Increased Oxidative Stress Exacerbates α-Synuclein Aggregation In Vivo

An antioxidant and anti-ER stress combination therapy elevates phosphorylation of α-Syn at serine 129 and alleviates post-TBI PD-like pathology in a sex-specific manner in mice

Clinical studies have shown that traumatic brain injury (TBI) increases the onset of Parkinson's disease (PD) in later life by >50%. Oxidative stress, endoplasmic reticulum (ER) stress, and inflammation are the major drivers of both TBI and PD pathologies. We presently evaluated if curtailing oxidative stress and ER stress concomitantly using a combination of apocynin and tert-butylhydroquinone and salubrinal during the acute stage after TBI in mice reduces the severity of late-onset PD-like pathology. The effect of multiple low doses of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) on post-TBI neurodegeneration was also evaluated. The combo therapy elevated the level of phosphorylation at serine 129 (pS129) of α-Syn in the pericontusional cortex of male mice at 72 h post-TBI. Motor and cognitive deficits induced by TBI lasted at least 3 months and the combo therapy curtailed these deficits in both sexes. At 3 months post-TBI, male mice given combo therapy exhibited significantly lesser α-Syn aggregates in the SN and higher TH+ cells in the SNpc, compared to vehicle control. However, the aggregate number was not significantly different between groups of female mice. Moreover, TBI-induced loss of TH+ cells was negligible in female mice irrespective of treatment. The MPTP treatment aggravated PD-like pathology in male mice but had a negligible effect on the loss of TH+ cells in female mice. Thus, the present study indicates that mitigation of TBI-induced oxidative stress and ER stress at the acute stage could potentially reduce the risk of post-TBI PD-like pathology at least in male mice, plausibly by elevating pS129-α-Syn level.

Neurotoxicology of dopamine: Victim or assailant?

Since the identification of dopamine as a neurotransmitter in the mid-20th century, investigators have examined the regulation of dopamine homeostasis at a basic biological level and in human disorders. Genetic animal models that manipulate the expression of proteins involved in dopamine homeostasis have provided key insight into the consequences of dysregulated dopamine. As a result, we have come to understand the potential of dopamine to act as an endogenous neurotoxin through the generation of reactive oxygen species and reactive metabolites that can damage cellular macromolecules. Endogenous factors, such as genetic variation and subcellular processes, and exogenous factors, such as environmental exposures, have been identified as contributors to the dysregulation of dopamine homeostasis. Given the variety of dysregulating factors that impact dopamine homeostasis and the potential for dopamine itself to contribute to further cellular dysfunction, dopamine can be viewed as both the victim and an assailant of neurotoxicity. Parkinson's disease has emerged as the exemplar case study of dopamine dysregulation due to the genetic and environmental factors known to contribute to disease risk, and due to the evidence of dysregulated dopamine as a pathologic and pathogenic feature of the disease. This review, inspired by the talk, "Dopamine in Durham: location, location, location" presented by Dr. Miller for the Jacob Hooisma Memorial Lecture at the International Neurotoxicology Association meeting in 2023, offers a primer on dopamine toxicity covering endogenous and exogenous factors that disrupt dopamine homeostasis and the actions of dopamine as an endogenous neurotoxin.

A Mutual Nexus Between Epilepsy and α-Synuclein: A Puzzle Pathway

Alpha-synuclein (α-Syn) is a specific neuronal protein that regulates neurotransmitter release and trafficking of synaptic vesicles. Exosome-associated α-Syn which is specific to the central nervous system (CNS) is involved in the pathogenesis of epilepsy. Therefore, this review aimed to elucidate the possible link between α-Syn and epilepsy, and how it affects the pathophysiology of epilepsy. A neurodegenerative protein such as α-Syn is implicated in the pathogenesis of epilepsy. Evidence from preclinical and clinical studies revealed that upregulation of α-Syn induces progressive neuronal dysfunctions through induction of oxidative stress, neuroinflammation, and inhibition of autophagy in a vicious cycle with subsequent development of severe epilepsy. In addition, accumulation of α-Syn in epilepsy could be secondary to the different cellular alterations including oxidative stress, neuroinflammation, reduction of brain-derived neurotrophic factor (BDNF) and progranulin (PGN), and failure of the autophagy pathway. However, the mechanism of α-Syn-induced-epileptogenesis is not well elucidated. Therefore, α-Syn could be a secondary consequence of epilepsy. Preclinical and clinical studies are warranted to confirm this causal relationship.

Black Phosphorus Nanosheets Protect Neurons by Degrading Aggregative α-syn and Clearing ROS in Parkinson's Disease

Although evidence indicates that the abnormal accumulation of α-synuclein (α-syn) in dopamine neurons of the substantia nigra is the main pathological feature of Parkinson's disease (PD), no compounds that have both α-syn antiaggregation and α-syn degradation functions have been successful in treating the disease in the clinic. Here, it is shown that black phosphorus nanosheets (BPNSs) interact directly with α-syn fibrils to trigger their disaggregation for PD treatment. Moreover, BPNSs have a specific affinity for α-syn through van der Waals forces. And BPNSs are found to activate autophagy to maintain α-syn homeostasis, improve mitochondrial dysfunction, reduce reactive oxygen species levels, and rescue neuronal death and synaptic loss in PC12 cells. It is also observed that BPNSs penetrate the blood-brain barrier and protect against dopamine neuron loss, alleviating behavioral disorders in 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) induced mouse model and hA53T α-syn transgenic mice. Together, the study reveals that BPNSs have the potential as a novel integrated nanomedicine for clinical diagnosis and treatment of neurological diseases.

The Contribution of Type 2 Diabetes to Parkinson's Disease Aetiology

Type 2 diabetes (T2D) and Parkinson's disease (PD) are chronic disorders that have a significant health impact on a global scale. Epidemiological, preclinical, and clinical research underpins the assumption that insulin resistance and chronic inflammation contribute to the overlapping aetiologies of T2D and PD. This narrative review summarises the recent evidence on the contribution of T2D to the initiation and progression of PD brain pathology. It also briefly discusses the rationale and potential of alternative pharmacological interventions for PD treatment.

Transcriptional mutagenesis of α-synuclein caused by DNA oxidation in Parkinson's disease pathogenesis

Oxidative stress plays an essential role in the development of Parkinson's disease (PD). 8-oxo-7,8-dihydroguanine (8-oxodG, oxidized guanine) is the most abundant oxidative stress-mediated DNA lesion. However, its contributing role in underlying PD pathogenesis remains unknown. In this study, we hypothesized that 8-oxodG can generate novel α-synuclein (α-SYN) mutants with altered pathologic aggregation through a phenomenon called transcriptional mutagenesis (TM). We observed a significantly higher accumulation of 8-oxodG in the midbrain genomic DNA from PD patients compared to age-matched controls, both globally and region specifically to α-SYN. In-silico analysis predicted that forty-three amino acid positions can contribute to TM-derived α-SYN mutation. Here, we report a significantly higher load of TM-derived α-SYN mutants from the midbrain of PD patients compared to controls using a sensitive PCR-based technique. We found a novel Serine42Tyrosine (S42Y) α-SYN as the most frequently detected TM mutant, which incidentally had the highest predicted aggregation score amongst all TM variants. Immunohistochemistry of midbrain sections from PD patients using a newly characterized antibody for S42Y identified S42Y-laden Lewy bodies (LB). We further demonstrated that the S42Y TM variant significantly accelerates WT α-SYN aggregation by cell and recombinant protein-based assays. Cryo-electron tomography revealed that S42Y exhibits considerable conformational heterogeneity compared to WT fibrils. Moreover, S42Y exhibited higher neurotoxicity compared to WT α-SYN as shown in mouse primary cortical cultures and AAV-mediated overexpression in the substantia nigra of C57BL/6 J mice. To our knowledge, this is the first report describing the possible contribution of TM-generated mutations of α-SYN to LB formation and PD pathogenesis.

Mitochondrial DNA damage triggers spread of Parkinson's disease-like pathology

In the field of neurodegenerative diseases, especially sporadic Parkinson's disease (sPD) with dementia (sPDD), the question of how the disease starts and spreads in the brain remains central. While prion-like proteins have been designated as a culprit, recent studies suggest the involvement of additional factors. We found that oxidative stress, damaged DNA binding, cytosolic DNA sensing, and Toll-Like Receptor (TLR)4/9 activation pathways are strongly associated with the sPDD transcriptome, which has dysregulated type I Interferon (IFN) signaling. In sPD patients, we confirmed deletions of mitochondrial (mt)DNA in the medial frontal gyrus, suggesting a potential role of damaged mtDNA in the disease pathophysiology. To explore its contribution to pathology, we used spontaneous models of sPDD caused by deletion of type I IFN signaling (Ifnb-/-/Ifnar-/- mice). We found that the lack of neuronal IFNβ/IFNAR leads to oxidization, mutation, and deletion in mtDNA, which is subsequently released outside the neurons. Injecting damaged mtDNA into mouse brain induced PDD-like behavioral symptoms, including neuropsychiatric, motor, and cognitive impairments. Furthermore, it caused neurodegeneration in brain regions distant from the injection site, suggesting that damaged mtDNA triggers spread of PDD characteristics in an "infectious-like" manner. We also discovered that the mechanism through which damaged mtDNA causes pathology in healthy neurons is independent of Cyclic GMP-AMP synthase and IFNβ/IFNAR, but rather involves the dual activation of TLR9/4 pathways, resulting in increased oxidative stress and neuronal cell death, respectively. Our proteomic analysis of extracellular vesicles containing damaged mtDNA identified the TLR4 activator, Ribosomal Protein S3 as a key protein involved in recognizing and extruding damaged mtDNA. These findings might shed light on new molecular pathways through which damaged mtDNA initiates and spreads PD-like disease, potentially opening new avenues for therapeutic interventions or disease monitoring.

