Biochemistry of postmortem brains in Parkinson's disease: historical overview and future prospects

Dopaminergic neuronal death via necroptosis in Parkinson's disease: A review of the literature

Parkinson's disease (PD) is a neurodegenerative disorder characterized by progressive dysfunction and loss of dopaminergic neurons of the substantia nigra pars compacta (SNc). Several pathways of programmed cell death are likely to play a role in dopaminergic neuron death, such as apoptosis, necrosis, pyroptosis and ferroptosis, as well as cell death associated with proteasomal and mitochondrial dysfunction. A better understanding of the molecular mechanisms underlying dopaminergic neuron death could inform the design of drugs that promote neuron survival. Necroptosis is a recently characterized regulated cell death mechanism that exhibits morphological features common to both apoptosis and necrosis. It requires activation of an intracellular pathway involving receptor-interacting protein 1 kinase (RIP1 kinase, RIPK1), receptor-interacting protein 3 kinase (RIP3 kinase, RIPK3) and mixed lineage kinase domain-like pseudokinase (MLKL). The potential involvement of this programmed cell death pathway in the pathogenesis of PD has been studied by analysing biomarkers for necroptosis, such as the levels and oligomerization of phosphorylated RIPK3 (pRIPK3) and phosphorylated MLKL (pMLKL), in several PD preclinical models and in PD human tissue. Although there is evidence that other types of cell death also have a role in DA neuron death, most studies support the hypothesis that this cell death mechanism is activated in PD tissues. Drugs that prevent or reduce necroptosis may provide neuroprotection for PD. In this review, we summarize the findings from these studies. We also discuss how manipulating necroptosis might open a novel therapeutic approach to reduce neuronal degeneration in PD.

Patients with Neurodegenerative Proteinopathies Exhibit Altered Tryptophan Metabolism in the Serum and Cerebrospinal Fluid

Some pathological conditions affecting the human body can also disrupt metabolic pathways and thus alter the overall metabolic profile. Knowledge of metabolic disturbances in specific diseases could thus enable the differential diagnosis of otherwise similar conditions. This work therefore aimed to comprehensively characterize changes in tryptophan metabolism in selected neurodegenerative diseases. Levels of 18 tryptophan-related neuroactive substances were determined by high throughput and sensitive ultrahigh-performance liquid chromatography-tandem mass spectrometry in time-linked blood serum and cerebrospinal fluid samples from 100 age-matched participants belonging to five cohorts: healthy volunteers (n = 21) and patients with Lewy body disease (Parkinson's disease and dementia with Lewy bodies; n = 31), four-repeat tauopathy (progressive supranuclear palsy and corticobasal syndrome; n = 10), multiple system atrophy (n = 13), and Alzheimer's disease (n = 25). Although these conditions have different pathologies and clinical symptoms, the discovery of new biomarkers is still important. The most statistically significant differences (with p-values of ≤0.05 to ≤0.0001) between the study cohorts were observed for three tryptophan metabolites: l-kynurenine in cerebrospinal fluid and 3-hydroxy-l-kynurenine and 5-hydroxy-l-tryptophan in blood serum. This led to the discovery of distinctive correlation patterns between the profiled cerebrospinal fluid and serum metabolites that could provide a basis for the differential diagnosis of neurodegenerative tauopathies and synucleinopathies. However, further large-scale studies are needed to determine the direct involvement of these metabolites in the studied neuropathologies, their response to medication, and their potential therapeutic relevance.

Endogenous GDNF Is Unable to Halt Dopaminergic Injury Triggered by Microglial Activation

Overactivation of microglial cells seems to play a crucial role in the degeneration of dopaminergic neurons occurring in Parkinson's disease. We have previously demonstrated that glial cell line-derived neurotrophic factor (GDNF) present in astrocytes secretome modulates microglial responses induced by an inflammatory insult. Therefore, astrocyte-derived soluble factors may include relevant molecular players of therapeutic interest in the control of excessive neuroinflammatory responses. However, in vivo, the control of neuroinflammation is more complex as it depends on the interaction between different types of cells other than microglia and astrocytes. Whether neurons may interfere in the astrocyte-microglia crosstalk, affecting the control of microglial reactivity exerted by astrocytes, is unclear. Therefore, the present work aimed to disclose if the control of microglial responses mediated by astrocyte-derived factors, including GDNF, could be affected by the crosstalk with neurons, impacting GDNF's ability to protect dopaminergic neurons exposed to a pro-inflammatory environment. Also, we aimed to disclose if the protection of dopaminergic neurons by GDNF involves the modulation of microglial cells. Our results show that the neuroprotective effect of GDNF was mediated, at least in part, by a direct action on microglial cells through the GDNF family receptor α-1. However, this protective effect seems to be impaired by other mediators released in response to the neuron-astrocyte crosstalk since neuron-astrocyte secretome, in contrast to astrocytes secretome, was unable to protect dopaminergic neurons from the injury triggered by lipopolysaccharide-activated microglia. Supplementation with exogenous GDNF was needed to afford protection of dopaminergic neurons exposed to the inflammatory environment. In conclusion, our results revealed that dopaminergic protective effects promoted by GDNF involve the control of microglial reactivity. However, endogenous GDNF is insufficient to confer dopaminergic neuron protection against an inflammatory insult. This reinforces the importance of further developing new therapeutic strategies aiming at providing GDNF or enhancing its expression in the brain regions affected by Parkinson's disease.

Catecholamines and Parkinson's disease: tyrosine hydroxylase (TH) over tetrahydrobiopterin (BH4) and GTP cyclohydrolase I (GCH1) to cytokines, neuromelanin, and gene therapy: a historical overview

The author identified the genes and proteins of human enzymes involved in the biosynthesis of catecholamines (dopamine, norepinephrine, epinephrine) and tetrahydrobiopterin (BH4): tyrosine hydroxylase (TH), aromatic L-amino acid decarboxylase (AADC), dopamine β-hydroxylase (DBH), phenylethanolamine N-methyltransferase (PNMT), and GTP cyclohydrolase I (GCH1). In Parkinson's disease (PD), the activities and levels of mRNA and protein of all catecholamine-synthesizing enzymes are decreased, especially in dopamine neurons in the substantia nigra. Hereditary GCH1 deficiency results in reductions in the levels of BH4 and the activities of TH, causing decreases in dopamine levels. Severe deficiencies in GCH1 or TH cause severe decreases in dopamine levels leading to severe neurological symptoms, whereas mild decreases in TH activity in mild GCH1 deficiency or in mild TH deficiency result in only modest reductions in dopamine levels and symptoms of DOPA-responsive dystonia (DRD, Segawa disease) or juvenile Parkinsonism. DRD is a treatable disease and small doses of L-DOPA can halt progression. The death of dopamine neurons in PD in the substantia nigra may be related to (i) inflammatory effect of extra neuronal neuromelanin, (ii) inflammatory cytokines which are produced by activated microglia, (iii) decreased levels of BDNF, and/or (iv) increased levels of apoptosis-related factors. This review also discusses progress in gene therapies for the treatment of PD, and of GCH1, TH and AADC deficiencies, by transfection of TH, AADC, and GCH1 via adeno-associated virus (AAV) vectors.

Pharmacological Inhibition of Ferroptosis as a Therapeutic Target for Neurodegenerative Diseases and Strokes

Emerging evidence suggests that ferroptosis, a unique regulated cell death modality that is morphologically and mechanistically different from other forms of cell death, plays a vital role in the pathophysiological process of neurodegenerative diseases, and strokes. Accumulating evidence supports ferroptosis as a critical factor of neurodegenerative diseases and strokes, and pharmacological inhibition of ferroptosis as a therapeutic target for these diseases. In this review article, the core mechanisms of ferroptosis are overviewed and the roles of ferroptosis in neurodegenerative diseases and strokes are described. Finally, the emerging findings in treating neurodegenerative diseases and strokes through pharmacological inhibition of ferroptosis are described. This review demonstrates that pharmacological inhibition of ferroptosis by bioactive small-molecule compounds (ferroptosis inhibitors) could be effective for treatments of these diseases, and highlights a potential promising therapeutic avenue that could be used to prevent neurodegenerative diseases and strokes. This review article will shed light on developing novel therapeutic regimens by pharmacological inhibition of ferroptosis to slow down the progression of these diseases in the future.

Serum glial cell line-derived neurotrophic factor (GDNF) a potential biomarker of executive function in Parkinson's disease

Objective

Evidence shows that the impairment of executive function (EF) is mainly attributed to the degeneration of frontal-striatal dopamine pathway. Glial cell line-derived neurotrophic factor (GDNF), as the strongest protective neurotrophic factor for dopaminergic neurons (DANs), may play a role in EF to some extent. This study mainly explored the correlation between serum GDNF concentration and EF performance in Parkinson's disease (PD).

Methods

This study recruited 45 healthy volunteers (health control, HC) and 105 PD patients, including 44 with mild cognitive impairment (PD-MCI), 20 with dementia (PD-D), and 20 with normal cognitive function (PD-N). Neuropsychological tests were performed to evaluate EF (working memory, inhibitory control, and cognitive flexibility), attention, language, memory, and visuospatial function. All subjects were tested for serum GDNF and homovanillic acid (HVA) levels by ELISA and LC-ESI-MS/MS, respectively.

