Synuclein, dopamine and oxidative stress: co-conspirators in Parkinson's disease?

Microbial Trojan Horses: Virulence Factors as Key Players in Neurodegenerative Diseases

Changes in population demographics indicate that the elderly population will reach 2.1 billion worldwide by 2050. In parallel, there will be an increase in neurodegenerative diseases such as Alzheimer's and Parkinson's. This review explores dysbiosis occurring in these pathologies and how virulence factors contribute to the worsening or development of clinical conditions, and it summarizes existing and potential ways to combat microorganisms related to these diseases. Microbiota imbalances can contribute to the progression of neurodegenerative diseases by increasing intestinal permeability, exchanging information through innervation, and even acting as a Trojan horse affecting immune cells. The microorganisms of the microbiota produce virulence factors to protect themselves from host defenses, many of which contribute to neurodegenerative diseases. These virulence factors are expressed according to the genetic composition of each microorganism, leading to a wide range of factors to be considered. Among the main virulence factors are LPS, urease, curli proteins, amyloidogenic proteins, VacA, and CagA. These factors can also be packed into bacterial outer membrane vesicles, which transport proteins, RNA, and DNA, enabling distal communication that impacts various diseases, including Alzheimer's and Parkinson's.

1,4-dihydroxy-2-naphthoic acid prevents 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine-induced motor function deficits

Parkinson's disease (PD), characterized by death of dopaminergic neurons in the substantia nigra, is the second most prevalent progressive neurodegenerative disease. However, the etiology of PD is largely elusive. This study employed the 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) rodent model to examine the effectiveness of 1,4-dihydroxy-2-naphthoic acid (1,4-DHNA), an aryl hydrocarbon receptor (AhR) active gut bacteria-derived metabolite, in mitigating MPTP's motoric deficits, and the role of AhR in mediating these effects. Male C57BL/6 mice were fed daily with vehicle, 20 mg/kg 1,4-DHNA, or AhR-inactive isomer 3,7-DHNA, for 3 weeks before administration of 80 mg/kg MPTP or vehicle. Four weeks later, mice were assessed for motoric functions. Both 1,4-DHNA and 3,7-DHNA prevented MPTP-induced deficits in the motor pole test and in the adhesive strip removal test. Additionally, 1,4-DHNA improved balance beam performance and completely prevented MPTP-induced reduction in stride length. In contrast, 3,7-DHNA, an AhR-inactive compound, did not improve balance beam performance and had only a partial effect on stride length. This study suggests that natural metabolites of gut microbiota, such as 1,4-DHNA, could be beneficial to counteract the development of motor deficits observed in PD. Thus, this study further supports the hypothesis that pathological and mitigating processes in the gut could play an essential role in PD development. Moreover, this indicates that 1,4-DHNA's ability to combat various motor deficits is likely mediated via multiple underlying molecular mechanisms. Specifically, AhR is involved, at least partially, in control of gait and bradykinesia, but it likely does not mediate the effects on fine motor skills.

Unraveling neuroprotection in Parkinson's disease: Nrf2-Keap1 pathway's vital role amidst pathogenic pathways

Parkinson's disease (PD) is an age-related chronic neurological condition characterized by progressive degeneration of dopaminergic neurons and the presence of Lewy bodies, primarily composed of alpha-synuclein and ubiquitin. The pathophysiology of PD encompasses alpha-synuclein aggregation, oxidative stress, neuroinflammation, mitochondrial dysfunction, and impaired autophagy and ubiquitin-proteasome systems. Among these, the Keap1-Nrf2 pathway is a key regulator of antioxidant defense mechanisms. Nrf2 has emerged as a crucial factor in managing oxidative stress and inflammation, and it also influences ubiquitination through p62 expression. Keap1 negatively regulates Nrf2 by targeting it for degradation via the ubiquitin-proteasome system. Disruption of the Nrf2-Keap1 pathway in PD affects cellular responses to oxidative stress and inflammation, thereby playing a critical role in disease progression. In addition, the role of neuroinflammation in PD has gained significant attention, highlighting the interplay between immune responses and neurodegeneration. This review discusses the various mechanisms responsible for neuronal degeneration in PD, with a special emphasis on the neuroprotective role of the Nrf2-Keap1 pathway. Furthermore, it explores the implications of inflammopharmacology in modulating these pathways to provide therapeutic insights for PD.

A sporadic Parkinson's disease model via silencing of the ubiquitin-proteasome/E3 ligase component, SKP1A

Our and other's laboratory microarray-derived transcriptomic studies in human PD substantia nigra pars compacta (SNpc) samples have opened an avenue to concentrate on potential gene intersections or cross-talks along the dopaminergic (DAergic) neurodegenerative cascade in sporadic PD (SPD). One emerging gene candidate identified was SKP1A (p19, S-phase kinase-associated protein 1A), found significantly decreased in the SNpc as confirmed later at the protein level. SKP1 is part of the Skp1, Cullin 1, F-box protein (SCF) complex, the largest known class of sophisticated ubiquitin-proteasome/E3-ligases and was found to directly interact with FBXO7, a gene defective in PARK15-linked PD. This finding has led us to the hypothesis that a targeted site-specific reduction of Skp1 levels in DAergic neuronal cell culture and animal systems may result in a progressive loss of DAergic neurons and hopefully recreate motor disabilities in animals. The second premise considers the possibility that both intrinsic and extrinsic factors (e.g., manipulation of selected genes and mitochondria impairing toxins), alleged to play central roles in DAergic neurodegeneration in PD, may act in concert as modifiers of Skp1 deficiency-induced phenotype alterations ('dual-hit' hypothesis of neurodegeneration). To examine a possible role of Skp1 in DAergic phenotype, we have initially knocked down the expression of SKP1A gene in an embryonic mouse SN-derived cell line (SN4741) with short hairpin RNA (shRNA) lentiviruses (LVs). The deficiency of SKP1A closely recapitulated cardinal features of the DAergic pathology of human PD, such as decreased expression of DAergic phenotypic markers and cell cycle aberrations. Furthermore, the knocked down cells displayed a lethal phenotype when induced to differentiate exhibiting proteinaceous round inclusion structures, which were almost identical in composition to human Lewy bodies, a hallmark of PD. These findings support a role for Skp1 in neuronal phenotype, survival, and differentiation. The identification of Skp1 as a key player in DAergic neuron function suggested that a targeted site-specific reduction of Skp1 levels in mice SNpc may result in a progressive loss of DAergic neurons and terminal projections in the striatum. The injected LV SKP1shRNA to mouse SN resulted in decreased expression of Skp1 protein levels within DAergic neurons and loss of tyrosine hydroxylase immunoreactivity (TH-IR) in both SNpc and striatum that was accompanied by time-dependent motor disabilities. The reduction of the vertical movements, that is rearing, may be reminiscent of the early occurrence of hypokinesia and axial, postural instability in PD. According to the 'dual-hit' hypothesis of neurodegenerative diseases, it is predicted that gene-gene and/or gene-environmental factors would act in concert or sequentially to propagate the pathological process of PD. Our findings are compatible with this conjecture showing that the genetic vulnerability caused by knock down of SKP1A renders DAergic SN4741 cells especially sensitive to genetic reduction of Aldh1 and exposure to the external stressors MPP+ and DA, which have been implicated in PD pathology. Future consideration should be given in manipulation SKP1A expression as therapeutic window, via its induction genetically or pharmacological, to prevent degeneration of the nigra striatal dopamine neurons, since UPS is defective.

