Novel Targets for Parkinson's Disease: Addressing Different Therapeutic Paradigms and Conundrums

Neuroprotective Activity of a Non-Covalent Imatinib+TP10 Conjugate in HT-22 Neuronal Cells In Vitro

This study evaluated the probable relevance of a non-covalent conjugate of imatinib with TP10 in the context of a neuroprotective effect in Parkinson's disease. Through the inhibition of c-Abl, which is a non-receptor tyrosine kinase and an indicator of oxidative stress, imatinib has shown promise in preclinical animal models of this disease. The poor distribution of imatinib within the brain tissue triggered experiments in which a conjugate was obtained by mixing the drug with TP10, which is known for exhibiting high translocation activity across the cell membrane. The conjugate was tested on the HT-22 cell line with respect to its impact on MPP+-induced oxidative stress, apoptosis, necrosis, cytotoxicity, and mortality. Additionally, it was checked whether the conjugate activated the ABCB1 protein. The experiments indicated that imatinib+PEG4+TP10 reduced the post-MPP+ oxidative stress, apoptosis, and mortality, and these effects were more prominent than those obtained after the exposition of the HT-22 cells to imatinib alone. Its cytotoxicity was similar to that of imatinib itself. In contrast to imatinib, the conjugate did not activate the ABCB1 protein. These favorable qualities of imatinib+PEG4+TP10 make it a potential candidate for further in vivo research, which would confirm its neuroprotective action in PD-affected brains.

Quassinoids from Twigs of Harrisonia perforata (Blanco) Merr and Their Anti-Parkinson's Disease Effect

Six new C-20 and one new C-19 quassinoids, named perforalactones F-L (1-7), were isolated from twigs of Harrisonia perforata. Spectroscopic and X-ray crystallographic experiments were conducted to identify their structures. Through oxidative degradation of perforalactone B to perforaqussin A, the biogenetic process from C-25 quassinoid to C-20 via Baeyer-Villiger oxidation was proposed. Furthermore, the study evaluated the anti-Parkinson's disease potential of these C-20 quassinoids for the first time on 6-OHDA-induced PC12 cells and a Drosophila Parkinson's disease model of PINK1B9. Perforalactones G and I (2 and 4) showed a 10-15% increase in cell viability of the model cells at 50 μM, while compounds 2 and 4 (100 μM) significantly improved the climbing ability of PINK1B9 flies and increased the dopamine level in the brains and ATP content in the thoraces of the flies.

Citrus Flavonoid Hesperetin Inhibits α-Synuclein Fibrillogenesis, Disrupts Mature Fibrils, and Reduces Their Cytotoxicity: In Vitro and In Vivo Studies

Misfolding and subsequent fibrillogenesis of α-synuclein (αSN) significantly influence the development of Parkinson's disease (PD). This study reports the inhibitory effect of citrus flavonoid hesperetin (Hst) on αSN fibrillation. Based on thioflavin T fluorometry and atomic force microscopy studies, Hst inhibited αSN fibrillation by interfering with initial nucleation and slowing the elongation rate. Furthermore, the inhibitory effect was concentration-dependent with a half-maximal inhibitory concentration of 24.4 μM. Cytotoxicity experiments showed that 100 μM Hst significantly reduced the cytotoxicity of αSN aggregates and maintained 98.4% cell activity. In addition, Hst disassembled the preprepared αSN fibrils into smaller and less-toxic aggregates. Excitingly, supplementation with 100 μM Hst inhibited the accumulation of 36.3% αSN in NL5901 and restored the amyloid-induced reduction in NL5901 lipid abundance, extending the mean lifespan of NL5901 to 23 d. These findings could support the use of Hst as a dietary supplement to regulate αSN fibrillation and prevent the development of PD.