Results

PD-MCI patients showed impairments in the trail making test (TMT) A (TMT-A), TMT-B, clock drawing test (CDT) and semantic fluency test (SFT), whereas PD-D patients performed worse in most EF tests. With the deterioration of cognitive function, the concentration of serum GDNF and HVA in PD patients decreased. In the PD group, the serum GDNF and HVA levels were negatively correlated with TMT-A (r _GDNF = -0.304, P < 0.01; r _HVA = -0.334, P < 0.01) and TMT-B (r _GDNF = -0.329, P < 0.01; r _HVA = -0.323, P < 0.01) scores. Serum GDNF levels were positively correlated with auditory verbal learning test (AVLT-H) (r = 0.252, P < 0.05) and SFT (r = 0.275, P < 0.05) scores. Serum HVA levels showed a positively correlation with digit span test (DST) (r = 0.277, P < 0.01) scores. Stepwise linear regression analysis suggested that serum GDNF and HVA concentrations and UPDRS-III were the influence factors of TMT-A and TMT-B performances in PD patients.

Conclusion

The decrease of serum GDNF concentration in PD patients was associated with impaired inhibitory control, cognitive flexibility, and attention performances. The changes of GDNF and HVA might synergistically participate in the occurrence and development of executive dysfunction in PD patients.

TiO2-Nanowired Delivery of Chinese Extract of Ginkgo biloba EGb-761 and Bilobalide BN-52021 Enhanced Neuroprotective Effects of Cerebrolysin Following Spinal Cord Injury at Cold Environment

Military personnel during combat or peacekeeping operations are exposed to extreme climates of hot or cold environments for longer durations. Spinal cord injury is quite common in military personnel following central nervous system (CNS) trauma indicating a possibility of altered pathophysiological responses at different ambient temperatures. Our previous studies show that the pathophysiology of brain injury is exacerbated in animals acclimated to cold (5 °C) or hot (30 °C) environments. In these diverse ambient temperature zones, trauma exacerbated oxidative stress generation inducing greater blood-brain barrier (BBB) permeability and cell damage. Extracts of Ginkgo biloba EGb-761 and BN-52021 treatment reduces brain pathology following heat stress. This effect is further improved following TiO₂ nanowired delivery in heat stress in animal models. Several studies indicate the role of EGb-761 in attenuating spinal cord induced neuronal damages and improved functional deficit. This is quite likely that these effects are further improved following nanowired delivery of EGb-761 and BN-52021 with cerebrolysin-a balanced composition of several neurotrophic factors and peptide fragments in spinal cord trauma. In this review, TiO₂ nanowired delivery of EGb-761 and BN-52021 with nanowired cerebrolysin is examined in a rat model of spinal cord injury at cold environment. Our results show that spinal cord injury aggravates cord pathology in cold-acclimated rats and nanowired delivery of EGb-761 and BN-52021 with cerebrolysin significantly induced superior neuroprotection, not reported earlier.

Neurotrophic factor-based pharmacological approaches in neurological disorders

Aging is a physiological event dependent on multiple pathways that are linked to lifespan and processes leading to cognitive decline. This process represents the major risk factor for aging-related diseases such as Alzheimer's disease, Parkinson's disease, and ischemic stroke. The incidence of all these pathologies increases exponentially with age. Research on aging biology has currently focused on elucidating molecular mechanisms leading to the development of those pathologies. Cognitive deficit and neurodegeneration, common features of aging-related pathologies, are related to the alteration of the activity and levels of neurotrophic factors, such as brain-derived neurotrophic factor, nerve growth factor, and glial cell-derived neurotrophic factor. For this reason, treatments that modulate neurotrophin levels have acquired a great deal of interest in preventing neurodegeneration and promoting neural regeneration in several neurological diseases. Those treatments include both the direct administration of neurotrophic factors and the induced expression with viral vectors, neurotrophins' binding with biomaterials or other molecules to increase their bioavailability but also cell-based therapies. Considering neurotrophins' crucial role in aging pathologies, here we discuss the involvement of several neurotrophic factors in the most common brain aging-related diseases and the most recent therapeutic approaches that provide direct and sustained neurotrophic support.

Isoalantolactone (IAL) Regulates Neuro-Inflammation and Neuronal Apoptosis to Curb Pathology of Parkinson's Disease

Parkinson's disease (PD) is a neurodegenerative disease in which neuronal apoptosis and associated inflammation are involved in its pathogenesis. However, there is still no specific treatment that can stop PD progression. Isoalantolactone (IAL) plays a role in many inflammation-related diseases. However, its effect and mechanism in PD remain unclear. In this study, results showed that IAL administration ameliorated 1-methyl-4-phenyl-1, 2, 3, 6-tetrahydropyridine (MPTP)-induced PD-related pathological impairment and decreased motor activity in mice. Results from in vitro mechanistic studies showed that IAL regulated apoptosis-related proteins by activating the AKT/Nrf2 pathway, thereby suppressing the apoptosis of SN4741 cells induced by N-methyl-4-phenylpyridinium Iodide (MPP⁺). On the other hand, IAL inhibited LPS-induced release of pro-inflammatory mediators in BV2 cells by activating the AKT/Nrf2/HO-1 pathway and inhibiting the NF-κB pathway. In addition, IAL protected SN4741 from microglial activation-mediated neurotoxicity. Taken together, these results highlight the beneficial role of IAL as a novel therapy and potential PD drug due to its pharmacological profile.

Neuromelanin in Parkinson's Disease: Tyrosine Hydroxylase and Tyrosinase

Parkinson's disease (PD) is an aging-related disease and the second most common neurodegenerative disease after Alzheimer's disease. The main symptoms of PD are movement disorders accompanied with deficiency of neurotransmitter dopamine (DA) in the striatum due to cell death of the nigrostriatal DA neurons. Two main histopathological hallmarks exist in PD: cytosolic inclusion bodies termed Lewy bodies that mainly consist of α-synuclein protein, the oligomers of which produced by misfolding are regarded to be neurotoxic, causing DA cell death; and black pigments termed neuromelanin (NM) that are contained in DA neurons and markedly decrease in PD. The synthesis of human NM is regarded to be similar to that of melanin in melanocytes; melanin synthesis in skin is via DOPAquinone (DQ) by tyrosinase, whereas NM synthesis in DA neurons is via DAquinone (DAQ) by tyrosine hydroxylase (TH) and aromatic L-amino acid decarboxylase (AADC). DA in cytoplasm is highly reactive and is assumed to be oxidized spontaneously or by an unidentified tyrosinase to DAQ and then, synthesized to NM. Intracellular NM accumulation above a specific threshold has been reported to be associated with DA neuron death and PD phenotypes. This review reports recent progress in the biosynthesis and pathophysiology of NM in PD.

Neurotrophins as Therapeutic Agents for Parkinson’s Disease; New Chances From Focused Ultrasound?

Magnetic Resonance–guided Focused Ultrasound (MRgFUS) represents an effective micro-lesioning approach to target pharmaco-resistant tremor, mostly in patients afflicted by essential tremor (ET) and/or Parkinson’s disease (PD). So far, experimental protocols are verifying the clinical extension to other facets of the movement disorder galaxy (i.e., internal pallidus for disabling dyskinesias). Aside from those neurosurgical options, one of the most intriguing opportunities of this technique relies on its capability to remedy the impermeability of blood–brain barrier (BBB). Temporary BBB opening through low-intensity focused ultrasound turned out to be safe and feasible in patients with PD, Alzheimer’s disease, and amyotrophic lateral sclerosis. As a mere consequence of the procedures, some groups described even reversible but significant mild cognitive amelioration, up to hippocampal neurogenesis partially associated to the increased of endogenous brain-derived neurotrophic factor (BDNF). A further development elevates MRgFUS to the status of therapeutic tool for drug delivery of putative neurorestorative therapies. Since 2012, FUS-assisted intravenous administration of BDNF or neurturin allowed hippocampal or striatal delivery. Experimental studies emphasized synergistic modalities. In a rodent model for Huntington’s disease, engineered liposomes can carry glial cell line–derived neurotrophic factor (GDNF) plasmid DNA (GDNFp) to form a GDNFp-liposome (GDNFp-LPs) complex through pulsed FUS exposures with microbubbles; in a subacute MPTP-PD model, the combination of intravenous administration of neurotrophic factors (either through protein or gene delivery) plus FUS did curb nigrostriatal degeneration. Here, we explore these arguments, focusing on the current, translational application of neurotrophins in neurodegenerative diseases.

Cellular and Molecular Events Leading to Paraquat-Induced Apoptosis: Mechanistic Insights into Parkinson’s Disease Pathophysiology

Parkinson’s disease (PD) is a progressive neurodegenerative disorder characterized by the cardinal features of tremor, bradykinesia, rigidity, and postural instability, in addition to other non-motor symptoms. Pathologically, PD is attributed to the loss of dopaminergic neurons in the substantia nigra pars compacta, with the hallmark of the presence of intracellular protein aggregates of α-synuclein in the form of Lewy bodies. The pathogenesis of PD is still yet to be fully elucidated due to the multifactorial nature of the disease. However, a myriad of studies has indicated several intracellular events in triggering apoptotic neuronal cell death in PD. These include oxidative stress, mitochondria dysfunction, endoplasmic reticulum stress, alteration in dopamine catabolism, inactivation of tyrosine hydroxylase, and decreased levels of neurotrophic factors. Laboratory studies using the herbicide paraquat in different in vitro and in vivo models have demonstrated the induction of many PD pathological features. The selective neurotoxicity induced by paraquat has brought a new dawn in our perspectives about the pathophysiology of PD. Epidemiological data have suggested an increased risk of developing PD in the human population exposed to paraquat for a long term. This model has opened new frontiers in the quest for new therapeutic targets for PD. The purpose of this review is to synthesize the relationship between the exposure of paraquat and the pathogenesis of PD in in vitro and in vivo models.