Design, Synthesis and Biological Evaluation of α-Synuclein Proteolysis-Targeting Chimeras

α-Synuclein aggregation under pathological conditions is one of the causes of related neurodegenerative diseases. PROTACs (proteolysis targeting chimeras) are bifunctional small molecules that induce a post-translational erasure of proteins via the ubiquitination of target proteins by E3 ubiquitin ligase and subsequent proteasomal degradation. However, few research studies have been conducted for targeted protein degradation of α-synuclein aggregates. In this article, we have designed and synthesized a series of small-molecule degraders 1-9 based on a known α-synuclein aggregation inhibitor sery384. In silico docking studies of sery384 with α-synuclein aggregates were accomplished to ensure that the compounds bound to α-synuclein aggregates specifically. The protein level of α-synuclein aggregates was determined to evaluate the degradation efficiency of PROTAC molecules on α-synuclein aggregates in vitro. The results show that compound 5 had the most significant degradation effect, with DC₅₀ of 5.049 μM, and could induce the degradation of α-synuclein aggregates in a time- and dose-dependent manner in vitro. Furthermore, compound 5 could inhibit the elevation of the ROS level caused by overexpression and aggregation of α-synuclein and protect H293T cells from α-synuclein toxicity. Conclusively, our results provide a new class of small-molecule degraders and an experimental basis for the treatment of α-synuclein related neurodegenerative diseases.

Structural and Biophysical Characterization of Stable Alpha-Synuclein Oligomers

The aggregation of α-synuclein (α-syn) into neurotoxic oligomers and fibrils is an important pathogenic feature of synucleinopatheis, including Parkinson's disease (PD). A further characteristic of PD is the oxidative stress that results in the formation of aldehydes by lipid peroxidation. It has been reported that the brains of deceased patients with PD contain high levels of protein oligomers that are cross-linked to these aldehydes. Increasing evidence also suggests that prefibrillar oligomeric species are more toxic than the mature amyloid fibrils. However, due to the heterogenous and metastable nature, characterization of the α-syn oligomeric species has been challenging. Here, we generated and characterized distinct α-syn oligomers in vitro in the presence of DA and lipid peroxidation products 4-hydroxy-2-nonenal (HNE) and 4-oxo-2-nonenal (ONE). HNE and ONE oligomer were stable towards the treatment with SDS, urea, and temperature. The secondary structure analysis revealed that only HNE and ONE oligomers contain β-sheet content. In the seeding assay, both DA and ONE oligomers significantly accelerated the aggregation. Furthermore, all oligomeric preparations were found to seed the aggregation of α-syn monomers in vitro and found to be cytotoxic when added to SH-SY5Y cells. Finally, both HNE and ONE α-syn oligomers can be used as a calibrator in an α-syn oligomers-specific ELISA.

Crosstalk between regulatory non-coding RNAs and oxidative stress in Parkinson’s disease

Parkinson’s disease is the second most common neurodegenerative disease after Alzheimer’s disease, which imposes an ever-increasing burden on society. Many studies have indicated that oxidative stress may play an important role in Parkinson’s disease through multiple processes related to dysfunction or loss of neurons. Besides, several subtypes of non-coding RNAs are found to be involved in this neurodegenerative disorder. However, the interplay between oxidative stress and regulatory non-coding RNAs in Parkinson’s disease remains to be clarified. In this article, we comprehensively survey and overview the role of regulatory ncRNAs in combination with oxidative stress in Parkinson’s disease. The interaction between them is also summarized. We aim to provide readers with a relatively novel insight into the pathogenesis of Parkinson’s disease, which would contribute to the development of pre-clinical diagnosis and treatment.

Neuroprotective Effects of Resveratrol in In vivo and In vitro Experimental Models of Parkinson's Disease: a Systematic Review

Parkinson's disease (PD) is currently the second most common neurodegenerative disease, being characterized by motor and non-motor symptoms. The therapeutic options available for its treatment are limited, do not slow the progression of the disease, and have serious side effects. For this reason, many studies have sought to find compounds with neuroprotective properties that bring additional benefits to current therapy. In this context, resveratrol is a phenolic compound, found in many plant species, capable of crossing the blood-brain barrier and having multiple biological properties. Experimental studies in vitro and in vivo have shown that it can prevent or slow the progression of a variety of diseases, including PD. In this systematic review, we summarize the effects of resveratrol in experimental in vivo and in vitro models of PD and discuss the molecular mechanisms involved in its action. The bibliographic search was performed in the databases of PubMed, Web of Science, SciELO, and Google Scholar, and based on the inclusion criteria, 41 articles were selected and discussed. Most of the included studies have demonstrated neuroprotective effects of resveratrol. In general, resveratrol prevented behavioral and/or neurological disorders, improved antioxidant defenses, reduced neuroinflammatory processes, and inhibited apoptosis. In summary, this systematic review offers important scientific evidence of neuroprotective effects of resveratrol in PD and also provide valuable information about its mechanism of action that can support future clinical studies.

Examining the Toxicity of α-Synuclein in Neurodegenerative Disorders

Simple Summary

Neurodegenerative disorders are complex disorders that display a variety of clinical manifestations. The second-most common neurodegenerative disorder is Parkinson’s disease, and the leading pathological protein of the disorder is considered to be α-synuclein. Nonetheless, α-synuclein accumulation also seems to result in multiple system atrophy and dementia with Lewy bodies. In order to obtain a more proficient understanding in the pathological progression of these synucleinopathies, it is crucial to observe the post-translational modifications of α-synuclein and the conformations of α-synuclein, as well as its role in the dysfunction of cellular pathways.