Polyphenolic glycosides with unusual four-membered ring possessing anti-Parkinson's disease potential from black wolfberry

This work reports the isolation of seven undescribed polyphenolic glycosides (1-7) together with fourteen known compounds (8-21) from the fruit of Lycium ruthenicum Murray. The structures of the undescribed compounds were identified based on comprehensive spectroscopic methods including IR, HRESIMS, NMR and ECD, and chemical hydrolysis. Compounds 1-3 possess an unusual four-membered ring, while 11-15 were firstly isolated from this fruit. Interestingly, compounds 1-3 inhibited monoamine oxidase B with IC₅₀ of 25.36 ± 0.44, 35.36 ± 0.54, and 25.12 ± 1.59 μM, respectively, and showed significant neuroprotective effect on PC12 cells injured by 6-OHDA. Moreover, compound 1 improved the lifespan, dopamine level, climbing behaviour, and olfactory ability of the PINK1^B9 flies, a Drosophila model of Parkinson's disease. This work presents the first in vivo neuroprotective evidence of the small molecular compounds in L. ruthenicum Murray fruit, indicating its good potential as neuroprotectant.

On the Chemical and Biological Characteristics of Multifunctional Compounds for the Treatment of Parkinson's Disease

Protein aggregation, mitochondrial dysfunction, iron dyshomeostasis, increased oxidative damage and inflammation are pathognomonic features of Parkinson's disease (PD) and other neurodegenerative disorders characterized by abnormal iron accumulation. Moreover, the existence of positive feed-back loops between these pathological components, which accelerate, and sometimes make irreversible, the neurodegenerative process, is apparent. At present, the available treatments for PD aim to relieve the symptoms, thus improving quality of life, but no treatments to stop the progression of the disease are available. Recently, the use of multifunctional compounds with the capacity to attack several of the key components of neurodegenerative processes has been proposed as a strategy to slow down the progression of neurodegenerative processes. For the treatment of PD specifically, the necessary properties of new-generation drugs should include mitochondrial destination, the center of iron-reactive oxygen species interaction, iron chelation capacity to decrease iron-mediated oxidative damage, the capacity to quench free radicals to decrease the risk of ferroptotic neuronal death, the capacity to disrupt α-synuclein aggregates and the capacity to decrease inflammatory conditions. Desirable additional characteristics are dopaminergic neurons to lessen unwanted secondary effects during long-term treatment, and the inhibition of the MAO-B and COMPT activities to increase intraneuronal dopamine content. On the basis of the published evidence, in this work, we review the molecular basis underlying the pathological events associated with PD and the clinical trials that have used single-target drugs to stop the progress of the disease. We also review the current information on multifunctional compounds that may be used for the treatment of PD and discuss the chemical characteristics that underlie their functionality. As a projection, some of these compounds or modifications could be used to treat diseases that share common pathology features with PD, such as Friedreich's ataxia, Multiple sclerosis, Huntington disease and Alzheimer's disease.

Emerging targets signaling for inflammation in Parkinson's disease drug discovery

Parkinson's disease (PD) patients not only show motor features such as bradykinesia, tremor, and rigidity but also non-motor features such as anxiety, depression, psychosis, memory loss, attention deficits, fatigue, sexual dysfunction, gastrointestinal issues, and pain. Many pharmacological treatments are available for PD patients; however, these treatments are partially or transiently effective since they only decrease the symptoms. As these therapies are unable to restore dopaminergic neurons and stop the development of Parkinson's disease, therefore, the need for an effective therapeutic approach is required. The current review summarizes novel targets for PD, that can be utilized to identify disease-modifying treatments.

Chalcones as Potential Ligands for the Treatment of Parkinson's Disease

Along with the increase in life expectancy, a significant increase of people suffering from neurodegenerative diseases (ND) has been noticed. The second most common ND, after Alzheimer’s disease, is Parkinson’s disease (PD), which manifests itself with a number of motor and non-motor symptoms that hinder the patient’s life. Current therapies can only alleviate those symptoms and slow down the progression of the disease, but not effectively cure it. So now, in addition to understanding the mechanism and causes of PD, it is also important to find a powerful way of treatment. It has been proved that in the etiology and course of PD, the essential roles are played by dopamine (DA) (an important neurotransmitter), enzymes regulating its level (e.g., COMT, MAO), and oxidative stress leading to neuroinflammation. Chalcones, due to their “simple” structure and valuable biological properties are considered as promising candidates for treatment of ND, also including PD. Here, we provide a comprehensive review of chalcones and related structures as potential new therapeutics for cure and prevention of PD. For this purpose, three databases (Pubmed, Scopus and Web of Science) were searched to collect articles published during the last 5 years (January 2018–February 2022). Chalcones have been described as promising enzyme inhibitors (MAO B, COMT, AChE), α-synuclein imaging probes, showing anti-neuroinflammatory activity (inhibition of iNOS or activation of Nrf2 signaling), as well as antagonists of adenosine A₁ and/or A_2A receptors. This review focused on the structure–activity relationships of these compounds to determine how a particular substituent or its position in the chalcone ring(s) (ring A and/or B) affects biological activity.

