Role of reactive nitrogen and reactive oxygen species against MPTP neurotoxicity in mice

Modulation of Autophagy and Nitric Oxide Signaling via Glycyrrhizic Acid and 7-Nitroindazole in MPTP-induced Parkinson's Disease Model

Background

Parkinson's disease (PD) is characterized by dopaminergic (DA) neuron loss, Lewy body build-up, and motor dysfunction. One of the primary pathogenic mechanisms of PD development is autophagy dysfunction and nitric oxide-mediated neurotoxicity.

Purpose

The current study focuses on autophagy and nitric oxide (NO) signaling roles in 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-intoxicated PD mice and their protection by their modulators.

Method

BALB/c mice were administered MPTP (30 mg/kg/i.p/day) for five consecutive days in order to create a PD model. Following MPTP poisoning, the doses of GA (16.8 mg/kg/day/i.p.), 7-nitroindazole (7-NI) (10 mg/kg/day/i.p.), and their combination were administered once daily for 14 days. Animals were observed for behavioral and locomotor changes, biochemical examination, inflammatory mediators, and analysis of molecular markers.

Results

GA, 7-NI alone significantly reduced MPTP-induced locomotor, behavioral, and oxidative damage. Additionally, in MPTP-intoxicated animals, 7-NI and GA had protective effects on dopamine levels, TH positive DA neurons, inflammatory cytokines interleukin 1β (IL-1β), tumor necrosis factor-alpha (TNF-α), nuclear factor-kappa B (NF-κB), and cyclooxygenase-2 (Cox-2) concentration. Furthermore, GA increases LC3BII expression, which in turn increases autophagy. It also decreases total NO content, and a significant response of 7-NI demonstrates their interaction, which is neuroprotective.

Conclusion

Present research suggests that dysregulation of autophagy and NO-mediated neuroinflammation are involved in the pathogenesis and progression of MPTP-induced PD. The use of two pharmacotherapeutics, GA and 7-NI, respectively, significantly reduces MPTP-induced PD distortions and their interaction enhances the overall protective effect, suggesting that these pharmacological agents may be used for the treatment of PD.

Nitric Oxide/Nitric Oxide Synthase System in the Pathogenesis of Neurodegenerative Disorders-An Overview

Nitric oxide, a ubiquitous molecule found throughout the natural world, is a key molecule implicated in many central and benefic molecular pathways and has a well-established role in the function of the central nervous system, as numerous studies have previously shown. Dysregulation of its metabolism, mainly the upregulation of nitric oxide production, has been proposed as a trigger and/or aggravator for many neurological affections. Increasing evidence supports the implication of this molecule in prevalent neurodegenerative diseases, such as Parkinson's disease, Alzheimer's disease, or amyotrophic lateral sclerosis. The mechanisms proposed for its neurotoxicity mainly center around the increased quantities of nitric oxide that are produced in the brain, their cause, and, most importantly, the pathological metabolic cascades created. These cascades lead to the formation of neuronal toxic substances that impair the neurons' function and structure on multiple levels. The purpose of this review is to present the main causes of increased pathological production, as well as the most important pathophysiological mechanisms triggered by nitric oxide, mechanisms that could help explain a part of the complex picture of neurodegenerative diseases and help develop targeted therapies.

Effect of sex and gonadectomy on brain MPTP toxicity and response to dutasteride treatment in mice

The main neuropathological feature of Parkinson's disease (PD) is degeneration of dopamine (DA) neurons in the substantia nigra (SN); PD prevalence is higher in men, suggesting a role of sex hormones in neuroprotection. This study sought the effects of sex hormones in the brain in a mouse model of PD and modulation of steroid metabolism/synthesis with the 5α-reductase inhibitor dutasteride shown to protect 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) male mice. Male and female mice were gonadectomized (GDX) or SHAM operated. They were treated with vehicle or dutasteride (5 mg/kg) for 10 days and administered a low dose of MPTP (5.5 mg/kg) or saline on the 5th day to model early PD; brains were collected thereafter. Striatal measures of the active metabolite 1-methyl-4-phenylpyridinium (MPP+) contents showed no difference supporting an effect of the experimental conditions investigated. In SHAM MPTP male mice loss of striatal DA and metabolites, DA transporter (DAT) and vesicular monoamine transporter 2 (VMAT2) specific binding in the striatum and SN was prevented by dutasteride treatment; these changes were inversely correlated with glial fibrillary acidic protein (GFAP, an astrogliosis marker) levels. In SHAM female mice MPTP treatment had little or no effect on striatal and SN DA markers and GFAP levels whereas GDX male and female mice showed a similar loss of striatal DA markers and increase of GFAP. No effect of dutasteride treatment was observed in GDX male and female mice. In conclusion, sex differences in mice MPTP toxicity and response to dutasteride were observed that were lost upon gonadectomy implicating neuroinflammation.

Decreased proteasomal cleavage at nitrotyrosine sites in proteins and peptides

Removal of moderately oxidized proteins is mainly carried out by the proteasome, while highly modified proteins are no longer degradable. However, in the case of proteins modified by nitration of tyrosine residues to 3-nitrotyrosine (NO₂Y), the role of the proteasome remains to be established. For this purpose, degradation assays and mass spectrometry analyses were performed using isolated proteasome and purified fractions of native cytochrome c (Cyt c) and tyrosine nitrated proteoforms (NO₂Y74-Cyt c and NO₂Y97-Cyt c). While Cyt c treated under mild conditions with hydrogen peroxide was preferentially degraded by the proteasome, NO₂Y74- and NO₂Y97-Cyt c species did not show an increased degradation rate with respect to native Cyt c. Peptide mapping analysis confirmed a decreased chymotrypsin-like cleavage at C-terminal of NO₂Y sites within the protein, with respect to unmodified Y residues. Additionally, studies with the proteasome substrate suc-LLVY-AMC (Y-AMC) and its NO₂Y-containing analog, suc-LLVNO₂Y-AMC (NO₂Y-AMC) were performed, both using isolated 20S-proteasome and astrocytoma cell lysates as the proteasomal source. Comparisons of both substrates showed a significantly decreased proteasome activity towards NO₂Y-AMC. Moreover, NO₂Y-AMC, but not Y-AMC degradation rates, were largely diminished by increasing the reaction pH, suggesting an inhibitory influence of the additional negative charge contained in NO₂Y-AMC secondary to nitration. The mechanism of slowing of proteasome activity in NO₂Y-contaning peptides was further substantiated in studies using the phenylalanine and nitro-phenylalanine peptide analog substrates. Finally, degradation rates of Y-AMC and NO₂Y-AMC with proteinase K were the same, demonstrating the selective inability of the proteasome to readily cleave at nitrotyrosine sites. Altogether, data indicate that the proteasome has a decreased capability to cleave at C-terminal of NO₂Y residues in proteins with respect to the unmodified residues, making this a possible factor that decreases the turnover of oxidized proteins, if they are not unfolded, and facilitating the accumulation of nitrated proteins.