Dietary Plant Polyphenols as the Potential Drugs in Neurodegenerative Diseases: Current Evidence, Advances, and Opportunities

Neurodegenerative diseases, including Alzheimer’s disease (AD), Parkinson’s disease (PD), and Huntington’s disease (HD), are characterized by the progressive degeneration of neurons. Although the etiology and pathogenesis of neurodegenerative diseases have been studied intensively, the mechanism is still in its infancy. In general, most neurodegenerative diseases share common molecular mechanisms, and multiple risks interact and promote the pathologic process of neurogenerative diseases. At present, most of the approved drugs only alleviate the clinical symptoms but fail to cure neurodegenerative diseases. Numerous studies indicate that dietary plant polyphenols are safe and exhibit potent neuroprotective effects in various neurodegenerative diseases. However, low bioavailability is the biggest obstacle for polyphenol that largely limits its adoption from evidence into clinical practice. In this review, we summarized the widely recognized mechanisms associated with neurodegenerative diseases, such as misfolded proteins, mitochondrial dysfunction, oxidative damage, and neuroinflammatory responses. In addition, we summarized the research advances about the neuroprotective effect of the most widely reported dietary plant polyphenols. Moreover, we discussed the current clinical study and application of polyphenols and the factors that result in low bioavailability, such as poor stability and low permeability across the blood-brain barrier (BBB). In the future, the improvement of absorption and stability, modification of structure and formulation, and the combination therapy will provide more opportunities from the laboratory into the clinic for polyphenols. Lastly, we hope that the present review will encourage further researches on natural dietary polyphenols in the treatment of neurodegenerative diseases.

Molecular Features of Parkinson's Disease in Patient-Derived Midbrain Dopaminergic Neurons

BACKGROUND

Despite intense efforts to develop an objective diagnostic test for Parkinson's disease, there is still no consensus on biomarkers that can accurately diagnose the disease.

OBJECTIVE

Identification of biomarkers for idiopathic Parkinson's disease (PD) may enable accurate diagnosis of the disease. We tried to find molecular and cellular differences in dopaminergic (DA) neurons derived from healthy subjects and idiopathic PD patients with or without rest tremor at onset.

METHODS

We measured the expression of genes controlling dopamine synthesis, sequestration, and catabolism as well as the levels of corresponding metabolites and reactive oxygen species in midbrain DA neurons differentiated from induced pluripotent stem cells (iPSCs) of healthy subjects and PD patients with or without rest tremor.

RESULTS

Significant differences in DA-related gene expression, metabolites, and oxidative stress were found between midbrain DA neurons derived from healthy subjects and patients with PD. DA neurons derived from PD patients with or without rest tremor at onset exhibited significant differences in the levels of some of these transcripts, metabolites, and oxidative stress.

CONCLUSION

The unique combination of these quantifiable molecular and cellular traits in iPSC-derived midbrain DA neurons can distinguish healthy subjects from idiopathic PD patients and segregate PD patients with or without rest tremor at onset. The strategy may be used to develop an objective diagnostic test for PD.

Production of 6-l-[18F]Fluoro-m-tyrosine in an Automated Synthesis Module for 11C-Labeling

6-l-[¹⁸F]Fluoro-m-tyrosine (6-l-[¹⁸F]FMT) represents a valuable alternative to 6-l-[¹⁸F]FDOPA which is conventionally used for the diagnosis and staging of Parkinson’s disease. However, clinical applications of 6-l-[¹⁸F]FMT have been limited by the paucity of practical production methods for its automated production. Herein we describe the practical preparation of 6-l-[¹⁸F]FMT using alcohol-enhanced Cu-mediated radiofluorination of Bpin-substituted chiral Ni(II) complex in the presence of non-basic Bu₄ONTf using a volatile iPrOH/MeCN mixture as reaction solvent. A simple and fast radiolabeling procedure afforded the tracer in 20.0 ± 3.0% activity yield within 70 min. The developed method was directly implemented onto a modified TracerLab FX C Pro platform originally designed for ¹¹C-labeling. This method enables an uncomplicated switch between ¹¹C- and ¹⁸F-labeling. The simplicity of the developed procedure enables its easy adaptation to other commercially available remote-controlled synthesis units and paves the way for a widespread application of 6-l-[¹⁸F]FMT in the clinic.

Impaired dopamine metabolism is linked to fatigability in mice and fatigue in Parkinson's disease patients

Fatigue is a common symptom of Parkinson’s disease that compromises significantly the patients’ quality of life. Despite that, fatigue has been under-recognized as symptom, its pathophysiology remains poorly understood, and there is no adequate treatment so far. Parkinson’s disease is characterized by the progressive loss of midbrain dopaminergic neurons, eliciting the classical motor symptoms including slowing of movements, muscular rigidity and resting tremor. The dopamine synthesis is mediated by the rate-limiting enzyme tyrosine hydroxylase, which requires tetrahydrobiopterin as a mandatory cofactor. Here, we showed that reserpine administration (1 mg/kg, two intraperitoneal injections with an interval of 48 h) in adult Swiss male mice (8–10 weeks; 35–45 g) provoked striatal depletion of dopamine and tetrahydrobiopterin, and intolerance to exercise. The poor exercise performance of reserpinized mice was not influenced by emotional or anhedonic factors, mechanical nociceptive thresholds, electrocardiogram pattern alterations or muscle-impaired bioenergetics. The administration of levodopa (100 mg/kg; i.p.) plus benserazide (50 mg/kg; i.p.) rescued reserpine-induced fatigability-like symptoms and restored striatal dopamine and tetrahydrobiopterin levels. Remarkably, it was observed, for the first time, that impaired blood dopamine metabolism inversely and idependently correlated with fatigue scores in eighteen idiopathic Parkinson’s disease patients (male n = 13; female n = 5; age 61.3 ± 9.59 years). Altogether, this study provides new experimental and clinical evidence that fatigue symptoms might be caused by the impaired striatal dopaminergic neurotransmission, pointing to a central origin of fatigue in Parkinson’s disease.

Atremorine in Parkinson's disease: From dopaminergic neuroprotection to pharmacogenomics

Atremorine is a novel bioproduct obtained by nondenaturing biotechnological processes from a genetic species of Vicia faba. Atremorine is a potent dopamine (DA) enhancer with powerful effects on the neuronal dopaminergic system, acting as a neuroprotective agent in Parkinson's disease (PD). Over 97% of PD patients respond to a single dose of Atremorine (5 g, p.o.) 1 h after administration. This response is gender-, time-, dose-, and genotype-dependent, with optimal doses ranging from 5 to 20 g/day, depending upon disease severity and concomitant medication. Drug-free patients show an increase in DA levels from 12.14 ± 0.34 pg/ml to 6463.21 ± 1306.90 pg/ml; and patients chronically treated with anti-PD drugs show an increase in DA levels from 1321.53 ± 389.94 pg/ml to 16,028.54 ± 4783.98 pg/ml, indicating that Atremorine potentiates the dopaminergic effects of conventional anti-PD drugs. Atremorine also influences the levels of other neurotransmitters (adrenaline, noradrenaline) and hormones which are regulated by DA (e.g., prolactin, PRL), with no effect on serotonin or histamine. The variability in Atremorine-induced DA response is highly attributable to pharmacogenetic factors. Polymorphic variants in pathogenic (SNCA, NUCKS1, ITGA8, GPNMB, GCH1, BCKDK, APOE, LRRK2, ACMSD), mechanistic (DRD2), metabolic (CYP2D6, CYP2C9, CYP2C19, CYP3A4/5, NAT2), transporter (ABCB1, SLC6A2, SLC6A3, SLC6A4) and pleiotropic genes (APOE) influence the DA response to Atremorine and its psychomotor and brain effects. Atremorine enhances DNA methylation and displays epigenetic activity via modulation of the pharmacoepigenetic network. Atremorine is a novel neuroprotective agent for dopaminergic neurons with potential prophylactic and therapeutic activity in PD.

Tetrahydrobioterin (BH4) Pathway: From Metabolism to Neuropsychiatry

Tetrahydrobipterin (BH4) is a pivotal enzymatic cofactor required for the synthesis of serotonin, dopamine and nitric oxide. BH4 is essential for numerous physiological processes at periphery and central levels, such as vascularization, inflammation, glucose homeostasis, regulation of oxidative stress and neurotransmission. BH4 de novo synthesis involves the sequential activation of three enzymes, the major controlling point being GTP cyclohydrolase I (GCH1). Complementary salvage and recycling pathways ensure that BH4 levels are tightly kept within a physiological range in the body. Even if the way of transport of BH4 and its ability to enter the brain after peripheral administration is still controversial, data showed increased levels in the brain after BH4 treatment. Available evidence shows that GCH1 expression and BH4 synthesis are stimulated by immunological factors, notably pro-inflammatory cytokines. Once produced, BH4 can act as an anti- inflammatory molecule and scavenger of free radicals protecting against oxidative stress. At the same time, BH4 is prone to autoxidation, leading to the release of superoxide radicals contributing to inflammatory processes, and to the production of BH2, an inactive form of BH4, reducing its bioavailability. Alterations in BH4 levels have been documented in many pathological situations, including Alzheimer's disease, Parkinson's disease and depression, in which increased oxidative stress, inflammation and alterations in monoaminergic function are described. This review aims at providing an update of the knowledge about metabolism and the role of BH4 in brain function, from preclinical to clinical studies, addressing some therapeutic implications.