Abstract

α-synuclein is considered the main pathological protein in a variety of neurodegenerative disorders, such as Parkinson’s disease, multiple system atrophy, and dementia with Lewy bodies. As of now, numerous studies have been aimed at examining the post-translational modifications of α-synuclein to determine their effects on α-synuclein aggregation, propagation, and oligomerization, as well as the potential cellular pathway dysfunctions caused by α-synuclein, to determine the role of the protein in disease progression. Furthermore, α-synuclein also appears to contribute to the fibrilization of tau and amyloid beta, which are crucial proteins in Alzheimer’s disease, advocating for α-synuclein’s preeminent role in neurodegeneration. Due to this, investigating the mechanisms of toxicity of α-synuclein in neurodegeneration may lead to a more proficient understanding of the timeline progression in neurodegenerative synucleinopathies and could thereby lead to the development of potent targeted therapies.

Cellular and molecular pathophysiology in the progression of Parkinson's disease

Parkinson's disease (PD) is a neurodegenerative disorder etiologically linked to the loss of substantia nigra (SN) dopaminergic neurons in the mid-brain. The etiopathology of sporadic PD is still unclear; however, the interaction of extrinsic and intrinsic factors may play a critical role in the onset and progression of the disease. Studies in animal models and human post-mortem tissue have identified distinct cellular and molecular changes in the diseased brain, suggesting complex interactions between different glial cell types and various molecular pathways. Small changes in the expression of specific genes in a single pathway or cell type possibly influence others at the cellular and system levels. These molecular and cellular signatures like neuroinflammation, oxidative stress, and autophagy have been observed in PD patients' brain tissue. While the etiopathology of PD is still poorly understood, the interplay between glial cells and molecular events may play a crucial role in disease onset and progression.

The Pathology of Parkinson's Disease and Potential Benefit of Dietary Polyphenols

Parkinson's disease (PD) is a progressive neurodegenerative disorder that is characterized by a loss of dopaminergic neurons, leading to bradykinesia, rigidity, tremor at rest, and postural instability, as well as non-motor symptoms such as olfactory impairment, pain, autonomic dysfunction, impaired sleep, fatigue, and behavioral changes. The pathogenesis of PD is believed to involve oxidative stress, disruption to mitochondria, alterations to the protein α-synuclein, and neuroinflammatory processes. There is currently no cure for the disease. Polyphenols are secondary metabolites of plants, which have shown benefit in several experimental models of PD. Intake of polyphenols through diet is also associated with lower PD risk in humans. In this review, we provide an overview of the pathology of PD and the data supporting the potential neuroprotective capacity of increased polyphenols in the diet. Evidence suggests that the intake of dietary polyphenols may inhibit neurodegeneration and the progression of PD. Polyphenols appear to have a positive effect on the gut microbiome, which may decrease inflammation that contributes to the disease. Therefore, a diet rich in polyphenols may decrease the symptoms and increase quality of life in PD patients.

Neuroprotective Properties of Green Tea (Camellia sinensis) in Parkinson's Disease: A Review

Neurodegenerative disease is a collective term given for the clinical condition, which results in progressive degeneration of neurons and the loss of functions associated with the affected brain region. Apart from the increase in age, neurodegenerative diseases are also partly affected by diet and lifestyle practices. Parkinson's disease (PD) is a slow onset neurodegenerative disorder and the second most common neurodegenerative disease, which affects the motor system. Although there is no prescribed treatment method to prevent and cure PD, clinical procedures help manage the disease symptoms. Green tea polyphenols are known for several health benefits, including antioxidant, anti-inflammatory, and neuroprotective activity. The current manuscript summarizes the possible mechanisms of neuroprotective potential of green tea with a special focus on PD. Studies have suggested that the consumption of green tea protects against free-radicals, inflammation, and neuro-damages. Several in vivo studies aid in understanding the overall mechanism of green tea. However, the same dose may not be sufficient in humans to elicit similar effects due to complex physiological, social, and cultural development. Future research focused on more clinical trials could identify an optimum dose that could impart maximum health benefits to impart neuroprotection in PD.

The Roles of Post-translational Modifications on α-Synuclein in the Pathogenesis of Parkinson's Diseases

Parkinson’s disease is the second most common neurodegenerative disorder. Although the pathogenesis of Parkinson’s disease is not entirely clear, the aberrant aggregation of α-synuclein has long been considered as an important risk factor. Elucidating the mechanisms that influence the aggregation of α-synuclein is essential for developing an effective diagnostic, preventative and therapeutic strategy to treat this devastating disease. The aggregation of α-synuclein is influenced by several post-translational modifications. Here, we summarized the major post-translational modifications (phosphorylation, ubiquitination, truncation, nitration, O-GlcNAcylation) of α-synuclein and the effect of these modifications on α-synuclein aggregation, which may provide potential targets for future therapeutics.

Critical Roles of Glutaredoxin in Brain Cells-Implications for Parkinson's Disease

SIGNIFICANCE

Glutaredoxin (Grx)1, an evolutionarily conserved and ubiquitous enzyme, regulates redox signal transduction and protein redox homeostasis by catalyzing reversible S-glutathionylation. Grx1 plays different roles in different cell types. In Parkinson's disease (PD), Grx1 regulates apoptosis signaling in dopaminergic neurons, so that loss of Grx1 leads to increased cell death; in microglial cells, Grx1 regulates proinflammatory signaling, so that upregulation of Grx1 promotes cytokine production. Here we examine the regulatory roles of Grx1 in PD with a view toward therapeutic innovation. Recent Advances: In postmortem midbrain PD samples, Grx1 was decreased relative to controls, specifically within dopaminergic neurons. In Caenorhabditis elegans models of PD, loss of the Grx1 homologue led to exacerbation of the neurodegenerative phenotype. This effect was partially relieved by overexpression of neuroprotective DJ-1, consistent with regulation of DJ-1 content by Grx1. Increased GLRX copy number in PD patients was associated with earlier PD onset; and Grx1 levels correlated with levels of proinflammatory tumor necrosis factor-α in mouse and human brain samples. In vitro studies showed Grx1 to be upregulated on proinflammatory activation of microglia. Direct overexpression of Grx1 increased microglial activation; silencing Grx1 diminished activation. Grx1 upregulation in microglia corresponded to increased neuronal cell death in coculture. Overall, these studies identify competing roles of Grx1 in PD etiology.