Caffeine, a natural methylxanthine nutraceutical, exerts dopaminergic neuroprotection

Parkinson's disease (PD) is a progressive neurodegenerative disorder that affects more than 10 million people worldwide. Oxidative stress and mitochondrial dysfunction play a significant role in altering the homeostasis of energy production and free radical generation. Current PD therapies are focused on reducing the cardinal symptoms rather than preventing disease progression in the patients. Adenosine A_2A receptor (A_2A R) antagonist (Istradephylline) combined with levodopa shows a promising therapy for PD. In animal studies, caffeine administration showed to improve motor functions and neuroprotective effect in the neurons. Caffeine is probably the most extensively used psychoactive substance. In this current study, we investigated the neuroprotective effect of caffeine against 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-induced neurodegeneration. Here, we demonstrate that caffeine improves behavioral and neurotransmitter recovery against MPTP-induced toxicity. Caffeine restores endogenous antioxidant levels and suppresses neuroinflammation. Our finding suggests that the blockage of A_2AR is a promising disease-modifying therapy for PD. Target engagement strategies could be more beneficial in preventing disease progression rather than symptomatic reliefs in PD patients.

Overexpression of thioredoxin reductase 1 can reduce DNA damage, mitochondrial autophagy and endoplasmic reticulum stress in Parkinson's disease

Parkinson's disease (PD) is a neurodegenerative disease characterized by the loss of dopaminergic neurons in the substantia nigra (SN). Several factors, including neuroinflammation, neuronal excitotoxicity, genetic mutations and incorrect protein folding are involved in PD pathophysiology. However, the precise mechanism that contributes to the decreased number of dopaminergic neurons is unknown. A growing body of research suggests that oxidative stress is a major factor in PD. Therefore, antioxidant therapy is an important approach for treating PD. The thioredoxin system is an important antioxidant system, and thioredoxin reductase 1 (TR1) is a major member of the thioredoxin system. The present study demonstrates that oxidative stress is increased and that the expression of TR1 is decreased in the SNc of A53T mice; TR1 has emerged as an important antioxidant agent in dopaminergic neurons. Therefore, we over-expressed TR1 in the MPP⁺-induced cellular model and in the A53T transgenic mouse model of PD. We confirmed that the overexpression of TR1 in neuronal cells decreased DNA damage and malondialdehyde (MDA) and ROS generation, increased T-SOD and GSH production, and decreased the ER stress, and autophagy in the PD model. In summary, our findings demonstrate that the overexpression of TR1 could be effective as a novel neuroprotective strategy for PD. This research suggests a novel direction in the treatment of PD.

Protective effect of thioredoxin reductase 1 in Parkinson's disease

Parkinson's disease (PD) is a neurodegenerative disease characterized by the loss of dopaminergic neurons in the substantia nigra (SN). Many factors can explain the mechanism. However, the precise mechanism that contributes to the decreased number of dopaminergic neurons is unknown. Our study shows that oxidative stress is increased in models of PD compared with WT mice; Thioredoxin reductase 1(TR1) has emerged as an important antioxidant agent in dopaminergic neurons. In summary, our findings demonstrate that the overexpression of TR1 could be developed into a novel neuroprotective strategy for PD and that the reduction of the expression of GSK-3β and NF-κB could also be promising therapeutic strategies for PD. This research suggests a new direction in the treatment of PD.

Naringenin Decreases α-Synuclein Expression and Neuroinflammation in MPTP-Induced Parkinson's Disease Model in Mice

The present study was designed to ascertain the role of naringenin (NGN), a citrus fruit flavanone, against 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-induced α-synuclein (SYN) pathology and neuroinflammation in a mouse model. NGN was administered to C57BL/6J mice once a day for 5 consecutive days prior to the MPTP intoxication. On day 5, 40-50 min after the NGN or vehicle administration, MPTP was injected in two divided doses (2× 40 mg/kg, i.p. at 16 h apart). The animals were observed for motor functions 48 h after the first MPTP injection. The animals were then euthanized, the brains collected to analyze SYN pathology, cytokines, and oxidative stress levels in the substantia nigra region. The NGN significantly downregulated SYN and upregulated dopamine transporter (DAT) and tyrosine hydroxylase (TH) protein expressions. It also downregulated tumor necrosis factor-α (TNFα) and interleukin 1β (IL1β) mRNA expressions and improved superoxide dismutase levels. It also reduced glutathione levels when compared to vehicle-treated PD animals. The upregulation of TH corroborates to an increase in dopamine, DOPAC, and homovanillic acid turnover and motor functions with NGN treatment. To summarize, NGN, a dietary flavone, has the potential to counteract MPTP-induced dopaminergic degeneration by regulating SYN pathology, neuroinflammation, and oxidative stress. This warrants the investigation of NGN's potential effects in a genetic model of PD.

Design, synthesis, immunocytochemistry evaluation, and molecular docking investigation of several 4-aminopyridine derivatives as potential neuroprotective agents for treating Parkinson's disease

Neuroprotection refers to the relative preservation of neuronal structure and function. Neuroprotective agents refer to substances that are capable of preserving brain function and structure. Currently, there are no neuroprotective agents available that can effectively relieve the progression of Parkinson's disease. In this work, five novel 4-aminopyridine derivatives, including three amides and two ureas, were designed, synthesized, and evaluated using the rat PC12 mice pheochromocytoma cell line as an in vitro model. As well as human Rho kinase inhibitory experiment was performed. Among them, compound 3, which exhibited high cell viability, low cytotoxicity and good efficacy of inhibition on α-synuclein, oxidation, inflammation and Rho kinase, was profound as potential agents for Parkinson's disease (PD).

Quantitative activation-induced manganese-enhanced MRI reveals severity of Parkinson's disease in mice

We demonstrate that activation-induced manganese-enhanced magnetic resonance imaging with quantitative determination of the longitudinal relaxation time (qAIM-MRI) reveals the severity of Parkinson's disease (PD) in mice. We first show that manganese ion-accumulation depends on neuronal activity. A highly active region was then observed by qAIM-MRI in the caudate-putamen in PD-model mice that was significantly correlated to the severity of PD, suggesting its involvement in the expression of PD symptoms.

