The biochemical and cellular basis for nutraceutical strategies to attenuate neurodegeneration in Parkinson's disease

Cell-Effective Transition-State Analogue of Phenylethanolamine N-Methyltransferase

Phenylethanolamine N-methyltransferase (PNMT) catalyzes the S-adenosyl-l-methionine (SAM)-dependent methylation of norepinephrine to form epinephrine. Epinephrine is implicated in the regulation of blood pressure, respiration, Alzheimer's disease, and post-traumatic stress disorder (PTSD). Transition-state (TS) analogues bind their target enzymes orders of magnitude more tightly than their substrates. A synthetic strategy for first-generation TS analogues of human PNMT (hPNMT) permitted structural analysis of hPNMT and revealed potential for second-generation inhibitors [Mahmoodi, N.; J. Am. Chem. Soc. 2020, 142, 14222-14233]. A second-generation TS analogue inhibitor of PNMT was designed, synthesized, and characterized to yield a Ki value of 1.2 nM. PNMT isothermal titration calorimetry (ITC) measurements of inhibitor 4 indicated a negative cooperative binding mechanism driven by large favorable entropic contributions and smaller enthalpic contributions. Cell-based assays with HEK293T cells expressing PNMT revealed a cell permeable, intracellular PNMT inhibitor with an IC50 value of 81 nM. Structural analysis demonstrated inhibitor 4 filling catalytic site regions to recapitulate both norepinephrine and SAM interactions. Conformation of the second-generation inhibitor in the catalytic site of PNMT improves contacts relative to those from the first-generation inhibitors. Inhibitor 4 demonstrates up to 51,000-fold specificity for PNMT relative to DNA and protein methyltransferases. Inhibitor 4 also exhibits a 12,000-fold specificity for PNMT over the α2-adrenoceptor.

Targeting Mitochondria by Plant Secondary Metabolites: A Promising Strategy in Combating Parkinson's Disease

Parkinson’s disease (PD) is one of the most prevalent and debilitating neurodegenerative conditions, and is currently on the rise. Several dysregulated pathways are behind the pathogenesis of PD; however, the critical targets remain unclear. Accordingly, there is an urgent need to reveal the key dysregulated pathways in PD. Prevailing reports have highlighted the importance of mitochondrial and cross-talked mediators in neurological disorders, genetic changes, and related complications of PD. Multiple pathophysiological mechanisms of PD, as well as the low efficacy and side effects of conventional neuroprotective therapies, drive the need for finding novel alternative agents. Recently, much attention has been paid to using plant secondary metabolites (e.g., flavonoids/phenolic compounds, alkaloids, and terpenoids) in the modulation of PD-associated manifestations by targeting mitochondria. In this line, plant secondary metabolites have shown promising potential for the simultaneous modulation of mitochondrial apoptosis and reactive oxygen species. This review aimed to address mitochondria and multiple dysregulated pathways in PD by plant-derived secondary metabolites.

Ameliorative Role of Nutraceuticals on Neurodegenerative Diseases Using the Drosophila melanogaster as a Discovery Model to Define Bioefficacy