CRITICAL ISSUES

The dilemma regarding Grx1 as a PD therapeutic target is whether to stimulate its upregulation for neuroprotection or inhibit its proinflammatory activity.

FUTURE DIRECTIONS

Further investigation is needed to understand the preponderant role of Grx1 regarding dopaminergic neuronal survival.

Light induced DNA-functionalized TiO2 nanocrystalline interface: Theoretical and experimental insights towards DNA damage detection

Owing to the emerging applications of DNA-functionalized TiO₂ nanocrystals towards DNA damage detection, it is inevitable to understand the better chemistry as well as in-depth molecular interaction phenomena. Fundamentally, energy difference underlies the layer-by-layer construction, resulted in the increase of the interaction energy and thus, altering the electrochemical behavior. Herein, Density functional theory (DFT) calculations were performed using DMol3 and DFTB+ codes successfully to elucidate the structural, electronics, and vibrational properties of the layer-by-layer components composing ss-DNA/dopamine/TiO₂/FTO. The obtained results are in good agreement with the experimental findings. The band gaps of FTO and TiO₂ were computationally obtained at 3.335 and 3.136 eV which are comparable with the experimental data (3.500 eV; FTO and 3.200 eV; TiO₂). Frontier orbital analysis is also considered to elucidate their electron transfer phenomena. Further, a 100 ns MD simulations are carried out using canonical ensemble embedded with COMPASS-Universal Forcefields generating useful thermodynamics parameters. Binding energies indicate increasing interaction energies for the layer-by-layer nanosystem, in agreement with the increasing diameter of electrochemical impedance spectroscopy (EIS) semicircle. Our results reveal the fundamental understanding of the DNA-functionalized TiO₂ nanocrystals down to molecular and electronic level and further, paving a way of its application towards nanoelectrochemical DNA biosensors.

Neurorescue by a ROS Decomposition Catalyst

The effect of the bis-sulfonated iron(III) corrole (1-Fe), a potent decomposition catalyst of reactive oxygen species, on rescuing SN4741 cells that were damaged by 6-hydroxydopamine (6-OHDA) was investigated as an in vitro model system for studying cell death of dopaminergic neurons in the substantia nigra. Important findings that accompanied the ability to rescue dopaminergic neurons were increased expression of phenotypic dopaminergic proteins, such as tyrosine hydroxylase (TH) and dopamine transporter (DAT), which were significantly depleted upon 6-OHDA-mediated damage. 1-Fe also elevated expression levels of aldehyde dehydrogenase 1 (ALDH-1), previously disclosed as a cardinal protein in the pathogenesis of Parkinson's disease. Since these findings suggested that 1-Fe affects quite a wide range of intracellular mechanisms, vital intracellular pathways that involve neuroplasticity, growth, differentiation and survival of neurons, were examined. Phosphatidylinositol 3-kinase (PI3K) and protein kinase c (PKC) were found to be involved, as pharmacological inhibitors of these kinases abolished the neurorescue effect of 1-Fe. 1-Fe also elevated the expression of antiapoptotic protein Bcl-2, which is essential for proper mitochondrial function and cellular survival. The overall conclusion is that 1-Fe is capable of rescuing already damaged neuronal cells by a variety of mechanisms that are beyond its antioxidant activity.

Neuroprotective effect of curcumin as evinced by abrogation of rotenone-induced motor deficits, oxidative and mitochondrial dysfunctions in mouse model of Parkinson's disease

Curcumin, a natural polyphenolic compound extracted from rhizomes of Curcuma longa (turmeric), a plant in the ginger family (Zingiberaceae) has been used worldwide and extensively in Southeast Asia. Curcumin exhibited numerous biological and pharmacological activities including potent antioxidant, cardiovascular disease, anticancer, anti-inflammatory effects and neurodegenerative disorders in cell cultures and animal models. Hence, the present study was designed in order to explore the possible neuroprotective role of curcumin against rotenone induced cognitive impairment, oxidative and mitochondrial dysfunction in mice. Chronic administration of rotenone (1mg/kg i.p.) for a period of three weeks significantly impaired cognitive function (actophotometer, rotarod and open field test), oxidative defense (increased lipid peroxidation, nitrite concentration and decreased activity of superoxide dismutase, catalase and reduced glutathione level) and mitochondrial complex (II and III) enzymes activities as compared to normal control group. Three weeks of curcumin (50, 100 and 200mg/kg, p.o.) treatment significantly improved behavioral alterations, oxidative damage and mitochondrial enzyme complex activities as compared to negative control (rotenone treated) group. Curcumin treated mice also mitigated enhanced acetylcholine esterase enzyme level as compared to negative control group. We found that curcumin restored motor deficits and enhanced the activities of antioxidant enzymes suggesting its antioxidant potential in vivo. The findings of the present study conclude neuroprotective role of curcumin against rotenone induced Parkinson's in mice and offer strong justification for the therapeutic prospective of this compound in the management of PD.

Tetramethylpyrazine Ameliorates Rotenone-Induced Parkinson's Disease in Rats: Involvement of Its Anti-Inflammatory and Anti-Apoptotic Actions

Parkinson's disease (PD) is a slowly progressive neurodegenerative movement disorder. Apoptosis, neuroinflammation, and oxidative stress are the current hypothesized mechanisms for PD pathogenesis. Tetramethylpyrazine (TMP), the major bioactive component of Ligusticum wallichii Franchat (ChuanXiong), Family Apiaceae, reportedly has anti-apoptotic, anti-inflammatory and antioxidant effects. This study investigated the role of 'TMP' in preventing rotenone-induced neurobiological and behavioral sequelae. A preliminary dose-response study was conducted where rats received TMP (10, 20, and 40 mg/kg, i.p.) concomitantly with rotenone (2 mg/kg, s.c.) for 4 weeks. Catalepsy, locomotor activity, striatal dopamine content, and tyrosine hydroxylase "TH" and α-synuclein immunoreactivity were evaluated. The selected TMP dose (20 mg/kg) was used for western blot analysis of Bax, Bcl2, and DJ-1, immunohistochemical detection of nuclear factor kappa B (NF-кB), inducible nitric oxide synthase (iNOS), cyclooxygenase-2 (COX2), and glial fibrillary acidic protein (GFAP) expression, in addition to biochemical analysis of caspase-3 activity, nuclear factor erythroid 2-related factor 2 (Nrf2), and heme oxygenase-1 (HO-1) levels. Results showed that TMP (20 mg/kg) significantly improved midbrain and striatal TH expression and striatal dopamine content as well as the motor deficits, compared to rotenone-treated group. These results were correlated with reduction in caspase-3 activity and α-synuclein expression, along with improvement of midbrain and striatal Bax/Bcl2 ratio compared to rotenone-treated group. TMP also attenuated rotenone-induced upregulation of Nrf2/HO-1 pathway. Furthermore, TMP downregulated rotenone-induced neuroinflammation markers: NF-кB, iNOS, COX2, and GFAP expression in both the midbrain and striatum. Taken together, the current study suggests that TMP is entitled to, at least partially, preventing PD neurobiological and behavioral deficits by virtue of its anti-apoptotic, anti-inflammatory, and antioxidant actions.