Examining the neuroprotective effects of protocatechuic acid and chrysin on in vitro and in vivo models of Parkinson disease

Polypharmacology-based strategies using drug combinations with different mechanisms of action are gaining increasing attention as a novel methodology to discover potentially innovative medicines for neurodegenerative disorders. We used this approach to examine the combined neuroprotective effects of two polyphenols, protocatechuic acid (PCA) and chrysin, identified from the fruits of Alpinia oxyphylla. Our results demonstrated synergistic neuroprotective effects, with chrysin enhancing the protective effects of PCA, resulting in greater cell viability and decreased lactate dehydrogenase release from 6-hydroxydopamine-treated PC12 cells. Their combination also significantly attenuated chemically induced dopaminergic neuron loss in both zebrafish and mice. We examined the molecular mechanisms underlying these collective cytoprotective effects through proteomic analysis of treated PC12 cells, resulting in the identification of 12 regulated proteins. Two were further characterized, leading to the determination that pretreatment with PCA and chrysin resulted in (i) increased nuclear factor-erythroid 2-related factor 2 protein expression and transcriptional activity; (ii) modulation of cellular redox status with the upregulated expression of hallmark antioxidant enzymes, including heme oxygenase-1, superoxide dismutase, and catalase; and (iii) decreased levels of malondialdehyde, a known lipid peroxidation product. Treatment with PCA and chrysin also inhibited activation of nuclear factor-κB and expression of inducible nitric oxide synthase. Our findings suggest that natural products, when used in combination, can be effective potential therapeutic agents for treating diseases such as Parkinson disease. A therapy involving both PCA and chrysin exhibits its enhanced neuroprotective effects through a combination of cellular mechanisms: antioxidant cytoprotection and anti-inflammation.

Increasing the Biological Stability Profile of a New Chemical Entity, UPEI-104, and Potential Use as a Neuroprotectant Against Reperfusion-Injury

Previous work in our laboratory demonstrated the utility of synthetic combinations of two naturally occurring, biologically active compounds. In particular, we combined two known anti-oxidant compounds, lipoic acid and apocynin, covalently linked via an ester bond (named UPEI-100). In an animal model of ischemia-reperfusion injury (tMCAO), UPEI-100 was shown to produce equivalent neuroprotection compared to each parent compound, but at a 100-fold lower dose. However, it was determined that UPEI-100 was undetectable in any tissue samples almost immediately following intravenous injection. Therefore, the present investigation was done to determine if biological stability of UPEI-100 could be improved by replacing the ester bond with a more bio cleavage-resistant bond, an ether bond (named UPEI-104). We then compared the stability of UPEI-104 to the original parent compound UPEI-100 in human plasma as well as liver microsomes. Our results demonstrated that both UPEI-100 and UPEI-104 could be detected in human plasma for over 120 min; however, only UPEI-104 was detectable for an average of 7 min following incubation with human liver microsomes. This increased stability did not affect the biological activity of UPEI-104 as measured using our tMCAO model. Our results suggest that combining compounds using an ether bond can improve stability while maintaining biological activity.

The novel tetramethylpyrazine bis-nitrone (TN-2) protects against MPTP/MPP+-induced neurotoxicity via inhibition of mitochondrial-dependent apoptosis

Mitochondrial-dependent apoptosis plays an important role in the degeneration of dopaminergic neurons in Parkinson's disease (PD). Methyl-4-phenyl-1,2,3,6-tetra- hydropyridine (MPTP), the most widely used neurotoxin to simulate PD, is converted to 1-methyl-4-phenylpyridinium (MPP(+)) in vivo. MPP(+) induces excessive intracellular reactive oxygen species (ROS), leading to mitochondrial-dependent apoptosis via sequentially opening mitochondria permeability transition pore (mPTP) to release cytochrome c from mitochondria into cytoplasm and activate pro-apoptotic caspase proteins. We have previously synthesized 2,5-[[(1,1-dimethylethyl)oxidoimino]methyl]-3,6-trimethylpyrazine (TN-2), a novel derivative of the Chinese herb medicine tetramethylpyrazine (TMP). TN-2 is armed with two powerful free radical-scavenging nitrone moieties. TN-2 significantly reversed the loss of dopaminergic neurons in the substantia nigra and the decrease in dopamine level in the striatum induced by MPTP in mice. TN-2 ameliorated the MPTP-induced decrease of brain superoxide dismutase activity and glutathione concentration and increase of brain malondialdehyde. In addition, TN-2 inhibited MPP(+)-induced neuronal damage/apoptosis in primary cerebellum granular neurons (CGNs) and SH-SY5Y cells. TN-2 decreased excessive intracellular ROS, prevented the loss of mitochondrial membrane potential, blocked the release of mitochondrial cytochrome c and inhibited the activation of caspase-3 and caspase-9. Moreover, TN-2 treatment increased the mRNA expression of mitochondrial biogenesis factors peroxisome proliferator-activated receptor (PPAR)-γ coactivator-1 (PGC- 1α and β) and mitochondrial transcription factor A (Tfam) in SH-SY5Y cells and CGNs. These results suggest that TN-2 protects dopaminergic neurons against MPTP/MPP(+)-induced neurotoxicity via the inhibition of mitochondrial-dependent apoptosis and possibly via the activation of mitochondrial biogenesis, indicating that TN-2 is a potential new treatment for PD.

Downregulation of thioredoxin reductase 1 expression in the substantia nigra pars compacta of Parkinson's disease mice

Because neurons are susceptible to oxidative damage and thioredoxin reductase 1 is extensively distributed in the central nervous system and has antioxidant properties, we speculated that the enzyme may be involved in the pathogenesis of Parkinson's disease. A Parkinson's disease model was produced by intraperitoneal injection of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine into C57BL/6 mice. Real-time reverse transcription-PCR, western blot analysis and colorimetric assay showed that the levels of thioredoxin reductase 1 mRNA and protein were decreased, along with a significant reduction in thioredoxin reductase activity, in the midbrain of Parkinson's disease mice compared with normal mice. Immunohistochemical staining revealed that the number of thioredoxin reductase 1-positive neurons in the substantia nigra pars compacta of Parkinson's disease mice was significantly decreased compared with normal mice. These experimental findings suggest that the expression of thioredoxin reductase 1 in the substantia nigra pars compacta of Parkinson's disease mice is significantly decreased, and that the enzyme may be associated with disease onset.

Posttranslational protein modifications by reactive nitrogen and chlorine species and strategies for their prevention and elimination

Proteins are subject to various posttranslational modifications, some of them being undesired from the point of view of metabolic efficiency. Prevention of such modifications is expected to provide new means of therapy of diseases and decelerate the process of aging. In this review, modifications of proteins by reactive nitrogen species and reactive halogen species, is briefly presented and means of prevention of these modifications and their sequelae are discussed, including the denitrase activity and inhibitors of myeloperoxidase.