Polyphenolic Glycosides from the Fruits Extract of Lycium ruthenicum Murr and Their Monoamine Oxidase B Inhibitory and Neuroprotective Activities

The fruits ofLycium ruthenicum Murr have long been consumed as health food and used in folk medicine in China. Apart from the well-known polysaccharides, the active small molecular constituents in this fruit have not been fully studied. In this work, a systematic phytochemical study was carried out to investigate the small molecules and their potential health benefits. Nine new polyphenolic glycosides, lyciumserin A-I (1-9), together with 16 known compounds (10-25), were isolated and elucidated by high-resolution electrospray ionization mass spectrometry and comprehensive NMR analyses in combination with chemical hydrolysis. Compounds 1, 2, and 16 exhibited moderate inhibitory activity of monoamine oxidase B (MAO-B), while compounds 1 (50 μM) and 2 (100 μM) displayed significant neuroprotective effects (69.22 and 72.38% of cell viability, respectively) in the 6-hydroxydopamine-induced injury of the PC12 cell model (54.41%), comparable to the positive drug rasagiline (70.45%). The neuroprotective effect of 1 and 2 was further evidenced by the observation of the morphological change and fluorescein diacetate/propidium iodide staining. In addition, the levels of the major active compounds (1, 3, 5/6, and 16-18) vary from 21.5 to 892.3 μg/g. This is the first report on phenolic glycosides from the fruits ofL. ruthenicum Murr that possess both significant MAO-B inhibitory and neuroprotective effects, indicating the promising potential of the fruits for the development of health care products and even therapeutic agents for the treatment of Parkinson's disease and other neurodegenerative diseases.

Garcinol blocks motor behavioural deficits by providing dopaminergic neuroprotection in MPTP mouse model of Parkinson's disease: involvement of anti-inflammatory response

Although the etiology of Parkinson's disease (PD) is poorly understood, studies in animal models revealed loss of dopamine and the dopaminergic neurons harbouring the neurotransmitter to be the principal cause behind this neuro-motor disorder. Neuroinflammation with glial cell activation is suggested to play a significant role in dopaminergic neurodegeneration. Several biomolecules have been reported to confer dopaminergic neuroprotection in different animal models of PD, owing to their anti-inflammatory potentials. Garcinol is a tri-isoprenylated benzophenone isolated from Garcinia sp. and accumulating evidences suggest that this molecule could provide neuroprotection by modulating oxidative stress and inflammation. However, direct evidence of dopaminergic neuroprotection by garcinol in the pre-clinical model of PD is not yet reported. The present study aims to investigate whether administration of garcinol in the MPTP mouse model of PD may ameliorate the cardinal motor behavioural deficits and prevent the loss of dopaminergic neurons. As expected, garcinol blocked the parkinsonian motor behavioural deficits which include akinesia, catalepsy, and rearing anomalies in the mice model. Most importantly, the degeneration of dopaminergic cell bodies in the substantia nigra region was significantly prevented by garcinol. Furthermore, garcinol reduced the inflammatory marker, glial fibrillary acidic protein, in the substantia nigra region. Since glial hyperactivation-mediated inflammation is inevitably associated with the loss of dopaminergic neurons, our study suggests the anti-inflammatory role of garcinol in facilitating dopaminergic neuroprotection in PD mice. Hence, in the light of the present study, it is suggested that garcinol is an effective anti-parkinsonian agent to block motor behavioural deficits and dopaminergic neurodegeneration in PD.

