Cognitive Impairment Associated with Parkinson's Disease: Role of Mitochondria

Effect of the Flavonoid Rutin on the Modulation of the Myenteric Plexuses in an Experimental Model of Parkinson's Disease

Recent discoveries have shown that enteric glial cells play an important role in different neurodegenerative disorders, such as Parkinson's disease (PD), which is characterized by motor dysfunctions caused by the progressive loss of dopaminergic neurons in the substance nigra pars compacta and non-motor symptoms including gastrointestinal dysfunction. In this study, we investigated the modulatory effects of the flavonoid rutin on the behavior and myenteric plexuses in a PD animal model and the response of enteric glia. Adult male Wistar rats were submitted to stereotaxic injection with 6-hydroxydopamine or saline, and they were untreated or treated with rutin (10 mg/kg) for 14 days. The ileum was collected to analyze tissue reactivity and immunohistochemistry for neurons (HuC/HuD) and enteric glial cells (S100β) in the myenteric plexuses. Behavioral tests demonstrated that treatment with rutin improved the motor capacity of parkinsonian animals and improved intestinal transit without interfering with the cell population; rutin treatment modulated the reactivity of the ileal musculature through muscarinic activation, reducing relaxation through the signaling pathway of nitric oxide donors, and increased the longitudinal contractility of the colon musculature in parkinsonian animals. Rutin revealed modulatory activities on the myenteric plexus, bringing relevant answers regarding the effect of the flavonoid in this system and the potential application of PD adjuvant treatment.

3-N-butylphthalide attenuates neuroinflammation in rotenone-induced Parkinson's disease models via the cGAS-STING pathway

Neuroinflammation is crucial in the onset and progression of dopaminergic neuron loss in Parkinson's disease (PD). We aimed to determine whether 3-N-Butylphthalide (NBP) can protect against PD by inhibiting the cyclic GMP-AMP synthase (cGAS)-stimulator of interferon genes (STING) pathway and the inflammatory response of microglia. MitoSOX/MitoTracker/Hoechst staining was used to detect the levels of mitochondrial reactive oxygen species (ROS) in BV2 cells. Quantitative Real-Time Polymerase Chain Reaction was used to measure the levels of free cytoplasmic mitochondrial DNA (mtDNA) in BV2 cells and mouse brain tissues. Behavioral impairments were assessed using rotarod, T-maze, and balance beam tests. Dopaminergic neurons and microglia were observed using immunohistochemical staining. Expression levels of cGAS, STING, nuclear factor kappa-B (NfκB), phospho- NfκB (p-NfκB), inhibitor of NfκBα (IκBα), and phospho-IκBα (p-IκBα) proteins in the substantia nigra and striatum were detected using Western Blot. NBP decreased mitochondrial ROS levels in rotenone-treated BV2 cells. NBP alleviated behavioral impairments and protected against rotenone-induced microgliosis and damage to dopaminergic neurons in the substantia nigra and striatum of rotenone-induced PD mice. NBP decreased rotenone-induced mtDNA leakage and mitigated neuroinflammation by inhibiting cGAS-STING pathway activation. NBP exhibited a protective effect in rotenone-induced PD models by significantly inhibiting the cGAS-STING pathway. Moreover, NBP can alleviate neuroinflammation, and is a potential therapeutic drug for alleviating clinical symptoms and delaying the progression of PD. This study provided insights for the potential role of NBP in PD therapy, potentially mitigating neurodegeneration, and consequently improving the quality of life and lifespan of patients with PD. The limitations are that we have not confirmed the exact mechanism by which NBP decreases mtDNA leakage, and this study was unable to observe the actual clinical therapeutic effect, so further cohort studies are required for validation.

