Neuroprotective Effects of Metallothionein Against Rotenone-Induced Myenteric Neurodegeneration in Parkinsonian Mice

Enteric neuroprotection-A matter of balancing redox potentials, limiting inflammation, and boosting resilience

The enteric nervous system (ENS) orchestrates intricate and autonomous functions throughout the gastrointestinal (GI) tract. Disruptions in ENS function are associated GI disorders. This mini review focuses on the past decade's research, utilizing rodent models, with an emphasis on protecting enteric neurons from loss. The review specifically looks at efforts to reduce oxidative stress, limit inflammation, and enhance neuronal resilience. Protective interventions including administration of antioxidants and compounds targeting cellular redox buffer systems, are evaluated for their effectiveness in preventing loss of enteric neurons in the ischemia-reperfusion model and streptozotocin-induced diabetes model. Interventions such as engrafting mesenchymal stem cells and targeting inflammatory signaling pathways in enteric neurons and glial cells are evaluated in inflammatory bowel disease models including the Winnie mouse, DSS-, and DNBS/TNBS-induced colitis models. The review also touches upon neuronal resilience, particularly in the context of Parkinson's disease models. Including estrogen's neuroprotective role, and the influence of metal ions on enteric neuronal protection. Understanding the dynamic interplay within the ENS and its role in disease pathogenesis holds promise for developing targeted therapies to effectively manage and treat various GI ailments.

From the Gut to the Brain: The Role of Enteric Glial Cells and Their Involvement in the Pathogenesis of Parkinson's Disease

The brain-gut axis has been identified as an important contributor to the physiopathology of Parkinson's disease. In this pathology, inflammation is thought to be driven by the damage caused by aggregation of α-synuclein in the brain. Interestingly, the Braak's theory proposes that α-synuclein misfolding may originate in the gut and spread in a "prion-like" manner through the vagus nerve into the central nervous system. In the enteric nervous system, enteric glial cells are the most abundant cellular component. Several studies have evaluated their role in Parkinson's disease. Using samples obtained from patients, cell cultures, or animal models, the studies with specific antibodies to label enteric glial cells (GFAP, Sox-10, and S100β) seem to indicate that activation and reactive gliosis are associated to the neurodegeneration produced by Parkinson's disease in the enteric nervous system. Of interest, Toll-like receptors, which are expressed on enteric glial cells, participate in the triggering of immune/inflammatory responses, in the maintenance of intestinal barrier integrity and in the configuration of gut microbiota; thus, these receptors might contribute to Parkinson's disease. External factors like stress also seem to be relevant in its pathogenesis. Some authors have studied ways to reverse changes in EGCs with interventions such as administration of Tryptophan-2,3-dioxygenase inhibitors, nutraceuticals, or physical exercise. Some researchers point out that beyond being activated during the disease, enteric glial cells may contribute to the development of synucleinopathies. Thus, it is still necessary to further study these cells and their role in Parkinson's disease.

Dyshomeostasis of Iron and Its Transporter Proteins in Cypermethrin-Induced Parkinson's Disease

The etiology of Parkinson's disease (PD) is highly complex and is still indefinable. However, a number of studies have indicated the involvement of pesticides and transition metals. Copper, magnesium, iron, and zinc have emerged as important metal contributors. Exposure to pesticides causes an accumulation of transition metals in the substantia nigra (SN) region of the brain. The cypermethrin model of PD is characterized by mitochondrial dysfunction, autophagy impairment, oxidative stress, etc. However, the effect of cypermethrin on metal homeostasis is not yet explored. The study was designed to delineate the role of metals and their transporter proteins in cypermethrin-induced animal and cellular models of PD. The level of copper, magnesium, iron, and zinc was checked in the nigrostriatal tissue and serum by atomic absorption spectroscopy. Since cypermethrin consistently increased iron content in the nigrostriatal tissue and serum after 12 weeks of exposure, the level of iron transporter proteins, such as divalent metal transporter-1 (DMT-1), ceruloplasmin, transferrin, ferroportin, and hepcidin, and their in silico interaction with cypermethrin were checked. 3,3'-Diaminobenzidine-enhanced Perl's staining showed an elevated number of iron-positive cells in the SN of cypermethrin-treated rats. Molecular docking studies revealed a strong binding affinity between cypermethrin and iron transporter protein receptors of humans and rats. Furthermore, cypermethrin increased the expression of DMT-1 and hepcidin while reducing the expression of transferrin, ceruloplasmin, and ferroportin in the nigrostriatal tissue and human neuroblastoma cells. These observations suggest that cypermethrin alters the expression of iron transporter proteins leading to iron dyshomeostasis, which could contribute to dopaminergic neurotoxicity.

Multi-OMIC analysis of Huntington disease reveals a neuroprotective astrocyte state