Neurodegeneration is the destruction of neurons, and once the neurons degenerate they can't revive. This is one of the most concerned health conditions among aged population, more than ∼70% of the elderly people are suffering from neurodegeneration. Among all of the neurodegenerative diseases, Alzheimer's disease (AD), Parkinson's disease (PD) and Poly-glutamine disease (Poly-Q) are the major one and affecting most of the people around the world and posing excessive burden on the society. In order to understand this disease in non-human animal models it is pertinent to examine in model organism and various animal model are being used for such diseases like rat, mice and non-vertebrate model like Drosophila. Drosophila melanogaster is one of the best animal proven by several eminent scientist and had received several Nobel prizes for uncovering mechanism of human related genes and highly efficient model for studying neurodegenerative diseases due to its great affinity with human disease-related genes. Another factor is also employed to act as therapeutic or preventive method that is nutraceuticals. Nutraceuticals are functional natural compounds with antioxidant properties and had extensively showed the neuroprotective effect in different organisms. These nutraceuticals having antioxidant properties act through scavenging free radicals or by increasing endogenous cellular antioxidant defense molecules. For the best benefit, we are trying to utilize these nutraceuticals, which will have no or negligible side effects. In this review, we are dealing with various types of such nutraceuticals which have potent value in the prevention and curing of the diseases related to neurodegeneration.HighlightsNeurodegeneration is the silently progressing disease which shows its symptoms when it is well rooted.Many chemical drugs (almost all) have only symptomatic relief with side effects.Potent mechanism of neurodegeneration and improvement effect by nutraceuticals is proposed.Based on the Indian Cuisine scientists are trying to find the medicine from the food or food components having antioxidant properties.The best model to study the neurodegenerative diseases is Drosophila melanogaster.Many nutraceuticals having antioxidant properties have been studied and attenuated various diseases are discussed.

Plant Foods Rich in Antioxidants and Human Cognition: A Systematic Review

Oxidative stress can compromise central nervous system integrity, thereby affecting cognitive ability. Consumption of plant foods rich in antioxidants could thereby protect cognition. We systematically reviewed the literature exploring the effects of antioxidant-rich plant foods on cognition. Thirty-one studies were included: 21 intervention, 4 cross-sectional (one with a cohort in prospective observation as well), and 6 prospective studies. Subjects belonged to various age classes (young, adult, and elderly). Some subjects examined were healthy, some had mild cognitive impairment (MCI), and some others were demented. Despite the different plant foods and the cognitive assessments used, the results can be summarized as follows: 7 studies reported a significant improvement in all cognitive domains examined; 19 found significant improvements only in some cognitive areas, or only for some food subsets; and 5 showed no significant improvement or no effectiveness. The impact of dietary plant antioxidants on cognition appears promising: most of the examined studies showed associations with significant beneficial effects on cognitive functions-in some cases global or only in some specific domains. There was typically an acute, preventive, or therapeutic effect in young, adult, and elderly people, whether they were healthy, demented, or affected by MCI. Their effects, however, are not attributable only to anti-oxidation.

Role of dietary polyphenols on gut microbiota, their metabolites and health benefits

The beneficial health roles of dietary polyphenols in preventing oxidative stress related chronic diseases have been subjected to intense investigation over the last two decades. As our understanding of the role of gut microbiota advances our knowledge of the antioxidant and anti-inflammatory functions of polyphenols accumulates, there emerges a need to examine the prebiotic role of dietary polyphenols. This review focused onthe role of different types and sources of dietary polyphenols on the modulation of the gut microbiota, their metabolites and how they impact on host health benefits. Inter-dependence between the gut microbiota and polyphenol metabolites and the vital balance between the two in maintaining the host gut homeostasis were discussed with reference to different types and sources of dietary polyphenols. Similarly, the mechanisms behind the health benefits by various polyphenolic metabolites bio-transformed by gut microbiota were also explained. However, further research should focus on the importance of human trials and profound links of polyphenols-gut microbiota-nerve-brain as they provide the key to unlock the mechanisms behind the observed benefits of dietary polyphenols found in vitro and in vivo studies.

Synergistic action of propolis with levodopa in the management of Parkinsonism in Drosophila melanogaster

Background The Phosphatase and tensin-induced putative kinase 1 (PINK1B9) mutant for Drosophila melanogaster is a key tool that has been used in assessing the pathology of Parkinsonism and its possible remedy. This research was targeted toward determining the effects of ethanolic extract of propolis, with levodopa therapy in the management of Parkinsonism. Method The PINK1B9 flies were divided into groups and fed with the different treatment doses of ethanoic extract of propolis. The treatment groups were subjected to 21 days of administration of propolis and the levodopa at different doses after which percentage climbing index, antioxidant activity and lifespan studies were done. Results Propolis alone improved motor activity, antioxidant and lifespan in Drosophila melanogaster than in PINK1 flies. Propolis in combination with levodopa significantly (P<0.05) improved physiological parameters at higher than lower concentrations in Parkinsonism Drosophila melanogaster demonstrating its importance in managing side effects associated with levodopa. Conclusion Propolis is a novel candidate as an alternative and integrative medicinal option to use in the management of Parkinsonism in both animals and humans at higher concentrations.