Alizarin and Purpurin from Rubia tinctorum L. Suppress Insulin Fibrillation and Reduce the Amyloid-Induced Cytotoxicity

Alizarin (1,2-dihydroxyanthraquinone) and purpurin (1,2,4-trihydroxyanthraquinone), natural anthraquinone compounds from Rubia tinctorum L., are reported to have diverse biological effects including antibacterial, antitumor, antioxidation, and so on, but the inhibition activity against amyloid aggregation has been rarely reported. In this study, we used insulin as a model protein to explore the anti-amyloid effects of the two compounds. The results showed that alizarin and purpurin inhibited the formation of insulin fibrils in a dose-dependent manner and reduced insulin-induced cytotoxicity. Meanwhile, purpurin had a more significant inhibitory effect on insulin amyloid fibrils compared with alizarin. In addition, computer simulations indicated that the two compounds interacted mainly with the hydrophobic residues of insulin chain B and interfered with the binding of phenylalanine residues. The research indicated that natural anthraquinone compounds had potential effects in preventing protein misfolding diseases and could be further used to design effective antiamyloidosis compounds.

Bilirubin: A Promising Therapy for Parkinson's Disease

Following the increase in life expectancy, the prevalence of Parkinson's disease (PD) as the most common movement disorder is expected to rise. Despite the incredibly huge efforts in research to find the definitive biomarker, to date, the diagnosis of PD still relies mainly upon clinical symptoms. A wide range of treatments is available for PD, mainly alleviating the clinical symptoms. However, none of these current therapies can stop or even slow down the disease evolution. Hence, disease-modifying treatment is still a paramount unmet medical need. On the other side, bilirubin and its enzymatic machinery and precursors have offered potential benefits by targeting multiple mechanisms in chronic diseases, including PD. Nevertheless, only limited discussions are available in the context of neurological conditions, particularly in PD. Therefore, in this review, we profoundly discuss this topic to understand bilirubin's therapeutical potential in PD.

Effects of task-oriented training combined with aerobic training on serum BDNF, GDNF, IGF-1, VEGF, TNF-α, and IL-1β levels in people with Parkinson's disease: A randomized controlled study

INTRODUCTION

Parkinson's disease (PD) is a chronic neurodegenerative disease characterized by the death of dopaminergic neurons in the substantia nigra pars compacta. Exercise training, which is incorporated both goal-based training such as task-oriented training (TOT) and aerobic training (AT), has been suggested to induce neuroprotection. However, molecular mechanisms which may underlie exercise-induced neuroprotection are still largely unknown. Thus, the aim of the present study was to investigate the effects of TOT combined with AT (TOT-AT) on serum brain-derived neurotrophic factor (BDNF), glial cell-derived growth factor (GDNF), insulin-like growth factor-1 (IGF-1), vascular endothelial growth factor (VEGF), tumor necrosis factor-α (TNF-α), and interleukin-1β (IL-1β) levels in people with PD (PwPD).

METHODS

Forty PwPD were randomized into 8-week of either exercise group (n = 20) or control group (n = 20). The exercise group received TOT-AT while the control group received only AT. Serum BDNF, GDNF, IGF-1, VEGF, TNF-α, and IL-1β levels determined with ELISA were assessed at baseline and after training.

RESULTS

A total of 29 PwPD completed this study. Our results showed no significant change in the serum BDNF, GDNF, IGF-1, VEGF, TNF-α, and IL-1β levels in both groups. After the intervention period, no significant difference was observed between the groups regarding the serum BDNF, GDNF, IGF-1, VEGF, TNF-α, and IL-1β levels.

CONCLUSION

TOT-AT could not be an effective exercise method for changing serum concentrations of BDNF, GDNF, IGF-1, VEGF, TNF-α, and IL-1β in the rehabilitation of PD.

The application of isatin-based multicomponent-reactions in the quest for new bioactive and druglike molecules

Oxindole derivatives are known for their great interest in the field of Medicinal Chemistry, as they display vast biological activities. Recent efforts concerning the preparation of oxindole derivatives using isatin-based multicomponent reactions (MCRs) constitute a great advance in generating druglike libraries fast and with wide scaffold diversity. In this review, we address those recent developments, exploring the synthetic pathways and biological activities described for these compounds, namely antitumor, antibacterial, antifungal, antiparasitic, antiviral, antioxidant, anti-inflammatory and central nervous system (CNS) pathologies. To add new depth to this work, we used a well-established web-based free tool (SwissADME) to evaluate the most promising scaffolds in what concerns their druglike properties, namely by evaluating their compliance with some of the most valuable rules applied by medicinal chemists in both academia and industrial settings (Lipinski, Ghose, Veber, Egan, Muegge). The aim of this review is to endorse isatin-based MCRs as a valuable synthetic approach to attain new hit compounds bearing the oxindole privileged structure, while critically exploring these scaffolds' druglike properties.