The interplay between iron accumulation, mitochondrial dysfunction, and inflammation during the execution step of neurodegenerative disorders

A growing set of observations points to mitochondrial dysfunction, iron accumulation, oxidative damage and chronic inflammation as common pathognomonic signs of a number of neurodegenerative diseases that includes Alzheimer’s disease, Huntington disease, amyotrophic lateral sclerosis, Friedrich’s ataxia and Parkinson’s disease. Particularly relevant for neurodegenerative processes is the relationship between mitochondria and iron. The mitochondrion upholds the synthesis of iron–sulfur clusters and heme, the most abundant iron-containing prosthetic groups in a large variety of proteins, so a fraction of incoming iron must go through this organelle before reaching its final destination. In turn, the mitochondrial respiratory chain is the source of reactive oxygen species (ROS) derived from leaks in the electron transport chain. The co-existence of both iron and ROS in the secluded space of the mitochondrion makes this organelle particularly prone to hydroxyl radical-mediated damage. In addition, a connection between the loss of iron homeostasis and inflammation is starting to emerge; thus, inflammatory cytokines like TNF-alpha and IL-6 induce the synthesis of the divalent metal transporter 1 and promote iron accumulation in neurons and microglia. Here, we review the recent literature on mitochondrial iron homeostasis and the role of inflammation on mitochondria dysfunction and iron accumulation on the neurodegenerative process that lead to cell death in Parkinson’s disease. We also put forward the hypothesis that mitochondrial dysfunction, iron accumulation and inflammation are part of a synergistic self-feeding cycle that ends in apoptotic cell death, once the antioxidant cellular defense systems are finally overwhelmed.

Selegiline rescues gait deficits and the loss of dopaminergic neurons in a subacute MPTP mouse model of Parkinson's disease

The monoamine oxidase type-B (MAO-B) inhibitor, selegiline, is often recommended as a first-line treatment for Parkinson's disease (PD) and has been shwon to possess neuroprotective effects. The aim of the present study was to determine whether selegiline increases the levels of the neurotrophic factors (NTFs), glial cell line-derived neurotrophic factor (GDNF) and brain-derived neurotrophic factor (BDNF), and whether it rescues motor dysfunction and the loss of dopaminergic neurons in mice with 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-induced lesions. We found that the oral administration of selegiline (1.0 mg/kg/day for 14 days) successfully suppressed the MPTP-induced reduction of nigral dopaminergic neurons and striatal fibers (192.68 and 162.76% of MPTP-exposed animals, respectively; both P<0.001). Moreover, improvements in gait dysfunction were observed after 7 and 14 days of a low dose of selegiline that is reported not to inhibit MAO‑B. Furthermore, there was a significant increase in GDNF and BDNF mRNA (2.10 and 2.75-fold) and protein levels (143.53 and 157.05%) in the selegiline-treated mice compared with the saline-treated MPTP-exposed mice. In addition, the Bax/Bcl-2 gene and protein expression ratios were significantly increased in the MPTP-exposed mice, and this effect was reversed by selegiline. Correlation analysis revealed that gait measurement and GDNF/BDNF levels positively correlated with the number of dopaminergic neurons. These findings demonstrate that selegiline has neurorescue effects that are possibly associated with the induction of NTFs and anti-apoptotic genes.

Sustained resistance to acute MPTP toxicity by hypothalamic dopamine neurons following chronic neurotoxicant exposure is associated with sustained up-regulation of parkin protein

Hypothalamic tuberoinfundibular dopamine (TIDA) neurons remain unaffected in Parkinson disease (PD) while there is significant degeneration of midbrain nigrostriatal dopamine (NSDA) neurons. A similar pattern of susceptibility is observed following acute exposure to the neurotoxicant 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP), and the resistance of TIDA neurons to MPTP is associated with increased expression of parkin and ubiquitin carboxy-terminal hydrolase L-1 (UCHL-1). In the present study, the response of TIDA and NSDA neurons to acute MPTP administration following chronic MPTP exposure was examined. Mice were treated with ten injections of either MPTP (20mg/kg; s.c.; every 3.5 days) or saline vehicle (10 ml/kg; s.c.; every 3.5 days). Following a 21 day recovery period, chronic saline- and MPTP-treated mice received an additional injection of either saline (10 ml/kg; s.c.) or MPTP (20mg/kg; s.c.) and were sacrificed 24h later. NSDA neurons displayed significant axon terminal degeneration (as reflected by decreases in DA, tyrosine hydroxylase (TH) and DA transporter concentrations in the striatum) as well as loss of TH-immunoreactive (IR) neurons in the substantia nigra (SN) following MPTP, whereas TIDA neurons revealed no overt axon terminal pathology or loss of TH-IR cell bodies. NSDA neuronal pathology was associated with transient decreases in concentrations of parkin and UCHL-1 protein in the SN, which returned to normal levels by 21 days following cessation of chronic neurotoxicant exposure. Resistance of TIDA neurons to MPTP toxicity was correlated with a transient increase in UCHL-1 and a sustained elevation in parkin in the arcuate nucleus. TIDA neurons represent a DA neuron population with a unique and inherent ability to adapt to acute and chronic toxicant administration with a sustained elevation of the neuroprotective protein parkin. The correlation between the ability to increase parkin and UCHL-1 expression and the resistance of DA neurons to neurotoxicant exposure is consistent with a functional link between these features and an underlying differential susceptibility to toxicant-associated neurodegeneration.

Inflammatory effects of highly pathogenic H5N1 influenza virus infection in the CNS of mice

The A/VN/1203/04 strain of the H5N1 influenza virus is capable of infecting the CNS of mice and inducing a number of neurodegenerative pathologies. Here, we examined the effects of H5N1 on several pathological aspects affected in parkinsonism, including loss of the phenotype of dopaminergic neurons located in the substantia nigra pars compacta (SNpc), expression of monoamines and indolamines in brain, alterations in SNpc microglia number and morphology, and expression of cytokines, chemokines, and growth factors. We find that H5N1 induces a transient loss of the dopaminergic phenotype in SNpc and now report that this loss recovers by 90 d after infection. A similar pattern of loss and recovery was seen in monoamine levels of the basal ganglia. The inflammatory response in lung and different regions of the brain known to be targets of the H5N1 virus (brainstem, substantia nigra, striatum, and cortex) were examined at 3, 10, 21, 60, and 90 d after infection. In each of these brain regions, we found a significant increase in the number of activated microglia that lasted at least 90 d. We also quantified expression of IL-1α, IL-1β, IL-2, IL-6, IL-9, IL-10, IL-12(p70), IL-13, TNF-α, IFN-γ, granulocyte-macrophage colony-stimulating factor, granulocyte colony-stimulating factor, macrophage colony-stimulating factor, eotaxin, interferon-inducible protein 10, cytokine-induced neutrophil chemoattractant, monocyte chemotactic protein-1, macrophage inflammatory protein (MIP) 1α, MIP-1β, and VEGF, and found that the pattern and levels of expression are dependent on both brain region and time after infection. We conclude that H5N1 infection in mice induces a long-lasting inflammatory response in brain and may play a contributing factor in the development of pathologies in neurodegenerative disorders.

