicity via its antioxidant properties

Parkinson’s disease (PD) is a progressive neurodegenerative disorder that is characterized by degeneration and loss of dopaminergic neurons of the substantia nigra. Increasing evidence has indicated that oxidative stress plays a pivotal role in the pathogenesis of Parkinson’s disease (PD). Therapeutic options that target the antioxidant machinery may have potential in the treatment of PD. Cordycepin, a nucleoside isolated from Cordyceps species displayed potent antioxidant, anti-inflammatory and anticancer properties. However, its neuroprotective effect against 6-OHDA neurotoxicity as well as underlying mechanisms is still unclear. In this present study, we investigated the protective effect of cordycepin against 6-hydroxydopamine (6-OHDA)-induced neurotoxicity and its underlying mechanism. We observed that cordycepin effectively inhibited 6-OHDA-induced cell death, apoptosis and mitochondrial dysfunction. Cordycepin also inhibited cell apoptosis induced by 6-OHDA as observed in the reduction of cytochrome c release from the mitochondrial as well as the inhibition of caspase-3. In addition cordycepin markedly reduced cellular malondialdehyde (MDA) content and intracellular reactive oxygen species (ROS) level. Cordycepin also significantly increased the antioxidant enzymes; superoxide dismutase (SOD) and glutathione peroxidase (GSH-Px) activities in 6-OHDA-treated cells. The results obtained unambiguously demonstrated that cordycepin protects PC12 cells against 6-OHDA-induced neurotoxicity through its potent antioxidant activity.     

ES cell therapy for Parkinson's disease

Neural transplantation, as a treatment for advanced Parkinson's disease (PD), has been studied for more than a decade due to the potential replacement of degenerated dopaminergic (DA) neurons. Several open-label studies on implantation of fetal nigral neurons revealed improvement in motor functions. However, the benefits were incomplete in double-blind trials. Progressive neural or embryonic stem (ES) cell research has raised hopes of creating novel cell replacement therapies for PD. DA neurons have been efficiently produced from primate ES cells in astrocyte-conditioned medium. Transplantation of neuronal stem cells derived from primate ES cells into a primate model of PD restored striatal DA function, suggesting ES cells are suitable donor cells.     

Embryonic stem cells as a cell source for treating Parkinson's disease

Parkinson's disease (PD) is a neurodegenerative disease characterised by a loss of midbrain dopaminergic (DA) neurons. Transplantation of DA neurons represents a promising treatment for PD, and embryonic stem (ES) cells are a good candidate source for DA neurons. However, although recent reports have demonstrated that DA neurons can be efficiently induced from ES cells and function therapeutically in an animal model of PD, many problems remain to be solved in order for ES cells to be used for clinical applications. This review will describe the current status of this field and the obstacles yet to be overcome, and will outline future research approaches from the clinical perspective.     

Environmental neurotoxic chemicals-induced ubiquitin proteasome system dysfunction in the pathogenesis and progression of Parkinson's disease

Proteolytic degradation of unwanted proteins by the ubiquitin-proteasome system (UPS) is critical for normal maintenance of various cellular functions. Parkinson's disease (PD), one of the most prevalent neurodegenerative disorders, is characterized by prominent and irreversible nigral dopaminergic neuronal loss and intracellular protein aggregations. Epidemiological studies imply both environmental neurotoxins and genetic predisposition as potential risk factors for PD, though mechanisms underlying selective dopaminergic degeneration remain unclear. Studies with experimental PD models and postmortem PD brains have provided explicit evidence for mitochondria dysfunction and oxidative stress in PD pathogenesis. Recent identification of mutants in PINK1, DJ-1, Parkin, and LRRK-2 genes compliments the oxidative stress and mitochondrial dysfunction hypotheses in dopaminergic neuronal degeneration in PD. Mutants of alpha-synuclein, Uch-L1 and Parkin support the involvement of UPS dysfunction in PD. Furthermore, various Parkinsonian toxicants have been shown to impair mitochondrial function, redox balances, and to some extent protein degradation machinery. Because environmental exposure to various neurotoxic agents is considered a dominant risk for development of PD, the interrelationship between neurotoxicant exposures and UPS dysfunction must be clearly understood. Elucidation of this interrelationship will help clarify 2 areas: (i) whether UPS dysfunction in PD is a primary pathogenic factor leading to nigral neuronal death or if it simply occurs as a consequence of oxidative stress and mitochondrial dysfunction and (ii) the interaction of genes and environment in the acceleration of nigral dopaminergic degeneration by targeting UPS. We review the recent evidence for UPS deficits in dopaminergic degeneration triggered by neurotoxins.     