Transition-State Analogues of Phenylethanolamine N-Methyltransferase

Phenylethanolamine N-methyltransferase (PNMT) is a critical enzyme in catecholamine synthesis. It transfers the methyl group of S-adenosylmethionine (SAM) to catalyze the synthesis of epinephrine from norepinephrine. Epinephrine has been associated with diverse human processes, including the regulation of blood pressure and respiration, as well as neurodegeneration found in Alzheimer's disease. Human PNMT (hPNMT) proceeds through an S_N2 transition state (TS) in which the transfer of the methyl group is rate limiting. TS analogue enzyme inhibitors are specific for their target and bind orders of magnitude more tightly than their substrates. Molecules resembling the TS of hPNMT were designed, synthesized, and kinetically characterized. This new inhibitory scaffold was designed to mimic the geometry and electronic properties of the hPNMT TS. Synthetic efforts resulted in a tight-binding inhibitor with a K_i value of 12.0 nM. This is among the first of the TS analogue inhibitors of methyltransferase enzymes to show an affinity in the nanomolar range. Isothermal titration calorimetry (ITC) measurements indicated negative cooperative binding of inhibitor to the dimeric protein, driven by favorable entropic contributions. Structural analysis revealed that inhibitor 3 binds to hPNMT by filling the catalytic binding pockets for the cofactor (SAM) and the substrate (norepinephrine) binding sites.

Rutin as a Potent Antioxidant: Implications for Neurodegenerative Disorders

A wide range of neurodegenerative diseases (NDs), including Alzheimer's disease, Parkinson's disease, Huntington's disease, and prion diseases, share common mechanisms such as neuronal loss, apoptosis, mitochondrial dysfunction, oxidative stress, and inflammation. Intervention strategies using plant-derived bioactive compounds have been offered as a form of treatment for these debilitating conditions, as there are currently no remedies to prevent, reverse, or halt the progression of neuronal loss. Rutin, a glycoside of the flavonoid quercetin, is found in many plants and fruits, especially buckwheat, apricots, cherries, grapes, grapefruit, plums, and oranges. Pharmacological studies have reported the beneficial effects of rutin in many disease conditions, and its therapeutic potential in several models of NDs has created considerable excitement. Here, we have summarized the current knowledge on the neuroprotective mechanisms of rutin in various experimental models of NDs. The mechanisms of action reviewed in this article include reduction of proinflammatory cytokines, improved antioxidant enzyme activities, activation of the mitogen-activated protein kinase cascade, downregulation of mRNA expression of PD-linked and proapoptotic genes, upregulation of the ion transport and antiapoptotic genes, and restoration of the activities of mitochondrial complex enzymes. Taken together, these findings suggest that rutin may be a promising neuroprotective compound for the treatment of NDs.

Deoxyelephantopin ameliorates lipopolysaccharides (LPS)-induced memory impairments in rats: Evidence for its anti-neuroinflammatory properties

AIM

Neuroinflammation is a critical pathogenic mechanism of most neurodegenerative disorders especially, Alzheimer's disease (AD). Lipopolysaccharides (LPS) are known to induce neuroinflammation which is evident from significant upsurge of pro-inflammatory mediators in in vitro BV-2 microglial cells and in vivo animal models. In present study, we investigated anti-neuroinflammatory properties of deoxyelephantopin (DET) isolated from Elephantopus scaber in LPS-induced neuroinflammatory rat model.