2-Aminoethoxydiphenyl borate ameliorates mitochondrial dysfunctions in MPTP/MPP+ model of Parkinson's disease

Mitochondrial dysfunction is closely linked with the pathophysiology of several neurodegenerative disorders including Parkinson's disease (PD). Despite several therapeutic advancements related to symptomatic modification of PD pathology, strategies targeting mitochondrial dysfunctions remain largely elusive. Recently, transient receptor potential (TRP) channels have been shown to play a pivotal role in the control of mitochondrial and neuronal functioning in PD. In this study, the effect of 2-aminoethoxydiphenyl borate (2-APB), TRP channel blocker was investigated in the context of mitochondrial dysfunctions in 1-methyl-4-phenylpyridinium (MPP⁺)-treated SH-SY5Y cells and 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-administered Sprague Dawley rats. MPP⁺-treated SH-SY5Y cells exhibited reductions in cell viability, generation of reactive oxygen species (ROS) and loss of mitochondrial membrane potential. Co-treatment with 2-APB led to an increase in cell viability, reduction in intracellular and mitochondrial ROS and improvement in mitochondrial membrane potential compared to MPP⁺-treated SH-SY5Y cells. In addition, intranigral administration of MPTP led to a significant reduction in motor function in the rats. Fourteen days of 2-APB (3 and 10 mg/kg, i.p.) treatment improved behavioural parameters. MPTP-induced decrease in complex I activity and mitochondrial potential were also blocked by 2-APB in the mitochondria isolated from the brain regions i.e. midbrain and striatum. MPTP-induced decrease in tyrosine hydroxylase levels were also restored by 2-APB. Moreover, MPTP-induced reduction in proteins involved in mitochondrial biogenesis, viz. peroxisome proliferator-activated-receptor-gamma coactivator and mitochondrial transcription factor-A were increased after 2-APB treatment in vivo. In summary, 2-APB has a promising neuroprotective role in the MPP⁺/MPTP models of PD via targeting mitochondrial dysfunctions and biogenesis.

Crosstalk between neurological, cardiovascular, and lifestyle disorders: insulin and lipoproteins in the lead role

Insulin resistance and impaired lipoprotein metabolism contribute to a plethora of metabolic and cardiovascular disorders. These alterations have been extensively linked with poor lifestyle choices, such as consumption of a high-fat diet, smoking, stress, and a redundant lifestyle. Moreover, these are also known to increase the co-morbidity of diseases like Type 2 diabetes mellitus and atherosclerosis. Under normal physiological conditions, insulin and lipoproteins exert a neuroprotective role in the central nervous system. However, the tripping of balance between the periphery and center may alter the normal functioning of the brain and lead to neurological disorders such as Alzheimer's disease, Parkinson's disease, stroke, depression, and multiple sclerosis. These neurological disorders are further characterized by certain behavioral and molecular changes that show consistent overlap with alteration in insulin and lipoprotein signaling pathways. Therefore, targeting these two mechanisms not only reveals a way to manage the co-morbidities associated with the circle of the metabolic, central nervous system, and cardiovascular disorders but also exclusively work as a disease-modifying therapy for neurological disorders. In this review, we summarize the role of insulin resistance and lipoproteins in the progression of various neurological conditions and discuss the therapeutic options currently in the clinical pipeline targeting these two mechanisms; in addition, challenges faced in designing these therapeutic approaches have also been touched upon briefly.

Targeting COVID-19 in Parkinson's Patients: Drugs Repurposed

The last couple of months have witnessed the world in a state of virtual standstill. The SARS-CoV-2 virus has overtaken the globe to economic and social lockdown. Many patients with COVID-19 have compromised immunity, especially in an aged population suffering from Parkinson 's disease (PD). Alteration in dopaminergic neurons and deficiency of dopamine in PD patients are the most common symptoms affecting 1% population above the age of 60 years. The compromised immune system and inflammatory manifestation in PD patients make them an easy target. The most common drugs under trial for COVID-19 are remdesivir, favipiravir, chloroquine and hydroxychloroquine, azithromycin along with adjunct drugs like amantadine with some monoclonal antibodies. Presently, clinically US FDA approved drugs in PD include Levodopa, catechol-O-methyl transferase (COMT) inhibitors, (Entacapone and Tolcapone), dopamine agonists (Bromocriptine, Ropinirole, Pramipexole, and Rotigotine), monoamine oxidase B (MAO-B) inhibitors (Selegiline and Rasagiline), amantadine and antimuscarinic drugs. The drugs have established mechanisms of action on PD patients with known pharmacodynamics and pharmacokinetic properties along with dose and adverse effects. Conclusion and relevance of this review focus on the drugs that can be tried on PD patients with SAR CoV-2 infection, in particular, amantadine that has been approved by all the developed countries as a common drug possessing both antiviral properties by downregulation of CTSL, lysosomal pathway disturbance and change in pH necessary to uncoat the viral proteins and anti- Parkinson properties. To deal with the significant prognostic adverse effect of SARS-CoV-2 on PD, the present-day treatment options, clinical presentation and various mechanisms are the need of the hour.