Huntington disease (HD) is an incurable neurodegenerative disease characterized by neuronal loss and astrogliosis. One hallmark of HD is the selective neuronal vulnerability of striatal medium spiny neurons. To date, the underlying mechanisms of this selective vulnerability have not been fully defined. Here, we employed a multi-omic approach including single nucleus RNAseq (snRNAseq), bulk RNAseq, lipidomics, HTT gene CAG repeat length measurements, and multiplexed immunofluorescence on post-mortem brain tissue from multiple brain regions of HD and control donors. We defined a signature of genes that is driven by CAG repeat length and found it enriched in astrocytic and microglial genes. Moreover, weighted gene correlation network analysis showed loss of connectivity of astrocytic and microglial modules in HD and identified modules that correlated with CAG-repeat length which further implicated inflammatory pathways and metabolism. We performed lipidomic analysis of HD and control brains and identified several lipid species that correlate with HD grade, including ceramides and very long chain fatty acids. Integration of lipidomics and bulk transcriptomics identified a consensus gene signature that correlates with HD grade and HD lipidomic abnormalities and implicated the unfolded protein response pathway. Because astrocytes are critical for brain lipid metabolism and play important roles in regulating inflammation, we analyzed our snRNAseq dataset with an emphasis on astrocyte pathology. We found two main astrocyte types that spanned multiple brain regions; these types correspond to protoplasmic astrocytes, and fibrous-like - CD44-positive, astrocytes. HD pathology was differentially associated with these cell types in a region-specific manner. One protoplasmic astrocyte cluster showed high expression of metallothionein genes, the depletion of this cluster positively correlated with the depletion of vulnerable medium spiny neurons in the caudate nucleus. We confirmed that metallothioneins were increased in cingulate HD astrocytes but were unchanged or even decreased in caudate astrocytes. We combined existing genome-wide association studies (GWAS) with a GWA study conducted on HD patients from the original Venezuelan cohort and identified a single-nucleotide polymorphism in the metallothionein gene locus associated with delayed age of onset. Functional studies found that metallothionein overexpressing astrocytes are better able to buffer glutamate and were neuroprotective of patient-derived directly reprogrammed HD MSNs as well as against rotenone-induced neuronal death in vitro. Finally, we found that metallothionein-overexpressing astrocytes increased the phagocytic activity of microglia in vitro and increased the expression of genes involved in fatty acid binding. Together, we identified an astrocytic phenotype that is regionally-enriched in less vulnerable brain regions that can be leveraged to protect neurons in HD.

Multifunctional Metallothioneins as a Target for Neuroprotection in Parkinson's Disease

Parkinson's disease (PD) is characterized by motor symptoms based on a loss of nigrostriatal dopaminergic neurons and by non-motor symptoms which precede motor symptoms. Neurodegeneration accompanied by an accumulation of α-synuclein is thought to propagate from the enteric nervous system to the central nervous system. The pathogenesis in sporadic PD remains unknown. However, many reports indicate various etiological factors, such as oxidative stress, inflammation, α-synuclein toxicity and mitochondrial impairment, drive neurodegeneration. Exposure to heavy metals contributes to these etiopathogenesis and increases the risk of developing PD. Metallothioneins (MTs) are cysteine-rich metal-binding proteins; MTs chelate metals and inhibit metal-induced oxidative stress, inflammation and mitochondrial dysfunction. In addition, MTs possess antioxidative properties by scavenging free radicals and exert anti-inflammatory effects by suppression of microglial activation. Furthermore, MTs recently received attention as a potential target for attenuating metal-induced α-synuclein aggregation. In this article, we summarize MTs expression in the central and enteric nervous system, and review protective functions of MTs against etiopathogenesis in PD. We also discuss neuroprotective strategies for the prevention of central dopaminergic and enteric neurodegeneration by targeting MTs. This review highlights multifunctional MTs as a target for the development of disease-modifying drugs for PD.

Ginkgo biloba protects striatal neurodegeneration and gut phagoinflammatory damage in rotenone-induced mice model of Parkinson's disease: Role of executioner caspase-3/Nrf2/ARE signaling

Asymptomatic and early clinical stages of Parkinson's disease (PD) have been linked with comorbid non-motor symptoms including dysfunction of the gastrointestinal (GI) tract. Notwithstanding, neuroprotective and gastroprotective effects of Ginkgo biloba supplements (GBS) have been investigated independently. Hence, whether GBS-mediated GIT-protective capacity could be helpful in PD via gut-brain anti-inflammatory signaling still remains unknown. Treatment with GBS significantly repressed the motor behavioral and neuromuscular deficits and prevented loss of striatal dopaminergic loss by improving the level of tyrosine hydroxylase enzyme and suppressing synucleinopathy development. Striatal neurons and ileal epithelial injury following intraperitoneal rotenone administration were accompanied with oxidoinflammatory/nitroinflammatory stress and marked inhibition of cholinergic transmission. Moreover, there was increased striatal executioner caspase-3 and decreased nuclear factor erythroid-2-related factor 2 (Nrf2) immunoexpression, loss of striatal pyramidal neuron with a marked decrease in length and width of the dendritic spines as well as significant hyperplasia of cryptal cells in the ileal epithelial tissues, all which were reversed by the pretreatment + concurrent (Pre-CONC) and concurrent (CONC) GBS treatment pattern. In sum, we proved the potential dual effects of GBS in preventing both dopaminergic neural-related impairments and gut wall abnormalities linked with PD.

Azepine-Indole Alkaloids From Psychotria nemorosa Modulate 5-HT2A Receptors and Prevent in vivo Protein Toxicity in Transgenic Caenorhabditis elegans

Nemorosine A (1) and fargesine (2), the main azepine-indole alkaloids of Psychotria nemorosa, were explored for their pharmacological profile on neurodegenerative disorders (NDs) applying a combined in silico–in vitro–in vivo approach. By using 1 and 2 as queries for similarity-based searches of the ChEMBL database, structurally related compounds were identified to modulate the 5-HT_2A receptor; in vitro experiments confirmed an agonistic effect for 1 and 2 (24 and 36% at 10 μM, respectively), which might be linked to cognition-enhancing properties. This and the previously reported target profile of 1 and 2, which also includes BuChE and MAO-A inhibition, prompted the evaluation of these compounds in several Caenorhabditis elegans models linked to 5-HT modulation and proteotoxicity. On C. elegans transgenic strain CL4659, which expresses amyloid beta (Aβ) in muscle cells leading to a phenotypic paralysis, 1 and 2 reduced Aβ proteotoxicity by reducing the percentage of paralyzed worms to 51%. Treatment of the NL5901 strain, in which α-synuclein is yellow fluorescent protein (YFP)-tagged, with 1 and 2 (10 μM) significantly reduced the α-synuclein expression. Both alkaloids were further able to significantly extend the time of metallothionein induction, which is associated with reduced neurodegeneration of aged brain tissue. These results add to the multitarget profiles of 1 and 2 and corroborate their potential in the treatment of NDs.