MATERIALS AND METHODS

In this study, DET (0.625. 1.25 and 2.5 mg/kg, i.p.) was administered in rats for 21 days and those animals were challenged with single injection of LPS (250 μg/kg, i.p.) for 7 days. Cognitive and behavioral assessment was carried out for 7 days followed by molecular assessment on brain hippocampus. Statistical significance was analyzed with one-way analysis of variance followed by Dunnett's test to compare the treatment groups with the control group.

KEY FINDINGS

DET ameliorated LPS-induced neuroinflammation by suppressing major pro-inflammatory mediators such as iNOS and COX-2. Furthermore, DET enhanced the anti-inflammatory cytokines and concomitantly suppressed the pro-inflammatory cytokines and chemokine production. DET treatment also reversed LPS-induced behavioral and memory deficits and attenuated LPS-induced elevation of the expression of AD markers. DET improved synaptic-functionality via enhancing the activity of pre- and post-synaptic markers, like PSD-95 and SYP. DET also prevented LPS-induced apoptotic neurodegeneration via inhibition of PARP-1, caspase-3 and cleaved caspase-3.

SIGNIFICANCE

Overall, our studies suggest DET can prevent neuroinflammation-associated memory impairment and neurodegeneration and it could be developed as a therapeutic agent for the treatment of neuroinflammation-mediated and neurodegenerative disorders, such as AD.

Alteration in biochemical parameters in the brain of transgenic Drosophila melanogaster model of Parkinson's disease exposed to apigenin

BACKGROUND

Oxidative stress is one of the key components of the pathology of various neurodegenerative disorders. Parkinson's disease (PD) is characterized by the progressive loss of dopaminergic neurons owing to the aggregation of alpha-synuclein (αS) in the brain. A number of polyphenols have been reported to inhibit the αS aggregation resulting in the possible prevention of PD. The involvement of free radicals in mediating the neuronal death in PD has also been implicated.

METHODS

In the present study, the transgenic flies expressing human αS in the brain were exposed to 10 μM, 20 μM, 40 μM, and 80 μM of apigenin established in diet for 24 days.

RESULTS

The flies showed an increase in life span, glutathione, and dopamine content. The exposure of PD flies to various doses of apigenin also results in the reduction of glutathione-S-transferase activity, lipid peroxidation, monoamine oxidase, caspase-3, and caspase-9 activity in a dose-dependent manner.

CONCLUSION

The results of the present study reveal that apigenin is potent in increasing the life span, dopamine content, reduced the oxidative stress as well as apoptosis in transgenic Drosophila model of PD.

Potential therapeutic effects of odorants through their ectopic receptors in pigmented cells

Several olfactory receptors (ORs) have been characterized outside the olfactory neuroepithelium in neuronal and non-neuronal tissues, where they were implicated in the recognition of diverse chemical signals. ORs have been found to regulate melanogenesis in skin melanocytes, and OR expression has been found in the human brain nigrostriatal dopaminergic neurons, where production of melanin occurs as neuromelanin and can change with age; OR expression is downregulated in Parkinson's disease. Therefore, we propose several odorants as new functional ligands to ORs expressed in non-olfactory pigmented cells as dopaminergic neurons and melanocytes, where, by acting on cAMP-induced melanin production, they could help to counteract melanogenic and neurodegenerative dysfunctions, including melanoma and Parkinson's disease.

Kinetic Isotope Effects and Transition State Structure for Human Phenylethanolamine N-Methyltransferase

Phenylethanolamine N-methyltransferase (PNMT) catalyzes the S-adenosyl-l-methionine (SAM)-dependent conversion of norepinephrine to epinephrine. Epinephrine has been associated with critical processes in humans including the control of respiration and blood pressure. Additionally, PNMT activity has been suggested to play a role in hypertension and Alzheimer's disease. In the current study, labeled SAM substrates were used to measure primary methyl-14C and 36S and secondary methyl-3H, 5'-3H, and 5'-14C intrinsic kinetic isotope effects for human PNMT. The transition state of human PNMT was modeled by matching kinetic isotope effects predicted via quantum chemical calculations to intrinsic values. The model provides information on the geometry and electrostatics of the human PNMT transition state structure and indicates that human PNMT catalyzes the formation of epinephrine through an early SN2 transition state in which methyl transfer is rate-limiting.