Nitric oxide and DOPAC-induced cell death: from GSH depletion to mitochondrial energy crisis

The molecular mechanisms inherent to cell death associated with Parkinson's disease are not clearly understood. Diverse pathways, sequence of events and models have been explored in several studies. Recently, we have proposed an integrative mechanism, encompassing the interaction of nitric oxide (•NO) and a major dopamine metabolite, dihydroxyphenylacetic (DOPAC), leading to a synergistic mitochondrial dysfunction and cell death that may be operative in PD. In this study, we have studied the sequence of events underlying the mechanisms of cell death in PC12 cells exposed to •NO and DOPAC in terms of: a) free radical production; b) modulation by glutathione (GSH); c) energetic status and d) outer membrane mitochondria permeability. Using Electron Paramagnetic Resonance (EPR) it is shown the early production of oxygen free radicals followed by a depletion of GSH reflected by an increase of GSSG/GSH ratio in the cells treated with the mixture of •NO/DOPAC, as compared with the cells individually exposed to each of the stimulus. Glutathione ethyl ester (GSH-EE) and N-acetylcysteine (NAC) may rescue cells from death, increasing GSH content and preventing ATP loss in cells treated with the mixture DOPAC/•NO but failed to exert similar effects in the cells challenged only with •NO. The depletion of GSH is accompanied by a decreased activity of mitochondrial complex I. At a later stage, the concerted action of DOPAC and •NO include a rise in the ratio Bax/Bcl-2, an observation not evident when cells were exposed only to •NO. The results support a free radical-induced pathway leading to cell death involving the concerted action of DOPAC and •NO and the critical role of GSH in maintaining a functional mitochondria.

Role of glial cells in neurotoxin-induced animal models of Parkinson's disease

Dopaminergic neurons are selectively vulnerable to oxidative stress and inflammatory attack. The neuronal cell loss in the substantia nigra is associated with a glial response composed markedly of activated microglia and, to a lesser extent, of reactive astrocytes although these glial responses may be the source of neurotrophic factors and can protect against oxidative stress such as reactive oxygen species and reactive nitrogen species. However, the glial response can also mediate a variety of deleterious events related to the production of pro-inflammatory, pro-oxidant reactive species, prostaglandins, cytokines, and so on. In this review, we discuss the possible protective and deleterious effects of glial cells in the neurodegenerative diseases and examine how these factors may contribute to the pathogenesis of Parkinson's disease. This review suggests that further investigation concerning glial reaction in Parkinson's disease may lead to disease-modifying therapeutic approaches and may contribute to the pathogenesis of this disease.

Damage to neurons and oligodendrocytes in the hippocampal CA1 sector after transient focal ischemia in rats

Focal brain lesions such as transient focal cerebral ischemia can lead to neuronal damage in remote areas, including the ipsilateral substantia nigra and hippocampus, as well as in the ischemic core. In this study, we investigated acute changes in the ipsilateral hippocampus from 1 up to 7 days after 90 min of transient focal cerebral ischemia in rats, using anti-NeuN (neuronal nuclei), anti-Cu/Zn-superoxide dismutase (Cu/Zn-SOD), anti-Mn-SOD, anti-neuronal nitric oxide synthase (nNOS), anti-inducible NOS (iNOS), anti-glial fibrillary acidic protein (GFAP), anti-ionized calcium-binding adaptor molecule 1(Iba 1) and anti-2',3'-cyclic nucleotide 3'-phosphodiesterase (CNPase) antibodies. In our western blot and histochemical analyses, present results show that transient focal cerebral ischemia in rats can cause a severe and acute damage of neurons and oligodendrocytes in the ipsilateral hippocampal CA1 sector. The present findings also demonstrate that the expression of iNOS produced by Iba 1-immunopositive microglia precedes the damage of neurons and oligodendrocytes in the ipsilateral hippocampal CA1 sector after transient focal cerebral ischemia. In contrast, our results suggest that increased reactive oxygen species (ROS) production during reperfusion cannot lead to damage of neurons and oligodendrocytes in the ipsilateral hippocampal CA1 sector after transient focal cerebral ischemia, because of an insufficient expression of Cu/Zn-SOD and Mn-SOD. Our double-labeled immunohistochemical study demonstrates that the overexpression of iNOS produced by Iba 1-immunopositive microglia may play a pivotal role in the damage of neurons and oligodendrocytes in the ipsilateral hippocampal CA1 sector at an acute stage after transient focal cerebral ischemia.

Hexokinase II gene transfer protects against neurodegeneration in the rotenone and MPTP mouse models of Parkinson's disease

A typical feature of Parkinson's disease is the progressive loss of dopaminergic neurons in the substantia nigra, in which inhibition of mitochondrial complex I activity may play an important role. Rotenone or 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) inhibit the mitochondrial complex I and they cause the death of substantia nigra dopaminergic neurons, thereby providing acute murine models of Parkinson's disease. We have found that increasing mitochondrial hexokinase II activity can prevent cell death in neuronal cultures treated with rotenone. As a result, we have studied the effects of hexokinase II gene transfer in vivo using a herpes simplex virus type 1 (HSV-1) amplicon vector. The placHK2 amplicon vector was injected into substantia nigra of mice that were subsequently administered rotenone or MPTP. Overexpression of hexokinase II prevented both rotenone and MPTP-induced dopaminergic neuronal cell death, as well as reducing the associated motor defects. Our results provide the first proof-of-principle that hexokinase II protects against dopaminergic neurodegeneration in vivo, emphasizing the role of this enzyme in promoting neuronal survival. Thus, the increase of hexokinase II expression by gene transfer or other means represents a promising approach to treat Parkinson's and other neurodegenerative diseases.