The effects of metallothionein in paraquat-induced Parkinson disease model of zebrafish

INTRODUCTION

Parkinson's disease (PD) is the second most common neurodegenerative disease caused by selective degeneration of dopaminergic neurons in the substantia nigra. Metallothionein has been shown to act as a neuroprotectant in various brain injury. Thus, this study aims to identify the effects of full-length human metallothionein 2 peptide (hMT2) in paraquat-induced brain injury in the zebrafish.

METHODOLOGY

A total of 80 adult zebrafish were divided into 4 groups namely control, paraquat-treated, pre-hMT2-treated, and post-hMT2-treated groups. Fish were treated with paraquat intraperitoneally every 3 days for 15 days. hMT2 were injected intracranially on day 0 (pre-treated group) and day 16 (post-treated group). Fish were sacrificed on day 22 and the brains were collected for qPCR, ELISA and immunohistochemistry analysis.

RESULTS

qPCR analysis showed that paraquat treatment down-regulated the expression of genes related to dopamine activity and biosynthesis (dat and th1) and neuroprotective agent (bdnf). Paraquat treatment also up-regulated the expression of the mt2, smtb and proinflammatory genes (il-1α, il-1β, tnf-α and cox-2). hMT2 treatment was able to reverse the effects of paraquat. Lipid peroxidation decreased in the paraquat and pre-hMT2-treated groups. However, lipid peroxidation increased in the post-hMT2-treated group. Paraquat treatment also led to a reduction of dopaminergic neurons while their numbers showed an increase following hMT2 treatment.

CONCLUSION

Paraquat has been identified as one of the pesticides that can cause the death of dopaminergic neurons and affect dopamine biosynthesis. Treatment with exogenous hMT2 could reverse the effects of paraquat in the zebrafish brain.

Global gene expression signatures in response to citrate-coated silver nanoparticles exposure

Silver nanoparticles (AgNPs) are widely used in medical and commercial products for their unique antibacterial functions. However, the impact of AgNPs on human neural development is not well understood. To investigate the effect of AgNPs on human neural development, various doses of 20 nm citrate-coated AgNP (AgSC) were administered to human embryonic stem cell derived neural progenitors during the neuronal differentiation. Immunofluorescence staining with neuronal progenitor markers SOX2 (sex determining region Y-box 2) and Nestin (VI intermediate filament protein) showed that AgSC inhibited rosette formation, neuronal progenitor proliferation, and neurite outgrowth. Furthermore, AgSC promoted astrocyte activation and neuronal apoptosis. These adverse effects can be partially recovered with ascorbic acid. A genome-wide transcriptome analysis of both AgSC treated and untreated samples indicated that the most up-graduated genes were a group of Metallothionein (1F, 1E, 2A) proteins, a metal-binding protein that plays an essential role in metal homeostasis, heavy metal detoxification, and cellular anti-oxidative defence. The most significantly down-regulated genes were neuronal differentiation 6 (NEUROD6) and fork head box G1 (FOXG1). GO analyse indicated that the regulation of cholesterol biosynthetic process, neuron differentiation, synapse organization and pattern specification, oliogenesis, and neuronal apoptosis were the most impacted biological processes. KEGG pathway analyse showed that the most significantly impacted pathways were C5 isoprenoid, axon guidance, Notch, WNT, RAS-MAPK signalling pathways, lysosome, and apoptosis. Our data suggests that AgSCs interfered with metal homeostasis and cholesterol biosynthesis which induced oxidative stress, inhibited neurogenesis, axon guidance, and promoted apoptosis. Supplementation with ascorbic acid could act as an antioxidant to prevent AgSC-mediated neurotoxicity.

Ginsenoside Rg3 exerts a neuroprotective effect in rotenone-induced Parkinson's disease mice via its anti-oxidative properties

Ginsenoside Rg3, extracted from Panax ginseng C.A. Meyer, has been shown to possess neuroprotective properties. The present study aims to investigate the neuroprotective effects of ginsenoside Rg3 on rotenone-induced Parkinson's disease mice. Rotenone, a mitochondrial complex I inhibitor, leads to the augmentation of reactive oxygen species production in cells. Male C57/BL6 mice were intragastrically administered rotenone (30 mg/kg) and then treated with ginsenoside Rg3 (5, 10, or 20 mg/kg). Pole, rotarod, and open field tests were performed to evaluate motor function. Ginsenoside Rg3 decreased the climbing time in the pole test (p < 0.01), whereas it increased the latency in the rotarod test (p < 0.01) and the total distance (p < 0.01) and mean speed in the open field test (p < 0.01). Ginsenoside Rg3 treatment augmented the number of tyrosine hydroxylase-positive neurons in the substantia nigra (p < 0.01), mean density of tyrosine hydroxylase-positive nerve fibers (p < 0.01), and dopamine content (p < 0.01) in the striatum and reduced the reactive oxygen species level in the substantia nigra (p < 0.01). Glutathione cysteine ligase regulatory subunit and glutathione cysteine ligase modulatory subunit expression levels were elevated in the ginsenoside Rg3 groups. Ginsenoside Rg3 also improved motor function in rotenone-induced Parkinson's disease mice. The neuroprotective effects of ginsenoside Rg3 are at least partly associated with its anti-oxidative properties via regulation of glutathione cysteine ligase modulatory subunit and glutathione cysteine ligase regulatory subunit expression.