Mitochondrial Target of Nobiletin's Action

Nobiletin is an O-methylated flavonoid found in citrus peels that have anticancer, antiviral, neuroprotective, anti-inflammatory activities and depending on the cell types exhibits both pro- or anti-apoptotic properties. We have found that nobiletin decreases oxygen consumption by bovine brain isolated mitochondria in the presence of glutamate and malate and increases in the presence of succinate. In parallel, nobiletin increases NADH oxidation, a-ketoglutarate dehydrogenase activities and through matrix substrate-level phosphorylation elevates the a-ketoglutarate-dependent production of ATP. In addition, nobiletin reduces the production of peroxides in the presence of complex I substrates and slightly enhances succinate-driven H2O2 formation. Besides, nobiletin induces transient elevation of membrane potential followed by mild depolarization. Affinity purified nobiletin binding proteins revealed one major anti-NDUFV1 positive protein with 52kD and NADH: ubiquinone oxidoreductase activity. This fraction can produce peroxide that is inhibited by nobiletin. We propose that nobiletin may act as a mild “uncoupler”, which through activation of a-ketoglutarate dehydrogenase (a-KGDH)-complex and acceleration of matrix substrate-level phosphorylation maintains membrane potential at an abnormal level. This switch in mitochondrial metabolism could elevate succinate-driven oxygen consumption that may underlay in both pro- and anti-apoptotic effects of nobiletin.

Nobiletin restores impaired hippocampal mitochondrial bioenergetics in hypothyroidism through activation of matrix substrate-level phosphorylation

OBJECTIVE

Evaluation of the effect of citrus flavonoid - nobiletin on the bioenergetics of synaptic and non-synaptic mitochondria in the hippocampus of hypothyroid rats.

METHODS

Male Wistar rats were divided into hypothyroid (methimazole-treated), nobiletin supplemented hypothyroid, thyroxine-treated hypothyroid, and euthyroid (control) groups. Synaptic and non-synaptic (cell) mitochondria were isolated from hippocampus. Oligomycin-sensitive, oligomycin-insensitive, α-ketoglutarate dehydrogenase-dependent synthesis of adenosine triphosphate (ATP), succinate dehydrogenase, and hexokinase activities were determined luminometrically and spectrophotometrically, respectively.

RESULTS

Decreased synthesis of oligomycin-sensitive and oligomycin-insensitive ATP in hypothyroid rat hippocampus was observed in synaptic and non-synaptic mitochondria. Supplementation of hypothyroid rats with nobiletin increases oligomycin-insensitive and α-ketoglutarate-dependent production of ATP in both types of mitochondria. The activity of succinate dehydrogenase in non-synaptic mitochondria and the activities of hexokinase in both types of mitochondria were normalized in nobiletin-treated hypothyroid rats.

DISCUSSION

Nobiletin restores reduced mitochondrial metabolism in hypothyroid rat hippocampus through acceleration of matrix substrate-level phosphorylation that may be important for the prevention of hypometabolic complications in neurological disorders.

Combination therapy: a new strategy to manage diabetes and its complications

Diabetes mellitus is the most common metabolic disorder. The major cause of mortality and morbidity here is due to the complications caused by increased glucose concentrations. All the available commercial antidiabetic drugs are associated with side effects. The combination therapy could be a new and highly effective therapeutic strategy to manage hyperglycemia. Combination of commercial drugs with phytochemicals may reduce the side effects caused by these synthetic drugs. Herbal products have been thought to be inherently safe, because of their natural origin and traditional use rather than based on systemic studies. New formulation and cocrystallisation strategies need to be adopted to match the bioavailability of the drug and the phytochemical. This review describes in detail, the observed synergy and mechanism of action between phytochemicals and synthetic drugs in effectively combating. The mode of action of combination differs significantly than that of the drugs alone; hence isolating a single component may lose its importance thereby simplifying the task of pharma industries.