Intranigral Administration of β-Sitosterol-β-D-Glucoside Elicits Neurotoxic A1 Astrocyte Reactivity and Chronic Neuroinflammation in the Rat Substantia Nigra

Chronic consumption of β-sitosterol-β-D-glucoside (BSSG), a neurotoxin contained in cycad seeds, leads to Parkinson's disease in humans and rodents. Here, we explored whether a single intranigral administration of BSSG triggers neuroinflammation and neurotoxic A1 reactive astrocytes besides dopaminergic neurodegeneration. We injected 6 μg BSSG/1 μL DMSO or vehicle into the left substantia nigra and immunostained with antibodies against tyrosine hydroxylase (TH) together with markers of microglia (OX42), astrocytes (GFAP, S100β, C3), and leukocytes (CD45). We also measured nitric oxide (NO), lipid peroxidation (LPX), and proinflammatory cytokines (TNF-α, IL-1β, IL-6). The Evans blue assay was used to explore the blood-brain barrier (BBB) permeability. We found that BSSG activates NO production on days 15 and 30 and LPX on day 120. Throughout the study, high levels of TNF-α were present in BSSG-treated animals, whereas IL-1β was induced until day 60 and IL-6 until day 30. Immunoreactivity of activated microglia (899.0 ± 80.20%) and reactive astrocytes (651.50 ± 11.28%) progressively increased until day 30 and then decreased to remain 251.2 ± 48.8% (microglia) and 91.02 ± 39.8 (astrocytes) higher over controls on day 120. C3(+) cells were also GFAP and S100β immunoreactive, showing they were neurotoxic A1 reactive astrocytes. BBB remained permeable until day 15 when immune cell infiltration was maximum. TH immunoreactivity progressively declined, reaching 83.6 ± 1.8% reduction on day 120. Our data show that BSSG acute administration causes chronic neuroinflammation mediated by activated microglia, neurotoxic A1 reactive astrocytes, and infiltrated immune cells. The severe neuroinflammation might trigger Parkinson's disease in BSSG intoxication.

Maillard Reaction Products and Phenolic Compounds from Roasted Peanut Flour Extracts Prevent Scopolamine-Induced Amnesia Via Cholinergic Modulation and Antioxidative Effects in Mice

Research on the beneficial effects of Maillard reaction products (MRPs) and phenolic compounds derived from roasted peanut flour on the nervous system remains insufficient. This study aimed to evaluate the effect of a 28-day oral administration of defatted peanut extract rich in MPRs and polyphenolic compounds on the cognitive impairments and oxidative injury induced by scopolamine in a mouse model. Light and dark extracts from peanut flour were prepared by heating peanuts at 187°C for two different times (8.6 and 12.7 min) and defatted using soxhlet apparatus. The mice were orally pretreated with either roasted defatted peanuts extracts (100 mg/kg) or donepezil (3 mg/kg) for 21 days. On day 19 and until day 28, mice were injected subcutaneously with water or scopolamine (1 mg/kg body weight) 15 min after roasted defatted peanuts extracts/water feeding. Mice were subsequently subjected to a battery of behavioral tests including open field locomotor activity assay, and Morris water maze test. Brain tissues were collected to measure acetylcholine, acetylcholinesterase, and oxidative parameters (glutathione and malondialdehyde). Roasted defatted peanuts (light and dark) (100 mg/kg) treatment significantly ameliorated cognitive performance and reversed the oxidative damage when compared with the scopolamine group. These data demonstrate the defatted peanuts extracts exert potent anti-amnesic effects via the modulation of cholinergic and antioxidant activities.

The effect of low dose amphetamine in rotenone-induced toxicity in a mice model of Parkinson's disease

OBJECTIVES

The effects of low dose amphetamine on oxidative stress and rotenone-induced neurotoxicity and liver injury were examined in vivo in a mice model of Parkinson's disease.

MATERIALS AND METHODS

Male mice were treated with rotenone (1.5 mg/kg, every other day for two weeks, subcutaneously). Mice received either the vehicle or amphetamine intraperitoneally at doses of 0.5, 1.0, or 2.0 mg/kg. Oxidative stress was assessed by measurement of the lipid peroxidation product malondialdehyde (MDA), nitric oxide (NO), total anti-oxidant capacity (TAC), and paraoxonase-1 (PON-1) activity in the brain and liver. In addition, brain concentrations of nuclear factor kappa B (NF-κB) and tyrosine hydroxylase were determined and histopathology and Bax/Bcl-2 immunohistochemistry were performed.

RESULTS

The levels of lipid peroxidation and NO were increased and TAC and PON-1 were decreased significantly compared with vehicle-injected control mice. There were also significantly increased NF-κB and decreased tyrosine hydroxylase in the brain following rotenone administration. These changes were significantly attenuated by amphetamine. Rotenone caused neurodegenerative changes in the substantia nigra, cerebral cortex, and hippocampus. The liver showed degenerative changes in hepatocytes and infiltration of Kupffer cells. Bax/Bcl2 ratio was significantly increased in brain and liver tissues. Amphetamine prevented these histopathological changes and the increase in apoptosis evoked by rotenone.

CONCLUSION

These results suggest that low dose amphetamine exerts anti-oxidant and anti-apoptotic effects, protects against rotenone-induced neurodegeneration, and could prevent neuronal cell degeneration in Parkinson's disease.

β-Catenin and TCFs/LEF signaling discordantly regulate IL-6 expression in astrocytes

Background

The Wnt/β-catenin signaling pathway is a prolific regulator of cell-to-cell communication and gene expression. Canonical Wnt/β-catenin signaling involves partnering of β-catenin with members of the TCF/LEF family of transcription factors (TCF1, TCF3, TCF4, LEF1) to regulate gene expression. IL-6 is a key cytokine involved in inflammation and is particularly a hallmark of inflammation in the brain. Astrocytes, specialized glial cells in the brain, secrete IL-6. How astrocytes regulate IL-6 expression is not entirely clear, although in other cells NFκB and C/EBP pathways play a role. We evaluated here the interface between β-catenin, TCFs/LEF and C/EBP and NF-κB in relation to IL-6 gene regulation in astrocytes.

Methods

We performed molecular loss and/or gain of function studies of β-catenin, TCF/LEF, NFκB, and C/EBP to assess IL-6 regulation in human astrocytes. Specifically, siRNA mediated target gene knockdown, cDNA over expression of target gene, and pharmacological agents for regulation of target proteins were used. IL-6 levels was evaluated by real time quantitative PCR and ELISA. We also cloned the IL-6 promoter under a firefly luciferase reporter and used bioinformatics, site directed mutagenesis, and chromatin immunoprecipitation to probe the interaction between β-catenin/TCFs/LEFs and IL-6 promoter activity.

Results

β-catenin binds to TCF/LEF to inhibits IL-6 while TCFs/LEF induce IL-6 transcription through interaction with ATF-2/SMADs. β-catenin independent of TCFs/LEF positively regulates C/EBP and NF-κB, which in turn activate IL-6 expression. The IL-6 promoter has two putative regions for TCFs/LEF binding, a proximal site located at -91 nt and a distal site at -948 nt from the transcription start site, both required for TCF/LEF induction of IL-6 independent of β-catenin.

Conclusion

IL-6 regulation in human astrocytes engages a discordant interaction between β-catenin and TCF/LEF. These findings are intriguing given that no role for β-catenin nor TCFs/LEF to date is associated with IL-6 regulation and suggest that β-catenin expression in astrocytes is a critical regulator of anti-inflammatory responses and its disruption can potentially mediate persistent neuroinflammation.

Effects of a Novel Psychomotor Stabilizer, IRL790, on Biochemical Measures of Synaptic Markers and Neurotransmission

The novel small-molecule psychomotor stabilizer, IRL790, is currently in clinical trial for treatment of levodopa-induced dyskinesia and psychosis in patients with Parkinson disease. Here, we used naïve mice to investigate the effects of acute systemic administration of IRL790 on protein levels and phosphorylation states of proteins relevant for synaptic plasticity and transmission. IRL790 increased pro-brain-derived neurotrophic factor protein levels and phosphorylation at Ser1303 of the N-methyl-D-aspartate (NMDA) subtype 2B glutamate receptor (NR2B) in prefrontal cortex. IRL790 also increased the phosphorylation states at Ser19, Ser31, and Ser40, respectively, of tyrosine hydroxylase in striatum. IRL790 reduced protein levels of the NR2B receptor in striatum but not in prefrontal cortex. Taken together, we report that systemically administered IRL790 rapidly elicits changes in protein level and phosphorylation state of proteins associated with a beneficial effect on synaptic markers and neurotransmission. SIGNIFICANCE STATEMENT: The novel small-molecule psychomotor stabilizer, IRL790, is currently in clinical trial for treatment of levodopa-induced dyskinesia and psychosis in patients with Parkinson disease. In this study, we report that systemically administered IRL790 rapidly elicits changes in protein level and phosphorylation state of proteins associated with a beneficial effect on synaptic markers and neurotransmission.