Role of Nanoparticle-Conjugates and Nanotheranostics in Abrogating Oxidative Stress and Ameliorating Neuroinflammation

Oxidative stress is a deteriorating condition that arises due to an imbalance between the reactive oxygen species and the antioxidant system or defense of the body. The key reasons for the development of such conditions are malfunctioning of various cell organelles, such as mitochondria, endoplasmic reticulum, and Golgi complex, as well as physical and mental disturbances. The nervous system has a relatively high utilization of oxygen, thus making it particularly vulnerable to oxidative stress, which eventually leads to neuronal atrophy and death. This advances the development of neuroinflammation and neurodegeneration-associated disorders such as Alzheimer's disease, Parkinson's disease, epilepsy, dementia, and other memory disorders. It is imperative to treat such conditions as early as possible before they worsen and progress to irreversible damage. Oxidative damage can be negated by two mechanisms: improving the cellular defense system or providing exogenous antioxidants. Natural antioxidants can normally handle such oxidative stress, but they have limited efficacy. The valuable features of nanoparticles and/or nanomaterials, in combination with antioxidant features, offer innovative nanotheranostic tools as potential therapeutic modalities. Hence, this review aims to represent novel therapeutic approaches like utilizing nanoparticles with antioxidant properties and nanotheranostics as delivery systems for potential therapeutic applications in various neuroinflammation- and neurodegeneration-associated disease conditions.

Is Hearing Loss a Risk Factor for Idiopathic Parkinson's Disease? An English Longitudinal Study of Ageing Analysis

Observations that hearing loss is a substantial risk factor for dementia may be accounted for by a common pathology. Mitochondrial oxidative stress and alterations in α-synuclein pathology may be common pathology candidates. Crucially, these candidate pathologies are implicated in Parkinson's disease (PD). Consequently, hearing loss may be a risk factor for PD. Subsequently, this prospective cohort study of the English Longitudinal Study of Ageing examines whether hearing loss is a risk factor for PD longitudinally. Participants reporting self-reported hearing capabilities and no PD diagnosis prior to entry (n = 14,340) were used. A joint longitudinal and survival model showed that during a median follow up of 10 years (SD = 4.67 years) increased PD risk (p < 0.001), but not self-reported hearing capability (p = 0.402). Additionally, an exploratory binary logistic regression modelling the influence of hearing loss identified using a screening test (n = 4812) on incident PD indicated that neither moderate (p = 0.794), nor moderately severe/severe hearing loss (p = 0.5210), increased PD risk, compared with normal hearing. Whilst discrepancies with prior literature may suggest a neurological link between hearing loss and PD, further large-scale analyses using clinically derived hearing loss are needed.

Inhibition of Protein Aggregation and Endoplasmic Reticulum Stress as a Targeted Therapy for α-Synucleinopathy

α-synuclein (α-syn) is an intrinsically disordered protein abundant in the central nervous system. Physiologically, the protein regulates vesicle trafficking and neurotransmitter release in the presynaptic terminals. Pathologies related to misfolding and aggregation of α-syn are referred to as α-synucleinopathies, and they constitute a frequent cause of neurodegeneration. The most common α-synucleinopathy, Parkinson's disease (PD), is caused by abnormal accumulation of α-syn in the dopaminergic neurons of the midbrain. This results in protein overload, activation of endoplasmic reticulum (ER) stress, and, ultimately, neural cell apoptosis and neurodegeneration. To date, the available treatment options for PD are only symptomatic and rely on dopamine replacement therapy or palliative surgery. As the prevalence of PD has skyrocketed in recent years, there is a pending issue for development of new disease-modifying strategies. These include anti-aggregative agents that target α-syn directly (gene therapy, small molecules and immunization), indirectly (modulators of ER stress, oxidative stress and clearance pathways) or combine both actions (natural compounds). Herein, we provide an overview on the characteristic features of the structure and pathogenic mechanisms of α-syn that could be targeted with novel molecular-based therapies.

Leveraging Plasma Membrane Repair Therapeutics for Treating Neurodegenerative Diseases

Plasma membrane repair is an essential cellular mechanism that reseals membrane disruptions after a variety of insults, and compromised repair capacity can contribute to the progression of many diseases. Neurodegenerative diseases are marked by membrane damage from many sources, reduced membrane integrity, elevated intracellular calcium concentrations, enhanced reactive oxygen species production, mitochondrial dysfunction, and widespread neuronal death. While the toxic intracellular effects of these changes in cellular physiology have been defined, the specific mechanism of neuronal death in certain neurodegenerative diseases remains unclear. An abundance of recent evidence indicates that neuronal membrane damage and pore formation in the membrane are key contributors to neurodegenerative disease pathogenesis. In this review, we have outlined evidence supporting the hypothesis that membrane damage is a contributor to neurodegenerative diseases and that therapeutically enhancing membrane repair can potentially combat neuronal death.

AAV-mediated expression of a new conformational anti-aggregated α-synuclein antibody prolongs survival in a genetic model of α-synucleinopathies

Prion-like transmission of pathology in α-synucleinopathies like Parkinson's disease or multiple system atrophy is increasingly recognized as one potential mechanism to address disease progression. Active and passive immunotherapies targeting insoluble, aggregated α-synuclein are already being actively explored in the clinic with mixed outcomes so far. Here, we report the identification of 306C7B3, a highly selective, aggregate-specific α-synuclein antibody with picomolar affinity devoid of binding to the monomeric, physiologic protein. 306C7B3 binding is Ser129-phosphorylation independent and shows high affinity to several different aggregated α-synuclein polymorphs, increasing the likelihood that it can also bind to the pathological seeds assumed to drive disease progression in patients. In support of this, highly selective binding to pathological aggregates in postmortem brains of MSA patients was demonstrated, with no staining in samples from other human neurodegenerative diseases. To achieve CNS exposure of 306C7B3, an adeno-associated virus (AAV) based approach driving expression of the secreted antibody within the brain of (Thy-1)-[A30P]-hα-synuclein mice was used. Widespread central transduction after intrastriatal inoculation was ensured by using the AAV2HBKO serotype, with transduction being spread to areas far away from the inoculation site. Treatment of (Thy-1)-[A30P]-hα-synuclein mice at the age of 12 months demonstrated significantly increased survival, with 306C7B3 concentration reaching 3.9 nM in the cerebrospinal fluid. These results suggest that AAV-mediated expression of 306C7B3, targeting extracellular, presumably disease-propagating aggregates of α-synuclein, has great potential as a disease-modifying therapy for α-synucleinopathies as it ensures CNS exposure of the antibody, thereby mitigating the selective permeability of the blood-brain barrier.

UBL3 Interacts with Alpha-Synuclein in Cells and the Interaction Is Downregulated by the EGFR Pathway Inhibitor Osimertinib

Ubiquitin-like 3 (UBL3) acts as a post-translational modification (PTM) factor and regulates protein sorting into small extracellular vesicles (sEVs). sEVs have been reported as vectors for the pathology propagation of neurodegenerative diseases, such as α-synucleinopathies. Alpha-synuclein (α-syn) has been widely studied for its involvement in α-synucleinopathies. However, it is still unknown whether UBL3 interacts with α-syn, and is influenced by drugs or compounds. In this study, we investigated the interaction between UBL3 and α-syn, and any ensuing possible functional and pathological implications. We found that UBL3 can interact with α-syn by the Gaussia princeps based split luciferase complementation assay in cells and immunoprecipitation, while cysteine residues at its C-terminal, which are considered important as PTM factors for UBL3, were not essential for the interaction. The interaction was upregulated by 1-methyl-4-phenylpyridinium exposure. In drug screen results, the interaction was significantly downregulated by the treatment of osimertinib. These results suggest that UBL3 interacts with α-syn in cells and is significantly downregulated by epidermal growth factor receptor (EGFR) pathway inhibitor osimertinib. Therefore, the UBL3 pathway may be a new therapeutic target for α-synucleinopathies in the future.