Oxidative stress,mitochondrial dysfunction and neurodegenerative diseases; a mechanistic insight

Mitochondria is one of the main source of oxidative stress (ROS), as it utilizes the oxygen for the energy production. ROS and RNS are normally generated by tightly regulated enzymes. Excessive stimulation of NAD(P)H and electron transport chain leads to the overproduction of ROS, results in oxidative stress, which is a good mediator to injure the cell structures, lipids, proteins, and DNA. Various oxidative events implicated in many diseases due to oxidative stress include alteration in mitochondrial proteins, mitochondrial lipids and mitochondrial DNA, Which in turn leads to the damage to nerve cell as they are metabolically very active. ROS/RNS at moderate concentrations also play roles in normal physiology of many processes like signaling pathways, induction of mitogenic response and in defense against infectious pathogens. Oxidative stress has been considered to be the main cause in the etiology of many diseases, which includes Parkinson’s and Alzheimer diseases. Several PD associated genes have been found to be involved in mitochondrial function, dynamics and morphology as well. This review includes source of free radical generation, chemistry and biochemistry of ROS/RNS and mitochondrial dysfunction and the mechanism involved in neurodegenerative diseases.     

Dopaminergic neurons generated from monkey embryonic stem cells function in a Parkinson primate model

Parkinson disease (PD) is a neurodegenerative disorder characterized by loss of midbrain dopaminergic (DA) neurons. ES cells are currently the most promising donor cell source for cell-replacement therapy in PD. We previously described a strong neuralizing activity present on the surface of stromal cells, named stromal cell-derived inducing activity (SDIA). In this study, we generated neurospheres composed of neural progenitors from monkey ES cells, which are capable of producing large numbers of DA neurons. We demonstrated that FGF20, preferentially expressed in the substantia nigra, acts synergistically with FGF2 to increase the number of DA neurons in ES cell-derived neurospheres. We also analyzed the effect of transplantation of DA neurons generated from monkey ES cells into 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine-treated (MPTP-treated) monkeys, a primate model for PD. Behavioral studies and functional imaging revealed that the transplanted cells functioned as DA neurons and attenuated MPTP-induced neurological symptoms.     

Gene therapy for Parkinson's disease

Recent advances in gene transfer methods, especially development of a high titer recombinant adeno-associated viral (AAV) vector, are making gene therapy for Parkinson's disease (PD) a feasible therapeutic option in the clinical arena. Efficient and long-term expression of genes for dopamine (DA)-synthesizing enzymes in the striatum restored local DA production and allowed behavioral recovery in animal models of PD. Moreover, sustained expression of a glial cell line-derived neurotrophic factor gene in the striatum rescued nigral neurons and led to functional recovery in a rat model of PD, even when treatment was delayed until after the onset of progressive degeneration. A clinical trial to evaluate the efficacy of subthalamic transduction to produce inhibitory transmitters is underway.     

Inflammatory process in Parkinson disease: neuroprotection by neuropeptide Y

Parkinson's disease (PD) is characterized by the degeneration of dopaminergic neurons in the nigro‐striatal pathway. Interestingly, it has already been shown that an intracerebral administration of neuropeptide Y (NPY) decreases the neurodegeneration induced by 6‐hydroxydopamine (6‐OHDA) in rodents and prevents loss of dopamine (DA) and DA transporter density. The etiology of idiopathic PD now suggest that chronic production of inflammatory mediators by activated microglial cells mediates the majority of DA‐neuronal tissue destruction. In an animal experimental model of PD, the present study shows that NPY inhibited the activation of microglia evaluated by the binding of the translocator protein (TSPO) ligand [3H]PK11195 in striatum and substantia nigra of 6‐OHDA rats. These results suggest a potential role for inflammation in the pathophysiology of the disease and a potential treatment by NPY in PD.     

Effect of (R)-salsolinol and N-methyl-(R)-salsolinol on the balance impairment between dopamine and acetylcholine in rat brain: involvement in pathogenesis of Parkinson disease

BACKGROUND: Parkinson disease (PD), a progressive neurodegenerative disease, affects at least 1% of population above the age of 65. Although the specific etiology of PD remains unclear, recently the endogenous neurotoxins such as (R)-salsolinol [(R)-Sal] and N-methyl-(R)-salsolinol [(R)-NMSal] have been thought to play a major role in PD. Much interest is focused on the degeneration of dopamine neurons induced by these neurotoxins. However, little literature is available on the impact of endogenous neurotoxins on the balance between dopamine (DA) and acetylcholine (ACh). METHODS: After injection of (R)-Sal or (R)-NMSal into the rat brain striatum, the concentrations of DA and its metabolites were detected by HPLC with electrochemical detection. We assessed the influence of neurotoxins on acetylcholinesterase (AChE) activity and developed a microdialysis-electrochemical device to measure ACh concentrations with enzyme-modified electrodes. RESULTS: (R)-Sal and (R)-NMSal led to concentration-dependent decreases in the activity of AChE. ACh concentrations in striatum treated with (R)-Sal or (R)-NMSal were increased to 131.7% and 239.8% of control, respectively. As to the dopaminergic system, (R)-NMSal caused a significant decrease in DA concentrations and (R)-Sal reduced the concentrations of DA metabolites in the striatum. CONCLUSIONS: (R)-Sal and (R)-NMSal exerted a considerable effect on the balance between DA and ACh by impairing the cholinergic system as well as the dopaminergic system. It is likely that the disruption of balance between DA and ACh plays a critical role in the pathogenesis of neurotoxin-induced PD.     