Parkinson's disease in women: Mechanisms underlying sex differences

Parkinson's disease is a neurodegenerative disease which is associated with different motor, cognitive and mood-related problems. Though it has been established that Parkinson's disease is less prevalent in women in comparison to men, the differences tend to diminish with the advancing age. Different genetic, hormonal, neuroendocrinal and molecular players contribute towards the differences in the Parkinson's disease pathogenesis. Furthermore, data available with respect to the therapeutic management of Parkinson's disease in females is limited; women often tend to suffer more from the side effects of the currently available drugs. The present review highlights the sex-specific differences which play a role in the manifestation of these symptoms and side effects of the currently available therapeutic strategies. We have also discussed the current and upcoming therapeutic strategies which are in the clinical trials such as adenosine 2A (A2A) receptor antagonists, estrogen replacement therapy, α-synuclein targeting vaccines and antibodies, Botulinum toxin A, Fas-associated factor-1 (FAF-1) inhibitors, thiazolidinediones, 5-HT1_A receptor agonists, dopamine D1/D5 receptor agonists, Glucagon-like peptide 1 (GLP-1) analogues and certain plant based principles for the treatment of Parkinson's disease in women.

Role of Microgliosis and NLRP3 Inflammasome in Parkinson's Disease Pathogenesis and Therapy

Parkinson's disease (PD) is a neurodegenerative disorder marked primarily by motor symptoms such as rigidity, bradykinesia, postural instability and resting tremor associated with dopaminergic neuronal loss in the Substantia Nigra pars compacta (SNpc) and deficit of dopamine in the basal ganglia. These motor symptoms can be preceded by pre-motor symptoms whose recognition can be useful to apply different strategies to evaluate risk, early diagnosis and prevention of PD progression. Although clinical characteristics of PD are well defined, its pathogenesis is still not completely known, what makes discoveries of therapies capable of curing patients difficult to be reached. Several theories about the cause of idiopathic PD have been investigated and among them, the key role of inflammation, microglia and the inflammasome in the pathogenesis of PD has been considered. In this review, we describe the role and relation of both the inflammasome and microglial activation with the pathogenesis, symptoms, progression and the possibilities for new therapeutic strategies in PD.

Mitochondrial abnormalities in neurodegenerative models and possible interventions: Focus on Alzheimer's disease, Parkinson's disease, Huntington's disease

Mitochondrial abnormalities in the brain are considered early pathological changes in neurogenerative diseases, such as Alzheimer's disease (AD), Parkinson's disease (PD) and Huntington's disease (HD). The mitochondrial dysfunction in the brain can be induced by toxic proteins, including amyloid-beta (Aβ), phosphorylated tau, alpha-synuclein (α-syn) and mutant huntingtin (mtHTT). These proteins cause mitochondrial genome damage, increased oxidative stress, decreased mitochondrial membrane permeability, and diminished ATP production. Consequently, synaptic dysfunction, synaptic loss, neuronal apoptosis, and ultimately cognitive impairment are exhibited. Therefore, the restoration of mitochondrial abnormalities in the brain is an alternative intervention to delay the progression of neurodegenerative diseases in addition to reducing the level of toxic proteins, especially Aβ, and restored synaptic dysfunction by interventions. Here we comprehensively review mitochondrial alterations in the brain of neurodegenerative models, specifically AD, PD and HD, from both in vitro and in vivo studies. Additionally, the correlation between mitochondrial changes, cognitive function, and disease progression from in vivo studies is described. This review also summarizes interventions that possibly attenuate mitochondrial abnormalities in AD, PD and HD models from both in vitro and in vivo studies. This may lead to the introduction of novel therapies that target on brain mitochondria to delay the progression of AD, PD and HD.