Tannic Acid Mitigates Rotenone-Induced Dopaminergic Neurodegeneration by Inhibiting Inflammation, Oxidative Stress, Apoptosis, and Glutamate Toxicity in Rats

Parkinson's disease (PD), a movement disorder, is a neurodegenerative disease characterized by the degeneration of dopaminergic neurons in the substantia nigra pars compacta (SNpc) region of the brain. The etiopathogenesis of PD involves increased oxidative stress, augmented inflammation, impaired autophagy, accumulation of α-synuclein, and α-Glutamate neurotoxicity. The treatment of PD is limited and there is a lack of agents to prevent the disease/delay its progression and inhibit the onset of pathogenic events. Many agents of natural and synthetic origin have been investigated employing experimental models of PD, mimicking human PD. In the present study, we assessed the effect of tannic acid (TA) in a rodent model of PD induced by rotenone (ROT), a pesticide and an environmental toxin of natural origin reported to cause PD in agricultural workers and farmers. Rotenone (2.5 mg/kg/day, i.p.) was administered for 28 days, and TA (50 mg/kg, orally) was administered 30 min before ROT injections. The study results showed an increase in oxidative stress, as evidenced by the depletion of endogenous antioxidants and enhanced formation of lipid peroxidation products, along with the onset of inflammation following a rise in inflammatory mediators and proinflammatory cytokines. ROT injections have also augmented apoptosis, impaired autophagy, promoted synaptic loss, and perturbed α-Glutamate hyperpolarization in rats. ROT injections also induced the loss of dopaminergic neurons subsequent to the activation of microglia and astrocytes. However, TA treatment was observed to reduce lipid peroxidation, prevent loss of endogenous antioxidants, and inhibit the release and synthesis of proinflammatory cytokines, in addition to the favorable modulation of apoptosis and autophagic pathways. Treatment with TA also attenuated the activation of microglia and astrocytes along with preservation of dopaminergic neurons following reduced loss of dopaminergic neurodegeneration and inhibition of synaptic loss and α-Glutamate cytotoxicity. The effects of TA in ROT-induced PD were attributed to the antioxidant, anti-inflammatory, antiapoptotic, and neurogenesis properties. Based on the present study findings, it can be concluded that TA may be a promising novel therapeutic candidate for pharmaceutical as well as nutraceutical development owing to its neuroprotective properties in PD. Further regulatory toxicology and translational studies are suggested for future clinical usage in PD.

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

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

Glucose Metabolism Impairment in Parkinson's Disease

Impairments in systematic and regional glucose metabolism exist in patients with Parkinson's disease (PD) at every stage of the disease course, and such impairments are associated with the incidence, progression, and special phenotypes of PD, which affect each physiological process of glucose metabolism including glucose uptake, glycolysis, tricarboxylic acid cycle, oxidative phosphorylation, and pentose phosphate shunt pathway. These impairments may be attributed to various mechanisms, such as insulin resistance, oxidative stress, abnormal glycated modification, blood-brain-barrier dysfunction, and hyperglycemia-induced damages. These mechanisms could subsequently cause excessive methylglyoxal and reactive oxygen species production, neuroinflammation, abnormal aggregation of protein, mitochondrial dysfunction, and decreased dopamine, and finally result in energy supply insufficiency, neurotransmitter dysregulation, aggregation and phosphorylation of α-synuclein, and dopaminergic neuron loss. This review discusses the glucose metabolism impairment in PD and its pathophysiological mechanisms, and briefly summarized the currently-available therapies targeting glucose metabolism impairment in PD, including glucagon-likepeptide-1 (GLP-1) receptor agonists and dual GLP-1/gastric inhibitory peptide receptor agonists, metformin, and thiazoledinediones.

Functions of Astrocytes under Normal Conditions and after a Brain Disease

In the central nervous system (CNS) there are a greater number of glial cells than neurons (between five and ten times more). Furthermore, they have a greater number of functions (more than eight functions). Glia comprises different types of cells, those of neural origin (astrocytes, radial glia, and oligodendroglia) and differentiated blood monocytes (microglia). During ontogeny, neurons develop earlier (at fetal day 15 in the rat) and astrocytes develop later (at fetal day 21 in the rat), which could indicate their important and crucial role in the CNS. Analysis of the phylogeny reveals that reptiles have a lower number of astrocytes compared to neurons and in humans this is reversed, as there have a greater number of astrocytes compared to neurons. These data perhaps imply that astrocytes are important and special cells, involved in many vital functions, including memory, and learning processes. In addition, astrocytes are involved in different mechanisms that protect the CNS through the production of antioxidant and anti-inflammatory proteins and they clean the extracellular environment and help neurons to communicate correctly with each other. The production of inflammatory mediators is important to prevent changes in brain homeostasis. On the contrary, excessive, or continued production appears as a characteristic element in many diseases, such as Alzheimer's disease (AD), amyotrophic lateral sclerosis (ALS), multiple sclerosis (MS), and in neurodevelopmental diseases, such as bipolar disorder, schizophrenia, and autism. Furthermore, different drugs and techniques have been developed to reverse oxidative stress and/or excess of inflammation that occurs in many CNS diseases, but much remains to be investigated. This review attempts to highlight the functional relevance of astrocytes in normal and neuropathological conditions by showing the molecular and cellular mechanisms of their role in the CNS.

Polymorphic Alpha-Synuclein Oligomers: Characterization and Differential Detection with Novel Corresponding Antibodies

The pathological hallmark of many neurodegenerative diseases is the accumulation of characteristic proteinaceous aggregates. Parkinson's disease and dementia with Lewy bodies can be characterized as synucleinopathies due to the abnormal accumulation of the protein alpha-synuclein (α-Syn). Studies have shown amyloidogenic proteins such as α-Syn and tau can exist as polymorphic aggregates, a theory widely studied mostly in their fibrillar morphology. It is now well understood that an intermediate state of aggregates, oligomers, are the most toxic species. We have shown α-Syn, when modified by different physiological inducers, result in distinct oligomeric conformations of α-Syn. Polymorphic α-Syn oligomers exhibit distinct properties such as aggregate size, conformation, and differentially interact with tau. In this study, we confirm α-Syn oligomeric polymorphs furthermore using in-house novel α-Syn toxic conformation monoclonal antibodies (SynTCs). It is unclear the biological relevance of α-Syn oligomeric polymorphisms. Utilizing a combination of biochemical, biophysical, and cell-based assays, we characterize α-Syn oligomeric polymorphs. We found α-Syn oligomeric polymorphs exhibit distinct immunoreactivity and SynTCs exhibit differential selectivity and binding affinity for α-Syn species. Isothermal titration calorimetry experiments suggest distinct α-Syn:SynTC binding enthalpies in a species-specific manner. Additionally, we found SynTCs differentially reduce α-Syn oligomeric polymorph-mediated neurotoxicity and propagation in primary cortical neurons in a polymorph-specific manner. These studies demonstrate the biological significance of polymorphic α-Syn oligomers along with the importance of polymorph-specific antibodies that target toxic α-Syn aggregates. Monoclonal antibodies that can target the conformational heterogeneity of α-Syn oligomeric species and reduce their mediated toxicity have promising immunotherapeutic potential.

Changing ROS, NAD and AMP: A path to longevity via mitochondrial therapeutics

Lifespan of many organisms, from unicellular yeast to extremely complex human organism, strongly depends on the genetic background and environmental factors. Being among most influential target energy metabolism is affected by macronutrients, their caloric values, and peculiarities of catabolism. Mitochondria are central organelles that respond for energy metabolism in eukaryotic cells. Mitochondria generate reactive oxygen species (ROS), which are lifespan modifying metabolites and a kind of biological clock. Oxidized nicotinamide adenine dinucleotide (NAD⁺) and adenosine monophosphate (AMP) are important metabolic intermediates and molecules that trigger or inhibit several signaling pathways involved in gene silencing, nutrient allocation, and cell regeneration and programmed death. A part of NAD⁺ and AMP metabolism is tied to mitochondria. Using substances that able to target mitochondria, as well as allotopic expression of specific enzymes, are envisioned to be innovative approaches to prolong lifespan by modulation of ROS, NAD⁺, and AMP levels. Among substances, an anti-diabetic drug metformin is believed to increase NAD⁺ and AMP levels, indirectly influencing histone deacetylases, involved in gene silencing, and AMP-activated protein kinase, an energy sensor of cells. Mitochondrially targeted derivatives of ubiquinone were found to interact with ROS. A mitochondrially targeted non-proton-pumping NADH dehydrogenase may influence both ROS and NAD⁺ levels. Chapter describes putative how mitochondria-targeted drugs and NADH dehydrogenase extend lifespan, perspectives of creating drugs with similar properties and their usage as senotherapeutic pills are discussed in the chapter.