Imaging DA release in a rat model of L-DOPA-induced dyskinesias: A longitudinal in vivo PET investigation of the antidyskinetic effect of MDMA

In the context of Parkinson's disease, motor symptoms result from the degeneration of nigrostriatal neurons. Dopamine (DA) replacement using l-3,4-dihydroxyphenylalanine (L-DOPA) has been the treatment of choice in the early stages of the disease. However, with disease progression, patients suffer from motor complications, which have been suggested to arise from DA released from serotonergic terminals according to the false neurotransmitter hypothesis. The synthetic amphetamine derivative (±) 3,4-methylenedioxymethamphetamine (MDMA) has been shown to significantly inhibit dyskinesia in humans and in animal models of PD. In this study, we examined the effect of MDMA on L-DOPA-induced DA release by using [(11)C]raclopride kinetic modeling to assess alterations in DA neurotransmission in a rat model of L-DOPA-induced dyskinesia (LID) in a longitudinal in vivo PET study. Rats were submitted to 6-OHDA lesions, and the lesions were confirmed to be sufficiently severe based on the performance during stepping tests and [(11)C]methylphenidate PET scans. The rats underwent two [(11)C]raclopride PET sessions before (baseline) and after two weeks of chronic L-DOPA treatment (priming). L-DOPA priming led to strong abnormal involuntary movements (AIMs). In group 1, L-DOPA priming reduced L-DOPA-induced DA release in the lesioned striatum with no effect on the healthy side, while the concomitant administration of L-DOPA and MDMA (group 2) increased the DA levels in the lesioned and healthy striatum. In addition, behavioral analysis, which was performed two weeks after the second PET session, confirmed the antidyskinetic effect of MDMA. Our data show that L-DOPA-induced DA release is attenuated in the Parkinsonian striatum after chronic L-DOPA pretreatment and that the antidyskinetic mechanism of MDMA does not depend primarily on dopaminergic neurotransmission.     

帕金森病的炎症及抗炎药物的研究进展

帕金森病是人类最常见的神经退行性运动障碍性疾病之一,其特征是中脑黑质致密部多巴胺能神经元变性丢失,纹状体内多巴胺水平降低,进而引起震颤、肌肉僵直、运动迟缓和姿势步态失调的症状。帕金森病的病理机制复杂,病因目前仍不清楚。但近年来,炎症反应在帕金森病中的作用引起人们的广泛关注,小胶质细胞的激活以及炎性因子的高表达参与帕金森病的发生、发展过程。应用抗炎药物延缓或阻止帕金森病的发生、发展已成为该领域新的研究热点。本文就帕金森病中的炎症机制以及抗炎药物的进展进行综述。     

Neurodegenerative diseases and oxidative stress.

Oxidative stress is now recognized as accountable for redox regulation involving reactive oxygen species (ROS) and reactive nitrogen species (RNS). Its role is pivotal for the modulation of critical cellular functions, notably for neurons astrocytes and microglia, such as apoptosis program activation, and ion transport, calcium mobilization, involved in excitotoxicity. Excitotoxicity and apoptosis are the two main causes of neuronal death. The role of mitochondria in apoptosis is crucial. Multiple apoptotic pathways emanate from the mitochondria. The respiratory chain of mitochondria that by oxidative phosphorylation, is the fount of cellular energy, i.e. ATP synthesis, is responsible for most of ROS and notably the first produced, superoxide anion (O(2)(;-)). Mitochondrial dysfunction, i.e. cell energy impairment, apoptosis and overproduction of ROS, is a final common pathogenic mechanism in aging and in neurodegenerative disease such as Alzheimer's disease (AD), Parkinson's disease (PD) and amyotrophic lateral sclerosis (ALS). Nitric oxide (NO(;)), an RNS, which can be produced by three isoforms of NO-synthase in brain, plays a prominent role. The research on the genetics of inherited forms notably ALS, AD, PD, has improved our understanding of the pathobiology of the sporadic forms of neurodegenerative diseases or of aging of the brain. ROS and RNS, i.e. oxidative stress, are not the origin of neuronal death. The cascade of events that leads to neurons, death is complex. In addition to mitochondrial dysfunction (apoptosis), excitotoxicity, oxidative stress (inflammation), the mechanisms from gene to disease involve also protein misfolding leading to aggregates and proteasome dysfunction on ubiquinited material.     

