Polyphenols in Parkinson's Disease: A Systematic Review of In Vivo Studies

Therapeutic potential of Hsp27 in neurological diseases

Background

Heat shock proteins (Hsps) are widely reported in normal cellular dynamics under stress and non-stress conditions, and parallelly, the studies regarding its role in disease condition are also progressing steadily. The function of Hsps in neurodegenerative disorders is puzzling and not fully understood. This review aims to focus on the role of Hsp27 in normal and diseased conditions and emphasize its therapeutic potential.

Hsp27

Hsp27, in particular, has shown to be involved in cell viability and actin cytoskeleton remodeling and also shown to improve many disease conditions. Phosphorylated Hsp27 modulates the p53 pathway by downregulating cellular senescence and also lowers reactive oxygen species to protect TNFα-mediated apoptosis. Hsp27 is also known to interfere with mitochondria-dependent and mitochondria-independent cell apoptotic stimulation.

Conclusion

This article will highlight the various functions of Hsp27 especially as an anti-apoptotic factor and stress response factor and its therapeutic potential in preventing neuronal apoptosis in neurological diseases. This review also includes a comparison of the therapeutic potential of Hsp27 with regard to other small Hsps.

Neuroprotective effects of urolithin A on H2O2-induced oxidative stress-mediated apoptosis in SK-N-MC cells

BACKGROUND/OBJECTIVES

Oxidative stress causes cell damage and death, which contribute to the pathogenesis of neurodegenerative diseases. Urolithin A (UA), a gut microbial-derived metabolite of ellagitannins and ellagic acid, has high bioavailability and various health benefits such as antioxidant and anti-inflammatory effects. However, it is unknown whether it has protective effects against oxidative stress-induced cell death. We investigated whether UA ameliorates H₂O₂-induced neuronal cell death.

MATERIALS/METHODS

We induced oxidative damage with 300 µM H₂O₂ after UA pretreatment at concentrations of 1.25, 2.5, and 5 µM in SK-N-MC cells. Cytotoxicity and cell viability were determined using the CCK-8 assay. The formation of reactive oxygen species (ROS) was measured using a 2,7-dichlorofluorescein diacetate assay. Hoechst 33342 staining was used to characterize morphological changes in apoptotic cells. The expressions of apoptosis proteins were measured using Western blotting.

RESULTS

UA significantly increased cell viability and decreased intracellular ROS production in a dose-dependent manner in SK-N-MC cells. It also decreased the Bax/Bcl-2 ratio and the expressions of cytochrome c, cleaved caspase-9, cleaved caspase-3, and cleaved PARP. In addition, it suppressed the phosphorylation of the p38 mitogen-activated protein kinase (MAPK) pathway.

CONCLUSIONS

UA attenuates oxidative stress-induced apoptosis via inhibiting the mitochondrial-related apoptosis pathway and modulating the p38 MAPK pathway, suggesting that it may be an effective neuroprotective agent.

Flavonoids as positive allosteric modulators of α7 nicotinic receptors

The use of positive allosteric modulators (PAM) of α7 nicotinic receptors is a promising therapy for neurodegenerative, inflammatory and cognitive disorders. Flavonoids are polyphenolic compounds showing neuroprotective, anti-inflammatory and pro-cognitive actions. Besides their well-known antioxidant activity, flavonoids trigger intracellular pathways and interact with receptors, including α7. To reveal how the beneficial actions of flavonoids are linked to α7 function, we evaluated the effects of three representative flavonoids -genistein, quercetin and the neoflavonoid 5,7-dihydroxy-4-phenylcoumarin- on whole-cell and single-channel currents. All flavonoids increase the maximal currents elicited by acetylcholine with minimal effects on desensitization and do not reactivate desensitized receptors, a behaviour consistent with type I PAMs. At the single-channel level, they increase the duration of the open state and produce activation in long-duration episodes with a rank order of efficacy of genistein > quercetin ≥ neoflavonoid. By using mutant and chimeric α7 receptors, we demonstrated that flavonoids share transmembrane structural determinants with other PAMs. The α7-PAM activity of flavonoids results in decreased cell levels of reactive oxygen species. Thus, allosteric potentiation of α7 may be an additional mechanism underlying neuroprotective actions of flavonoids, which may be used as scaffolds for designing new therapeutic agents.