Using Rotenone to Model Parkinson's Disease in Mice: A Review of the Role of Pharmacokinetics

Rotenone is a naturally occurring toxin that inhibits complex I of the mitochondrial electron transport chain. Several epidemiological studies have shown an increased risk of Parkinson's disease (PD) in individuals exposed chronically to rotenone, and it has received great attention for its ability to reproduce many critical features of PD in animal models. Laboratory studies of rotenone have repeatedly shown that it induces in vivo substantia nigra dopaminergic cell loss, a hallmark of PD neuropathology. Additionally, rotenone induces in vivo aggregation of α-synuclein, the major component of Lewy bodies and Lewy neurites found in the brain of PD patients and another hallmark of PD neuropathology. Some in vivo rotenone models also reproduce peripheral signs of PD, such as reduced intestinal motility and peripheral α-synuclein aggregation, both of which are thought to precede classical signs of PD in humans, such as cogwheel rigidity, bradykinesia, and resting tremor. Nevertheless, variability has been noted in cohorts of animals exposed to the same rotenone exposure regimen and also between cohorts exposed to similar doses of rotenone. Low doses, administered chronically, may reproduce PD symptoms and neuropathology more faithfully than excessively high doses, but overlap between toxicity and parkinsonian motor phenotypes makes it difficult to separate if behavior is examined in isolation. Rotenone degrades when exposed to light or water, and choice of vehicle may affect outcome. Rotenone is metabolized extensively in vivo, and choice of route of exposure influences greatly the dose used. However, male rodents may be capable of greater metabolism of rotenone, which could therefore reduce their total body exposure when compared with female rodents. The pharmacokinetics of rotenone has been studied extensively, over many decades. Here, we review these pharmacokinetics and models of PD using this important piscicide.

[Therapeutic strategy for Parkinson's disease: targeting zinc-binding protein in astrocytes]

Parkinson's disease (PD) is a progressive neurodegenerative disease with motor symptoms, such as tremor, akinesia/bradykinesia, rigidity and postural instability due to a loss of nigrostriatal dopaminergic neurons; PD patients also exhibit non-motor symptoms, such as hyposmia, orthostatic hypotension and constipation, which precede motor symptoms. Pathologically, Lewy bodies and neurites, which contains α-synuclein, are observed in the central and peripheral nervous system. To date, it is hypothesized that PD pathology appears first in the olfactory bulb and the enteric nervous system, and propagates progressively through the substantia nigra to finally reach the cerebral cortex. Major medications at present are nosotropic treatments to improve motor dysfunction in PD. Therefore, development of disease-modifying drug is required to slow or prevent PD progression. Astrocytes are known to play an important role in the maintenance of the neuronal environment and exert neuroprotective effects by production of antioxidants and neurotrophic factors and clearing toxic molecules. In the previous study, we demonstrated that astrocytes produced antioxidative molecules metallothionein (MT)-1/2 in response to oxidative stress and protected dopaminergic neurons against oxidative stress. MTs are cysteine-rich proteins possessing antioxidative properties. MTs bind to metals such as zinc (Zn) and copper (Cu) and function in metal homeostasis and detoxification; MTs regulate Zn-mediated transcriptional activation of various genes. Recently, it is reported that MTs prevent Cu-induced aggregation of α-synuclein. In this article, we review a new therapeutic strategy of neuroprotection in PD by targeting MTs in astrocytes.

[Anti-oxidants in astrocytes as target of neuroprotection for Parkinson's disease]

Recently, it has been reported that dysfunction of astrocytes is involved vulnerability of neuronal cells in several neurological disorders. Glutathione (GSH) is the most abundant intrinsic antioxidant in the central nervous system, and its substrate cysteine is readily becomes the oxidized dimeric cystine. Since neurons lack a cystine transport system, neuronal GSH synthesis depends on cystine uptake via the cystine/glutamate exchange transporter (xCT), GSH synthesis and release in/from surrounding astrocytes. The expression and release of the zinc-binding protein metallothionein (MT) in astrocytes, which is a strong antioxidant, is induced and exerts neuroprotective in the case of dopaminergic neuronal damage. In addition, the transcription factor Nrf2 induces expression of MT-1 and GSH related molecules. We previously revealed that several antiepileptic drugs, serotonin 5-HT1A receptor agonists, plant-derived chemicals (phytochemicals) increased xCT expression, Nrf2 activation, GSH or MT expression and release in/from astrocytes, and exerted a neuroprotective effect against dopaminergic neurodegeneration in Parkinson's disease model. Our serial studies on neuroprotection via antioxidant defense mechanism of astrocytes have found three target molecular systems of astrocytes for neuroprotection: (1) xCT-GSH synthetic system, (2) Nrf2 system and (3) 5-HT1A receptor-Nrf2-MT system, 5-HT1A-S100β system. In this article, possible neuroprotective strategy for Parkinson's disease has been reviewed targeting antioxidative molecules in astrocytes.

Neuron-Astrocyte Interactions in Parkinson's Disease

Parkinson’s disease (PD) is the second most common neurodegenerative disease. PD patients exhibit motor symptoms such as akinesia/bradykinesia, tremor, rigidity, and postural instability due to a loss of nigrostriatal dopaminergic neurons. Although the pathogenesis in sporadic PD remains unknown, there is a consensus on the involvement of non-neuronal cells in the progression of PD pathology. Astrocytes are the most numerous glial cells in the central nervous system. Normally, astrocytes protect neurons by releasing neurotrophic factors, producing antioxidants, and disposing of neuronal waste products. However, in pathological situations, astrocytes are known to produce inflammatory cytokines. In addition, various studies have reported that astrocyte dysfunction also leads to neurodegeneration in PD. In this article, we summarize the interaction of astrocytes and dopaminergic neurons, review the pathogenic role of astrocytes in PD, and discuss therapeutic strategies for the prevention of dopaminergic neurodegeneration. This review highlights neuron-astrocyte interaction as a target for the development of disease-modifying drugs for PD in the future.

Kolaviron protects against nigrostriatal degeneration and gut oxidative damage in a stereotaxic rotenone model of Parkinson's disease

The asymptomatic and clinical stages of Parkinson's disease (PD) are associated with comorbid non-motor symptoms including gastrointestinal (GI) dysfunction. Although the neuroprotective and gastroprotective roles of kolaviron (KV) have been reported independently, whether KV-mediated GI-protective capacity could be beneficial in PD is unknown. We therefore investigated the modulatory effects of KV on the loss of dopaminergic neurons, locomotor abnormalities, and ileal oxidative damage when rats are lesioned in the nigrostriatal pathway. KV treatment markedly suppressed the behavioral deficit and apomorphine-induced rotations associated with rotenone lesioning. KV attenuated the loss of nigrostriatal dopaminergic neurons and perturbations in the striatal glucose-regulated protein (GRP78) and X-box binding protein 1 (XBP1) levels. Ileal epithelial injury following stereotaxic rotenone infusion was associated with oxidative stress and marked inhibition of acetylcholine esterase activity and reduced expression of occludin in the crypt and villi. While KV treatment attenuated the redox imbalance in the gut and enhanced occludin immunoreactivity, acetylcholinesterase activity was not affected. Our data demonstrate ileal oxidative damage as a characteristic non-motor gut dysfunction in PD while showing the potential dual efficacy of KV in the attenuation of both neural defects and gut abnormalities associated with PD.