Sphingosine-1-Phosphate Receptors Modulators Decrease Signs of Neuroinflammation and Prevent Parkinson's Disease Symptoms in the 1-Methyl-4-Phenyl-1,2,3,6-Tetrahydropyridine Mouse Model

Sphingosine-1-phosphate (S1P) is a potent bioactive lipid mediator that acts as a natural ligand upon binding to five different receptors that are located in astrocytes, oligodendrocytes, microglial and neuronal cells. Recently, global activation of these receptors by FTY720 (fingolimod) has been suggested to provide neuroprotection in animal model of Parkinson’s disease (PD). Among S1P receptors, the subtype 1 (S1P1R) has been linked to features of neuroprotection and, using the selective agonist SEW2871, the present investigation assessed potential benefits (and mechanisms) of this receptor subtype in an established animal model of PD. We demonstrated that oral treatments with SEW2871 are able to provide protection to the same levels as FTY720 against loss of dopaminergic neurons and motor deficits in the 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) (30 mg/kg, i.p., 5 days) mouse model of PD. At the molecular level, we observed that the beneficial effects of both S1PR agonists were not associated with alterations in ERK and Akt levels, two markers of molecular adaptations in the striatum neurons. However, these compounds have the capacity to prevent signs of neuroinflammation such as the activation of astrocytes and glial cells, as well as MPTP-induced reduction of BDNF levels in key regions of the brain implicated in motor functions. These findings suggest that selective S1P1R modulation has the ability to provide neuroprotection in response to MPTP neurotoxicity. Targeting S1P1R in PD therapy may represent a prominent candidate for treatment of this neurodegenerative conditions.

BDNF as a Promising Therapeutic Agent in Parkinson's Disease

Brain-derived neurotrophic factor (BDNF) promotes neuroprotection and neuroregeneration. In animal models of Parkinson’s disease (PD), BDNF enhances the survival of dopaminergic neurons, improves dopaminergic neurotransmission and motor performance. Pharmacological therapies of PD are symptom-targeting, and their effectiveness decreases with the progression of the disease; therefore, new therapeutical approaches are needed. Since, in both PD patients and animal PD models, decreased level of BDNF was found in the nigrostriatal pathway, it has been hypothesized that BDNF may serve as a therapeutic agent. Direct delivery of exogenous BDNF into the patient’s brain did not relieve the symptoms of disease, nor did attempts to enhance BDNF expression with gene therapy. Physical training was neuroprotective in animal models of PD. This effect is mediated, at least partly, by BDNF. Animal studies revealed that physical activity increases BDNF and tropomyosin receptor kinase B (TrkB) expression, leading to inhibition of neurodegeneration through induction of transcription factors and expression of genes related to neuronal proliferation, survival, and inflammatory response. This review focuses on the evidence that increasing BDNF level due to gene modulation or physical exercise has a neuroprotective effect and could be considered as adjunctive therapy in PD.

Parkinson's Disease-Associated Changes in the Expression of Neurotrophic Factors and their Receptors upon Neuronal Differentiation of Human Induced Pluripotent Stem Cells

Parkinson's disease (PD) is a neurodegenerative pathology resulting from the degeneration of dopaminergic (DA) neurons in the substantia nigra (SN). Neurotrophic factors (NTFs) and their receptors are key regulators of the survival, differentiation, and development of neurons. However, the role of these factors in the pathogenesis of PD is still unclear. Here, we analyzed the expression of NTFs and their receptors in human induced pluripotent stem cells (iPSCs) derived from the fibroblasts of patients with PD and healthy donors (HDs). Four PD-derived iPSC lines with different mutations and three cell lines from HDs at different stages of neuronal differentiation were used for RT-qPCR analysis and ELISA. We found that the mRNA levels of most analyzed genes were altered in PD-derived cells compared with those in HD-derived cells at all stages. Importantly, irrespective of PD-associated mutations, the mRNA levels of the BDNF and GDNF genes were mostly increased or unchanged in predominantly DA terminally differentiated neurons (TDNs) compared with those in HD-derived cells. Strikingly, in contrast to BDNF and GDNF mRNA levels, BDNF and GDNF protein levels were lower in almost all PD-derived TDNs than in HD-derived cells, thus indicating the dysregulation of NTF expression at the post-transcriptional level. We suggest that this dysregulation is one of the important signs of PD development.

Computational modeling reveals multiple abnormalities of myocardial noradrenergic function in Lewy body diseases

BACKGROUND

Lewy body diseases, a family of aging-related neurodegenerative disorders, entail loss of the catecholamine dopamine in the nigrostriatal system and equally severe deficiency of the closely related catecholamine norepinephrine in the heart. The myocardial noradrenergic lesion is associated with major non-motor symptoms and decreased survival. Numerous mechanisms determine norepinephrine stores, and which of these are altered in Lewy body diseases has not been examined in an integrated way. We used a computational modeling approach to assess comprehensively pathways of cardiac norepinephrine synthesis, storage, release, reuptake, and metabolism in Lewy body diseases. Application of a novel kinetic model identified a pattern of dysfunctional steps contributing to norepinephrine deficiency. We then tested predictions from the model in a new cohort of Parkinson disease patients.

METHODS

Rate constants were calculated for 17 reactions determining intra-neuronal norepinephrine stores. Model predictions were tested by measuring post-mortem apical ventricular concentrations and concentration ratios of catechols in controls and patients with Parkinson disease.

RESULTS

The model identified low rate constants for three types of processes in the Lewy body group-catecholamine biosynthesis via tyrosine hydroxylase and L-aromatic-amino-acid decarboxylase, vesicular storage of dopamine and norepinephrine, and neuronal norepinephrine reuptake via the cell membrane norepinephrine transporter. Post-mortem catechols and catechol ratios confirmed this triad of model-predicted functional abnormalities.

CONCLUSION

Denervation-independent impairments of neurotransmitter biosynthesis, vesicular sequestration, and norepinephrine recycling contribute to the myocardial norepinephrine deficiency attending Lewy body diseases. A proportion of cardiac sympathetic nerves are "sick but not dead," suggesting targeted disease-modification strategies might retard clinical progression.

TRIAL REGISTRATION

This study was not a clinical trial.

FUNDING

The research reported here was supported by the Division of Intramural Research, NINDS.

Pyrethroid exposure and neurotoxicity: a mechanistic approach

Pyrethroids are a class of synthetic insecticides that are used widely in and around households to control the pest. Concerns about exposure to this group of pesticides are now mainly related to their neurotoxicity and nigrostriatal dopaminergic neurodegeneration seen in Parkinson’s disease. The main neurotoxic mechanisms include oxidative stress, inflammation, neuronal cell loss, and mitochondrial dysfunction. The main neurodegeneration targets are ion channels. However, other receptors, enzymes, and several signalling pathways can also participate in disorders induced by pyrethroids. The aim of this review is to elucidate the main mechanisms involved in neurotoxicity caused by pyrethroids deltamethrin, permethrin, and cypermethrin. We also review common targets and pathways of Parkinson’s disease therapy, including Nrf2, Nurr1, and PPARγ, and how they are affected by exposure to pyrethroids. We conclude with possibilities to be addressed by future research of novel methods of protection against neurological disorders caused by pesticides that may also find their use in the management/treatment of Parkinson’s disease.

Mitochondrially targeted cytochrome P450 2D6 is involved in monomethylamine-induced neuronal damage in mouse models

Parkinson's disease (PD) is a major human disease associated with degeneration of the central nervous system. Evidence suggests that several endogenously formed 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-mimicking chemicals that are metabolic conversion products, especially β-carbolines and isoquinolines, act as neurotoxins that induce PD or enhance progression of the disease. We have demonstrated previously that mitochondrially targeted human cytochrome P450 2D6 (CYP2D6), supported by mitochondrial adrenodoxin and adrenodoxin reductase, can efficiently catalyze the conversion of MPTP to the toxic 1-methyl-4-phenylpyridinium ion. In this study, we show that the mitochondrially targeted CYP2D6 can efficiently catalyze MPTP-mimicking compounds, i.e. 2-methyl-1,2,3,4-tetrahydroisoquinoline, 2-methyl-1,2,3,4-tetrahydro-β-carboline, and 9-methyl-norharmon, suspected to induce PD in humans. Our results reveal that activity and respiration in mouse brain mitochondrial complex I are significantly affected by these toxins in WT mice but remain unchanged in Cyp2d6 locus knockout mice, indicating a possible role of CYP2D6 in the metabolism of these compounds both in vivo and in vitro These metabolic effects were minimized in the presence of two CYP2D6 inhibitors, quinidine and ajmalicine. Neuro-2a cells stably expressing predominantly mitochondrially targeted CYP2D6 were more sensitive to toxin-mediated respiratory dysfunction and complex I inhibition than cells expressing predominantly endoplasmic reticulum-targeted CYP2D6. Exposure to these toxins also induced the autophagic marker Parkin and the mitochondrial fission marker Dynamin-related protein 1 (Drp1) in differentiated neurons expressing mitochondrial CYP2D6. Our results show that monomethylamines are converted to their toxic cationic form by mitochondrially directed CYP2D6 and result in neuronal degradation in mice.

Antioxidant hydrolyzed peptides from Manchurian walnut (Juglans mandshurica Maxim.) attenuate scopolamine-induced memory impairment in mice

BACKGROUND

Walnut protein, which is obtained as a by-product of oil expression, has not been used efficiently. Although walnuts are beneficial for cognitive functioning, the potential of their protein composition in strengthening learning and memory functions remains unknown. In this study, the inhibition of memory impairment by the Manchurian walnut hydrolyzed peptide (MWHP) was evaluated.