Therapeutic effect of a novel anti-parkinsonian agent zonisamide against MPTP (1-methyl-4-phenyl-1,2,3,6- tetrahydropyridine) neurotoxicity in mice

We investigated the therapeutic effect of zonisamide against 1-methyl-4-phenyl- 1,2,3,6-tetrahydropyridine (MPTP) neurotoxicity in mice, using Western blot analysis, immunohistochemistry and behavioral test. Our Western blot analysis and immunohistochemical study showed that the post-treatment with zonisamide prevented significantly dopaminergic cell damage, the depletion of tyrosine-hydroxylase (TH) protein levels and the proliferation of microglia in the striatum and/or substantia nigra 8 days after MPTP treatment. Furthermore, our behavioral study showed that the post-treatment with zonisamide attenuated significantly the motor deficits 7 days after MPTP treatment. These results show that zonisamide has the therapeutic effect in the MPTP model of Parkinson's disease (PD) in mice. Our study also demonstrates the neuroprotective effect of zonisamide against dopaminergic cell damage after MPTP treatment in mice. Thus our present findings suggest that therapeutic strategies targeted to the activation of TH protein and/or the inhibition of microglial activation with zonisamide may offer a great potential for restoring the functional capacity of the surviving dopaminergic neurons in individuals affected with PD.

Poly(ADP-ribose)polymerase inhibitor can attenuate the neuronal death after 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine-induced neurotoxicity in mice

An excessive expression of poly(ADP-ribose)polymerase (PARP) has been demonstrated to play a key role in the pathogenesis of Parkinson's disease (PD). Here we investigated the therapeutic effect of the PARP inhibitor benzamide against 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) neurotoxicity in mice. In our HPLC and Western blot analysis, pretreatment with benzamide showed a neuroprotective effect against MPTP neurotoxicity in mice. Posttreatment with benzamide also attenuated MPTP neurotoxicity in mice. Furthermore, our immunohistochemical study showed that posttreatment with benzamide significantly prevented neuronal damage by suppressing overexpression of neuronal, microglial, and astroglial PARP after MPTP treatment. These findings have important implications for the therapeutic time window and choice of PARP inhibitors in PD patients. Our present findings provide further evidence that PARP inhibitor may offer a novel therapeutic strategy for PD.

Biochemical alterations of the striatum in an MPTP-treated mouse model of Parkinson's disease

We investigated the biochemical alterations of the striatum of mice subjected to seven experimental schedules with 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine hydrochloride (MPTP) treatment. The mice were treated intraperitoneally (i.p.) with MPTP (20 mg/kg in saline) four times a day at 2-hr intervals showed severe and persistent depletions of dopamine, 3,4-dihydroxyphenylacetic acid (DOPAC) and homovanillic acid (HVA) in the striatum, as compared with those (1) treated with MPTP (15 mg/kg in saline, i.p.) once a day for 14 consecutive days; (2)MPTP (30 mg/kg in saline, i.p.) twice a day for 5 consecutive days; (3) MPTP (10 mg/kg in saline, i.p.) four times a day at 1-hr intervals for 2 consecutive days; (4) MPTP (20 mg/kg in saline, i.p.) once a day for 4 consecutive days; (5) MPTP (20 mg/kg in saline, i.p.) twice a day for 2 consecutive days; (6) MPTP (20 mg/kg in saline, i.p.) twice a day for 4 consecutive days. In our Western blot analysis, furthermore, the mice that received MPTP (20 mg/kg in saline) four times a day at 2-hr intervals showed a severe decrease of the striatal tyrosine hydroxylase (TH) protein levels and a significant increase of the striatal glial fibrillary acidic protein (GFAP) levels. These results demonstrate that the model with acute MPTP treatment can cause severe neuronal damage in the mouse striatum, as compared to the model with continuous treatment with MPTP. Thus our findings may support the validity of acute MPTP treatment model for unraveling in the neurodegenerative processes in PD.

Therapeutic effect of a novel anti-parkinsonian agent zonisamide against MPTP (1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine) neurotoxicity in mice

We investigated the therapeutic effect of zonisamide against 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) neurotoxicity in mice, using Western blot analysis, immunohistochemistry and behavioral test. Our Western blot analysis and immunohistochemical study showed that the post-treatment with zonisamide prevented significantly dopaminergic cell damage, the depletion of tyrosine-hydroxylase (TH) protein levels and the proliferation of microglia in the striatum and/or substantia nigra 8 days after MPTP treatment. Furthermore, our behavioral study showed that the post-treatment with zonisamide attenuated significantly the motor deficits 7 days after MPTP treatment. These results show that zonisamide has the therapeutic effect in the MPTP model of Parkinson's disease (PD) in mice. Our study also demonstrates the neuroprotective effect of zonisamide against dopaminergic cell damage after MPTP treatment in mice. Thus our present findings suggest that therapeutic strategies targeted to the activation of TH protein and/or the inhibition of microglial activation with zonisamide may offer a great potential for restoring the functional capacity of the surviving dopaminergic neurons in individuals affected with PD.

Neurotrophic and neurorescue effects of Echinacoside in the subacute MPTP mouse model of Parkinson's disease

Many experiments support the notion that augmentation of neurotrophic factors' (NTFs) activity, especially glial cell line-derived neurotrophic factor (GDNF) and brain-derived neurotrophic factor (BDNF) could prevent or halt the progress of neurodegeneration in Parkinson's disease (PD). However, application of NTFs as therapeutic agents for PD is hampered by the difficulty in delivering them to specific brain regions safely and effectively. Another potential strategy is to stimulate the endogenous expression of NTFs. In this study, we investigated the effects of Echinacoside (ECH), a monomer extracted from herbs, on rescuing dopaminergic function in 1-methyl-4-phenyl-1, 2, 3, 6-tetrahydropyridine (MPTP)-lesioned mice. We found that oral administration of ECH (30 mg/kg/day for 14 days) to MPTP-treated mice, commencing after impairment of the nigrstriatal system, suppressed the reduction of nigral dopaminergic neurons, striatal fibers, dopamine and dopamine transporter to 134.24%, 203.17%, 147.25% and 154.72 of MPTP-lesioned animals respectively (p<0.05). There was a relative elevation in expression of GDNF and BDNF mRNA (2.94 and 3.75-fold) and protein (184.34% and 185.93%) in ECH treated mice compared with vehicle-treated MPTP-lesioned mice (p<0.05). In addition, the apoptosis cells and Bax/Bcl-2 ratio of mRNA and protein in MPTP-lesioned mice significantly increased, and these effects could be prevented by ECH. At the 7th and 14th days of ECH treatment, the gait disorder displayed obvious improvement (p<0.05). These findings demonstrate that ECH is probably a novel, orally active, non-peptide inducer of NTFs and inhibitor of apoptosis, and they provide preclinical support for therapeutic potential of this compound in the treatment of PD.