Defective autophagy in Parkinson's disease: role of oxidative stress

Parkinson's disease (PD) is a paradigmatic example of neurodegenerative disorder with a critical role of oxidative stress in its etiopathogenesis. Genetic susceptibility factors of PD, such as mutations in Parkin, PTEN-induced kinase 1, and DJ-1 as well as the exposure to pesticides and heavy metals, both contribute to altered redox balance and degeneration of dopaminergic neurons in the substantia nigra. Dysregulation of autophagy, a lysosomal-driven process of self degradation of cellular organelles and protein aggregates, is also implicated in PD and PD-related mutations, and environmental toxins deregulate autophagy. However, experimental evidence suggests a complex and ambiguous role of autophagy in PD since either impaired or abnormally upregulated autophagic flux has been shown to cause neuronal loss. Finally, it is generally believed that oxidative stress is a strong proautophagic stimulus. However, some evidence coming from neurobiology as well as from other fields indicate an inhibitory role of reactive oxygen species and reactive nitrogen species on the autophagic machinery. This review examines the scientific evidence supporting different concepts on how autophagy is dysregulated in PD and attempts to reconcile apparently contradictory views on the role of oxidative stress in autophagy regulation. The complex relationship between autophagy and oxidative stress is also considered in the context of the ongoing search for a novel PD therapy.

Effect of L-ascorbic Acid on the climbing ability and protein levels in the brain of Drosophila model of Parkinson's disease

In the present study, the effect of l-ascorbic acid (AA) was studied on the climbing ability of the Parkinson's disease (PD) model Drosophila expressing normal human alpha synuclein (h-αs) in the neurons. These flies show locomotor dysfunction as the age progresses. AA at final concentration of 11.35 × 10(-5) M, 22.71 × 10(-5) M, 45.42 × 10(-5) M, and 68.13 × 10(-5) M was added to the diet, and the flies were allowed to feed for 21 days. AA at 11.35 × 10(-5) M did not show any significant delay in the loss of climbing ability of PD model flies. However, AA at 22.71 × 10(-5) M, 45.42 × 10(-5) M, and 68.13 × 10(-5) M showed a dose dependent significant (p < .05) delay in the loss of climbing ability of PD model flies as compared to the untreated PD flies. The total protein concentration in brain homogenate was measured in treated as well as control groups after 21 days, no significant difference was obtained between treated as well as control (PD flies and l-dopa) groups. The results suggest that AA is potent in delaying the climbing disability of the PD model flies expressing h-αs in the neurons.

Influence of RNA interference on the mitochondrial subcellular localization of alpha-synuclein and on the formation of Lewy body-like inclusions in the cytoplasm of human embryonic kidney 293 cells induced by the overexpression of alpha-synuclein

The specific and effective α-synuclein RNA interference (RNAi) plasmids, and the α-synuclein-pEGFP recombinant plasmids were co-transfected into human embryonic kidney 293 (HEK293) cells using the lipofectamine method. Using an inverted fluorescence microscope, α-synuclein proteins were observed to aggregate in the cytoplasm and nucleus. Wild-type α-synuclein proteins co-localized with mitochondria. Hematoxylin-eosin staining revealed round eosinophilic bodies (Lewy body-like inclusions) in the cytoplasm of some cells transfected with α-synuclein-pEGFP plasmid. However, the formation of Lewy body-like inclusions was not observed following transfection with the RNAi pSYN-1 plasmid. RNAi blocked Lewy body-like inclusions in the cytoplasm of HEK293 cells induced by wild-type α-synuclein overexpression, but RNAi did not affect the subcellular localization of wild-type α-synuclein in mitochondria.