Disease-modifying treatment of Parkinson's disease by phytochemicals: targeting multiple pathogenic factors

Phytochemicals Modulate Biosynthesis and Function of Serotonin, Dopamine, and Norepinephrine for Treatment of Monoamine Neurotransmission-Related Psychiatric Diseases

Serotonin (5-HT), dopamine (DA), and norepinephrine (NE) are key monoamine neurotransmitters regulating behaviors, mood, and cognition. 5-HT affects early brain development, and its dysfunction induces brain vulnerability to stress, raising the risk of depression, anxiety, and autism in adulthood. These neurotransmitters are synthesized from tryptophan and tyrosine via hydroxylation and decarboxylation, and are metabolized by monoamine oxidase (MAO). This review aims to summarize the current findings on the role of dietary phytochemicals in modulating monoamine neurotransmitter biosynthesis, metabolism, and function, with an emphasis on their potential therapeutic applications in neuropsychiatric disorders. Phytochemicals exert antioxidant, neurotrophic, and neurohormonal activities, regulate gene expression, and induce epigenetic modifications. Phytoestrogens activate the estrogen receptors or estrogen-responsive elements of the promoter of target genes, enhance transcription of tryptophan hydroxylase and tyrosine hydroxylase, while inhibiting that of MAO. These compounds also influence the interaction between genetic and environmental factors, potentially reversing dysregulated neurotransmission and the brain architecture associated with neuropsychiatric conditions. Despite promising preclinical findings, clinical applications of phytochemicals remain challenging. Advances in nanotechnology and targeted delivery systems offer potential solutions to enhance clinical efficacy. This review discusses mechanisms, challenges, and strategies, underscoring the need for further research to advance phytochemical-based interventions for neuropsychiatric diseases.

Toxic interactions between dopamine, α-synuclein, monoamine oxidase, and genes in mitochondria of Parkinson's disease

Parkinson's disease is characterized by its distinct pathological features; loss of dopamine neurons in the substantia nigra pars compacta and accumulation of Lewy bodies and Lewy neurites containing modified α-synuclein. Beneficial effects of L-DOPA and dopamine replacement therapy indicate dopamine deficit as one of the main pathogenic factors. Dopamine and its oxidation products are proposed to induce selective vulnerability in dopamine neurons. However, Parkinson's disease is now considered as a generalized disease with dysfunction of several neurotransmitter systems caused by multiple genetic and environmental factors. The pathogenic factors include oxidative stress, mitochondrial dysfunction, α-synuclein accumulation, programmed cell death, impaired proteolytic systems, neuroinflammation, and decline of neurotrophic factors. This paper presents interactions among dopamine, α-synuclein, monoamine oxidase, its inhibitors, and related genes in mitochondria. α-Synuclein inhibits dopamine synthesis and function. Vice versa, dopamine oxidation by monoamine oxidase produces toxic aldehydes, reactive oxygen species, and quinones, which modify α-synuclein, and promote its fibril production and accumulation in mitochondria. Excessive dopamine in experimental models modifies proteins in the mitochondrial electron transport chain and inhibits the function. α-Synuclein and familiar Parkinson's disease-related gene products modify the expression and activity of monoamine oxidase. Type A monoamine oxidase is associated with neuroprotection by an unspecific dose of inhibitors of type B monoamine oxidase, rasagiline and selegiline. Rasagiline and selegiline prevent α-synuclein fibrillization, modulate this toxic collaboration, and exert neuroprotection in experimental studies. Complex interactions between these pathogenic factors play a decisive role in neurodegeneration in PD and should be further defined to develop new therapies for Parkinson's disease.