Neuroprotective and anti-inflammatory activities of ketogenic diet on MPTP-induced neurotoxicity

Ketogenic diet (KD) is a high-fat, low-protein and low-carbohydrate diet. It is reported that KD can provide the neuroprotection for the neurodegenerative diseases such as Alzheimer's disease, Parkinson's disease (PD) and amyotrophic lateral sclerosis. The main clinical symptom of PD is motor dysfunction derived from the loss of dopaminergic neurons in the substantia nigra (SN) and dopamine content in the striatum subsequently. It is well known that treatments with 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) in mice produce motor dysfunction, biochemical, and neurochemical changes remarkably similar to idiopathic PD patients. In this study, we investigated the neuroprotective and anti-inflammatory effects of KD in MPTP-treated mice. The data showed that pretreatment with KD alleviated the motor dysfunction induced by MPTP. The decrease of Nissl-staining and tyrosine hydroxylase (TH)-positive neurons induced by MPTP was inhibited in the SN. The change of dopamine was very similar to dopaminergic neurons in the SN. KD inhibited the activation of microglia induced by MPTP in the SN. The levels of proinflammatory cytokines (interleukin-1 beta, interleukin-6, and tumor necrosis factor-alpha) in the SN were also decreased and induced by MPTP. So, we concluded that KD was neuroprotective and anti-inflammatory against MPTP-neurotoxicity.

Gender differences on MPTP (1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine) neurotoxicity in C57BL/6 mice

The aim of this study was to investigate the impact of gender difference in the 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-treated animal model of Parkinson's disease (PD). In the present study, we investigated the time-dependent alterations of dopamine and its metabolites, striatal tyrosine hydroxylase (TH) protein, dopamine transporter (DAT) protein, glial fibrillary acidic protein (GFAP) protein and midbrain TH protein and motor function in male and female mice 5h and 1, 3 and 7 days after four administrations of MPTP (20mg/kg) at 2-h intervals. The present study showed that the decrease of dopamine, DOPAC (3,4-dihydroxyphenylacetic acid) and HVA (homovanillic acid) content in female mice was more pronounced than that in male animals 1, 3 and 7 days after MPTP treatment. Our Western blot analysis study also demonstrated that the decrease of both striatal and midbrain TH protein levels in female mice was more pronounced than that in male animals from 1 to 7 days after MPTP treatment. As compared to male mice, in contrast, the increase of striatal GFAP protein levels in female mice was observed from 5h to 7 days after MPTP treatment. Furthermore, the present study showed that motor deficits were found in both male and female mice 1 and 7 days after MPTP treatment. In the present study, moreover, the decrease of striatal DAT protein levels in female mice was more pronounced than that in male animals 1, 3 and 7 days after MPTP treatment. These results demonstrate that our administrations of MPTP at 2-h intervals can cause more severe damage in female mice as compared with male animals. The gender difference may be due to the decrease of DAT expression caused by MPTP. Thus our findings provide further valuable information for the pathogenesis of PD.

Nitric oxide in cell survival: a janus molecule

Nitric oxide (NO), plays multiple roles in the nervous system. In addition to regulating proliferation, survival and differentiation of neurons, NO is involved in synaptic activity, neural plasticity, and memory function. Nitric oxide promotes survival and differentiation of neural cells and exerts long-lasting effects through regulation of transcription factors and modulation of gene expression. Signaling by reactive nitrogen species is carried out mainly by targeted modifications of critical cysteine residues in proteins, including S-nitrosylation and S-oxidation, as well as by lipid nitration. NO and other reactive nitrogen species are also involved in neuroinflammation and neurodegeneration, such as in Alzheimer disease, amyotrophic lateral sclerosis, Parkinson disease, multiple sclerosis, Friedreich ataxia, and Huntington disease. Susceptibility to NO and peroxynitrite exposure may depend on factors such as the intracellular reduced glutathione and cellular stress resistance signaling pathways. Thus, neurons, in contrast to astrocytes, appear particularly vulnerable to the effects of nitrosative stress. This article reviews the current understanding of the cytotoxic versus cytoprotective effects of NO in the central nervous system, highlighting the Janus-faced properties of this small molecule. The significance of NO in redox signaling and modulation of the adaptive cellular stress responses and its exciting future perspectives also are discussed.

Neurodegenerative disorders and nanoformulated drug development

Degenerative and inflammatory diseases of the CNS include, but are not limited to, Alzheimer's and Parkinson's disease, amyotrophic lateral sclerosis, stroke, multiple sclerosis and HIV-1-associated neurocognitive disorders. These are common, debilitating and, unfortunately, hold few therapeutic options. In recent years, the application of nanotechnologies as commonly used or developing medicines has served to improve pharmacokinetics and drug delivery specifically to CNS-diseased areas. In addition, nanomedical advances are leading to therapies that target CNS pathobiology and as such, can interrupt disordered protein aggregation, deliver functional neuroprotective proteins and alter the oxidant state of affected neural tissues. This article focuses on the pathobiology of common neurodegenerative disorders with a view towards how nanomedicine may be used to improve the clinical course of neurodegenerative disorders.

MPTP-induced neuroblast apoptosis in the subventricular zone is not regulated by dopamine or other monoamine transporters

For 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) to exert neurotoxicity on dopaminergic neurons, 1-methyl-4-phenylpyridinium (MPP+), a metabolite of MPTP, must be taken up into the dopaminergic neuron via the dopamine transporter (DAT). Previous reports have shown that MPTP also causes neuroblast apoptosis in the subventricular zone (SVZ) of adult mice. The aim of this study is to elucidate the role of DAT and other monoamine transporters including vesicular monoamine transporter 2 (VMAT2), the serotonin transporter (SERT), and the norepinephrine transporter (NET) on the neuroblast apoptosis induced by MPTP administration. There were no DAT-positive neuroblasts in the SVZ, whereas some neuroblasts were immunopositive for VMAT2 and SERT. To examine whether these transporters are involved in MPTP-induced neuroblast apoptosis in the SVZ, terminal deoxynucleotidyl transferase-mediated dUTP endlabeling (TUNEL)-positive cells were semiquantitatively analyzed after the injection of GBR12909 (GBR), a DAT inhibitor; tetrabenazine (TBZ), a VMAT2 inhibitor; fluoxetine (FLU), a SERT inhibitor, or desipramine (DES), a NET inhibitor, prior to MPTP injection. However, the injection of these transporter inhibitors had no influence on the MPTP-induced neuroblast apoptosis in the SVZ. It is likely that neither DAT nor other monoamine transporters are involved in MPTP-induced neuroblast apoptosis. The present findings suggest that the neurotoxicity of MPTP to neuroblasts in the SVZ does not require DAT or other monoamine transporters, and the apoptosis it induces may be executed through other unknown pathways.