RESULTS

Small-molecular-weight MWHP (<3 kDa) achieved the optimal antioxidative activity. Therefore, MWHP (<3 kDa) was subjected to the following mice trials to evaluate its attenuation effect on memory impairment. In the Morris water maze test, MWHP shortened the total path for searching the platform, reduced the escape latency, and increased the dwelling distance and time in the coverage zone. MWHP also prolonged the latency and diminished errors in the passive avoidance response tests. These behavioral tests demonstrated that MWHP could inhibit scopolamine-induced memory impairment. MWHP improved memory by reducing oxidative stress, inhibiting apoptosis, regulating neurotransmitter functions, maintaining hippocampal CA3 pyramidal neurons, and increasing calmodulin-dependent protein kinase II levels in brain tissues.

CONCLUSION

Experimental results proved that MWHP exhibits potential in improving memory and should be used to develop novel functional food. © 2018 Society of Chemical Industry.

Preprocessing of 18F-DMFP-PET Data Based on Hidden Markov Random Fields and the Gaussian Distribution

¹⁸F-DMFP-PET is an emerging neuroimaging modality used to diagnose Parkinson's disease (PD) that allows us to examine postsynaptic dopamine D_2/3 receptors. Like other neuroimaging modalities used for PD diagnosis, most of the total intensity of ¹⁸F-DMFP-PET images is concentrated in the striatum. However, other regions can also be useful for diagnostic purposes. An appropriate delimitation of the regions of interest contained in ¹⁸F-DMFP-PET data is crucial to improve the automatic diagnosis of PD. In this manuscript we propose a novel methodology to preprocess ¹⁸F-DMFP-PET data that improves the accuracy of computer aided diagnosis systems for PD. First, the data were segmented using an algorithm based on Hidden Markov Random Field. As a result, each neuroimage was divided into 4 maps according to the intensity and the neighborhood of the voxels. The maps were then individually normalized so that the shape of their histograms could be modeled by a Gaussian distribution with equal parameters for all the neuroimages. This approach was evaluated using a dataset with neuroimaging data from 87 parkinsonian patients. After these preprocessing steps, a Support Vector Machine classifier was used to separate idiopathic and non-idiopathic PD. Data preprocessed by the proposed method provided higher accuracy results than the ones preprocessed with previous approaches.

Modafinil Improves Catalepsy in a Rat 6-Hydroxydopamine Model of Parkinson's Disease; Possible Involvement of Dopaminergic Neurotransmission

Purpose: Modafinil is a vigilance-enhancing drug licensed for narcolepsy. The use of modafinil leads to various neuromodulatory effects with very low abuse potential. A body of evidence suggested that modafinil may have anti-parkinsonian effects. This study was designed to evaluate whether modafinil could improve motor dysfunction in the 6-hydroxydopamine (6-OHDA)-induced rat model of Parkinson’s disease.

Methods: Male Wistar rats (180-220 g, n= 98) were used in this study. Parkinsonism was induced by injection of 6-hydroxydopamine (10 μg/2μl in 0.2 % ascorbic acid-saline) into the right striatum. Parkinsonian rats received intraperitoneal (ip) injections of modafinil (50, 75, and 100 mg/kg) and catalepsy-like immobility was assessed by the bar test (BT). Furthermore, involvement of dopamine D₁ and D₂ receptors in modafinil’s anti-parkinsonian effects was studied. For this purpose, parkinsonian animals were pretreated with SCH23390 and raclopride (the dopamine D₁ and D₂ receptor anatgonists, respectively) or SCH23390 + raclopride, and then assessed by the BT.

Results: Modafinil (100 mg/kg) showed anti-cataleptic effects in the BT. Notably, the effect of modafinil in the BT was reversed in parkinsonian rats pretreated with raclopride (1.25 mg/kg) and/or SCH23390 + raclopride (0.75 and 1.25 mg/kg, respectively), but not in those pretreated with SCH23390 (0.75 mg/kg).

Conclusion: Acute administration of modafinil improves 6-OHDA-induced motor impairment possibly through activation of dopamine D₂ receptors.

Parkinson's Disease: From Pathogenesis to Pharmacogenomics

Parkinson's disease (PD) is the second most important age-related neurodegenerative disorder in developed societies, after Alzheimer's disease, with a prevalence ranging from 41 per 100,000 in the fourth decade of life to over 1900 per 100,000 in people over 80 years of age. As a movement disorder, the PD phenotype is characterized by rigidity, resting tremor, and bradykinesia. Parkinson's disease -related neurodegeneration is likely to occur several decades before the onset of the motor symptoms. Potential risk factors include environmental toxins, drugs, pesticides, brain microtrauma, focal cerebrovascular damage, and genomic defects. Parkinson's disease neuropathology is characterized by a selective loss of dopaminergic neurons in the substantia nigra pars compacta, with widespread involvement of other central nervous system (CNS) structures and peripheral tissues. Pathogenic mechanisms associated with genomic, epigenetic and environmental factors lead to conformational changes and deposits of key proteins due to abnormalities in the ubiquitin-proteasome system together with dysregulation of mitochondrial function and oxidative stress. Conventional pharmacological treatments for PD are dopamine precursors (levodopa, l-DOPA, l-3,4 dihidroxifenilalanina), and other symptomatic treatments including dopamine agonists (amantadine, apomorphine, bromocriptine, cabergoline, lisuride, pergolide, pramipexole, ropinirole, rotigotine), monoamine oxidase (MAO) inhibitors (selegiline, rasagiline), and catechol-O-methyltransferase (COMT) inhibitors (entacapone, tolcapone). The chronic administration of antiparkinsonian drugs currently induces the "wearing-off phenomenon", with additional psychomotor and autonomic complications. In order to minimize these clinical complications, novel compounds have been developed. Novel drugs and bioproducts for the treatment of PD should address dopaminergic neuroprotection to reduce premature neurodegeneration in addition to enhancing dopaminergic neurotransmission. Since biochemical changes and therapeutic outcomes are highly dependent upon the genomic profiles of PD patients, personalized treatments should rely on pharmacogenetic procedures to optimize therapeutics.

Anti-inflammatory and neuroprotective activity of boswellic acids in rotenone parkinsonian rats

There is evidence that inflammation and oxidative stress contribute to the neurodegenerative changes observed in Parkinson's disease. Unfortunately, there is a lack of curative treatment for this debilitating movement disorder. Boswellic acids (BAs) are pentacyclic triterpene molecules of plant origin that have been utilized for treating many inflammatory conditions. The current study was conducted to explore the protective role of BAs against rotenone-induced experimental parkinsonism. Twenty-four rats were assigned to one of four treatment groups. The first two groups were a vehicle group (no rotenone) and a rotenone control group in which rats received rotenone (1 mg/kg) every 48 h. The next 2 groups received rotenone (1 mg/kg every 48 h) plus protective oral doses of BAs (125 or 250 mg/kg daily). Rats in the rotenone group showed motor dysfunction when tested in the open-field arena and cylinder and rotarod tests. Moreover, inflammatory markers increased, whereas the dopamine level was lower in the striata of rats in the rotenone group versus those in the vehicle group. BAs taken by rats with rotenone-induced parkinsonism showed enhanced general motor performance, reduced inflammatory markers, and increased striatal dopamine level and nigral tyrosine hydroxylase immunostaining. In conclusion, BAs are promising agents in slowing the progression of Parkinson's disease if appropriate data become available about their safety and efficacy in humans.

Depletion of AADC activity in caudate nucleus and putamen of Parkinson's disease patients; implications for ongoing AAV2-AADC gene therapy trial

In Parkinson’s disease (PD), aromatic L-amino acid decarboxylase (AADC) is the rate-limiting enzyme in the conversion of L-DOPA (Sinemet) to dopamine (DA). Previous studies in PD animal models demonstrated that lesion of dopaminergic neurons is associated with profound loss of AADC activity in the striatum, blocking efficient conversion of L-DOPA to DA. Relatively few studies have directly analyzed AADC in PD brains. Thus, the aim of this study was to gain a better understanding of regional changes in AADC activity, DA, serotonin and their monoamine metabolites in the striatum of PD patients and experimentally lesioned animals (rat and MPTP-treated nonhuman primate, NHP). Striatal AADC activity was determined post mortem in neuropathologically confirmed PD subjects, animal models and controls. A regional analysis was performed for striatal AADC activity and monoamine levels in NHP tissue. Interestingly, analysis of putaminal AADC activity revealed that control human striatum contained much less AADC activity than rat and NHP striata. Moreover, a dramatic loss of AADC activity in PD striatum compared to controls was detected. In MPTP-treated NHP, caudate nucleus was almost as greatly affected as putamen, although mean DA turnover was higher in caudate nucleus. Similarly, DA and DA metabolites were dramatically reduced in different regions of PD brains, including caudate nucleus, whereas serotonin was relatively spared. After L-DOPA administration in MPTP-treated NHP, very poor conversion to DA was detected, suggesting that AADC in NHP nigrostriatal fibers is mainly responsible for L-DOPA to DA conversion. These data support further the rationale behind viral gene therapy with AAV2-hAADC to restore AADC levels in putamen and suggest further the advisability of expanding vector delivery to include coverage of anterior putamen and the caudate nucleus.

