Beneficial Effects of Green Tea Catechins on Neurodegenerative Diseases

Regulation of Neprilysin Activity and Cognitive Functions in Rats After Prenatal Hypoxia

The amyloid-degrading enzyme neprilysin (NEP) is one of the therapeutic targets in prevention and treatment of Alzheimer's disease (AD). As we have shown previously NEP expression in rat parietal cortex (Cx) and hippocampus (Hip) decreases with age and is also significantly reduced after prenatal hypoxia. Following the paradigms for enhancement of NEP expression and activity developed in cell culture, we analysed the efficacy of various compounds able to upregulate NEP using our model of prenatal hypoxia in rats. In addition to the previous data demonstrating that valproic acid can upregulate NEP expression both in neuroblastoma cells and in rat Cx and Hip we have further confirmed that caspase inhibitors can also restore NEP expression in rat Cx reduced after prenatal hypoxia. Here we also report that administration of a green tea catechin epigallocatechin-3-gallate (EGCG) to adult rats subjected to prenatal hypoxia increased NEP activity in blood plasma, Cx and Hip as well as improved memory performance in the 8-arm maze and novel object recognition tests. Moreover, EGCG administration led to an increased number of dendritic spines in the hippocampal CA1 area which correlated with memory enhancement. The data obtained allowed us to conclude that the decrease in the activity of the amyloid-degrading enzyme NEP, as well as a reduction in the number of labile interneuronal contacts in the hippocampus, contribute to early cognitive deficits caused by prenatal hypoxia and that there are therapeutic avenues to restore these deficits via NEP activation which could also be used for designing preventive strategies in AD.

Plant Extracts and Phytochemicals Targeting α-Synuclein Aggregation in Parkinson's Disease Models

α-Synuclein (α-syn) is a presynaptic protein that regulates the release of neurotransmitters from synaptic vesicles in the brain. α-Syn aggregates, including Lewy bodies, are features of both sporadic and familial forms of Parkinson's disease (PD). These aggregates undergo several key stages of fibrillation, oligomerization, and aggregation. Therapeutic benefits of drugs decline with disease progression and offer only symptomatic treatment. Novel therapeutic strategies are required which can either prevent or delay the progression of the disease. The link between α-syn and the etiopathogenesis and progression of PD are well-established in the literature. Studies indicate that α-syn is an important therapeutic target and inhibition of α-syn aggregation, oligomerization, and fibrillation are an important disease modification strategy. However, recent studies have shown that plant extracts and phytochemicals have neuroprotective effects on α-syn oligomerization and fibrillation by targeting different key stages of its formation. Although many reviews on the antioxidant-mediated, neuroprotective effect of plant extracts and phytochemicals on PD symptoms have been well-highlighted, the antioxidant mechanisms show limited success for translation to clinical studies. The identification of specific plant extracts and phytochemicals that target α-syn aggregation will provide selective molecules to develop new drugs for PD. The present review provides an overview of plant extracts and phytochemicals that target α-syn in PD and summarizes the observed effects and the underlying mechanisms. Furthermore, we provide a synopsis of current experimental models and techniques used to evaluate plant extracts and phytochemicals. Plant extracts and phytochemicals were found to inhibit the aggregation or fibril formation of oligomers. These also appear to direct α-syn oligomer formation into its unstructured form or promote non-toxic pathways and suggested to be valuable drug candidates for PD and related synucleinopathy. Current evidences from in vitro studies require confirmation in the in vivo studies. Further studies are needed to ascertain their potential effects and safety in preclinical studies for pharmaceutical/nutritional development of these phytochemicals or dietary inclusion of the plant extracts in PD treatment.