Human-Specific Transcriptome of Ventral and Dorsal Midbrain Dopamine Neurons

Objective

Neuronal loss in the substantia nigra pars compacta (SNpc) in Parkinson disease (PD) is not uniform, as dopamine neurons from the ventral tier are lost more rapidly than those of the dorsal tier. Identifying the intrinsic differences that account for this differential vulnerability may provide a key for developing new treatments for PD.

Methods

Here, we compared the RNA‐sequenced transcriptomes of ~100 laser captured microdissected SNpc neurons from each tier from 7 healthy controls.

Results

Expression levels of dopaminergic markers were similar across the tiers, whereas markers specific to the neighboring ventral tegmental area were virtually undetected. After accounting for unwanted sources of variation, we identified 106 differentially expressed genes (DEGs) between the SNpc tiers. The genes higher in the dorsal/resistant SNpc tier neurons displayed coordinated patterns of expression across the human brain, their protein products had more interactions than expected by chance, and they demonstrated evidence of functional convergence. No significant shared functionality was found for genes higher in the ventral/vulnerable SNpc tier. Surprisingly but importantly, none of the identified DEGs was among the familial PD genes or genome‐wide associated loci. Finally, we found some DEGs in opposite tier orientation between human and analogous mouse populations.

Interpretation

Our results highlight functional enrichments of vesicular trafficking, ion transport/homeostasis and oxidative stress genes showing higher expression in the resistant neurons of the SNpc dorsal tier. Furthermore, the comparison of gene expression variation in human and mouse SNpc populations strongly argues for the need of human‐focused omics studies. ANN NEUROL 2020;87:853–868

Dopaminergic neuroprotective effects of rotigotine via 5-HT1A receptors: Possibly involvement of metallothionein expression in astrocytes

Astrocytes exert neuroprotective effects through production of antioxidant molecules and neurotrophic factors. A recent study showed that stimulation of astrocyte serotonin 1A (5-HT1A) receptors promotes astrocyte proliferation and upregulation of the antioxidant molecules metallothionein (MT)-1,2, which protect dopaminergic neurons against oxidative stress. Rotigotine, an anti-parkinsonian drug, can bind to dopamine and 5-HT1A receptors. In this study, we examined neuroprotective effects of rotigotine in models of Parkinson's disease and involvement of astrocyte 5-HT1A receptors in neuroprotective effects of rotigotine against dopaminergic neurodegeneration. Rotigotine increased the number of astrocytes and MT-1,2 expression in cultured astrocytes. Pretreatment with conditioned media from rotigotine-treated astrocytes significantly inhibited 6-hydroxydopamine (6-OHDA)-induced dopaminergic neurotoxicity. These effects were completely blocked by a 5-HT1A antagonist or MT-1,2 specific antibody. Subcutaneous administration of rotigotine increased MT-1,2 expression in striatal astrocytes and prevented reduction of dopaminergic neurons in the substantia nigra of a 6-OHDA-lesioned mouse model of Parkinson's disease. These effects were blocked by co-administration with a 5-HT1A antagonist. These results suggest that rotigotine exerts neuroprotective effects through upregulation of MT expression in astrocytes by targeting 5-HT1A receptors. Our findings provide a possible therapeutic application of rotigotine to prevent dopaminergic neurodegeneration in Parkinson's disease.

Lactobacillus frumenti improves antioxidant capacity via nitric oxide synthase 1 in intestinal epithelial cells

Oxidative damages have adverse effects on mammals. Growing studies have focused on exploring new antioxidants. Here, we report that Lactobacillus frumenti increases the total antioxidation capacity activities and decreases the total reactive oxygen species levels in porcine intestinal epithelial cells. Comparative proteomics revealed that expressions of peroxiredoxin 2, isocitrate dehydrogenase 1, NAD(P)H dehydrogenase quinone 1, antioxidant protein 1, and metallothionein-2A, which are associated with antioxidant defense system, were significantly increased with L. frumenti treatment. In germ-free mice, L. frumenti treatment also remarkably improves the intestinal antioxidant capacity. We further illustrated that nitric oxide production-mediated by nitric oxide synthase 1 activation is essential for L. frumenti-induced improvements in intestinal epithelial antioxidant capacity and barrier function. This study suggested that L. frumenti may be a potential probiotic used to prevent oxidative stress-induced aging and diseases in mammals.-Nie, Y., Hu, J., Hou, Q., Zheng, W., Zhang, X., Yang, T., Ma, L., Yan, X. Lactobacillus frumenti improves antioxidant capacity via nitric oxide synthase 1 in intestinal epithelial cells.

Effects of Enteric Environmental Modification by Coffee Components on Neurodegeneration in Rotenone-Treated Mice

Epidemiological studies have shown that coffee consumption decreases the risk of Parkinson's disease (PD). Caffeic acid (CA) and chlorogenic acid (CGA) are coffee components that have antioxidative properties. Rotenone, a mitochondrial complex I inhibitor, has been used to develop parkinsonian models, because the toxin induces PD-like pathology. Here, we examined the neuroprotective effects of CA and CGA against the rotenone-induced degeneration of central dopaminergic and peripheral enteric neurons. Male C57BL/6J mice were chronically administered rotenone (2.5 mg/kg/day), subcutaneously for four weeks. The animals were orally administered CA or CGA daily for 1 week before rotenone exposure and during the four weeks of rotenone treatment. Administrations of CA or CGA prevented rotenone-induced neurodegeneration of both nigral dopaminergic and intestinal enteric neurons. CA and CGA upregulated the antioxidative molecules, metallothionein (MT)-1,2, in striatal astrocytes of rotenone-injected mice. Primary cultured mesencephalic or enteric cells were pretreated with CA or CGA for 24 h, and then further co-treated with a low dose of rotenone (1⁻5 nM) for 48 h. The neuroprotective effects and MT upregulation induced by CA and CGA in vivo were reproduced in cultured cells. Our data indicated that intake of coffee components, CA and CGA, enhanced the antioxidative properties of glial cells and prevents rotenone-induced neurodegeneration in both the brain and myenteric plexus.