Gene therapy approaches in the non-human primate model of Parkinson's disease

The field of gene therapy has recently witnessed a number of major conceptual changes. Besides the traditional thinking that comprises the use of viral vectors for the delivery of a given therapeutic gene, a number of original approaches have been recently envisaged, focused on using vectors carrying genes to further modify basal ganglia circuits of interest. It is expected that these approaches will ultimately induce a therapeutic potential being sustained by gene-induced changes in brain circuits. Among others, at present, it is technically feasible to use viral vectors to (1) achieve a controlled release of neurotrophic factors, (2) conduct either a transient or permanent silencing of any given basal ganglia circuit of interest, (3) perform an in vivo cellular reprogramming by promoting the conversion of resident cells into dopaminergic-like neurons, and (4) improving levodopa efficacy over time by targeting aromatic L-amino acid decarboxylase. Furthermore, extensive research efforts based on viral vectors are currently ongoing in an attempt to better replicate the dopaminergic neurodegeneration phenomena inherent to the progressive intraneuronal aggregation of alpha-synuclein. Finally, a number of incoming strategies will soon emerge over the horizon, these being sustained by the underlying goal of promoting alpha-synuclein clearance, such as, for instance, gene therapy initiatives based on increasing the activity of glucocerebrosidase. To provide adequate proof-of-concept on safety and efficacy and to push forward true translational initiatives based on these different types of gene therapies before entering into clinical trials, the use of non-human primate models undoubtedly plays an instrumental role.

Perspective on the Road toward Gene Therapy for Parkinson's Disease

Many therapeutic strategies aimed at relieving symptoms of Parkinson’s disease (PD) are currently used for treatment of this disease. With a hallmark of progressive degeneration of dopaminergic neurons, the absence of properly operational dopaminergic circuitry becomes a therapeutic target. Following diagnosis, dopamine replacement can be given in the form of L-DOPA (L-3,4-dihydroxyphenylalanine). Even though it is recognized as standard of care, this treatment strategy does not prevent the affected neurons from degenerating. Therefore, studies have been performed using gene therapy (GT) to make dopamine (DA) available from within the brain using an artificial DA circuitry. One approach is to administer a GT aimed at delivering the key enzymes for DA synthesis using a lentiviral vector system (Palfi et al., 2014). A similar approach has been investigated with adeno-associated virus (AAV) expressing aromatic L-amino acid decarboxylase, tyrosine hydroxylase, and GTP-cyclohydrolase I (Bankiewicz et al., 2000), which are downregulated in PD. Another GT approach to mitigate symptoms of PD used AAV-mediated delivery of GAD-67 (glutamate decarboxylase) (Kaplitt et al., 2007). This approach mimics the inhibitory effect of DA neurons on their targets, in reducing motor abnormalities. Finally, disease modifying strategies have been undertaken using neurotrophic factors such as neurturin (NTN) (Marks et al., 2008; Bartus et al., 2013a) or are ongoing with the closely related Glial cell line-derived neurotrophic factor. Those approaches are aiming at rescuing the degenerating neurons. All of the above mentioned strategies have their own merits, but also some disadvantages. So far, none of clinical applied GT studies has resulted in significant clinical benefit, although some clinical studies are ongoing and results are expected over the next few years.

Neurotrophic factors in Alzheimer's and Parkinson's diseases: implications for pathogenesis and therapy

Neurotrophic factors comprise essential secreted proteins that have several functions in neural and non-neural tissues, mediating the development, survival and maintenance of peripheral and central nervous system. Therefore, neurotrophic factor issue has been extensively investigated into the context of neurodegenerative diseases. Alzheimer's disease and Parkinson's disease show changes in the regulation of specific neurotrophic factors and their receptors, which appear to be critical for neuronal degeneration. Indeed, neurotrophic factors prevent cell death in degenerative processes and can enhance the growth and function of affected neurons in these disorders. Based on recent reports, this review discusses the main findings related to the neurotrophic factor support – mainly brain-derived neurotrophic factor and glial cell line-derived neurotrophic factor – in the survival, proliferation and maturation of affected neurons in Alzheimer's disease and Parkinson's disease as well as their putative application as new therapeutic approach for these diseases management.

Asiatic acid attenuated apoptotic and inflammatory stress in the striatum of MPTP-treated mice

The effects of post-treatments with asiatic acid (AA) at 20, 40 or 80 mg per kg BW per day against apoptotic, oxidative and inflammatory injury in the striatum of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-treated mice were examined. The results showed that AA supplements at 40 and 80 mg per kg BW per day increased AA deposit in the striatum, increased glutathione content and decreased reactive oxygen species production in the striatum. AA supplements at 20-80 mg per kg BW per day dose-dependently lowered striatal levels of nitric oxide, 3-nitrotyrosine, interleukin (IL)-1beta, IL-6, tumor necrosis factor-alpha and prostaglandin E2. AA supplements at 40 and 80 mg per kg BW per day down-regulated striatal p47(phox) and gp91(phox) expression; but, at three test doses suppressed striatal expression of inducible nitric oxide synthase and cyclooxygenase-2. AA post-treatments at 40 and 80 mg per kg BW per day enhanced Bcl-2 expression, and lowered Bax, apoptosis-inducing factor and caspase-3 expression in the striatum. AA at 20-80 mg per kg BW per day up-regulated striatal tyrosine hydroxylase expression, and suppressed Toll-like receptors (TLR)2 and nuclear factor kappa B p65 expression. AA treatments at 40 and 80 mg per kg BW per day decreased striatal expression of α-synuclein and TLR4, increased striatal levels of dopamine, brain-derived nerve growth factor and glial cell line-derived neurotrophic factor. These novel findings suggest that asiatic acid is a potent nutraceutical agent against the progression of Parkinson's disease.

Determinants of denervation-independent depletion of putamen dopamine in Parkinson's disease and multiple system atrophy

BACKGROUND

Severe putamen dopamine depletion characterizes Parkinson's disease (PD) and multiple system atrophy (MSA). The extent of the depletion is greater than can be accounted for by loss of nigrostriatal dopaminergic terminals alone. We used putamen tissue levels and ratios of cysteinyl and parent catechols to explore possible denervation-independent abnormalities of dopamine synthesis and fate in PD and MSA. 5-S-Cysteinyldopa (Cys-DOPA) is produced from spontaneous oxidation of DOPA and 5-S-cysteinyldopamine (Cys-DA) from spontaneous oxidation of DA.

METHODS

Post-mortem putamen tissue samples from 17 PD and 25 MSA patients and 30 controls were assayed for endogenous catechols including DA, its cytoplasmic metabolites (Cys-DA, 3,4-dihydroxyphenylacetic acid, 3,4-dihydroxyphenylethanol, and 3,4-dihydroxyphenylacetaldehyde), and tyrosine hydroxylation products proximal to DA (DOPA and Cys-DOPA).

RESULTS

The PD and MSA groups did not differ in mean values of parent or cysteinyl catechols, and the data for the two groups were lumped. In the patients an index of vesicular storage of DA (the ratio of DA to the sum of its cytoplasmic metabolites) averaged 54% of control (p = 0.001), and an index of L-aromatic-amino-acid decarboxylase (LAAAD) activity (the ratio of DA and the sum of its cytoplasmic metabolites to the sum of DOPA + Cys-DOPA) averaged 21% of control (p < 0.0001). An index of innervation (the sum of DOPA + Cys-DOPA) averaged 63% of control (p = 0.01).

INTERPRETATION

Based on patterns of parent and cysteinyl catechols in putamen, PD and MSA involve decreased vesicular uptake and decreased LAAAD activity in the residual dopaminergic terminals. The combination seems to contribute importantly to dopamine depletion in these diseases.

Tyrosine hydroxylase (TH), its cofactor tetrahydrobiopterin (BH4), other catecholamine-related enzymes, and their human genes in relation to the drug and gene therapies of Parkinson's disease (PD): historical overview and future prospects

Tyrosine hydroxylase (TH), which was discovered at the National Institutes of Health (NIH) in 1964, is a tetrahydrobiopterin (BH4)-requiring monooxygenase that catalyzes the first and rate-limiting step in the biosynthesis of catecholamines (CAs), such as dopamine, noradrenaline, and adrenaline. Since deficiencies of dopamine and noradrenaline in the brain stem, caused by neurodegeneration of dopamine and noradrenaline neurons, are mainly related to non-motor and motor symptoms of Parkinson's disease (PD), we have studied human CA-synthesizing enzymes [TH; BH4-related enzymes, especially GTP-cyclohydrolase I (GCH1); aromatic L-amino acid decarboxylase (AADC); dopamine β-hydroxylase (DBH); and phenylethanolamine N-methyltransferase (PNMT)] and their genes in relation to PD in postmortem brains from PD patients, patients with CA-related genetic diseases, mice with genetically engineered CA neurons, and animal models of PD. We purified all human CA-synthesizing enzymes, produced their antibodies for immunohistochemistry and immunoassay, and cloned all human genes, especially the human TH gene and the human gene for GCH1, which synthesizes BH4 as a cofactor of TH. This review discusses the historical overview of TH, BH4-, and other CA-related enzymes and their genes in relation to the pathophysiology of PD, the development of drugs, such as L-DOPA, and future prospects for drug and gene therapy for PD, especially the potential of induced pluripotent stem (iPS) cells.