Octadecaneuropeptide (ODN) Induces N2a Cells Differentiation through a PKA/PLC/PKC/MEK/ERK-Dependent Pathway: Incidence on Peroxisome, Mitochondria, and Lipid Profiles

Neurodegenerative diseases are characterized by oxidative stress, mitochondrial damage, and death of neuronal cells. To counteract such damage and to favor neurogenesis, neurotrophic factors could be used as therapeutic agents. Octadecaneuropeptide (ODN), produced by astrocytes, is a potent neuroprotective agent. In N2a cells, we studied the ability of ODN to promote neuronal differentiation. This parameter was evaluated by phase contrast microscopy, staining with crystal violet, cresyl blue, and Sulforhodamine 101. The effect of ODN on cell viability and mitochondrial activity was determined with fluorescein diacetate and DiOC₆(3), respectively. The impact of ODN on the topography of mitochondria and peroxisomes, two tightly connected organelles involved in nerve cell functions and lipid metabolism, was evaluated by transmission electron microscopy and fluorescence microscopy: detection of mitochondria with MitoTracker Red, and peroxisome with an antibody directed against the ABCD3 peroxisomal transporter. The profiles in fatty acids, cholesterol, and cholesterol precursors were determined by gas chromatography, in some cases coupled with mass spectrometry. Treatment of N2a cells with ODN (10^-14 M, 48 h) induces neurite outgrowth. ODN-induced neuronal differentiation was associated with modification of topographical distribution of mitochondria and peroxisomes throughout the neurites and did not affect cell viability and mitochondrial activity. The inhibition of ODN-induced N2a differentiation with H89, U73122, chelerythrine and U0126 supports the activation of a PKA/PLC/PKC/MEK/ERK-dependent signaling pathway. Although there is no difference in fatty acid profile between control and ODN-treated cells, the level of cholesterol and some of its precursors (lanosterol, desmosterol, lathosterol) was increased in ODN-treated cells. The ability of ODN to induce neuronal differentiation without cytotoxicity reinforces the interest for this neuropeptide with neurotrophic properties to overcome nerve cell damage in major neurodegenerative diseases.

Nutritional Risk Factors, Microbiota and Parkinson's Disease: What Is the Current Evidence?

Parkinson’s disease (PD) is a frequent neurodegenerative disease among elderly people. Genetic and underlying environmental factors seem to be involved in the pathogenesis of PD related to degeneration of dopaminergic neurons in the striatum. In previous experimental researches oxidative stress, mitochondrial dysfunction, homocysteine, and neuroinflammation have been reported as potential mechanisms. Among environmental factors, nutrition is one of the most investigated areas as it is a potentially modifiable factor. The purpose of this review is to provide current knowledge regarding the relation between diet and PD risk. We performed a comprehensive review including the most relevant studies from the year 2000 onwards including prospective studies, nested case-control studies, and meta-analysis. Among dietary factors we focused on specific nutrients and food groups, alcoholic beverages, uric acid, and dietary patterns. Furthermore, we included studies on microbiota as recent findings have shown a possible impact on neurodegeneration. As a conclusion, there are still many controversies regarding the relationship between PD and diet which, beside methodological differences among studies, may be due to underlying genetic and gender-specific factors. However, some evidence exists regarding a potential protective effect of uric acid, poly-unsaturated fatty acids, coffee, and tea but mainly in men, whereas dairy products, particularly milk, might increase PD risk through contaminant mediated effect.

Effects of carvacrol and physical exercise on motor and memory impairments associated with Parkinson's disease

The present study was undertaken to investigate the effects of carvacrol and treadmill exercise on memory deficit, rotational behavior and oxidative stress biomarkers in a 6-OHDA-lesioned rat model of Parkinson's disease. Wistar rats were treated with carvacrol at a dose of 25 mg/kg and/or ran on a treadmill for a week. Then, 6-OHDA was microinjected into the medial forebrain bundle and treatments continued for six more weeks. Aversive memory, rotational behavior and oxidative stress biomarkers were assessed at the end of week six. The 6-OHDA-lesioned group showed a significant increase in rotational behavior and a decrease in step-through latency in the passive avoidance test compared with the sham group. These behaviors were accompanied by increased lipid peroxidation levels and decreased total thiol concentration in the striatum and/or hippocampus of the hemiparkinsonian rats. Moreover, treatment with carvacrol and exercise reduced rotational behavior and improved aversive memory deficit, which was accompanied by decreased lipid peroxidation levels and increased total thiol concentration in the striatum and/or hippocampus. In conclusion, treatment with carvacrol and treadmill exercise ameliorated motor and memory deficits by modulating oxidative stress in the striatum and hippocampus of hemiparkinsonian rats. Therefore, the combination of carvacrol and treadmill exercise could be an effective therapeutic tool for treatment of neurobehavioral deficits in Parkinson's disease patients.