Systemic administration of proteasome inhibitor protects against MPTP neurotoxicity in mice

Dysfunction of the proteasome has been suggested to contribute in the degeneration of nigrostriatal dopaminergic neurons. Here, we investigated to determine whether systematic administration of proteasome inhibitor, carbobenzoxy-L: -gamma-t-butyl-L: -glutamyl-L: -alanyl-L: -leucinal (PSI) protects against MPTP (1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine) neurotoxicity in mice. Three administrations of MPTP at 1-h intervals to mice reduced significantly the concentration of dopamine, DOPAC (3,4-dihydroxyphenylacetic acid) and HVA (homovanillic acid) in the striatum after 5 days. In contrast, PSI (0.3 and 1.0 mg/kg) prevented a significant decrease in dopamine, DOPAC and HVA contents of the striatum 5 days after MPTP treatment. In our Western blot analysis study, PSI at a dose of 1.0 mg/kg prevented a significant decrease in TH (tyrosine hydroxylase) protein and a significant increase in glial fibrillary acidic protein 5 days after MPTP treatment. Furthermore, our immunohistochemical study showed that PSI at a dose of 1.0 mg/kg prevented a significant loss in TH immunopositive neurons in the striatum and substantia nigra 5 days after MPTP treatment. In contrast, PSI caused a significant increase in the number of intense ubiquitin immunopositive cells in the striatum and substantia nigra 5 days after MPTP treatment. These results indicate that proteasome inhibitors can protect against MPTP neurotoxicity in mice. The neuroprotective effect of PSI against dopaminergic cell damage may be mediated by the elevation of ubiquitination. Thus, our findings provide further valuable information for the pathogenesis of Parkinson's disease.

Effects of estrogens on striatal damage after 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) neurotoxicity in male and female mice

Emerging evidence shows a beneficial effect of estrogens for Parkinson's disease, yet the exact potency of these compounds implicated remain obscured. In this study, we investigated the neuroprotective effect of 17beta-estradiol and estrone against 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-induced striatal toxicity in mice. The neuroprotective effects of both compounds were evaluated by HPLC and Western blot analyses 5 days after the last of 4 consecutive injections of MPTP at 1-h intervals to mice. Subacute treatment (10 days) with estrone or 17beta-estradiol at low doses (0.05 and 0.2mg/kg) showed no significant changes against MPTP-induced damage of striatal dopamine terminals in mice. Furthermore, acute treatment with estrone at high doses (0.5 and 2.0mg/kg) showed no significant alterations against MPTP-induced damage of striatal dopamine terminals in mice. In contrast, acute treatment with 17beta-estradiol at high doses exhibited a neuroprotective effect against the damage of striatal dopamine terminals in both male and female mice after MPTP treatments. The results demonstrate that estrogen therapy with high doses may have a neuroprotective effect on the damage of striatal dopamine terminals in the MPTP-induced mice. These findings may lead to be development of estrogen therapy for the prevention and treatment of Parkinson's disease.

The effect of alpha-synuclein knockdown on MPP+ toxicity in models of human neurons

The protein alpha-synuclein is central to the pathophysiology of Parkinson's disease (PD) but its role in the development of neurodegeneration remains unclear. alpha-Synuclein-knockout mice develop without gross abnormality and are resistant to 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP), a mitochondrial inhibitor widely used to model parkinsonism. Here we show that differentiated human dopaminergic neuron-like cells also have increased resistance to 1-methyl-4-phenylpyridine (MPP+), the active metabolite of MPTP, when alpha-synuclein is knocked down using RNA interference. In attempting to understand how this occurred we found that lowering alpha-synuclein levels caused changes to intracellular vesicles, dopamine transporter (DAT) and vesicular monoamine transporter (VMAT2), each of which is known to be an important component of the early events leading to MPP+ toxicity. Knockdown of alpha-synuclein reduced the availability of DAT on the neuronal surface by 50%, decreased the total number of intracellular vesicles by 37% but increased the density of VMAT2 molecules per vesicle by 2.8-fold. However, these changes were not associated with any reduction in MPP+ -induced superoxide production, suggesting that alpha-synuclein knockdown may have other downstream effects which are important. We then showed that alpha-synuclein knockdown prevented MPP+ -induced activation of nitric oxide synthase (NOS). Activation of NOS is an essential step in MPTP toxicity and increasing evidence points to nitrosative stress as being important in neurodegeneration. Overall, these results show that as well as having a number of effects on cellular events upstream of mitochondrial dysfunction alpha-synuclein affects pathways downstream of superoxide production, possibly involving regulation of NOS activity.

Role of nuclear transcription factor kappa B (NF-kappaB) for MPTP (1-methyl-4-phenyl-1,2,3,6-tetrahyropyridine)-induced apoptosis in nigral neurons of mice

The biochemical and cellular changes that occur following treatment with MPTP (1-methyl-4-phenyl-1,2,3,6-tetrahyropyridine) are remarkably similar to that seen in idiopathic Parkinson's disease. In this study, we investigated the time course changes of NF-kappaB (Nuclear factor kappa B) p65 protein and apoptosis in the substantia nigra after MPTP treatment in mice. Four administrations of MPTP at 2 h intervals showed a significant and severe decrease of the number of TH (tyrosine hydroxylase) immunopositive neurons in the substantia nigra of mice from 5 h up to 21 days posttreatment. Densities of DAT (dopamine transporter) immunoreactivity were also significantly decreased in nigral neurons of mice from 1 up to 21 days after MPTP treatment. GFAP (glial fibrillary acidic protein) immunopositive cells were increased significantly in the substantia nigra from 5 h up to 21 days after MPTP treatment. In contrast, isolectin B(4) positive microglia were increased markedly in the substantia nigra only 3 and 7 days after MPTP treatment. On the other hand, a significant increase of NF-kappaB p65 immunoreactivity was observed mainly in glial cells of the substantia nigra from 5 h to 3 days after MPTP treatment. A significant increase of ssDNA (single stranded DNA) immunopositive apoptotic neurons was also observed in the substantia nigra from 5 h to 3 days after MPTP treatment. These results demonstrate that dopaminergic neuronal loss may be caused by apoptosis due to increased cytokines and apoptosis-related proteins via the activation of NF-kappaB in reactive astrocytes of the substantia nigra after MPTP treatment in mice. Thus our findings suggest that the inhibition of NF-kappaB activation in astrocytes may be useful intervention in Parkinson's disease and other neurogenerative disorders where apoptosis or inflammation plays a key role in disease pathogenesis.