Cannabidiol Recovers Dopaminergic Neuronal Damage Induced by Reserpine or α-synuclein in Caenorhabditis elegans

Progressive neurodegenerative disorders such as Parkinson Disease (PD) lack curative or long-term treatments. At the same time, the increase of the worldwide elderly population and, consequently, the extension in the prevalence of age-related diseases have promoted research interest in neurodegenerative disorders. Caenorhabditis elegans is a free-living nematode widely used as an animal model in studies of human diseases. Here we evaluated cannabidiol (CBD) as a possible neuroprotective compound in PD using the C. elegans models exposed to reserpine. Our results demonstrated that CBD reversed the reserpine-induced locomotor alterations and this response was independent of the NPR-19 receptors, an orthologous receptor for central cannabinoid receptor type 1. Morphological alterations of cephalic sensilla (CEP) dopaminergic neurons indicated that CBD also protects neurons from reserpine-induced degeneration. That is, CBD attenuates the reserpine-induced increase of worms with shrunken soma and dendrites loss, increasing the number of worms with intact CEP neurons. Finally, we found that CBD also reduced ROS formation and α-syn protein accumulation in mutant worms. Our findings collectively provide new evidence that CBD acts as neuroprotector in dopaminergic neurons, reducing neurotoxicity and α-syn accumulation highlighting its potential in the treatment of PD.

Synergistic effects of lipopolysaccharide and rotenone on dopamine neuronal damage in rats

INTRODUCTION

The etiology of Parkinson's disease (PD) is still unknown. Until now, oxidative stress and neuroinflammation play a crucial role in the pathogenesis of PD. However, the specific synergistic role of oxidative stress and neuroinflammation in the occurrence and development of PD remains unclear.

METHODS

The changes in motor behavior, dopamine (DA) neurons quantification and their mitochondrial respiratory chain, glial cells activation and secreted cytokines, Nrf2 signaling pathway, and redox balance in the brain of rats were evaluated.

RESULTS

Lipopolysaccharide (LPS)-induced neuroinflammation and rotenone (ROT)-induced oxidative stress synergistically aggravated motor dysfunction, DA neuron damage, activation of glial cells, and release of related mediators, activation of Nrf2 signaling and destruction of oxidative balance. In addition, further studies indicated that after ROT-induced oxidative stress caused direct damage to DA neurons, LPS-induced inflammatory effects had stronger promoting neurotoxic effects on the above aspects.

CONCLUSIONS

Neuroinflammation and oxidative stress synergistically aggravated DA neuronal loss. Furtherly, oxidative stress followed by neuroinflammation caused more DA neuronal loss than neuroinflammation followed by oxidative stress.

Integrated Multi-Cohort Analysis of the Parkinson's Disease Gut Metagenome

BACKGROUND

The gut microbiome is altered in several neurologic disorders, including Parkinson's disease (PD).

OBJECTIVES

The aim is to profile the fecal gut metagenome in PD for alterations in microbial composition, taxon abundance, metabolic pathways, and microbial gene products, and their relationship with disease progression.

METHODS

Shotgun metagenomic sequencing was conducted on 244 stool donors from two independent cohorts in the United States, including individuals with PD (n = 48, n = 47, respectively), environmental household controls (HC, n = 29, n = 30), and community population controls (PC, n = 41, n = 49). Microbial features consistently altered in PD compared to HC and PC subjects were identified. Data were cross-referenced to public metagenomic data sets from two previous studies in Germany and China to determine generalizable microbiome features.

RESULTS

We find several significantly altered taxa between PD and controls within the two cohorts sequenced in this study. Analysis across global cohorts returns consistent changes only in Intestinimonas butyriciproducens. Pathway enrichment analysis reveals disruptions in microbial carbohydrate and lipid metabolism and increased amino acid and nucleotide metabolism in PD. Global gene-level signatures indicate an increased response to oxidative stress, decreased cellular growth and microbial motility, and disrupted intercommunity signaling.

CONCLUSIONS

A metagenomic meta-analysis of PD shows consistent and novel alterations in functional metabolic potential and microbial gene abundance across four independent studies from three continents. These data reveal that stereotypic changes in the functional potential of the gut microbiome are a consistent feature of PD, highlighting potential diagnostic and therapeutic avenues for future research. © 2023 The Authors. Movement Disorders published by Wiley Periodicals LLC on behalf of International Parkinson and Movement Disorder Society.

Dysfunction of the noradrenergic system drives inflammation, α-synucleinopathy, and neuronal loss in mouse colon

Clinical and pathological evidence revealed that α-synuclein (α-syn) pathology seen in PD patients starts in the gut and spreads via anatomically connected structures from the gut to the brain. Our previous study demonstrated that depletion of central norepinephrine (NE) disrupted brain immune homeostasis, producing a spatiotemporal order of neurodegeneration in the mouse brain. The purpose of this study was 1) to determine the role of peripheral noradrenergic system in the maintenance of gut immune homeostasis and in the pathogenesis of PD and 2) to investigate whether NE-depletion induced PD-like α-syn pathological changes starts from the gut. For these purposes, we investigated time-dependent changes of α-synucleinopathy and neuronal loss in the gut following a single injection of DSP-4 (a selective noradrenergic neurotoxin) to A53T-SNCA (human mutant α-syn) over-expression mice. We found DPS-4 significantly reduced the tissue level of NE and increased immune activities in gut, characterized by increased number of phagocytes and proinflammatory gene expression. Furthermore, a rapid-onset of α-syn pathology was observed in enteric neurons after 2 weeks and delayed dopaminergic neurodegeneration in the substantia nigra was detected after 3-5 months, associated with the appearance of constipation and impaired motor function, respectively. The increased α-syn pathology was only observed in large, but not in the small, intestine, which is similar to what was observed in PD patients. Mechanistic studies reveal that DSP-4-elicited upregulation of NADPH oxidase (NOX2) initially occurred only in immune cells during the acute intestinal inflammation stage, and then spread to enteric neurons and mucosal epithelial cells during the chronic inflammation stage. The upregulation of neuronal NOX2 correlated well with the extent of α-syn aggregation and subsequent enteric neuronal loss, suggesting that NOX2-generated reactive oxygen species play a key role in α-synucleinopathy. Moreover, inhibiting NOX2 by diphenyleneiodonium or restoring NE function by salmeterol (a β2-receptor agonist) significantly attenuated colon inflammation, α-syn aggregation/propagation, and enteric neurodegeneration in the colon and ameliorated subsequent behavioral deficits. Taken together, our model of PD shows a progressive pattern of pathological changes from the gut to the brain and suggests a potential role of the noradrenergic dysfunction in the pathogenesis of PD.

Oxidative Stress in Age-Related Neurodegenerative Diseases: An Overview of Recent Tools and Findings

Reactive oxygen species (ROS) have been described to induce a broad range of redox-dependent signaling reactions in physiological conditions. Nevertheless, an excessive accumulation of ROS leads to oxidative stress, which was traditionally considered as detrimental for cells and organisms, due to the oxidative damage they cause to biomolecules. During ageing, elevated ROS levels result in the accumulation of damaged proteins, which may exhibit altered enzymatic function or physical properties (e.g., aggregation propensity). Emerging evidence also highlights the relationship between oxidative stress and age-related pathologies, such as protein misfolding-based neurodegenerative diseases (e.g., Parkinson's (PD), Alzheimer's (AD) and Huntington's (HD) diseases). In this review we aim to introduce the role of oxidative stress in physiology and pathology and then focus on the state-of-the-art techniques available to detect and quantify ROS and oxidized proteins in live cells and in vivo, providing a guide to those aiming to characterize the role of oxidative stress in ageing and neurodegenerative diseases. Lastly, we discuss recently published data on the role of oxidative stress in neurological disorders.

Dopamine, Immunity, and Disease

The neurotransmitter dopamine is a key factor in central nervous system (CNS) function, regulating many processes including reward, movement, and cognition. Dopamine also regulates critical functions in peripheral organs, such as blood pressure, renal activity, and intestinal motility. Beyond these functions, a growing body of evidence indicates that dopamine is an important immunoregulatory factor. Most types of immune cells express dopamine receptors and other dopaminergic proteins, and many immune cells take up, produce, store, and/or release dopamine, suggesting that dopaminergic immunomodulation is important for immune function. Targeting these pathways could be a promising avenue for the treatment of inflammation and disease, but despite increasing research in this area, data on the specific effects of dopamine on many immune cells and disease processes remain inconsistent and poorly understood. Therefore, this review integrates the current knowledge of the role of dopamine in immune cell function and inflammatory signaling across systems. We also discuss the current understanding of dopaminergic regulation of immune signaling in the CNS and peripheral tissues, highlighting the role of dopaminergic immunomodulation in diseases such as Parkinson's disease, several neuropsychiatric conditions, neurologic human immunodeficiency virus, inflammatory bowel disease, rheumatoid arthritis, and others. Careful consideration is given to the influence of experimental design on results, and we note a number of areas in need of further research. Overall, this review integrates our knowledge of dopaminergic immunology at the cellular, tissue, and disease level and prompts the development of therapeutics and strategies targeted toward ameliorating disease through dopaminergic regulation of immunity. SIGNIFICANCE STATEMENT: Canonically, dopamine is recognized as a neurotransmitter involved in the regulation of movement, cognition, and reward. However, dopamine also acts as an immune modulator in the central nervous system and periphery. This review comprehensively assesses the current knowledge of dopaminergic immunomodulation and the role of dopamine in disease pathogenesis at the cellular and tissue level. This will provide broad access to this information across fields, identify areas in need of further investigation, and drive the development of dopaminergic therapeutic strategies.