Mitochondrial stress-induced dopamine efflux and neuronal damage by malonate involves the dopamine transporter

Endogenous striatal dopamine (DA) overflow has been associated with neuropathological conditions resulting from ischemia, psychostimulants, and metabolic inhibition. Malonate, a reversible inhibitor of succinate dehydrogenase, models the effects of energy impairment in neurodegenerative disorders. We have previously reported that the striatal DA efflux and damage to DA nerve terminals resulting from intrastriatal malonate infusions is prevented by prior DA depletion, suggesting that DA plays a role in the neuronal damage. We presently report that the malonate-induced DA efflux is partially mediated by reverse transport of DA from the cytosol to the extracellular space via the DA transporter (DAT). Pharmacological blockade of the DAT with a series of structurally different inhibitors [cocaine, mazindol, 1-(2-(bis(4-fluophenyl methoxy) ethyl)-4-(3-(4-fluorophenyl)-propyl)piperazine) dimethane sulfonate (GBR 13098) and methyl(-)-3beta-(p-fluorophenyl)-1alphaH,5alphaH-tropane-2beta-carboxylate1,5-naphthalene (Win 35,428)] attenuated malonate-induced DA overflow in vivo and protected mice against subsequent damage to DA nerve terminals. Consistent with these findings, the DAT inhibitors prevented malonate-induced damage to DA neurons in mesencephalic cultures and also protected against the loss of GABA neurons in this system. The DAT inhibitors did not modify malonate-induced formation of reactive oxygen species or lactate production, indicating that the DAT inhibitors neither exert antioxidant effects nor interfere with the actions of malonate. Taken together, these findings provide direct evidence that mitochondrial impairment and metabolic stress cause striatal DA efflux via the DAT and suggest that disruptions in DA homeostasis resulting from energy impairment may contribute to the pathogenesis of neurodegenerative diseases.     

Levodopa is toxic to dopamine neurons in an in vitro but not an in vivo model of oxidative stress

Levodopa is the "gold standard" for the symptomatic treatment of Parkinson's disease (PD). There is a theoretical concern, however, that levodopa might accelerate the rate of nigral degeneration, because it undergoes oxidative metabolism and is toxic to cultured dopaminergic neurons. Most in vivo studies do not show evidence of levodopa toxicity; levodopa is not toxic to normal rodents, nonhuman primates, or humans and is not toxic to dopamine neurons in dopamine-lesioned rodents or nonhuman primates in most studies. However, the potential for levodopa to be toxic in vivo has not been tested under conditions of oxidative stress such as exist in PD. To assess whether levodopa is toxic under these circumstances, we have examined the effects of levodopa on dopamine neurons in mesencephalic cultures and rat pups in which glutathione synthesis has been inhibited by L-buthionine sulfoximine. Levodopa toxicity to cultured dopaminergic neurons was enhanced by glutathione depletion and diminished by antioxidants. In contrast, treatment of neonatal rats with levodopa, administered either alone or in combination with glutathione depletion, did not cause damage to the dopamine neurons of the substantia nigra or changes in striatal levels of dopamine and its metabolites. This study provides further evidence to support the notion that although levodopa can be toxic to dopamine neurons in vitro, it is not likely to be toxic to dopamine neurons in vivo and specifically in conditions such as PD.     

Oxidative stress in neurodegenerative diseases: therapeutic implications for superoxide dismutase mimetics

Evidence of oxidative stress is apparent in both acute and chronic neurodegenerative diseases, such as stroke, Parkinson's disease (PD) and amyotrophic lateral sclerosis (ALS). Increased generation of reactive oxygen species simply overwhelm endogenous antioxidant defences, leading to subsequent oxidative damage and cell death. Tissue culture and animal models have been developed to mimic some of the biochemical changes and neuropathology found in these diseases. In doing so, it has been experimentally demonstrated that oxidative stress plays a critical role in neuronal cell death. Antioxidant enzymes, such as superoxide dismutase (SOD), catalase and glutathione peroxidase (GPx) have demonstrated therapeutic efficacy in models of neurodegeneration. However, delivery and stability issues have reduced the enthusiasm to clinically develop these proteins. Most recently, SOD mimetics, small molecules which mimic the activity of endogenous superoxide dismutase, have come to the forefront of antioxidant therapeutics. This review will examine the experimental evidence supporting the use of scavengers of superoxide anions in treating some neurodegenerative diseases, such as stroke, PD and ALS, but also the pitfalls that have met antioxidant molecules in clinical trials.