Enhancement of neuroprotective activity of Sagunja-tang by fermentation with lactobacillus strains

BACKGROUND

Sagunja-tang (SGT) is widely used in traditional herbal medicine to treat immune system and gastrointestinal disorders and reportedly has protective effects against inflammation, cancer, and osteoporosis. In this study, we fermented SGT with different Latobacillus strains and investigated the change in phytochemical compositions in SGT and enhancement of it neuroprotective effects in SH-SY5Y human neuroblastoma.

METHODS

Marker components, including ginsenoside Rg₁, glycyrrhizin, liquiritin, liquiritigenin, atractylenolide I, atractylenolide II, atractylenolide III, and pachymic acid, in SGT, were qualitatively and quantitatively analyzed using high-performance liquid chromatography-diode array detection and liquid chromatography-mass spectrometry. SGT was fermented with eight different Lactobacillus strains to yield eight fermented SGTs (FSGTs). The conversion efficiencies of SGT marker components were determined in each FSGT. To detect the protective effect of SGT and FSGT, reactive oxygen species (ROS) assay and mitochondrial membrane potentials (MMPs) assay were performed in SH-SY5Y cells.

RESULTS

Compared with the other FSGTs, SGT166, i.e., SGT fermented with L. plantarum 166, had high conversion efficiency, as indicated by increased amounts of glycyrrhizin, liquiritigenin, and atractylenolides I-III. In SH-SY5Y cells, protection against cell death induced by H₂O₂ and etoposide was high using SGT166 and very low using SGT. Furthermore, ROS production and mitochondrial membrane potential disruption in SH-SY5Y cells were markedly suppressed by SGT166 treatment, which demonstrated that inhibition of ROS generation may be one of the neuroprotective mechanisms of SGT166.

CONCLUSIONS

This study demonstrated that fermentation of SGT with L. plantarum 166 enhanced suppression of oxidative stress and MMP loss. This enhanced neuroprotective effect was thought to be caused by the conversion of SGT phytochemicals by fermentation. SGT166 shows potential for treating neurological damage-related diseases.

Synthesis and neuroprotective effects of the complex nanoparticles of iron and sapogenin isolated from the defatted seeds of Camellia oleifera

CONTEXT

The defatted seeds of Camellia oleifera var. monosperma Hung T. Chang (Theaceae) are currently discarded without effective utilization. However, sapogenin has been isolated and shows antioxidative, anti-inflammatory and analgesic activities suggestive of its neuroprotective function.

OBJECTIVE

In order to improve the activities of sapogenin, the nanoparticles of iron-sapogenin have been synthesized, and the neuroprotective effects are evaluated.

MATERIALS AND METHODS

Structural characters of the nanoparticles were analyzed, and the antioxidant effect was assessed by DPPH method, and the neuroprotective effect was evaluated by rotenone-induced neurodegeneration in Kunming mice injected subcutaneously into the back of neck with rotenone (50 mg/kg/day) for 6 weeks and then treated by tail intravenous injection with the iron-sapogenin at the dose of 25, 50 and 100 mg/kg for 7 days. Mice behaviour and neurotransmitters were tested.

RESULTS

The product had an average size of 162 nm with spherical shape, and scavenged more than 90% DPPH radicals at 0.8 mg/mL concentration. It decreased behavioural disorder and malondialdehyde content in mice brain, and increased superoxide dismutase activity, tyrosine hydroxylase expression, dopamine and acetylcholine levels in brain in dose dependence, and their maximum changes were respectively up to 60.83%, 25.17%, 22.13%, 105.26%, 42.17% and 22.89% as compared to vehicle group. Iron-sapogenin nanoparticle shows significantly better effects than the sapogenin.

DISCUSSION AND CONCLUSION

Iron-sapogenin alleviates neurodegeneration of mice injured by neurotoxicity of rotenone, it is a superior candidate of drugs for neuroprotection.

Melandrii Herba Extract Attenuates H₂O₂-Induced Neurotoxicity in Human Neuroblastoma SH-SY5Y Cells and Scopolamine-Induced Memory Impairment in Mice

Oxidative stress plays a significant role in the etiology of a variety of neurodegenerative diseases. In this study, we found that Melandrii Herba extract (ME) attenuated oxidative-induced damage in cells. Mechanistically, ME exhibited protection from H₂O₂-induced neurotoxicity via caspase-3 inactivation, Bcl-2 downregulation, Bax upregulation, and MAPK activation (ERK 1/2, JNK 1/2, and p38 MAPK) in vitro. Moreover, our in vivo data showed that ME was able to attenuate scopolamine-induced cognitive impairment. These results provide in vitro and in vivo evidence that ME exhibits neuroprotective properties against oxidative stress, which suggests that ME is worthy of further investigation as a complementary, or even as an alternative, product for preventing and treating neurodegenerative disorders.