Gut-brain axis: Review on the association between Parkinson's disease and plant lectins

Gastrointestinal (GI) involvement in the pathogenesis of Parkinson's Disease (PD) has been widely recognized and supported in recent literature. Prospective and retrospective studies found non-motor symptoms within the GI, specifically constipation, precede cardinal signs and cognitive decline by almost 20 years. In 2002, Braak et al. were the first to propose that PD is a six-stage propagating neuropathological process originating from the GI tract (GIT). Aggregated α-synuclein (α-syn) protein from the GIT is pathognomonic for the development of PD. This article reviews the current literature from the past 10 years as well as original research found in PubMed on the combined effects of enteric glial cells and lectins on the development of Parkinson's Disease. Studies have found that these aggregated and phosphorylated proteins gain access to the brain via retrograde transport through fast and slow fibers of intestinal neurons. Plant lectins, commonly found within plant-based diets, have been found to induce Leaky Gut Syndrome and can activate enteric glial cells, causing the release of pro-inflammatory cytokines. Oxidative stress on the enteric neurons, caused by a chronic neuro-inflammatory state, can cause a-syn aggregation and lead to Lewy Body formation, a hallmark finding in PD. Although the current literature provides a connection between the consumption of plant lectins and the pathophysiology of PD, further research is required to evaluate confounding variables such as food antigen mimicry and other harmful substances found in our diets.

Neuronal Oxidative Stress Promotes α-Synuclein Aggregation In Vivo

Both genetic and environmental factors increase risk for Parkinson's disease. Many of the known genetic factors influence α-synuclein aggregation or degradation, whereas most of the identified environmental factors produce oxidative stress. Studies using in vitro approaches have identified mechanisms by which oxidative stress can accelerate the formation of α-synuclein aggregates, but there is a paucity of evidence supporting the importance of these processes over extended time periods in brain. To assess this issue, we evaluated α-synuclein aggregates in brains of three transgenic mouse strains: hSyn mice, which overexpress human α-synuclein in neurons and spontaneously develop α-synuclein aggregates; EAAT3^-/- mice, which exhibit a neuron-specific impairment in cysteine uptake and resultant neuron-selective chronic oxidative stress; and double-transgenic hSyn/EAAT3^-/- mice. Aggregate formation was evaluated by quantitative immunohistochemistry for phosphoserine 129 α-synuclein and by an α-synuclein proximity ligation assay. Both methods showed that the double transgenic hSyn/EAAT3^-/- mice exhibited a significantly higher α-synuclein aggregate density than littermate hSyn mice in each brain region examined. Negligible aggregate formation was observed in the EAAT3^-/- mouse strain, suggesting a synergistic rather than additive interaction between the two genotypes. A similar pattern of results was observed in assessments of motor function: the pole test and rotarod test. Together, these observations indicate that chronic, low-grade neuronal oxidative stress promotes α-synuclein aggregate formation in vivo. This process may contribute to the mechanism by which environmentally induced oxidative stress contributes to α-synuclein pathology in idiopathic Parkinson's disease.

Neuronal hyperactivity-induced oxidant stress promotes in vivo α-synuclein brain spreading

Interneuronal transfer and brain spreading of pathogenic proteins are features of neurodegenerative diseases. Pathophysiological conditions and mechanisms affecting this spreading remain poorly understood. This study investigated the relationship between neuronal activity and interneuronal transfer of α-synuclein, a Parkinson-associated protein, and elucidated mechanisms underlying this relationship. In a mouse model of α-synuclein brain spreading, hyperactivity augmented and hypoactivity attenuated protein transfer. Important features of neuronal hyperactivity reported here were an exacerbation of oxidative and nitrative reactions, pronounced accumulation of nitrated α-synuclein, and increased protein aggregation. Data also pointed to mitochondria as key targets and likely sources of reactive oxygen and nitrogen species within hyperactive neurons. Rescue experiments designed to counteract the increased burden of reactive oxygen species reversed hyperactivity-induced α-synuclein nitration, aggregation, and interneuronal transfer, providing first evidence of a causal link between these pathological effects of neuronal stimulation and indicating a mechanistic role of oxidant stress in hyperactivity-induced α-synuclein spreading.

Role of post-translational modifications on the alpha-synuclein aggregation-related pathogenesis of Parkinson’s disease

Together with neuronal loss, the existence of insoluble inclusions of alpha-synuclein (α-syn) in the brain is widely accepted as a hallmark of synucleinopathies including Parkinson’s disease (PD), multiple system atrophy, and dementia with Lewy body. Because the α-syn aggregates are deeply involved in the pathogenesis, there have been many attempts to demonstrate the mechanism of the aggregation and its potential causative factors including post-translational modifications (PTMs). Although no concrete conclusions have been made based on the previous study results, growing evidence suggests that modifications such as phosphorylation and ubiquitination can alter α-syn characteristics to have certain effects on the aggregation process in PD; either facilitating or inhibiting fibrillization. In the present work, we reviewed studies showing the significant impacts of PTMs on α-syn aggregation. Furthermore, the PTMs modulating α-syn aggregation-induced cell death have been discussed. 

NXP031 prevents dopaminergic neuronal loss and oxidative damage in the AAV-WT-α-synuclein mouse model of Parkinson’s disease

Parkinson’s disease (PD) is a neurodegenerative disease characterized by inclusions of aggregated α-synuclein (α-Syn). Oxidative stress plays a critical role in nigrostriatal degeneration and is responsible for α-Syn aggregation in PD. Vitamin C or ascorbic acid acts as an effective antioxidant to prevent free radical damage. However, vitamin C is easily oxidized and often loses its physiological activity, limiting its therapeutic potential. The objective of this study was to evaluate whether NXP031, a new compound we developed consisting of Aptamin C and Vitamin C, is neuroprotective against α-synucleinopathy. To model α-Syn induced PD, we stereotactically injected AAV particles overexpressing human α-Syn into the substantia nigra (SN) of mice. One week after AAV injection, NXP031 was administered via oral gavage every day for eight weeks. We found that oral administration of NXP031 ameliorated motor deficits measured by the rotarod test and prevented the loss of nigral dopaminergic neurons caused by WT-α-Syn overexpression in the SN. Also, NXP031 blocked the propagation of aggregated α-Syn into the hippocampus by alleviating oxidative stress. These results indicate that NXP031 can be a potential therapeutic for PD.

Hypoxia and Alpha-Synuclein: Inextricable Link Underlying the Pathologic Progression of Parkinson's Disease

Parkinson's disease (PD) is the second most common neurodegenerative disease after Alzheimer's disease, with typical motor symptoms as the main clinical manifestations. At present, there are about 10 million patients with PD in the world, and its comorbidities and complications are numerous and incurable. Therefore, it is particularly important to explore the pathogenesis of PD and find possible therapeutic targets. Because the etiology of PD is complex, involving genes, environment, and aging, finding common factors is the key to identifying intervention targets. Hypoxia is ubiquitous in the natural environment and disease states, and it is considered to be closely related to the etiology of PD. Despite research showing that hypoxia increases the expression and aggregation of alpha-synuclein (α-syn), the most important pathogenic protein, there is still a lack of systematic studies on the role of hypoxia in α-syn pathology and PD pathogenesis. Considering that hypoxia is inextricably linked with various causes of PD, hypoxia may be a co-participant in many aspects of the PD pathologic process. In this review, we describe the risk factors for PD, and we discuss the possible role of hypoxia in inducing PD pathology by these risk factors. Furthermore, we attribute the pathological changes caused by PD etiology to oxygen uptake disorder and oxygen utilization disorder, thus emphasizing the possibility of hypoxia as a critical link in initiating or promoting α-syn pathology and PD pathogenesis. Our study provides novel insight for exploring the pathogenesis and therapeutic targets of PD.

Therapeutic functions of astrocytes to treat α-synuclein pathology in Parkinson’s disease

Intraneuronal inclusions of misfolded α-synuclein (α-syn) and prion-like spread of the pathologic α-syn contribute to progressive neuronal death in Parkinson’s disease (PD). Despite the pathologic significance, no efficient therapeutic intervention targeting α-synucleinopathy has been developed. In this study, we provide evidence that astrocytes, especially those cultured from the ventral midbrain (VM), show therapeutic potential to alleviate α-syn pathology in multiple in vitro and in vivo α-synucleinopathic models. Regulation of neuronal α-syn proteostasis underlies the therapeutic function of astrocytes. Specifically, VM-derived astrocytes inhibited neuronal α-syn aggregation and transmission in a paracrine manner by correcting not only intraneuronal oxidative and mitochondrial stresses but also extracellular inflammatory environments, in which α-syn proteins are prone to pathologic misfolding. The astrocyte-derived paracrine factors also promoted disassembly of extracellular α-syn aggregates. In addition to the aggregated form of α-syn, VM astrocytes reduced total α-syn protein loads both by actively scavenging extracellular α-syn fibrils and by a paracrine stimulation of neuronal autophagic clearance of α-syn. Transplantation of VM astrocytes into the midbrain of PD model mice alleviated α-syn pathology and protected the midbrain dopamine neurons from neurodegeneration. We further showed that cografting of VM astrocytes could be exploited in stem cell–based therapy for PD, in which host-to-graft transmission of α-syn pathology remains a critical concern for long-term cell therapeutic effects.