Chronic exposure of homocysteine in mice contributes to dopamine loss by enhancing oxidative stress in nigrostriatum and produces behavioral phenotypes of Parkinson's disease

Increased homocysteine (Hcy) level has been implicated as an independent risk factor for various neurological disorders, including Parkinson’s disease (PD). Hcy has been reported to cause dopaminergic neuronal loss in rodents and causes the behavioral abnormalities. This study is an attempt to investigate molecular mechanisms underlying Hcy-induced dopaminergic neurotoxicity after its chronic systemic administration. Male Swiss albino mice were injected with different doses of Hcy (100 and 250 mg/kg; intraperitoneal) for 60 days. Animals subjected to higher doses of Hcy, but not the lower dose, produces motor behavioral abnormalities with significant dopamine depletion in the striatum. Significant inhibition of mitochondrial complex-I activity in nigra with enhanced activity of antioxidant enzymes in the nigrostriatum have highlighted the involvement of Hcy-induced oxidative stress. While, chronic exposure to Hcy neither significantly alters the nigrostriatal glutathione level nor it causes any visible change in tyrosine hydroxylase-immunoreactivity of dopaminergic neurons. The finding set us to hypothesize that the mild oxidative stress due to prolonged Hcy exposure to mice is conducive to striatal dopamine depletion leading to behavioral abnormalities similar to that observed in PD.

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Chronic intraperitoneal Hcy injection causes parkinsonian like motor abnormalities.

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Hcy injection caused complex-I inhibition in nigra and striatal dopamine depletion.

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Hcy injection caused enhanced activity of antioxidant enzymes in nigrostriatum.

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Hcy-induced mild oxidative stress is not sufficient to alter GSH and TH.

Levodopa increases oxidative stress and repulsive guidance molecule A levels: a pilot study in patients with Parkinson's disease

Exposure to free radicals influences synthesis, degradation and function of proteins, such as repulsive guidance molecule A. Decay of this protein is essential for neuronal maintenance and recovery. Levodopa elevates oxidative stress. Therefore levodopa may impact repulsive guidance molecule A metabolism. Objectives were to investigate plasma concentrations of repulsive guidance molecule A, levodopa, cysteine and cysteinyl-glycine before and 1 h after levodopa application in patients with Parkinson's disease. Cysteine and cysteinyl-glycine as biomarkers for oxidative stress exposure decreased, repulsive guidance molecule A and levodopa rose. Repulsive guidance molecule A remained unchanged in levodopa naïve patients, but particularly went up in patients on a prior chronic levodopa regimen. Decay of cysteine specifically cysteinyl-glycine results from an elevated glutathione generation with rising cysteine consumption respectively from the alternative glutathione transformation to its oxidized form glutathione disulfide after free radical scavenging. Repulsive guidance molecule A rise may inhibit physiologic mechanisms for neuronal survival.

Interaction of α-synuclein with biomembranes in Parkinson's disease--role of cardiolipin

One of the key molecular events underlying the pathogenesis of Parkinson's disease (PD) is the aberrant misfolding and aggregation of the α-synuclein (αS) protein into higher-order oligomers that play a key role in neuronal dysfunction and degeneration. A wealth of experimental data supports the hypothesis that the neurotoxicity of αS oligomers is intrinsically linked with their ability to interact with, and disrupt, biological membranes; especially those membranes having negatively-charged surfaces and/or lipid packing defects. Consequences of αS-lipid interaction include increased membrane tension, permeation by pore formation, membrane lysis and/or leakage due to the extraction of lipids from the bilayer. Moreover, we assert that the interaction of αS with a liquid-disordering phospholipid uniquely enriched in mitochondrial membranes, namely cardiolipin (1,3-diphosphatidyl-sn-glycerol, CL), helps target the αS oligomeric complexes intracellularly to mitochondria. Binding mediated by CL may thus represent an important pathomechanism by which cytosolic αS could physically associate with mitochondrial membranes and disrupt their integrity. Impaired mitochondrial function culminates in a cellular bioenergetic crisis and apoptotic death. To conclude, we advocate the accelerated discovery of new drugs targeting this pathway in order to restore mitochondrial function in PD.

Protection of MPTP-induced neuroinflammation and neurodegeneration by rotigotine-loaded microspheres

AIMS

The aim of the study is to evaluate the neuroprotective effects of continuous dopaminergic stimulation (CDS) by rotigotine-loaded microspheres (RoMS) in a mouse model of MPTP-induced Parkinson's disease (PD) and to elucidate the potential mechanism underlying these effects.

MAIN METHODS

Male C57BL/6 mice were treated either intramuscularly once with RoMS or twice daily for two weeks with rotigotine, and from the 9th day, MPTP (30 mg/kg, i.p.) was injected for the last 5 days. Following treatment, Parkinsonism scores were calculated and oxidative stress-related indicators in the striatum were performed. Neuroinflammatory cytokines, such as tumor necrosis factor-α (TNF-α), interleukin-1β (IL-1β), and interleukin-6 (IL-6) were detected in the striatum. Expression of apoptosis-related proteins B-cell leukemia/lymphoma 2 (Bcl-2) and Bcl-2-associated X protein (BAX) was measured in the striatum by Western blot. Nigral tyrosine hydroxylase (TH)-positive neurons and microglial cell markers, i.e., ionized calcium binding adaptor molecule-1 (Iba-1) and neuronal synaptosomes, were quantified to assess the neuroprotective efficacy of RoMS.