5-S-cysteinyl-dopamine, a neurotoxic endogenous metabolite of dopamine: Implications for Parkinson's disease

Parkinson's disease (PD) is the second most common neurodegenerative disease worldwide and is characterized for being an idiopathic and multifactorial disease. Extensive research has been conducted to explain the origin of the disease, but it still remains elusive. It is well known that dopamine oxidation, through the endogenous formation of toxic metabolites, is a key process in the activation of a cascade of molecular events that leads to cellular death in the hallmark of PD. Thio-catecholamines, such as 5-S-cysteinyl-dopamine, 5-S-glutathionyl-dopamine and derived benzothiazines, are endogenous metabolites formed in the dopamine oxidative degradation pathway. Those metabolites have been shown to be highly toxic to neurons in the substantia nigra pars compacta, activating molecular mechanisms that ultimately lead to neuronal death. In this review we describe the origin, formation and the toxic effects of 5-S-cysteinyl-dopamine and its oxidative derivatives that cause death to dopaminergic neurons. Furthermore, we correlate the formation of those metabolites with the neurodegeneration progress in PD. In addition, we present the reported neuroprotective strategies of products that protect against the cellular damage of those thio-catecholamines. Finally, we discuss the advantages in the use of 5-S-cysteinyl-dopamine as a potential biomarker for PD.

Neuroprotective Effects of Methanolic Extract of Avocado Persea americana (var. Colinred) Peel on Paraquat-Induced Locomotor Impairment, Lipid Peroxidation and Shortage of Life Span in Transgenic knockdown Parkin Drosophila melanogaster

Parkinson's disease (PD) is a progressive neurodegenerative disorder associated with oxidative stress. Therefore, finding new antioxidant sources might be beneficial for its treatment. Avocado Persea americana is a fruit widely cultivated in tropical and subtropical climates worldwide. Although avocado by-products in the form of peel, seed coat and seeds are currently of no commercial use, they constitute a natural source of bioactive compounds. Methanolic (80%) extract obtained from lyophilized ground peels, seed coats, and seeds of the avocado Hass, Fuerte, Reed and Colinred varieties were analyzed for their total phenolic content (TPC) and their correlations with antioxidant capacity (AC) were assessed by ABTS, FRAP, and ORAC assays. For all varieties, the var. Colinred peel shows the highest TPC and AC. Further analysis showed that the var. Colinred peel presented major phenolic compounds B-type procyanidins and epicatechin according to HPLC-MS. The antioxidant effect of peel extract was evaluated upon in vivo oxidative stress (OS) model. We show for the first time that the peel extract can protect and/or prevent transgenic parkinDrosophila melanogaster fly against paraquat-induced OS, movement impairment and lipid peroxidation, as model of PD. Our findings offer an exceptional opportunity to test natural disease-modifying substances from avocado's by-products.

Metal Chelation Therapy and Parkinson's Disease: A Critical Review on the Thermodynamics of Complex Formation between Relevant Metal Ions and Promising or Established Drugs

The present review reports a list of approximately 800 compounds which have been used, tested or proposed for Parkinson's disease (PD) therapy in the year range 2014-2019 (April): name(s), chemical structure and references are given. Among these compounds, approximately 250 have possible or established metal-chelating properties towards Cu(II), Cu(I), Fe(III), Fe(II), Mn(II), and Zn(II), which are considered to be involved in metal dyshomeostasis during PD. Speciation information regarding the complexes formed by these ions and the 250 compounds has been collected or, if not experimentally available, has been estimated from similar molecules. Stoichiometries and stability constants of the complexes have been reported; values of the cologarithm of the concentration of free metal ion at equilibrium (pM), and of the dissociation constant Kd (both computed at pH = 7.4 and at total metal and ligand concentrations of 10-6 and 10-5 mol/L, respectively), charge and stoichiometry of the most abundant metal-ligand complexes existing at physiological conditions, have been obtained. A rigorous definition of the reported amounts is given, the possible usefulness of this data is described, and the need to characterize the metal-ligand speciation of PD drugs is underlined.