Dual Effects of Presynaptic Membrane Mimetics on α-Synuclein Amyloid Aggregation

Aggregation of intrinsically disordered α-synuclein (αSN) under various conditions is closely related to synucleinopathies. Although various biological membranes have shown to alter the structure and aggregation propensity of αSN, a thorough understanding of the molecular and mechanical mechanism of amyloidogenesis in membranes remains unanswered. Herein, we examined the structural changes, binding properties, and amyloidogenicity of three variations of αSN mutants under two types of liposomes, 1,2-Dioleoyl-sn-glycero-3-Phosphocholine (DOPC) and presynaptic vesicle mimetic (Mimic) membranes. While neutrally charged DOPC membranes elicited marginal changes in the structure and amyloid fibrillation of αSNs, negatively charged Mimic membranes induced dramatic helical folding and biphasic amyloid generation. At low concentration of Mimic membranes, the amyloid fibrillation of αSNs was promoted in a dose-dependent manner. However, further increases in the concentration constrained the fibrillation process. These results suggest the dual effect of Mimic membranes on regulating the amyloidogenesis of αSN, which is rationalized by the amyloidogenic structure of αSN and condensation-dilution of local αSN concentration. Finally, we propose physicochemical properties of αSN and membrane surfaces, and their propensity to drive electrostatic interactions as decisive factors of amyloidogenesis.

Biological Potential, Gastrointestinal Digestion, Absorption, and Bioavailability of Algae-Derived Compounds with Neuroprotective Activity: A Comprehensive Review

Currently, there is no known cure for neurodegenerative disease. However, the available therapies aim to manage some of the symptoms of the disease. Human neurodegenerative diseases are a heterogeneous group of illnesses characterized by progressive loss of neuronal cells and nervous system dysfunction related to several mechanisms such as protein aggregation, neuroinflammation, oxidative stress, and neurotransmission dysfunction. Neuroprotective compounds are essential in the prevention and management of neurodegenerative diseases. This review will focus on the neurodegeneration mechanisms and the compounds (proteins, polyunsaturated fatty acids (PUFAs), polysaccharides, carotenoids, phycobiliproteins, phenolic compounds, among others) present in seaweeds that have shown in vivo and in vitro neuroprotective activity. Additionally, it will cover the recent findings on the neuroprotective effects of bioactive compounds from macroalgae, with a focus on their biological potential and possible mechanism of action, including microbiota modulation. Furthermore, gastrointestinal digestion, absorption, and bioavailability will be discussed. Moreover, the clinical trials using seaweed-based drugs or extracts to treat neurodegenerative disorders will be presented, showing the real potential and limitations that a specific metabolite or extract may have as a new therapeutic agent considering the recent approval of a seaweed-based drug to treat Alzheimer’s disease.

Early Forms of α-Synuclein Pathology Are Associated with Neuronal Complex I Deficiency in the Substantia Nigra of Individuals with Parkinson’s Disease

Idiopathic Parkinson’s disease (iPD) is characterized by degeneration of the dopaminergic substantia nigra pars compacta (SNc), typically in the presence of Lewy pathology (LP) and mitochondrial respiratory complex I (CI) deficiency. LP is driven by α-synuclein aggregation, morphologically evolving from early punctate inclusions to Lewy bodies (LBs). The relationship between α-synuclein aggregation and CI deficiency in iPD is poorly understood. While studies in models suggest they are causally linked, observations in human SNc show that LBs preferentially occur in CI intact neurons. Since LBs are end-results of α-synuclein aggregation, we hypothesized that the relationship between LP and CI deficiency may be better reflected in neurons with early-stage α-synuclein pathology. Using quadruple immunofluorescence in SNc tissue from eight iPD subjects, we assessed the relationship between neuronal CI or CIV deficiency and early or late forms of LP. In agreement with previous findings, we did not observe CI-negative neurons with late LP. In contrast, early LP showed a significant predilection for CI-negative neurons (p = 6.3 × 10⁻⁵). CIV deficiency was not associated with LP. Our findings indicate that early α-syn aggregation is associated with CI deficiency in iPD, and suggest a double-hit mechanism, where neurons exhibiting both these pathologies are selectively lost.

Icaritin attenuates 6-OHDA-induced MN9D cell damage by inhibiting oxidative stress

Background

We assessed whether ICT can alleviate 6-OHDA-induced cell damage via inhibition of oxidative stress by evaluating the protective effect of icaritin (ICT) against 6-hydroxydopamine (6-OHDA)-induced MN9D cell damage and further determined the mechanism by which ICT reduces oxidative stress.

Methods

MN9D cells were treated with 6-OHDA, to study the mechanism underlying the neuroprotective effect of ICT. MN9D cell damage was assessed by the CCK-8 assay, flow cytometry was performed to measure the content of reactive oxygen species (ROS) in cells, a superoxide dismutase (SOD) kit was used to evaluate SOD activity, and Western blotting was used to measure the expression of α-synuclein (α-Syn), Tyrosine hydroxylase (TH), nuclear factor erythroid-2 related factor 2 (Nrf2), and heme oxygenase-1 (HO-1).

Results

ICT reduced damage to MN9D cells induced by 6-OHDA. ICT increased SOD activity and TH expression and reduced ROS production and α-Syn expression. ICT promoted the translocation of Nrf2 from the cytoplasm to the nucleus and further increased the protein expression of HO-1.

Conclusions

ICT protects against 6-OHDA-induced dopaminergic neuronal cell injury by attenuating oxidative stress, and the mechanism is related to modulate the activities of Nrf2, HO-1 protein, and SOD.

Identification of Novel Oxindole Compounds That Suppress ER Stress-Induced Cell Death as Chemical Chaperones

Endoplasmic reticulum (ER) stress and oxidative stress lead to protein misfolding, and the resulting accumulation of protein aggregates is often associated with the pathogenesis of neurodegenerative diseases, including Alzheimer's disease, Parkinson's disease, amyotrophic lateral sclerosis, and prion disease. Small molecules preventing these pathogenic processes may be effective interventions for such neurodegenerative disorders. In this paper, we identify several novel oxindole compounds that can prevent ER stress- and oxidative stress-induced cell death. Among them, derivatives of the lead compound GIF-0726-r in which a hydrogen atom at the oxindole ring 5 position is substituted with a methyl (GIF-0852-r), bromine (GIF-0854-r), or nitro (GIF-0856-r) group potently suppressed global ER stress. Furthermore, GIF-0854-r and -0856-r prevented protein aggregate accumulation in vitro and in cultured hippocampal HT22 neuronal cells, indicating that these two compounds function effectively as chemical chaperones. In addition, GIF-0852-r, -0854-r, and -0856-r prevented glutamate-induced oxytosis and erastin-induced ferroptosis. Collectively, these results suggest that the novel oxindole compounds GIF-0854-r and -0856-r may be useful therapeutics against protein-misfolding diseases as well as valuable research tools for studying the molecular mechanisms of ER and oxidative stress.

Effects of oligomer toxicity, fibril toxicity and fibril spreading in synucleinopathies

Protein misfolding is a general hallmark of protein deposition diseases, such as Alzheimer’s disease or Parkinson’s disease, in which different types of aggregated species (oligomers, protofibrils and fibrils) are generated by the cells. Despite widespread interest, the relationship between oligomers and fibrils in the aggregation process and spreading remains elusive. A large variety of experimental evidences supported the idea that soluble oligomeric species of different proteins might be more toxic than the larger fibrillar forms. Furthermore, the lack of correlation between the presence of the typical pathological inclusions and disease sustained this debate. However, recent data show that the β-sheet core of the α-Synuclein (αSyn) fibrils is unable to establish persistent interactions with the lipid bilayers, but they can release oligomeric species responsible for an immediate dysfunction of the recipient neurons. Reversibly, such oligomeric species could also contribute to pathogenesis via neuron-to-neuron spreading by their direct cell-to-cell transfer or by generating new fibrils, following their neuronal uptake. In this Review, we discuss the various mechanisms of cellular dysfunction caused by αSyn, including oligomer toxicity, fibril toxicity and fibril spreading.