KEY FINDINGS

The administration of rotigotine significantly improved the Parkinsonism score, protected dopaminergic neurons with antioxidants, reduced microglial cell activation and the release of neuroinflammatory cytokines, and balanced the expression of Bcl-2 and Bax in MPTP-treated mice. Interestingly, the neuroprotective properties of rotigotine were remarkably amplified by CDS treatment with RoMS.

SIGNIFICANCE

These results suggest that CDS therapy can play a neuroprotective role in an MPTP mouse model. Neuroprotective disease-modifying therapy may have the potential benefits of early treatment by normalizing compensatory mechanisms and may also help to delay dyskinesia in the later stages of PD.

Oxidation of survival factor MEF2D in neuronal death and Parkinson's disease

AIMS

Dysfunction of myocyte enhancer factor 2D (MEF2D), a key survival protein and transcription factor, underlies the pathogenic loss of dopaminergic (DA) neurons in Parkinson's disease (PD). Both genetic factors and neurotoxins associated with PD impair MEF2D function in vitro and in animal models of PD. We investigated whether distinct stress conditions target MEF2D via converging mechanisms.

RESULTS

We showed that exposure of a DA neuronal cell line to 6-hyroxydopamine (6-OHDA), which causes PD in animals models, led to direct oxidative modifications of MEF2D. Oxidized MEF2D bound to heat-shock cognate protein 70 kDa, the key regulator for chaperone-mediated autophagy (CMA), at a higher affinity. Oxidative stress also increased the level of lysosomal-associated membrane protein 2A (LAMP2A), the rate-limiting receptor for CMA substrate flux, and stimulated CMA activity. These changes resulted in accelerated degradation of MEF2D. Importantly, 6-OHDA induced MEF2D oxidation and increased LAMP2A in the substantia nigra pars compacta region of the mouse brain. Consistently, the levels of oxidized MEF2D were much higher in postmortem PD brains compared with the controls. Functionally, reducing the levels of either MEF2D or LAMP2A exacerbated 6-OHDA-induced death of the DA neuronal cell line. Expression of an MEF2D mutant that is resistant to oxidative modification protected cells from 6-OHDA-induced death.

INNOVATION

This study showed that oxidization of survival protein MEF2D is one of the pathogenic mechanisms involved in oxidative stress-induced DA neuronal death.

CONCLUSION

Oxidation of survival factor MEF2D inhibits its function, underlies oxidative stress-induced neurotoxicity, and may be a part of the PD pathogenic process.

Mutations in PRKN and SNCA Genes Important for the Progress of Parkinson's Disease

Although Parkinson’s disease (PD) was first described almost 200 years ago, it remains an incurable disease with a cause that is not fully understood. Nowadays it is known that disturbances in the structure of pathological proteins in PD can be caused by more than environmental and genetic factors. Despite numerous debates and controversies in the literature about the role of mutations in the SNCA and PRKN genes in the pathogenesis of PD, it is evident that these genes play a key role in maintaining dopamine (DA) neuronal homeostasis and that the dysfunction of this homeostasis is relevant to both familial (FPD) and sporadic (SPD) PD with different onset. In recent years, the importance of alphasynuclein (ASN) in the process of neurodegeneration and neuroprotective function of the Parkin is becoming better understood. Moreover, there have been an increasing number of recent reports indicating the importance of the interaction between these proteins and their encoding genes. Among others interactions, it is suggested that even heterozygous substitution in the PRKN gene in the presence of the variants +2/+2 or +2/+3 of NACP-Rep1 in the SNCA promoter, may increase the risk of PD manifestation, which is probably due to ineffective elimination of over-expressed ASN by the mutated Parkin protein. Finally, it seems that genetic testing may be an important part of diagnostics in patients with PD and may improve the prognostic process in the course of PD. However, only full knowledge of the mechanism of the interaction between the genes associated with the pathogenesis of PD is likely to help explain the currently unknown pathways of selective damage to dopaminergic neurons in the course of PD.

A loss in cellular protein partners promotes α-synuclein aggregation in cells resulting from oxidative stress

There is a consensus that oxidative stress promotes neurodegeneration and may be linked to plaque formation. α-Synuclein is the main component of neurodegenerative plaques. We have found that α-synuclein binds strongly to the enzyme phospholipase Cβ1 (PLCβ1) in vitro and in cells affecting both its G protein activation and its degradation. Because PLCβ1 binds to α-synuclein in cells, we tested whether decreasing its level would promote α-synuclein aggregation and whether overproducing PLCβ1 would inhibit aggregation. By imaging fluorescent α-synuclein in living HEK293, PC12, and SK-H-SH cells, we find that α-synuclein aggregation is directly related to the level of PLCβ1. Importantly, we found that oxidative stress does not affect the cellular levels of α-synuclein but results in the down-regulation of PLCβ1 thereby promoting α-synuclein aggregation. A peptide that mimics part of the α-synuclein binding site to PLCβ prevents aggregation. Our studies indicate that PLCβ1 can reduce cell damage under oxidative stress and offers a potential site that might be exploited to prevent α-synuclein aggregation.

Microglial activation and antioxidant responses induced by the Parkinson's disease protein α-synuclein

Parkinson’s disease (PD) is the second most common age-related neurodegenerative disorder typified by tremor, rigidity, akinesia and postural instability due in part to the loss of dopamine within the nigrostriatal system. The pathologic features of this disorder include the loss of substantia nigra dopamine neurons and attendant striatal terminals, the presence of large protein-rich neuronal inclusions containing fibrillar α-synuclein and increased numbers of activated microglia. Evidence suggests that both misfolded α-synuclein and oxidative stress play an important role in the pathogenesis of sporadic PD. Here we review evidence that α-synuclein activates glia inducing inflammation and that Nrf2-directed phase-II antioxidant enzymes play an important role in PD. We also provide new evidence that the expression of antioxidant enzymes regulated in part by Nrf2 is increased in a mouse model of α-synuclein overexpression. We show that misfolded α-synuclein directly activates microglia inducing the production and release of the proinflammatory cytokine, TNF-α, and increasing antioxidant enzyme expression. Importantly, we demonstrate that the precise structure of α-synuclein is important for induction of this proinflammatory pathway. This complex α-synuclein-directed glial response highlights the importance of protein misfolding, oxidative stress and inflammation in PD and represents a potential locus for the development of novel therapeutics focused on induction of the Nrf2-directed antioxidant pathway and inhibition of protein misfolding.