Phytochemicals targeting Alzheimer's disease via the AMP-activated protein kinase pathway, effects, and mechanisms of action

Alzheimer's disease (AD), characterized by cognitive dysfunction and other behavioral abnormalities, is a progressive neurodegenerative disease that occurs due to aging. Currently, effective drugs to mitigate or treat AD remain unavailable. AD is associated with several abnormalities in neuronal energy metabolism, such as decreased glucose uptake, mitochondrial dysfunction, and defects in cholesterol metabolism. Amp-activated protein kinase (AMPK) is an important serine/threonine protein kinase that regulates the energy status of cells. AMPK is widely present in eukaryotic cells and can sense and regulate energy metabolism to maintain energy supply and demand balance, making it a promising target for energy metabolism-based AD therapy. Therefore, this review aimed to discuss the molecular mechanism of AMPK in the pathogenesis of AD to provide a theoretical basis for the development of new anti-AD drugs. To review the mechanisms of phytochemicals in the treatment of AD via AMPK pathway regulation, we searched PubMed, Google Scholar, Web of Science, and Embase databases using specific keywords related to AD and phytochemicals in September 2023. Phytochemicals can activate AMPK or regulate the AMPK pathway to exert therapeutic effects in AD. The anti-AD mechanisms of these phytochemicals include inhibiting Aβ aggregation, preventing Tau hyperphosphorylation, inhibiting inflammatory response and glial activation, promoting autophagy, and suppressing anti-oxidative stress. Additionally, several AMPK-related pathways are involved in the anti-AD mechanism, including the AMPK/CaMKKβ/mTOR, AMPK/SIRT1/PGC-1α, AMPK/NF-κB/NLRP3, AMPK/mTOR, and PERK/eIF2α pathways. Notably, urolithin A, artemisinin, justicidin A, berberine, stigmasterol, arctigenin, and rutaecarpine are promising AMPK agonists with anti-AD effects. Several phytochemicals are effective AMPK agonists and may have potential applications in AD treatment. Overall, phytochemical-based drugs may overcome the barriers to the effective treatment of neurodegenerative diseases.

Anti-obesity Properties of Phytochemicals: Highlighting their Molecular Mechanisms against Obesity

Obesity is a complex, chronic and inflammatory disease that affects more than one-third of the world's population, leading to a higher incidence of diabetes, dyslipidemia, metabolic syndrome, cardiovascular diseases, and some types of cancer. Several phytochemicals are used as flavoring and aromatic compounds, also exerting many benefits for public health. This study aims to summarize and scrutinize the beneficial effects of the most important phytochemicals against obesity. Systematic research of the current international literature was carried out in the most accurate scientific databases, e.g., Pubmed, Scopus, Web of Science and Google Scholar, using a set of critical and representative keywords, such as phytochemicals, obesity, metabolism, metabolic syndrome, etc. Several studies unraveled the potential positive effects of phytochemicals such as berberine, carvacrol, curcumin, quercetin, resveratrol, thymol, etc., against obesity and metabolic disorders. Mechanisms of action include inhibition of adipocyte differentiation, browning of the white adipose tissue, inhibition of enzymes such as lipase and amylase, suppression of inflammation, improvement of the gut microbiota, and downregulation of obesity-inducing genes. In conclusion, multiple bioactive compounds-phytochemicals exert many beneficial effects against obesity. Future molecular and clinical studies must be performed to unravel the multiple molecular mechanisms and anti-obesity activities of these naturally occurring bioactive compounds.

Investigating molecular interactions between human transferrin and resveratrol through a unified experimental and computational approach: Role of natural compounds in Alzheimer's disease therapeutics

Disruptions to iron metabolism and iron homeostasis have emerged as significant contributors to the development and progression of Alzheimer's disease (AD). Human transferrin plays a key part in maintaining iron equilibrium throughout the body, highlighting its importance in AD. Many plant-derived compounds and dietary constituents show promise for preventing AD. Polyphenols that are abundant in fruits, vegetables, teas, coffee, and herbs possess neuroprotective attributes. Resveratrol is a natural polyphenol present in various plant sources like grapes, berries, peanuts, and red wine that has garnered research interest due to its wide range of biological activities. Notably, resveratrol exhibits neuroprotective effects that may help prevent or treat AD through multiple mechanisms. In the present study, we employed a combination of molecular docking and all-atom molecular dynamic simulations (MD) along with experimental approaches to unravel the intricate interactions between transferrin and resveratrol deciphering the binding mechanism. Through molecular docking analysis, it was determined that resveratrol occupies the iron binding pocket of transferrin. Furthermore, MD simulations provided a more profound insight into the stability and conformational dynamics of the complex suggesting that the binding of resveratrol introduced localized flexibility, while maintaining overall stability. The spectroscopic observations yielded clear evidence of substantial binding between resveratrol and transferrin, confirming the computational findings. The identified binding mechanism and conformational stability hold potential for advancing the development of innovative therapeutic approaches targeting AD through resveratrol, particularly concerning iron homeostasis. These insights serve as a platform for considering the natural compounds in the realm of AD therapeutics.