A comprehensive review of monoamine oxidase inhibitors as Anti-Alzheimer's disease agents: A review

Monoamine oxidases (MAO-A and MAO-B) are mammalian flavoenzyme, which catalyze the oxidative deamination of several neurotransmitters like norepinephrine, dopamine, tyramine, serotonin, and some other amines. The oxidative deamination produces several harmful side products like ammonia, peroxides, and aldehydes during the biochemical reaction. The concentration of biochemical neurotransmitter alteration in the brain by MAO is directly related with several neurological disorders like Alzheimer's disease and Parkinson's disease (PD). Activated MAO also contributes to the amyloid beta (Aβ) aggregation by two successive cleft β-secretase and γ-secretase of amyloid precursor protein (APP). Additionally, activated MAO is also involved in aggregation of neurofibrillary tangles and cognitive destruction through the cholinergic neuronal damage and disorder of the cholinergic system. MAO inhibition has general anti-Alzheimer's disease effect as a consequence of oxidative stress reduction prompted by MAO enzymes. In this review, we outlined and addressed recent understanding on MAO enzymes such as their structure, physiological function, catalytic mechanism, and possible therapeutic goals in AD. In addition, it also highlights the current development and discovery of potential MAO inhibitors (MAOIs) from various chemical scaffolds.

Inhibiting thrombin improves motor function and decreases oxidative stress in the LRRK2 transgenic Drosophila melanogaster model of Parkinson's disease

Parkinson's disease (PD) is a complex neurodegenerative disease characterized by the presence of tremors, loss of dopaminergic neurons and accumulation of α-synuclein. While there is no single direct cause of PD, genetic mutations, exposure to pesticides, diet and traumatic brain injury have been identified as risk factors. Increasing evidence suggests that oxidative stress and neuroinflammation contribute to the pathogenesis of neuronal injury in neurodegenerative diseases such as PD and Alzheimer's disease (AD). We have previously documented that the multifunctional inflammatory mediator thrombin contributes to oxidative stress and neuroinflammation in AD. Here, for the first time, we explore the role of thrombin in a transgenic PD model, the LRRK2 mutant Drosophila melanogaster. Transgenic flies were treated with the direct thrombin inhibitor dabigatran for 7 days and locomotor activity and indices of oxidative stress evaluated. Our data show that dabigatran treatment significantly (p < 0.05) improved climbing activity, a measurement of locomotor ability, in male but had no effect on locomotor performance in female flies. Dabigatran treatment had no effect on tyrosine hydroxylase levels. Analysis of oxidative stress in male flies showed that dabigatran was able to significantly (p < 0.01) lower reactive oxygen species levels. Furthermore, Western blot analysis showed that the pro-oxidant proteins iNOS and NOX4 are elevated in LRRK2 male flies compared to wildtype and that treatment with dabigatran reduced expression of these proteins. Our results indicate that dabigatran treatment could improve motor function in PD by reducing oxidative stress. These data suggest that targeting thrombin may improve oxidative stress related pathologies in PD.

Peroxisomal Dysfunction and Oxidative Stress in Neurodegenerative Disease: A Bidirectional Crosstalk

Peroxisomes are multifunctional organelles best known for their role in cellular lipid and hydrogen peroxide metabolism. In this chapter, we review and discuss the diverse functions of this organelle in brain physiology and neurodegeneration, with a particular focus on oxidative stress. We first briefly summarize what is known about the various nexuses among peroxisomes, the central nervous system, oxidative stress, and neurodegenerative disease. Next, we provide a comprehensive overview of the complex interplay among peroxisomes, oxidative stress, and neurodegeneration in patients suffering from primary peroxisomal disorders. Particular examples that are discussed include the prototypic Zellweger spectrum disorders and X-linked adrenoleukodystrophy, the most prevalent peroxisomal disorder. Thereafter, we elaborate on secondary peroxisome dysfunction in more common neurodegenerative disorders, including Alzheimer's disease, Parkinson's disease, and multiple sclerosis. Finally, we highlight some issues and challenges that need to be addressed to progress towards therapies and prevention strategies preserving, normalizing, or improving peroxisome activity in patients suffering from neurodegenerative conditions.