Therapeutic potential of pharmacological agents targeting TRP channels in CNS disorders

Central nervous system (CNS) disorders like Alzheimer's disease (AD), Parkinson disease (PD), stroke, epilepsy, depression, and bipolar disorder have a high impact on both medical and social problems due to the surge in their prevalence. All of these neuronal disorders share some common etiologies including disruption of Ca²⁺ homeostasis and accumulation of misfolded proteins. These misfolded proteins further disrupt the intracellular Ca²⁺ homeostasis by disrupting the activity of several ion channels including transient receptor potential (TRP) channels. TRP channel families include non-selective Ca²⁺ permeable channels, which act as cellular sensors activated by various physio-chemical stimuli, exogenous, and endogenous ligands responsible for maintaining the intracellular Ca²⁺ homeostasis. TRP channels are abundantly expressed in the neuronal cells and disturbance in their activity leads to various neuronal diseases. Under the pathological conditions when the activity of TRP channels is perturbed, there is a disruption of the neuronal homeostasis through increased inflammatory response, generation of reactive oxygen species, and mitochondrial dysfunction. Therefore, there is a potential of pharmacological interventions targeting TRP channels in CNS disorders. This review focuses on the role of TRP channels in neurological diseases; also, we have highlighted the current insights into the pharmacological modulators targeting TRP channels.

The Role of NOX4 in Parkinson's Disease with Dementia

The neuropathology of Parkinson's disease with dementia (PDD) has been reported to involve heterogeneous and various disease mechanisms. Alpha-synuclein (α-syn) and amyloid beta (Aβ) pathology are associated with the cognitive status of PDD, and NADPH oxidase (NOX) is known to affect a variety of cognitive functions. We investigated the effects of NOX on cognitive impairment and on α-syn and Aβ expression and aggregation in PDD. In the 6-hydroxydopamine (6-OHDA)-injected mouse model, cognitive and motor function, and the levels of α-syn, Aβ, and oligomer A11 after inhibition of NOX4 expression in the hippocampal dentate gyrus (DG) were measured by the Morris water maze, novel object recognition, rotation, and rotarod tests, as well as immunoblotting and immunohistochemistry. After 6-OHDA administration, the death of nigrostriatal dopamine neurons and the expression of α-syn and NOX1 in the substantia nigra were increased, and phosphorylated α-syn, Aβ, oligomer A11, and NOX4 were upregulated in the hippocampus. 6-OHDA dose-dependent cognitive impairment was observed, and the increased cognitive impairment, Aβ expression, and oligomer A11 production in 6-OHDA-treated mice were suppressed by NOX4 knockdown in the hippocampal DG. Our results suggest that increased expression of NOX4 in the hippocampal DG in the 6-OHDA-treated mouse induces Aβ expression and oligomer A11 production, thereby reducing cognitive function.

P38 Mitogen-activated Protein Kinase and Parkinson's Disease

Parkinson's disease, the second major neurodegenerative disease, has created a great impact on the elder people. Although the mechanisms underlying Parkinson's disease are not fully understood, considerable evidence suggests that neuro-inflammation, oxidative stress, mitochondrial dysfunction, cell proliferation, differentiation and apoptosis are involved in the disease. p38MAPK, an important member of the mitogen-activated protein family, controls several important functions in the cell, suggesting a potential pathogenic role in PD. This review provides a brief description of the role and mechanism of p38MAPK in Parkinson's disease.

Nrf2 Signaling in Sodium Azide-Treated Oligodendrocytes Restores Mitochondrial Functions

Mitochondrial dysfunctions mark a critical step in many central nervous system (CNS) pathologies, including multiple sclerosis (MS). Such dysfunctions lead to depolarization of mitochondrial membranes and imbalanced redox homeostasis. In this context, reactive oxygen species (ROS) are potentially deleterious but can also act as an important signaling step for cellular maintenance. The transcription factor nuclear factor (erythroid-derived 2)-like 2 (Nrf2), the key regulator in the cellular oxidative stress-response, induces a battery of genes involved in repair and regeneration. Here, we investigated the relevance of Nrf2 signaling for the prevention of cellular damage caused by dysfunctional mitochondria. We employed sodium azide (SA) as mitochondrial inhibitor on oligodendroglial OliNeu cells in vitro, and the cuprizone model with wild type and GFAP-Cre⁺::Keap1^loxP/loxP mice to induce mitochondrial defects. The importance of Nrf2 for cellular functions and survival after SA treatment was elucidated by in vitro knockdown experiments with shRNA directed against Nrf2 and its inhibitor Keap1 as well as by methysticin treatment. Metabolic activity, cytotoxicity, and depolarization of the mitochondrial membrane were analyzed after SA treatment. The expression of Nrf2 target genes as well as endoplasmic reticulum stress response genes was additionally measured by real-time PCR (in vitro) and PCR gene arrays (in vivo). Treatment of OliNeu cells with SA resulted in significant depolarization of the mitochondrial membrane, decreased metabolic activity, and increased cytotoxicity. This was partly counteracted in Nrf2-hyperactivated cells and intensified in Nrf2-knockdown cells. Our studies demonstrate a key role of Nrf2 in maintaining cellular functions and survival in the context of mitochondrial dysfunction.