Catalytic antimicrobial therapy using nanozymes

Nanozymes are nanomaterials with enzyme-like characteristics, which catalyze the conversion of enzyme substrates and follow enzymatic kinetics under physiological conditions. As a new generation of artificial enzymes, nanozymes provide alternative approaches for those upon enzymatic catalysis. Compared with natural enzymes, nanozymes have the advantages of simple preparation, good stability and low cost, which makes nanozymes promising for application in many fields, such as antimicrobial infection treatment. Many studies have reported that nanozymes are capable of killing a number of pathogenic bacteria with resistance, fungi as well as viruses, and have shown great curative effects for diseases caused by these pathogens. Herein, we summarize the application of nanozymes for antibacterial, antiviral, and antifungal therapies and outline the issues needing resolution in the future. This article is categorized under: Therapeutic Approaches and Drug Discovery > Nanomedicine for Infectious Disease.

Akkermansia muciniphila induces mitochondrial calcium overload and α -synuclein aggregation in an enteroendocrine cell line

The gut microbiota influence neurodevelopment, modulate behavior, and contribute to neurodegenerative disorders. Several studies have consistently reported a greater abundance of Akkermansia muciniphila in Parkinson disease (PD) fecal samples. Therefore, we investigated whether A.muciniphila-conditioned medium (CM) could initiate α-synuclein (αSyn) misfolding in enteroendocrine cells (EEC) — a component of the gut epithelium featuring neuron-like properties. We found that A. muciniphila CM composition is influenced by the ability of the strain to degrade mucin. Our in vitro experiments showed that the protein-enriched fraction of mucin-free CM induces RyR-mediated Ca²⁺ release and increased mitochondrial Ca²⁺ uptake leading to ROS generation and αSyn aggregation. Oral administration of A. muciniphila cultivated in the absence of mucin to mice led to αSyn aggregation in cholecystokinin (CCK)-positive EECs but no motor deficits were observed. Noteworthy, buffering mitochondrial Ca²⁺ reverted the damaging effects observed. These molecular insights offer evidence that bacterial proteins can induce αSyn aggregation in EECs.

•

Gut bacterium Akkermansia muciniphila is increased in patients with Parkinson disease

•

A. muciniphila-conditioned medium induces mitochondrial Ca²⁺ overload in EECs

•

Mitochondrial Ca²⁺ overload leads to ROS generation and αSyn aggregation in vitro

•

Buffering mitochondrial Ca²⁺ inhibits A. muciniphila-induced αSyn aggregation

Novel Psychoactive Substances: The Razor's Edge between Therapeutical Potential and Psychoactive Recreational Misuse

BACKGROUND

Novel psychoactive substances (NPS) are compounds of natural and synthetic origin, similar to traditional drugs of abuse. NPS are involved in a contemporary trend whose origin lies in a thinner balance between legitimate therapeutic drug research and legislative control. The contemporary NPS trend resulted from the replacement of MDMA by synthetic cathinones in 'ecstasy' during the 2000s. The most common NPS are synthetic cannabinoids and synthetic cathinones. Interestingly, during the last 50 years, these two classes of NPS have been the object of scientific research for a set of health conditions.

METHODS

Searches were conducted in the online database PubMed using boolean equations.

RESULTS

Synthetic cannabinoids displayed protective and therapeutic effects for inflammatory, neurodegenerative and oncologic pathologies, activating the immune system and reducing inflammation. Synthetic cathinones act similarly to amphetamine-type stimulants and can be used for depression and chronic fatigue.

CONCLUSIONS

Despite the scientific advances in this field of research, pharmacological application of NPS is being jeopardized by fatalities associated with their recreational use. This review addresses the scientific achievements of these two classes of NPS and the toxicological data, ending with a reflection on Illicit and NPS control frames.

Lactobacillus plantarum DP189 Reduces α-SYN Aggravation in MPTP-Induced Parkinson's Disease Mice via Regulating Oxidative Damage, Inflammation, and Gut Microbiota Disorder

This study aimed to evaluate the attenuating effect of Lactobacillus plantarum DP189 on α-synuclein (α-SYN) aggregates in the substantia nigra (SN) of Parkinson's disease (PD) mice via 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-induced. Our results indicated that L. plantarum DP189 increased the levels of superoxide dismutase (SOD), glutathione peroxide (GSH-Px), and interleukin-10 (IL-10) and decreased the levels of malondialdehyde (MDA), reactive oxygen species (ROS), tumor necrosis factor-α (TNF-α), interleukin-6 (IL-6), and interleukin-1β (IL-1β). Moreover, L. plantarum DP189 reduced the α-SYN accumulation in SN. Mechanistically, L. plantarum DP189 activated the expression of nuclear factor erythroid 2-related factor (Nrf2)/ARE and PGC-1α pathways and suppressed the NLRP3 inflammasome. Furthermore, fecal analysis showed that L. plantarum DP189 reshaped the gut microbiota in PD mice by reducing the number of pathogenic bacteria (Proteobacteria and Actinobacteria) and increased the abundance of probiotics (Lactobacillus and Prevotella). Our results suggested that L. plantarum DP189 could delay the neurodegeneration caused by the accumulation of α-SYN in the SN of PD mice via suppressing oxidative stress, repressing proinflammatory response, and modulating gut microbiota.

The Gut-Brain Axis and Its Relation to Parkinson's Disease: A Review

Parkinson's disease is a chronic neurodegenerative disease characterized by the accumulation of misfolded alpha-synuclein protein (Lewy bodies) in dopaminergic neurons of the substantia nigra and other related circuitry, which contribute to the development of both motor (bradykinesia, tremors, stiffness, abnormal gait) and non-motor symptoms (gastrointestinal issues, urinogenital complications, olfaction dysfunction, cognitive impairment). Despite tremendous progress in the field, the exact pathways and mechanisms responsible for the initiation and progression of this disease remain unclear. However, recent research suggests a potential relationship between the commensal gut bacteria and the brain capable of influencing neurodevelopment, brain function and health. This bidirectional communication is often referred to as the microbiome-gut-brain axis. Accumulating evidence suggests that the onset of non-motor symptoms, such as gastrointestinal manifestations, often precede the onset of motor symptoms and disease diagnosis, lending support to the potential role that the microbiome-gut-brain axis might play in the underlying pathological mechanisms of Parkinson's disease. This review will provide an overview of and critically discuss the current knowledge of the relationship between the gut microbiota and Parkinson's disease. We will discuss the role of α-synuclein in non-motor disease pathology, proposed pathways constituting the connection between the gut microbiome and the brain, existing evidence related to pre- and probiotic interventions. Finally, we will highlight the potential opportunity for the development of novel preventative measures and therapeutic options that could target the microbiome-gut-brain axis in the context of Parkinson's disease.

Opposite Roles of Co-enzyme Q10 and Formaldehyde in Neurodegenerative Diseases

Most of neurodegenerative diseases (NDD) have no cure. The common etiology of neurodegenerations is unclear. Air pollutant-gaseous formaldehyde is notoriously known to induce demyelination and cognitive impairments. Unexpectedly, an amount of formaldehyde has been detected in the brains. Multiple factors can induce the generation and accumulation of endogenous formaldehyde. Excessive formaldehyde can induce oxidative stress to generate H2O2; in turn, H2O2 promote formaldehyde production. Clinical investigations have shown that an abnormal high level of formaldehyde but low level of coenzyme Q10 (coQ10) was observed in patients with NDD. Further studies have proven that excessive formaldehyde directly inactivates coQ10, reduces the ATP generation, enhances oxidative stress, initiates inflammation storm, induces demyelination; subsequently, it results in neurodegeneration. Although the low water solubility of coQ10 limits its clinical application, nanomicellar water-soluble coQ10 exhibits positive therapeutical effects. Hence, nanopackage of coQ10 may be a promising strategy for treating NDD.

Toward a Disease-Modifying Therapy of Alpha-Synucleinopathies: New Molecules and New Approaches Came into the Limelight

The accumulation of the various products of alpha-synuclein aggregation has been associated with the etiology and pathogenesis of several neurodegenerative conditions, including both familial and sporadic forms of Parkinson’s disease (PD) and dementia with Lewy bodies (DLB). It is now well established that the aggregation and spread of alpha-synuclein aggregation pathology activate numerous pathogenic mechanisms that contribute to neurodegeneration and, ultimately, to disease progression. Therefore, the development of a safe and effective disease-modifying therapy that limits or prevents the accumulation of the toxic intermediate products of alpha-synuclein aggregation and the spread of alpha-synuclein aggregation pathology could provide significant positive clinical outcomes in PD/DLB cohorts. It has been suggested that this goal can be achieved by reducing the intracellular and/or extracellular levels of monomeric and already aggregated alpha-synuclein. The principal aim of this review is to critically evaluate the potential of therapeutic strategies that target the post-transcriptional steps of alpha-synuclein production and immunotherapy-based approaches to alpha-synuclein degradation in PD/DLB patients. Strategies aimed at the downregulation of alpha-synuclein production are at an early preclinical stage of drug development and, although they have shown promise in animal models of alpha-synuclein aggregation, many limitations need to be resolved before in-human clinical trials can be seriously considered. In contrast, many strategies aimed at the degradation of alpha-synuclein using immunotherapeutic approaches are at a more advanced stage of development, with some in-human Phase II clinical trials currently in progress. Translational barriers for both strategies include the limitations of alpha-synuclein aggregation models, poor understanding of the therapeutic window for the alpha-synuclein knockdown, and variability in alpha-synuclein pathology across patient cohorts. Overcoming such barriers should be the main focus of further studies. However, it is already clear that these strategies do have the potential to achieve a disease-modifying effect in PD and DLB.