Oxidative stress and microglial cells in Parkinson's disease

Significant evidence has now been accumulated that microglial cells play a central role in the degeneration of DA neurons in animal models of PD. The oxidative stress response by microglial cells, most notably the activity of the enzyme NADPH oxidase, appears to play a central role in the pathology of PD. This oxidative stress response occurs in microglia through the activation of the ERK signaling pathway by proinflammatory stimuli, leading to the phosphorylation and translocation of the p47(phox) and p67(phox) cytosolic subunits, the activation of membrane-bound PHOX, and the production of ROS. Therapeutic anti-inflammatories which prevent DA neurodegeneration in PD, including anti-inflammatory cytokines, morphinan compounds, NADPH oxidase inhibitors, NF-κB inhibitors, and β2-AR agonists, all function to inhibit the activation of the PHOX in microglial cells. These observations suggest a central role for the oxidative stress response in microglial cells as a mediator or regulator of DA neurodegeneration in PD.

Mechanisms of altered redox regulation in neurodegenerative diseases--focus on S--glutathionylation

SIGNIFICANCE

Neurodegenerative diseases are characterized by progressive loss of neurons. A common feature is oxidative stress, which arises when reactive oxygen species (ROS) and/or reactive nitrogen species (RNS) exceed amounts required for normal redox signaling. An imbalance in ROS/RNS alters functionality of cysteines and perturbs thiol-disulfide homeostasis. Many cysteine modifications may occur, but reversible protein mixed disulfides with glutathione (GSH) likely represents the common steady-state derivative due to cellular abundance of GSH and ready conversion of cysteine-sulfenic acid and S-nitrosocysteine precursors to S-glutathionylcysteine disulfides. Thus, S-glutathionylation acts in redox signal transduction and serves as a protective mechanism against irreversible cysteine oxidation. Reversal of protein-S-glutathionylation is catalyzed specifically by glutaredoxin which thereby plays a critical role in cellular regulation. This review highlights the role of oxidative modification of proteins, notably S-glutathionylation, and alterations in thiol homeostatic enzyme activities in neurodegenerative diseases, providing insights for therapeutic intervention.

RECENT ADVANCES

Recent studies show that dysregulation of redox signaling and sulfhydryl homeostasis likely contributes to onset/progression of neurodegeneration. Oxidative stress alters the thiol-disulfide status of key proteins that regulate the balance between cell survival and cell death.

CRITICAL ISSUES

Much of the current information about redox modification of key enzymes and signaling intermediates has been gleaned from studies focused on oxidative stress situations other than the neurodegenerative diseases.

FUTURE DIRECTIONS

The findings in other contexts are expected to apply to understanding neurodegenerative mechanisms. Identification of selectively glutathionylated proteins in a quantitative fashion will provide new insights about neuropathological consequences of this oxidative protein modification.

The association between Mediterranean diet adherence and Parkinson's disease

BACKGROUND

Recent studies have demonstrated an association between a Mediterranean-type diet and Alzheimer's risk. We assessed the association between Mediterranean-type diet adherence and Parkinson's disease (PD) status.

METHODS

Two hundred and fifty-seven PD participants and 198 controls completed the Willett semiquantitative questionnaire that quantifies diet during the past year. Scores were calculated using a 9-point scale; higher scores indicated greater adherence to the Mediterranean-type diet. Logistic regression models were used to assess the association between PD status and Mediterranean-type diet, adjusting for caloric intake, age, sex, education, and ethnicity. Adjusted linear regression models were used to examine the association between Mediterranean-type diet adherence and PD age at onset.

RESULTS

Higher Mediterranean-type diet adherence was associated with reduced odds for PD after adjustment for all covariates (OR, 0.86; 95% CI, 0.77-0.97; P = .010). Lower Mediterranean-type diet score was associated with earlier PD age at onset (β = 1.09; P = .006).

CONCLUSIONS

PD patients adhere less than controls to a Mediterranean-type diet. Dietary behavior may be associated with age at onset.

Development of a novel biosensor using cationic antimicrobial Peptide and nickel phthalocyanine ultrathin films for electrochemical detection of dopamine

The antimicrobial peptide dermaseptin 01 (DS 01), from the skin secretion of Phyllomedusa hypochondrialis frogs, was immobilized in nanostructured layered films in conjunction with nickel tetrasulfonated phthalocyanines (NiTsPc), widely used in electronic devices, using layer-by-layer technique. The films were used as a biosensor to detect the presence of dopamine (DA), a neurotransmitter associated with diseases such as Alzheimer's and Parkinson's, with detection limits in the order of 10⁻⁶ mol L⁻¹. The use of DS 01 in LbL film generated selectivity in the detection of DA despite the presence of ascorbic acid found in biological fluids. This work is the first to report that the antimicrobial peptide and NiTsPc LbL film exhibits electroanalytical activity to DA oxidation. The selectivity in the detection of DA is a fundamental aspect for the development of electrochemical sensors with potential applications in the biomedical and pharmaceutical industries.

Melatonin reduces the expression of alpha-synuclein in the dopamine containing neuronal regions of amphetamine-treated postnatal rats

Alpha-synuclein (α-syn) is a neuronal protein that is involved in various degenerative disorders such as Parkinson's disease. It is found in the presynaptic terminals and perinuclear zones of many brain regions. Amphetamine (AMPH), a psychostimulant drug abused progressively more commonly in recent years, has been known to induce neurotoxicity in the central dopaminergic pathway, which is associated with increased oxidative stress. Recently, AMPH has been shown to significantly increase the level of α-syn in dopaminergic neuroblastoma cell cultures. Melatonin is recognized as an antioxidant for the nervous system. This study tested whether melatonin can attenuate the effect of AMPH on the expression of α-syn in the dopaminergic pathway of the neonatal rat. Four-day old postnatal rats (P4) were injected subcutaneously with either AMPH (increasing dose, 5-10 mg/kg daily) alone or AMPH with melatonin (2 mg/kg) daily at 10:00 AM for 7 consecutive days. As determined using Western blot, the level of α-syn was significantly increased in the substantia nigra, dorsal striatum, nucleus accumbens, and prefrontal cortex of the AMPH-treated group, while melatonin treatment either prior to AMPH or alone decreased the accumulation of the protein to 77%, 96%, 78%, and 77% of the control value, respectively. Furthermore, an immunofluorescent study showed that the α-syn-immunoreactivity increased noticeably in the nuclei of cell bodies and nerve terminals of the AMPH-treated group. Again, melatonin lowered this immunoreactivity. These results indicate that melatonin has a direct or indirect effect in reducing the expression of α-syn in the postnatal rat. The exact mechanism of this mitigation should be further investigated.