Mitochondria as pharmacological targets in Down syndrome

Mitochondria play a pivotal role in cellular energy-generating processes and are considered master regulators of cell life and death fate. Mitochondrial function integrates signalling networks in several metabolic pathways controlling neurogenesis and neuroplasticity. Indeed, dysfunctional mitochondria and mitochondrial-dependent activation of intracellular stress cascades are critical initiating events in many human neurodegenerative or neurodevelopmental diseases including Down syndrome (DS). It is well established that trisomy of human chromosome 21 can cause DS. DS is associated with neurodevelopmental delay, intellectual disability and early neurodegeneration. Recently, molecular mechanisms responsible for mitochondrial damage and energy deficits have been identified and characterized in several DS-derived human cells and animal models of DS. Therefore, therapeutic strategies targeting mitochondria could have great potential for new treatment regimens in DS. The purpose of this review is to highlight recent studies concerning mitochondrial impairment in DS, focusing on alterations of the molecular pathways controlling mitochondrial function. We will also discuss the effects and molecular mechanisms of naturally occurring and chemically synthetized drugs that exert neuroprotective effects through modulation of mitochondrial function and attenuation of oxidative stress. These compounds might represent novel therapeutic tools for the modulation of energy deficits in DS.

Pink1 interacts with α-synuclein and abrogates α-synuclein-induced neurotoxicity by activating autophagy

Parkinson’s disease (PD) is one of the most common neurodegenerative diseases, characterized by degeneration of dopaminergic neurons in the substantia nigra. α-synuclein (α-syn) and PTEN-induced putative kinase (PINK)1 are two critical proteins associated with the pathogenesis of PD. α-syn induces mitochondrial deficits and apoptosis, PINK1 was found to alleviate α-syn-induced toxicity, but the mechanistic details remain obscure. Here, we show that PINK1 interacts with α-syn mainly in the cytoplasm, where it initiates autophagy. This interaction was dependent on the kinase activity of PINK1 and was abolished by deletion of the kinase domain or a G309D point mutation, an inactivating mutation in the kinase domain. Interaction between PINK1 and α-syn stimulated the removal of excess α-syn, which prevented mitochondrial deficits and apoptosis. Our findings provide evidence for a novel mechanism underlying the protective effects of PINK1 against α-syn-induced neurodegeneration and highlight a novel therapeutic target for PD treatment.

Therapeutic Potential of Induced Neural Stem Cells for Parkinson's Disease

Parkinson's disease (PD) is a chronic, neurodegenerative disorder that results from the loss of cells in the substantia nigra (SN) which is located in the midbrain. However, no cure is available for PD. Recently, fibroblasts have been directly converted into induced neural stem cells (iNSCs) via the forced expression of specific transcription factors. Therapeutic potential of iNSC in PD has not been investigated yet. Here, we show that iNSCs directly converted from mouse fibroblasts enhanced functional recovery in an animal model of PD. The rotational behavior test was performed to assess recovery. Our results indicate that iNSC transplantation into the striatum of 6-hydroxydopamine (6-OHDA)-injected mice can significantly reduce apomorphine-induced rotational asymmetry. The engrafted iNSCs were able to survive in the striatum and migrated around the medial forebrain bundle and the SN pars compacta. Moreover, iNSCs differentiated into all neuronal lineages. In particular, the transplanted iNSCs that committed to the glial lineage were significantly increased in the striatum of 6-OHDA-injected mice. Engrafted iNSCs differentiated to dopaminergic (DA) neurons and migrated into the SN in the 6-OHDA lesion mice. Therefore, iNSC transplantation serves as a valuable tool to enhance the functional recovery in PD.