The Potential of Flavonoids for the Treatment of Neurodegenerative Diseases

Neurodegenerative diseases, including Alzheimer’s disease (AD), Parkinson’s disease (PD), Huntington’s disease (HD), and amyotrophic lateral sclerosis (ALS), currently affect more than 6 million people in the United States. Unfortunately, there are no treatments that slow or prevent disease development and progression. Regardless of the underlying cause of the disorder, age is the strongest risk factor for developing these maladies, suggesting that changes that occur in the aging brain put it at increased risk for neurodegenerative disease development. Moreover, since there are a number of different changes that occur in the aging brain, it is unlikely that targeting a single change is going to be effective for disease treatment. Thus, compounds that have multiple biological activities that can impact the various age-associated changes in the brain that contribute to neurodegenerative disease development and progression are needed. The plant-derived flavonoids have a wide range of activities that could make them particularly effective for blocking the age-associated toxicity pathways associated with neurodegenerative diseases. In this review, the evidence for beneficial effects of multiple flavonoids in models of AD, PD, HD, and ALS is presented and common mechanisms of action are identified. Overall, the preclinical data strongly support further investigation of specific flavonoids for the treatment of neurodegenerative diseases.

Neuroprotective Effects of Thymol, a Dietary Monoterpene Against Dopaminergic Neurodegeneration in Rotenone-Induced Rat Model of Parkinson's Disease

Parkinson’s disease (PD), a multifactorial movement disorder that involves progressive degeneration of the nigrostriatal system affecting the movement ability of the patient. Oxidative stress and neuroinflammation both are shown to be involved in the etiopathogenesis of PD. The aim of this study was to evaluate the therapeutic potential of thymol, a dietary monoterpene phenol in rotenone (ROT)-induced neurodegeneration in rats that precisely mimics PD in humans. Male Wistar rats were injected ROT at a dose of 2.5 mg/kg body weight for 4 weeks, to induce PD. Thymol was co-administered for 4 weeks at a dose of 50 mg/kg body weight, 30 min prior to ROT injection. The markers of dopaminergic neurodegeneration, oxidative stress and inflammation were estimated using biochemical assays, enzyme-linked immunosorbent assay, western blotting and immunocytochemistry. ROT challenge increased the oxidative stress markers, inflammatory enzymes and cytokines as well as caused significant damage to nigrostriatal dopaminergic system of the brain. Thymol treatment in ROT challenged rats appears to significantly attenuate dopaminergic neuronal loss, oxidative stress and inflammation. The present study showed protective effects of thymol in ROT-induced neurotoxicity and neurodegeneration mediated by preservation of endogenous antioxidant defense networks and attenuation of inflammatory mediators including cytokines and enzymes.

Therapeutic potential of mistletoe in CNS-related neurological disorders and the chemical composition of Viscum species

ETHNOPHARMACOLOGICAL RELEVANCE

Viscum album L., commonly known as mistletoe, has been used for centuries in traditional medicine to treat various neurological diseases, including epilepsy, hysteria, nervousness, hysterical psychosis, dizziness and headaches.

AIM OF THE STUDY

The aim of this review is to summarize existing evidence confirming the influence of mistletoe on the central nervous system and to investigate the compounds that may be responsible for this activity.

MATERIALS AND METHODS

Available information from studies of various species of the Viscum L. genus was collected from scientific journals, books, and reports via a library and an electronic data search (Elsevier, Google Scholar, PubMed, Springer, Science Direct, ResearchGate, and ACS).

RESULTS

The main chemical constituents of Viscum L. species are viscotoxins, lectins, flavonoids, phenolic acids, terpenoids, sterols, phenylpropanoids, and alkaloids. Various extracts of Viscum album L. showed central nervous system activity, including antiepileptic, sedative, antipsychotic, anxiolytic, antidepressant and antinociceptive effects in mice and rats. Additionally, the extracts increased the level of brain-derived neurotrophic factor, prevented apoptotic neuronal death induced by amyloid β and weakly inhibited cholinesterase activity.

CONCLUSIONS

Numerous historical references describe the use of mistletoe for the treatment of central nervous system disorders. In recent years, studies have started to confirm the antiepileptic, antipsychotic, sedative and antinociceptive effects of mistletoe. Additionally, mistletoe can be used as a complementary treatment for Alzheimer's disease. The therapeutic effect of mistletoe might be a result of the synergistic interactions of various secondary metabolites, including mistletoe-specific lectins. Further studies of the chemical composition and CNS activity of mistletoe are required. The mechanisms of action, target sites, pharmacokinetics, metabolic mechanisms, adverse effects and interactions of mistletoe with other drugs must also be investigated, as well.