Dopamine and paraquat enhance α-synuclein-induced alterations in membrane conductance

We have previously demonstrated that α-synuclein overexpression increases the membrane conductance of dopaminergic-like cells. Although α-synuclein is thought to play a central role in the pathogenesis of several neurodegenerative diseases including Parkinson's disease, multiple system atrophy, and diffuse Lewy body disease, the mechanism of action is not completely understood. In this study, we sought to determine whether multiple factors act together with α-synuclein to engender cell vulnerability through an augmentation of membrane conductance. In this article, we employed a cell model that mimics dopaminergic neurons coupled with α-synuclein overexpression and oxidative stressors. We demonstrate an enhancement of α-synuclein-induced toxicity in the presence of combined treatment with dopamine and paraquat, two molecules known to incite oxidative stress. In addition, we show that combined dopamine and paraquat treatment increases the expression of heme oxygenase-1, an antioxidant response protein. Finally, we demonstrate for the first time that combined treatment of dopaminergic cells with paraquat and dopamine enhances α-synuclein-induced leak channel properties resulting in increased membrane conductance. Importantly, these increases are most robust when both paraquat and dopamine are present suggesting the need for multiple oxidative insults to augment α-synuclein-induced disruption of membrane integrity.

Levodopa activates apoptosis signaling kinase 1 (ASK1) and promotes apoptosis in a neuronal model: implications for the treatment of Parkinson's disease

Oxidative stress is implicated in the etiology of Parkinson's disease (PD), the second most common neurodegenerative disease. PD is treated with chronic administration of l-3,4-dihydroxyphenylalanine (levodopa, L-DOPA), and typically, increasing doses are used during progression of the disease. Paradoxically, L-DOPA is a pro-oxidant and induces cell death in cellular models of PD through disruption of sulfhydryl homeostasis involving loss of the thiol-disulfide oxidoreductase functions of the glutaredoxin (Grx1) and thioredoxin (Trx1) enzyme systems [Sabens, E. A., Distler, A. M., and Mieyal, J. J. (2010) Biochemistry 49 (12), 2715-2724]. Considering this loss of both Grx1 and Trx1 activities upon L-DOPA treatment, we sought to elucidate the mechanism(s) of L-DOPA-induced apoptosis. In other contexts, both the NFκB (nuclear factor κB) pathway and the ASK1 (apoptosis signaling kinase 1) pathway have been shown to be regulated by both Grx1 and Trx1, and both pathways have been implicated in cell death signaling in model systems of PD. Moreover, mixed lineage kinase (MLK) has been considered as a potential therapeutic target for PD. Using SHSY5Y cells as model dopaminergic neurons, we found that NFκB activity was not altered by L-DOPA treatment, and the selective MLK inhibitor (CEP-1347) did not protect the cells from L-DOPA. In contrast, ASK1 was activated with L-DOPA treatment as indicated by phosphorylation of its downstream mitogen-activated protein kinases (MAPK), p38 and JNK. Chemical inhibition of either p38 or JNK provided protection from L-DOPA-induced apoptosis. Moreover, direct knockdown of ASK1 protected from L-DOPA-induced neuronal cell death. These results identify ASK1 as the main pro-apoptotic pathway activated in response to L-DOPA treatment, implicating it as a potential target for adjunct therapy in PD.

Imbalanced estrogen metabolism in the brain: possible relevance to the etiology of Parkinson's disease

Damage to DNA by dopamine quinone and/or catechol estrogen quinones may play a significant role in the initiation of Parkinson's disease (PD). Depurinating estrogen-DNA adducts are shed from cells and excreted in urine. The aim of this study was to discover whether higher levels of estrogen-DNA adducts are associated with PD. Forty estrogen metabolites, conjugates, and DNA adducts were analyzed in urine samples from 20 PD cases and 40 matched controls by using ultra performance liquid chromatography/tandem mass spectrometry. The levels of adducts in cases versus controls (P < 0.005) suggest that unbalanced estrogen metabolism could play a causal role in the initiation of PD.

Mitochondrial abnormalities in the putamen in Parkinson's disease dyskinesia

Prolonged treatment of Parkinson's disease (PD) with levodopa leads to disabling side effects collectively referred to as 'dyskinesias'. We hypothesized that bioenergetic function in the putamen might play a crucial role in the development of dyskinesias. To test this hypothesis, we used post mortem samples of the human putamen and applied real time-PCR approaches and gene expression microarrays. We found that mitochondrial DNA (mtDNA) levels are decreased in patients who have developed dyskinesias, and mtDNA damage is concomitantly increased. These pathologies were not observed in PD subjects without signs of dyskinesias. The group of nuclear mRNA transcripts coding for the proteins of the mitochondrial electron transfer chain was decreased in patients with dyskinesias to a larger extent than in patients who had not developed dyskinesias. To examine whether dopamine fluctuations affect mtDNA levels in dopaminoceptive neurons, rat striatal neurons in culture were repeatedly exposed to levodopa, dopamine or their metabolites. MtDNA levels were reduced after treatment with dopamine, but not after treatment with dopamine metabolites. Levodopa led to an increase in mtDNA levels. We conclude that mitochondrial susceptibility in the putamen plays a role in the development of dyskinesias.

Peripheral biomarkers of Parkinson's disease as early reporters of central neurodegeneration

Parkinson's disease (PD) is the most common age-related movement disorder, with a prevalence of approximately 2% among people over 65 years of age. The diagnosis of PD is currently based on the clinical manifestations of the disease; therefore, the availability of peripheral biomarkers would have a great impact. In this review, we discuss and compare several attempts made to find peripheral biomarkers of PD to achieve early diagnosis, differential diagnosis, therapy assessment and classification of disease subtypes. Several investigators focused on proteins that are involved in PD pathogenesis. However, the best choice for a sensible biomarker-discovery procedure makes use of global approaches such as metabolomics and proteomics. In addition, the tissue or compartment where biomarkers are located, plays a basic role. In this context, lymphocytes are of particular interest because they are circulating dopaminergic cells, and display several functional modifications in PD.