Severe and Regionally Widespread Increases in Tissue Urea in the Human Brain Represent a Novel Finding of Pathogenic Potential in Parkinson's Disease Dementia

Widespread elevations in brain urea have, in recent years, been reported in certain types of age-related dementia, notably Alzheimer’s disease (AD) and Huntington’s disease (HD). Urea increases in these diseases are substantive, and approximate in magnitude to levels present in uraemic encephalopathy. In AD and HD, elevated urea levels are widespread, and not only in regions heavily affected by neurodegeneration. However, measurements of brain urea have not hitherto been reported in Parkinson’s disease dementia (PDD), a condition which shares neuropathological and symptomatic overlap with both AD and HD. Here we report measurements of tissue urea from nine neuropathologically confirmed regions of the brain in PDD and post-mortem delay (PMD)-matched controls, in regions including the cerebellum, motor cortex (MCX), sensory cortex, hippocampus (HP), substantia nigra (SN), middle temporal gyrus (MTG), medulla oblongata (MED), cingulate gyrus, and pons, by applying ultra-high-performance liquid chromatography-tandem mass spectrometry (UHPLC-MS/MS). Urea concentrations were found to be substantively elevated in all nine regions, with average increases of 3–4-fold. Urea concentrations were remarkably consistent across regions in both cases and controls, with no clear distinction between regions heavily affected or less severely affected by neuronal loss in PDD. These urea elevations mirror those found in uraemic encephalopathy, where equivalent levels are generally considered to be pathogenic, and those previously reported in AD and HD. Increased urea is a widespread metabolic perturbation in brain metabolism common to PDD, AD, and HD, at levels equal to those seen in uremic encephalopathy. This presents a novel pathogenic mechanism in PDD, which is shared with two other neurodegenerative diseases.

Rab7 reduces α-synuclein toxicity in rats and primary neurons

During the pathogenesis of Parkinson's disease (PD), aggregation of alpha-synuclein (αSyn) induces a vicious cycle of cellular impairments that lead to neurodegeneration. Consequently, removing toxic αSyn aggregates constitutes a plausible strategy against PD. In this work, we tested whether stimulating the autolysosomal degradation of αSyn aggregates through the Ras-related in brain 7 (Rab7) pathway can reverse αSyn-induced cellular impairment and prevent neurodegeneration in vivo. The disease-related A53T mutant of αSyn was expressed in primary neurons and in dopaminergic neurons of the rat brain simultaneously with wild type (WT) Rab7 or the T22N mutant as negative control. The cellular integrity was quantified by morphological and biochemical analyses. In primary neurons, WT Rab7 rescued the αSyn-induced loss of neurons and neurites. Furthermore, Rab7 decreased the amount of reactive oxygen species and the amount of Triton X-100 insoluble αSyn. In rat brain, WT Rab7 reduced αSyn-induced loss of dopaminergic axon terminals in the striatum and the loss of dopaminergic dendrites in the substantia nigra pars reticulata. Further, WT Rab7 lowered αSyn pathology as quantified by phosphorylated αSyn staining. Finally, WT Rab7 attenuated αSyn-induced DNA damage in primary neurons and rat brain. In brief, Rab7 reduced αSyn-induced pathology, ameliorated αSyn-induced neuronal degeneration, oxidative stress and DNA damage. These findings indicate that Rab7 is able to disrupt the vicious cycle of cellular impairment, αSyn pathology and neurodegeneration present in PD. Stimulation of Rab7 and the autolysosomal degradation pathway could therefore constitute a beneficial strategy for PD.

Anti-Oxidative, Anti-Inflammatory and Anti-Apoptotic Effects of Flavonols: Targeting Nrf2, NF-κB and p53 Pathways in Neurodegeneration

Neurodegenerative diseases are one of the leading causes of disability and death worldwide. Intracellular transduction pathways that end in the activation of specific transcription factors are highly implicated in the onset and progression of pathological changes related to neurodegeneration, of which those related to oxidative stress (OS) and neuroinflammation are particularly important. Here, we provide a brief overview of the key concepts related to OS- and neuroinflammation-mediated neuropathological changes in neurodegeneration, together with the role of transcription factors nuclear factor erythroid 2-related factor 2 (Nrf2) and nuclear factor-κB (NF-κB). This review is focused on the transcription factor p53 that coordinates the cellular response to diverse genotoxic stimuli, determining neuronal death or survival. As current pharmacological options in the treatment of neurodegenerative disease are only symptomatic, many research efforts are aimed at uncovering efficient disease-modifying agents. Natural polyphenolic compounds demonstrate powerful anti-oxidative, anti-inflammatory and anti-apoptotic effects, partially acting as modulators of signaling pathways. Herein, we review the current understanding of the therapeutic potential and limitations of flavonols in neuroprotection, with emphasis on their anti-oxidative, anti-inflammatory and anti-apoptotic effects along the Nrf2, NF-κB and p53 pathways. A better understanding of cellular and molecular mechanisms of their action may pave the way toward new treatments.

Novel Therapies for Parkinsonian Syndromes-Recent Progress and Future Perspectives

Background: Atypical parkinsonian syndromes are rare, fatal neurodegenerative diseases associated with abnormal protein accumulation in the brain. Examples of these syndromes include progressive supranuclear palsy, multiple system atrophy, and corticobasal degeneration. A common clinical feature in parkinsonism is a limited improvement with levodopa. So far, there are no disease-modifying treatments to address these conditions, and therapy is only limited to the alleviation of symptoms. Diagnosis is devastating for patients, as prognosis is extremely poor, and the disease tends to progress rapidly. Currently, potential causes and neuropathological mechanisms involved in these diseases are being widely investigated. Objectives: The goal of this review is to summarize recent advances and gather emerging disease-modifying therapies that could slow the progression of atypical parkinsonian syndromes. Methods: PubMed and Google Scholar databases were searched regarding novel perspectives for atypical parkinsonism treatment. The following medical subject headings were used: "atypical parkinsonian syndromes-therapy," "treatment of atypical parkinsonian syndromes," "atypical parkinsonian syndromes-clinical trial," "therapy of tauopathy," "alpha-synucleinopathy treatment," "PSP therapy/treatment," "CBD therapy/treatment," "MSA therapy/treatment," and "atypical parkinsonian syndromes-disease modifying." All search results were manually reviewed prior to inclusion in this review. Results: Neuroinflammation, mitochondrial dysfunction, microglia activation, proteasomal impairment, and oxidative stress play a role in the neurodegenerative process. Ongoing studies and clinical trials target these components in order to suppress toxic protein accumulation. Various approaches such as stem cell therapy, anti-aggregation/anti-phosphorylation agent administration, or usage of active and passive immunization appear to have promising results. Conclusion: Presently, disease-modifying strategies for atypical parkinsonian syndromes are being actively explored, with encouraging preliminary results. This leads to an assumption that developing accurate, safe, and progression-halting treatment is not far off. Nevertheless, the further investigation remains necessary.

Toxic Feedback Loop Involving Iron, Reactive Oxygen Species, α-Synuclein and Neuromelanin in Parkinson's Disease and Intervention with Turmeric

Parkinson's disease (PD) is a movement disorder associated with severe loss of mainly dopaminergic neurons in the substantia nigra. Pathological hallmarks include Lewy bodies, and loss of neuromelanin, due to degeneration of neuromelanin-containing dopaminergic neurons. Despite being described over 200 years ago, the etiology of PD remains unknown. Here, we highlight the roles of reactive oxygen species (ROS), iron, alpha synuclein (α-syn) and neuromelanin in a toxic feedback loop culminating in neuronal death and spread of the disease. Dopaminergic neurons are particularly vulnerable due to decreased antioxidant concentration with aging, constant exposure to ROS and presence of neurotoxic compounds (e.g. ortho-quinones). ROS and iron increase each other's levels, creating a state of oxidative stress. α-Syn aggregation is influenced by ROS and iron but also increases ROS and iron via its induced mitochondrial dysfunction and ferric-reductase activity. Neuromelanin's binding affinity is affected by increased ROS and iron. Furthermore, during neuronal death, neuromelanin is degraded in the extracellular space, releasing its bound toxins. This cycle of events continues to neighboring neurons in the form of a toxic loop, causing PD pathology. The increase in ROS and iron may be an important target for therapies to disrupt this toxic loop, and therefore diets rich in certain 'nutraceuticals' may be beneficial. Turmeric is an attractive candidate, as it is known to have anti-oxidant and iron chelating properties. More studies are needed to test this theory and if validated, this would be a step towards development of lifestyle-based therapeutic modalities to complement existing PD treatments.