Gut-brain and brain-gut axis in Parkinson's disease models: Effects of a uridine and fish oil diet

Recent investigations have focused on the potential role of gastrointestinal (GI) abnormalities in the pathogenesis of Parkinson's disease (PD). The 'dual-hit' hypothesis of PD speculates that a putative pathogen enters the brain via two routes: the olfactory system and the GI system. Here, we investigated (1) whether local exposures of the neurotoxin rotenone in the gut or the brain of mice could induce PD-like neurological and GI phenotypes as well as a characteristic neuropathology in accordance with this 'dual-hit hypothesis' and (2) the effects of a diet containing uridine and fish oil providing docosahexaenoic acid (DHA), in both models. Mice were given rotenone either orally or by an injection in the striatum. Dietary interventions were started 1 week before rotenone exposures. We found that (1) both oral and intrastriatal administration of rotenone induced similar PD-like motor deficits, dopaminergic cell loss, delayed intestinal transit, inflammation, and alpha-synuclein accumulation in the colon; (2) the uridine and DHA containing diet prevented rotenone-induced motor and GI dysfunctions in both models. The models suggest possible bidirectional communication between the gut and the brain for the genesis of PD-like phenotype and pathology. The dietary intervention may provide benefits in the prevention of motor and non-motor symptoms in PD.

Neuroprotective effect of fermented papaya preparation by activation of Nrf2 pathway in astrocytes

OBJECTIVES

Nuclear factor erythroid 2-related factor (Nrf2) in astrocyte plays important roles in brain homeostasis. Fermented papaya preparation (FPP) has anti-oxidative, anti-inflammatory, immunoregulatory properties. The present study investigated the effects of FPP on activation of Nrf2 and release of Nrf2-regulated neuroprotective antioxidants and detoxifying molecules.

METHODS

Primary cultured astrocytes from rat embryos were treated with FPP for 6 or 24 hours. The expression levels of nuclear Nrf2 and cytoplasmic Nrf2-regulated molecules were determined by western blot analysis and immunohistochemistry. Glutathione levels were measured in cells and medium. Dopaminergic neurons were exposed 6-hydroxydopamine (6-OHDA) with/without pre-treatment with FPP astrocytes. Mice were treated orally with FPP for 2 weeks.

RESULTS

FPP increased nuclear translocation of Nrf2 in striatal astrocytes, induced up-regulation of NAD(P)H quinine oxidoreductase-1, glutathione-S transferase and hemeoxygenase-1, and increased glutathione level and the percentage of metallothionein-expressing astrocytes. Moreover, FPP suppressed 6-OHDA-induced dopaminergic neuronal loss in not only neuron-astrocyte mixed culture, but also neuron-rich cultures pre-treated with glial conditioned medium. Two-week oral treatment of mice with FPP resulted in Nrf2 activation and increase in glutathione level in striatum.

DISCUSSION

The results indicated that FPP enhances the anti-oxidative capacity through activation of Nrf2 in astrocytes, suggesting it may provide neuroprotection in oxidative stress-related neurodegenerative diseases.

Mammalian Metallothionein-2A and Oxidative Stress

Mammalian metallothionein-2A (MT2A) has received considerable attention in recent years due to its crucial pathophysiological role in anti-oxidant, anti-apoptosis, detoxification and anti-inflammation. For many years, most studies evaluating the effects of MT2A have focused on reactive oxygen species (ROS), as second messengers that lead to oxidative stress injury of cells and tissues. Recent studies have highlighted that oxidative stress could activate mitogen-activated protein kinases (MAPKs), and MT2A, as a mediator of MAPKs, to regulate the pathogenesis of various diseases. However, the molecule mechanism of MT2A remains elusive. A deeper understanding of the functional, biochemical and molecular characteristics of MT2A would be identified, in order to bring new opportunities for oxidative stress therapy.

Impact of Plant-Derived Flavonoids on Neurodegenerative Diseases

Neurodegenerative disorders have a common characteristic that is the involvement of different cell types, typically the reactivity of astrocytes and microglia, characterizing gliosis, which in turn contributes to the neuronal dysfunction and or death. Flavonoids are secondary metabolites of plant origin widely investigated at present and represent one of the most important and diversified among natural products phenolic groups. Several biological activities are attributed to this class of polyphenols, such as antitumor activity, antioxidant, antiviral, and anti-inflammatory, among others, which give significant pharmacological importance. Our group have observed that flavonoids derived from Brazilian plants Dimorphandra mollis Bent., Croton betulaster Müll. Arg., e Poincianella pyramidalis Tul., botanical synonymous Caesalpinia pyramidalis Tul. also elicit a broad spectrum of responses in astrocytes and neurons in culture as activation of astrocytes and microglia, astrocyte associated protection of neuronal progenitor cells, neuronal differentiation and neuritogenesis. It was observed the flavonoids also induced neuronal differentiation of mouse embryonic stem cells and human pluripotent stem cells. Moreover, with the objective of seeking preclinical pharmacological evidence of these molecules, in order to assess its future use in the treatment of neurodegenerative disorders, we have evaluated the effects of flavonoids in preclinical in vitro models of neuroinflammation associated with Parkinson's disease and glutamate toxicity associated with ischemia. In particular, our efforts have been directed to identify mechanisms involved in the changes in viability, morphology, and glial cell function induced by flavonoids in cultures of glial cells and neuronal cells alone or in interactions and clarify the relation with their neuroprotective and morphogetic effects.

Investigation of tyrosine hydroxylase and BDNF in a low-dose rotenone model of Parkinson's disease

Tyrosine hydroxylase (TH, the rate limiting-enzyme in catecholamine synthesis) is regulated acutely via phosphorylation of 3 serine residues--Ser19, 31 and 40, and chronically via changes in TH protein levels. In this study, we aimed to investigate how TH is regulated in the brain, gut and adrenal gland as well as changes in mature brain-derived neurotrophic factor (mBDNF) and proBDNF levels in a low-dose (2 mg/kg, 5 days/week for 4 weeks) rotenone model of Parkinson's disease (PD). Rearing behaviour decreased by week 3 in the rotenone group (p<0.01), with further decreases in rearing by week 4 (p<0.001); however, TH remained unchanged in the substantia nigra (SN) and striatum; TH levels were also unaltered in other catecholaminergic cell groups of the brainstem such as A1C1 neurons or locus coeruleus. In the olfactory bulb, TH protein decreased (2.5-fold, p<0.01) while Ser31 phosphorylation increased (1.4-fold, p<0.05) in the rotenone group. In contrast, TH protein was increased in the adrenal gland (2-fold, p<0.05) and colon (5-fold, p<0.05) of rotenone rats. mBDNF levels were not changed in the SN but were significantly reduced in plasma and significantly increased in the colon (2-fold, p<0.01) of rotenone-treated rats. This is the first study to assess TH and BDNF in the brain and periphery in the rotenone model before SN/striatum degeneration is evident. Together these results suggest that low-dose rotenone may have some potential to model the early stages of PD.