Early life exposure to permethrin: a progressive animal model of Parkinson's disease

INTRODUCTION

Oxidative stress, alpha-synuclein changes, mitochondrial complex I defects and dopamine loss, observed in the striatum of rats exposed to the pesticide permethrin in early life, could represent neuropathological hallmarks of Parkinson's disease (PD). Nevertheless, an animal model of PD should also fulfill criteria of face and predictive validities. This study was designed to: 1) verify dopaminergic status in the striatum and substantia nigra pars compacta; 2) recognize non-motor symptoms; 3) investigate the time-course development of motor disabilities; 4) assess L-Dopa effectiveness on motor symptoms in rats previously exposed to permethrin in early life.

METHODS

The permethrin-treated group received 34mg/kg daily of permethrin from postnatal day 6 to 21, whereas the age-matched control group was administered with the vehicle only.

RESULTS

At adolescent age, the permethrin-treated group showed decreased levels of dopamine in the striatum, loss of dopaminergic neurons in the substantia nigra pars compacta and cognitive impairments. Motor coordination defects appeared at adult age (150days old) in permethrin-treated rats on rotarod and beam walking tasks, whereas no differences between the treated and control groups were detected on the foot print task. Predictive validity was evaluated by testing the ability of L-Dopa (5, 10 or 15mg/kg, os) to restore the postural instability in permethrin-treated rats (150days old) tested in a beam walking task. The results revealed full reversal of motor deficits starting from 10mg/kg of L-Dopa.

DISCUSSION

The overall results indicate that this animal model replicates the progressive, time-dependent nature of the neurodegenerative process in Parkinson's disease.

Oxidative stress and mitochondrial dysfunction are the underlying events of dopaminergic neurodegeneration in homocysteine rat model of Parkinson's disease

Homocysteine (Hcy) when injected intranigrally in rat caused parkinsonian behavioural phenotypes and loss of nigral dopaminergic neurons but the underlying mechanisms of neurotoxicity remains elusive. In the present study, we focused on oxidative stress as one of the mechanisms of neurotoxicity in Hcy-induced hemiparkinsonian rat model. Unilateral intranigral infusion of Hcy (1.0 μmol in 2 μl) caused inhibition of mitochondrial complex-I activity, decrease in the level of striatal dopamine, loss of midbrain dopaminergic neurons, and motor abnormalities. Hcy caused oxidative stress in the nigrostriatal pathway, with increase in generation of hydroxyl radicals, depletion in the level of reduced glutathione and enhanced activity of antioxidant enzymes (superoxide dismutase and catalase). Our results provided the evidence of critical involvement of oxidative stress as one of the mechanisms underlying Hcy-induced dopaminergic neurotoxicity in nigrostriatal pathway. As oxidative stress is one of the prime mechanisms of neurodegeneration in different animal models of Parkinson's disease, and since Hcy caused equivalent parkinsonian pathologies in rat model, the present study proclaims Hcy-induced rat model as a viable rodent model of Parkinson's disease.

Elevated cerebrospinal fluid ratios of cysteinyl-dopamine/3,4-dihydroxyphenylacetic acid in parkinsonian synucleinopathies

INTRODUCTION

There is intense interest in identifying cerebrospinal fluid (CSF) biomarkers of Parkinson's disease (PD), both for early diagnosis and to track effects of putative treatments. Nigrostriatal dopamine depletion characterizes PD. Predictably, CSF levels of 3,4-dihydroxyphenylacetic acid (DOPAC), the main neuronal metabolite of dopamine, are decreased in PD, even in patients with recent onset of the movement disorder. Whether low CSF DOPAC is associated specifically with parkinsonism has been unclear. In the neuronal cytoplasm dopamine undergoes not only enzymatic oxidation to form DOPAC but also spontaneous oxidation to form 5-S-cysteinyl-dopamine (Cys-DA). Theoretically, oxidative stress or decreased activity of aldehyde dehydrogenase (ALDH) in the residual nigrostriatal dopaminergic neurons would increase CSF Cys-DA levels with respect to DOPAC levels. PD, parkinsonian multiple system atrophy (MSA-P), and pure autonomic failure (PAF) are synucleinopathies; however, PAF does not entail parkinsonism. We examined whether an elevated Cys-DA/DOPAC ratio provides a specific biomarker of parkinsonism in synucleinopathy patients.

METHODS

CSF catechols were assayed in PD (n = 24), MSA-P (n = 32), PAF (n = 18), and control subjects (n = 32).

RESULTS

Compared to controls, CSF DOPAC was decreased in PD and MSA-P (p < 0.0001 each). In both diseases Cys-DA/DOPAC ratios averaged more than twice control (0.14 ± 0.02 and 0.13 ± 0.02 vs. 0.05 ± 0.01, p < 0.0001 each), whereas in PAF the mean Cys-DA/DOPAC ratio was normal (0.05 ± 0.01).

CONCLUSIONS

CSF Cys-DA/DOPAC ratios are substantially increased in PD and MSA-P and are normal in PAF. Thus, in synucleinopathies an elevated CSF Cys-DA/DOPAC ratio seems to provide a specific biomarker of parkinsonism.

Estrogen modulation of calretinin and BDNF expression in midbrain dopaminergic neurons of ovariectomised mice

Estrogen attenuates the loss of dopamine neurons from the substantia nigra in animal models of Parkinson's disease (PD) and excitatory amino-acid induced neurotoxicity by interactions with brain-derived neurotrophic factor (BDNF), and calretinin (CR) containing dopaminergic (DA) neurons. To examine this interaction more closely, we treated the ovariectomised (OVX) mice with estrodial for 10days, and compared these mice to those OVX mice injected with the vehicle or control mice. Estrogen treatment in OVX mice had significantly more tyrosine hydroxylase (TH) positive neurons in the substantia nigra pars compacta (SNpc). Dopamine transporter (DAT) mRNA and BDNF mRNA levels in the midbrain were also significantly increased by estrogen treatment (P<0.05). OVX markedly decreased the number of TH/CR double stained cells in the SNpc (P<0.05), a trend which could be reversed by estrogen treatment. However, the number of GFAP positive cells in the substantia nigra did not show significant changes (P >0.05) after vehicle or estrodial treatment. Furthermore, we found that estrogen treatment abrogated the OVX-induced decrease in the phosphorylated AKT (p-AKT), but not p-ERK. We hypothesize that short-term treatment with estrogen confers neuroprotection to DA neurons by increasing CR in the DA neurons and BDNF in the midbrain, which possibly related to activation of the PI3K/Akt signaling pathway.

Genetic and Transcriptomic Profiles of Inflammation in Neurodegenerative Diseases: Alzheimer, Parkinson, Creutzfeldt-Jakob and Tauopathies

Polymorphisms in certain inflammatory-related genes have been identified as putative differential risk factors of neurodegenerative diseases with abnormal protein aggregates, such as sporadic Alzheimer’s disease (AD) and sporadic Parkinson’s disease (sPD). Gene expression studies of cytokines and mediators of the immune response have been made in post-mortem human brain samples in AD, sPD, sporadic Creutzfeldt-Jakob disease (sCJD) subtypes MM1 and VV2, Pick’s disease (PiD), progressive supranuclear palsy (PSP) and frontotemporal lobar degeneration linked to mutation P301L in MAPT Frontotemporal lobar degeneration-tau (FTLD-tau). The studies have disclosed variable gene regulation which is: (1) disease-dependent in the frontal cortex area 8 in AD, sPD, sCJD MM1 and VV2, PiD, PSP and FTLD-tau; (2) region-dependent as seen when comparing the entorhinal cortex, orbitofrontal cortex, and frontal cortex area 8 (FC) in AD; the substantia nigra, putamen, FC, and angular gyrus in PD, as well as the FC and cerebellum in sCJD; (3) genotype-dependent as seen considering sCJD MM1 and VV2; and (4) stage-dependent as seen in AD at different stages of disease progression. These observations show that regulation of inflammation is much more complicated and diverse than currently understood, and that new therapeutic approaches must be designed in order to selectively act on specific targets in particular diseases and at different time points of disease progression.

Converging mediators from immune and trophic pathways to identify Parkinson disease dementia

Objective:

To identify a panel of peripheral inflammatory/immune mediators that could discriminate Parkinson disease with dementia (PDD) from Parkinson disease (PD) without dementia.

Methods:

Plasma samples from 52 patients with PD and 22 patients with PDD were prepared from freshly collected blood following an institutional review board–approved protocol. A total of 160 proteins were measured using a multiplex antibody array. Plasma α-synuclein levels were analyzed by an electrochemiluminescence immunoassay. The main objective of the statistical analyses was to identify PDD discriminants using the plasma protein profile alone or in combination with age.

Results:

The PD and PDD groups differed significantly in cognitive measurements (Mini-Mental State Examination, Auditory Verbal Learning Test-A7, and Clinical Dementia Rating) and age. The age-adjusted levels of thymus and activation-regulated chemokine (TARC) and platelet-derived growth factor (PDGF)-AA were significantly different between disease groups. The levels of plasma α-synuclein significantly correlated with 26 proteins; among them, PDGF-BB, TARC, PDGF-AA, and epidermal growth factor were the highest. Linear discriminant analysis with leave-one-out cross-validation identified a 14-protein panel with age as discriminants of PDD (96% sensitivity, 89% specificity, area under the curve = 0.9615).

Conclusions:

We showed that multiple proteins that are mediators of growth/trophic and immune response-related pathways had discriminatory power for identifying PDD in patients with PD. Validation of this discovery-based study in longitudinal population-based studies is warranted.

Classification of evidence:

This study provides Class III evidence that a 14-protein panel plasma assay combined with age has a sensitivity of 96% and a specificity of 89% for PDD.