Endoplasmic reticulum-mitochondria crosstalk: from junction to function across neurological disorders

The endoplasmic reticulum (ER) and mitochondria are fundamental organelles highly interconnected with a specialized set of proteins in cells. ER-mitochondrial interconnections form specific microdomains, called mitochondria-associated ER membranes, that have been found to play important roles in calcium signaling and lipid homeostasis, and more recently in mitochondrial dynamics, inflammation, and autophagy. It is not surprising that perturbations in ER-mitochondria connections can result in the progression of disease, especially neurological disorders; hence, their architecture and regulation are crucial in determining the fate of cells and disease. The molecular identity of the specialized proteins regulating ER-mitochondrial crosstalk remains unclear. Our discussion here describes the physical and functional crosstalk between these two dynamic organelles and emphasizes the outcome of altered ER-mitochondrial interconnections in neurological disorders.

Evolving Evidence of Calreticulin as a Pharmacological Target in Neurological Disorders

Calreticulin (CALR), a lectin-like ER chaperone, was initially known only for its housekeeping function, but today it is recognized for many versatile roles in different compartments of a cell. Apart from canonical roles in protein folding and calcium homeostasis, it performs a variety of noncanonical roles, mostly in CNS development. In the past, studies have linked Calreticulin with various other biological components which are detrimental in deciding the fate of neurons. Many neurological disorders that differ in their etiology are commonly associated with aberrant levels of Calreticulin, that lead to modulation of apoptosis and phagocytosis, and impact on transcriptional pathways, impairment in proteostatis, and calcium imbalances. Such multifaceted properties of Calreticulin are the reason why it has been implicated in vital roles of the nervous system in recent years. Hence, understanding its role in the physiology of neurons would help to unearth its involvement in the spectrum of neurological disorders. This Review aims toward exploring the interplay of Calreticulin in neurological disorders which would aid in targeting Calreticulin for developing novel neurotherapeutics.

Interplay between Mitophagy and Inflammasomes in Neurological Disorders

Mitophagy and inflammasomes have a pivotal role in the development of neuropathology. Molecular mechanisms behind mitophagy and inflammasomes are well-understood, but lacunae prevail in understanding the crosstalk between them in various neurological disorders. As mitochondrial dysfunction is the prime event in neurodegeneration, the clearance of impaired mitochondria is one of the main tasks for maintaining cell integrity in the majority of neuropathologies. Along with it, inflammasome activation also plays a major role, which is usually followed by mitochondrial dysfunction. The present review highlights basics of autophagy, mitophagy, and inflammasomes and the molecular mechanisms involved, and more importantly, it tries to elaborate the interplay between mitophagy and inflammasomes in various neurological disorders. This will help in upgrading the reader's understanding in exploring the link between mitophagy and inflammasomes, which has dealt with limitations in past studies.

Dihydromyricetin Inhibits α-Synuclein Aggregation, Disrupts Preformed Fibrils, and Protects Neuronal Cells in Culture against Amyloid-Induced Cytotoxicity

Fibrillogenesis of α-synuclein (αSN) is associated with the onset and progression of Parkinson's disease (PD). Dihydromyricetin (DHM), a natural flavonoid compound extracted from Ampelopsis grossedentata, has proven antioxidative, antineuroinflammatory, and neuroprotective effects in dementia. However, it remains unclear if DHM can impede αSN fibrillogenesis and attenuate the corresponding cytotoxicity. Herein, we found that DHM could inhibit αSN fibrillogenesis and destabilize mature αSN fibrils in a dose-dependent manner. Moreover, DHM protected against αSN-induced cytotoxicity by improving the cell viability by 34.73 ± 3.68% at a 1:1 molar ratio of αSN to DHM. Molecular dynamics simulations showed that DHM interacts with the αSN trimer mainly via nonpolar mechanisms. The key residues by which αSN interacts with DHM were hydrophobic, and their side chains and main chains showed a synergistic effect via hydrophobic and hydrogen-bonding interactions. These findings suggest that DHM possesses great potential to be developed into a new aggregation inhibitor for αSN.

Vitamin B12 inhibits α-synuclein fibrillogenesis and protects against amyloid-induced cytotoxicity

VB12, a necessary micronutrient, is a potential functional factor to ameliorate PD by inhibiting α-synuclein fibrillogenesis and reducing cytotoxicity.