Molecular Interaction of Pea Glutelin and Lipophilic Bioactive Compounds: Structure-Binding Relationship and Nano-/Microcomplexation

This study investigated the impact of ionic strength and lipophilicity of bioactive compounds on their interaction with the alkaline soluble pea glutelin fraction (ASF) using the fluorescence quenching technique. A Stern-Volmer quenching constant, KD, of 8.9 ± 0.10, 5.3 ± 0.06, 4.0 ± 0.01, 1.1 ± 0.00, 0.9 ± 0.02, and 0.1 ± 0.00 (×104 M-1) was observed for curcumin-ASF (CuASF), astaxanthin-ASF (AsASF), cholecalciferol-ASF (ChASF), β-carotene-ASF (βCaASF), coenzyme Q10-ASF (Q10ASF), and β-sitosterol-ASF (βSiASF) complexes, respectively. An increase in ionic strength did not significantly change KD, the effective quenching constant K, and the bimolecular quenching rate constant KQ. However, it changed the mode of interaction of the ASF with cholecalciferol, β-carotene, coenzyme Q10, and β-sitosterol from static to static-dynamic quenching. Transmission electron microscopy showed that the morphology formed with protein (spherical nanocomplexes, microaggregates, or fiber-like particles) differed among the compounds. The favorable binding of CuASF, AsASF, ChASF, and βCaASF complexes provides stable matrices for formulating protein-based delivery systems for lipophilic nutraceuticals.

Alpha Synuclein: Neurodegeneration and Inflammation

Alpha-Synuclein (α-Syn) is one of the most important molecules involved in the pathogenesis of Parkinson's disease and related disorders, synucleinopathies, but also in several other neurodegenerative disorders with a more elusive role. This review analyzes the activities of α-Syn, in different conformational states, monomeric, oligomeric and fibrils, in relation to neuronal dysfunction. The neuronal damage induced by α-Syn in various conformers will be analyzed in relation to its capacity to spread the intracellular aggregation seeds with a prion-like mechanism. In view of the prominent role of inflammation in virtually all neurodegenerative disorders, the activity of α-Syn will also be illustrated considering its influence on glial reactivity. We and others have described the interaction between general inflammation and cerebral dysfunctional activity of α-Syn. Differences in microglia and astrocyte activation have also been observed when in vivo the presence of α-Syn oligomers has been combined with a lasting peripheral inflammatory effect. The reactivity of microglia was amplified, while astrocytes were damaged by the double stimulus, opening new perspectives for the control of inflammation in synucleinopathies. Starting from our studies in experimental models, we extended the perspective to find useful pointers to orient future research and potential therapeutic strategies in neurodegenerative disorders.

Molecular and Cellular Interactions in Pathogenesis of Sporadic Parkinson Disease

An increasing number of the population all around the world suffer from age-associated neurodegenerative diseases including Parkinson’s disease (PD). This disorder presents different signs of genetic, epigenetic and environmental origin, and molecular, cellular and intracellular dysfunction. At the molecular level, α-synuclein (αSyn) was identified as the principal molecule constituting the Lewy bodies (LB). The gut microbiota participates in the pathogenesis of PD and may contribute to the loss of dopaminergic neurons through mitochondrial dysfunction. The most important pathogenetic link is an imbalance of Ca²⁺ ions, which is associated with redox imbalance in the cells and increased generation of reactive oxygen species (ROS). In this review, genetic, epigenetic and environmental factors that cause these disorders and their cause-and-effect relationships are considered. As a constituent of environmental factors, the example of organophosphates (OPs) is also reviewed. The role of endothelial damage in the pathogenesis of PD is discussed, and a ‘triple hit hypothesis’ is proposed as a modification of Braak’s dual hit one. In the absence of effective therapies for neurodegenerative diseases, more and more evidence is emerging about the positive impact of nutritional structure and healthy lifestyle on the state of blood vessels and the risk of developing these diseases.