Metallothionein 2 regulates endothelial cell migration through transcriptional regulation of vegfc expression

Analysis of developmental angiogenesis can help to identify regulatory networks, which also contribute to disease-related vascular growth. Vascular endothelial growth factors (Vegf) drive angiogenic processes such as sprouting, endothelial cell (EC) migration and proliferation. However, how Vegf expression is regulated during development is not well understood. By analyzing developmental zebrafish angiogenesis, we have identified Metallothionein 2 (Mt2) as a novel regulator of vegfc expression. While Metallothioneins (Mts) have been extensively analyzed for their capability of regulating homeostasis and metal detoxification, we demonstrate that Mt2 is required for EC migration, proliferation and angiogenic sprouting upstream of vegfc expression. We further demonstrate that another Mt family member cannot compensate Mt2 deficiency and therefore postulate that Mt2 regulates angiogenesis independent of its canonical Mt function. Our data not only reveal a non-canonical function of Mt2 in angiogenesis, but also propose Mt2 as a novel regulator of vegfc expression.

Neuroprotective effects of Liriope platyphylla extract against hydrogen peroxide-induced cytotoxicity in human neuroblastoma SH-SY5Y cells

Background

Oxidative stress is involved in neuronal cell death and mitochondrial dysfunction in neurodegenerative diseases. Liriope platyphylla (LP) has been suggested to have anti-inflammation, anti-bacterial, and anti-cancer effects. However, whether LP exerts neuroprotective effects on neuronal cells is unknown.

Methods

The present study was performed to investigate the neuroprotective effects of LP extract (LPE) against hydrogen peroxide (H₂O₂)-induced injury in human neuroblastoma cells SH-SY5Y. To test neuroprotective effects of LPE, we performed cell viability assay, flow cytometry analysis and western blot analysis. In addition, mitochondrial membrane potential (MMP) and oxidative stress were performed to evaluate the anti-apoptotic and anti-oxidant effects.

Results

LPE pretreatment conferred significant protection against the H₂O₂-induced decrease of SH-SY5Y cell viability. H₂O₂-induced increases of intracellular oxidative stress and mitochondrial dysfunction were attenuated by LPE pretreatment. Therefore, LPE pretreatment prevented SH-SY5Y cell injury. Treatment with H₂O₂ significantly induced poly(ADP ribose) polymerase (PARP) and caspase-3 cleavage, which was blocked by LPE. We found that p38 activation was involved in the neuroprotective effects of LPE.

Conclusions

Current findings suggest that LPE exerts neuroprotective effects against H₂O₂-induced apoptotic cell death by modulating p38 activation in SH-SY5Y cells. Therefore, LPE has potential anti-apoptotic effects that may be neuroprotective in neurodegenerative diseases and aging-related dementia.

Neurotoxin mechanisms and processes relevant to Parkinson's disease: an update

The molecular mechanism responsible for degenerative process in the nigrostriatal dopaminergic system in Parkinson's disease (PD) remains unknown. One major advance in this field has been the discovery of several genes associated to familial PD, including alpha synuclein, parkin, LRRK2, etc., thereby providing important insight toward basic research approaches. There is an consensus in neurodegenerative research that mitochon dria dysfunction, protein degradation dysfunction, aggregation of alpha synuclein to neurotoxic oligomers, oxidative and endoplasmic reticulum stress, and neuroinflammation are involved in degeneration of the neuromelanin-containing dopaminergic neurons that are lost in the disease. An update of the mechanisms relating to neurotoxins that are used to produce preclinical models of Parkinson´s disease is presented. 6-Hydroxydopamine, 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine, and rotenone have been the most wisely used neurotoxins to delve into mechanisms involved in the loss of dopaminergic neurons containing neuromelanin. Neurotoxins generated from dopamine oxidation during neuromelanin formation are likewise reviewed, as this pathway replicates neurotoxin-induced cellular oxidative stress, inactivation of key proteins related to mitochondria and protein degradation dysfunction, and formation of neurotoxic aggregates of alpha synuclein. This survey of neurotoxin modeling-highlighting newer technologies and implicating a variety of processes and pathways related to mechanisms attending PD-is focused on research studies from 2012 to 2014.

An update on the rotenone models of Parkinson's disease: their ability to reproduce the features of clinical disease and model gene-environment interactions

Parkinson's disease (PD) is the second most common neurodegenerative disorder that is characterized by two major neuropathological hallmarks: the degeneration of dopaminergic neurons in the substantia nigra (SN) and the presence of Lewy bodies in the surviving SN neurons, as well as other regions of the central and peripheral nervous system. Animal models have been invaluable tools for investigating the underlying mechanisms of the pathogenesis of PD and testing new potential symptomatic, neuroprotective and neurorestorative therapies. However, the usefulness of these models is dependent on how precisely they replicate the features of clinical PD with some studies now employing combined gene-environment models to replicate more of the affected pathways. The rotenone model of PD has become of great interest following the seminal paper by the Greenamyre group in 2000 (Betarbet et al., 2000). This paper reported for the first time that systemic rotenone was able to reproduce the two pathological hallmarks of PD as well as certain parkinsonian motor deficits. Since 2000, many research groups have actively used the rotenone model worldwide. This paper will review rotenone models, focusing upon their ability to reproduce the two pathological hallmarks of PD, motor deficits, extranigral pathology and non-motor symptoms. We will also summarize the recent advances in neuroprotective therapies, focusing on those that investigated non-motor symptoms and review rotenone models used in combination with PD genetic models to investigate gene-environment interactions.