Neuroprotective Function of Rasagiline and Selegiline, Inhibitors of Type B Monoamine Oxidase, and Role of Monoamine Oxidases in Synucleinopathies

Synucleinopathies are a group of neurodegenerative disorders caused by the accumulation of toxic species of α-synuclein. The common clinical features are chronic progressive decline of motor, cognitive, behavioral, and autonomic functions. They include Parkinson’s disease, dementia with Lewy body, and multiple system atrophy. Their etiology has not been clarified and multiple pathogenic factors include oxidative stress, mitochondrial dysfunction, impaired protein degradation systems, and neuroinflammation. Current available therapy cannot prevent progressive neurodegeneration and “disease-modifying or neuroprotective” therapy has been proposed. This paper presents the molecular mechanisms of neuroprotection by the inhibitors of type B monoamine oxidase, rasagiline and selegiline. They prevent mitochondrial apoptosis, induce anti-apoptotic Bcl-2 protein family, and pro-survival brain- and glial cell line-derived neurotrophic factors. They also prevent toxic oligomerization and aggregation of α-synuclein. Monoamine oxidase is involved in neurodegeneration and neuroprotection, independently of the catalytic activity. Type A monoamine oxidases mediates rasagiline-activated signaling pathways to induce neuroprotective genes in neuronal cells. Multi-targeting propargylamine derivatives have been developed for therapy in various neurodegenerative diseases. Preclinical studies have presented neuroprotection of rasagiline and selegiline, but beneficial effects have been scarcely presented. Strategy to improve clinical trials is discussed to achieve disease-modification in synucleinopathies.

Neuroprotective Effects of Phytochemicals against Aluminum Chloride-Induced Alzheimer’s Disease through ApoE4/LRP1, Wnt3/β-Catenin/GSK3β, and TLR4/NLRP3 Pathways with Physical and Mental Activities in a Rat Model

Background: Alzheimer’s disease (AD) is a neurodegenerative disorder that is associated with abnormal cognition. AD is aided in its initiation and progression by hereditary and environmental factors. Aluminum (Al) is a neurotoxic agent that causes oxidative stress, which is linked to AD progression. Additionally, Nrf2/HO-1, APOE4/LRP1, Wnt3/β-catenin, and TLR4/NLRP3 are the main signaling pathways involved in AD pathogenesis. Several phytochemicals are promising options in delaying AD evolution. Objectives: This study aimed at studying the neuroprotective effects of some phytochemicals as morin (MOR), thymol (TML), and thymoquinone (TMQ) on physical and mental activities (PhM) in Al chloride (AlCl₃)-induced AD rat model. Another objective was to determine the specificity of phytochemicals to AD signaling pathways using molecular docking. Methods: Eighty male Dawley rats were divided into eight groups. Each group received: saline (control group), AlCl₃, (ALAD), PhM, either alone or with a combination of MOR, TML, and/or TMQ for five weeks. Animals were then subjected to behavioral evaluation. Brain tissues were used for histopathological and biochemical analyses to determine the extent of neurodegeneration. The effect of phytochemicals on AlCl₃-induced oxidative stress and the main signaling pathways involved in AD progression were also investigated. Results: AlCl₃ caused a decline in spatial learning and memory, as well as histopathological changes in the brains of rats. Phytochemicals combined with PhM restored antioxidant activities, increased HO-1 and Nrf2 levels, blocked inflammasome activation, apoptosis, TLR4 expression, amyloide-β generation, and tau hyperphophorylation. They also brought ApoE4 and LRP1 levels back to normal and regulated Wnt3/β-catenin/GSK3β signaling pathway. Conclusions: The use of phytochemicals with PhM is a promising strategy for reducing AD by modulating Nrf2/HO-1, TLR4/NLRP3, APOE4/LRP1, and Wnt3/β-catenin/GSK-3β signaling pathways.