Polyphenol Health Effects on Cardiovascular and Neurodegenerative Disorders: A Review and Meta-Analysis

Several studies have demonstrated that polyphenol-enriched diets may have beneficial effects against the development of degenerative diseases, including atherosclerosis and disorders affecting the central nervous system. This activity has been associated not only with antioxidant and anti-inflammatory properties, but also with additional mechanisms, such as the modulation of lipid metabolism and gut microbiota function. However, long-term studies on humans provided controversial results, making the prediction of polyphenol impact on health uncertain. The aim of this review is to provide an overview and critical analysis of the literature related to the effects of the principal dietary polyphenols on cardiovascular and neurodegenerative disorders. We critically considered and meta-analyzed randomized controlled clinical trials involving subjects taking polyphenol-based supplements. Although some polyphenols might improve specific markers of cardiovascular risk and cognitive status, many inconsistent data are present in literature. Therefore, definitive recommendations for the use of these compounds in the prevention of cardiovascular disease and cognitive decline are currently not applicable. Once pivotal aspects for the definition of polyphenol bioactivity, such as the characterization of pharmacokinetics and safety, are addressed, it will be possible to have a clear picture of the realistic potential of polyphenols for disease prevention.

Exploring the efficacy of natural products in alleviating Alzheimer's disease

Alzheimer’s disease (hereafter AD) is a progressive neurodegenerative disorder that affects the central nervous system. There are multiple factors that cause AD, viz., accumulation of extracellular Amyloid-beta 42 plaques, intracellular hyper-phosphorylated Tau tangles, generation of reactive oxygen species due to mitochondrial dysfunction and genetic mutations. The plaques and tau tangles trigger aberrant signaling, which eventually cause cell death of the neurons. As a result, there is shrinkage of brain, cognitive defects, behavioral and psychological problems. To date, there is no direct cure for AD. Thus, scientists have been testing various strategies like screening for the small inhibitor molecule library or natural products that may block or prevent onset of AD. Historically, natural products have been used in many cultures for the treatment of various diseases. The research on natural products have gained importance as the active compounds extracted from them have medicinal values with reduced side effects, and they are bioavailable. The natural products may target the proteins or members of signaling pathways that get altered in specific diseases. Many natural products are being tested in various animal model systems for their role as a potential therapeutic target for AD, and to address questions about how these natural products can rescue AD or other neurodegenerative disorders. Some of these products are in clinical trials and results are promising because of their neuroprotective, anti-inflammatory, antioxidant, anti-amyloidogenic, anticholinesterase activities and easy availability. This review summarizes the use of animal model systems to identify natural products, which may serve as potential therapeutic targets for AD.

Neuroprotective Role of Phytochemicals

Neurodegenerative diseases are normally distinguished as disorders with loss of neurons. Various compounds are being tested to treat neurodegenerative diseases (NDs) but they possess solitary symptomatic advantages with numerous side effects. Accumulative studies have been conducted to validate the benefit of phytochemicals to treat neurodegenerative diseases including Alzheimer's disease (AD) and Parkinson's disease (PD). In this present review we explored the potential efficacy of phytochemicals such as epigallocatechin-3-galate, berberin, curcumin, resveratrol, quercetin and limonoids against the most common NDs, including Alzheimer's disease (AD) and Parkinson's disease (PD). The beneficial potentials of these phytochemicals have been demonstrated by evidence-based but more extensive investigation needs to be conducted for reducing the progression of AD and PD.

Polyphenols Derived from Lychee Seed Suppress Aβ (1-42)-Induced Neuroinflammation

Amyloid-β (Aβ) is commonly recognized as the most important factor that results in neuronal cell death and accelerates the progression of Alzheimer’s disease (AD). Increasing evidence suggests that microglia activated by Aβ release an amount of neurotoxic inflammatory cytokines that contribute to neuron death and aggravate AD pathology. In our previous studies, we found that lychee seed fraction (LSF), an active fraction derived from the lychee seed, could significantly improve the cognitive function of AD rats and inhibit Aβ-induced neuroinflammation in vitro, and decrease neuronal injuries in vivo and in vitro. In the current study, we aimed to isolate and identify the specific components in LSF that were responsible for the anti-neuroinflammation effect using preparative high performance liquid chromatography (pre-HPLC), liquid chromatography-mass spectrometry (LC-MS), and nuclear magnetic resonance (NMR) methods. To this end, we confirmed two polyphenols including catechin and procyanidin A2 that could improve the morphological status of BV-2 cells and suppress the release, mRNA levels, and protein expression of pro-inflammatory cytokines such as tumor necrosis factor-α (TNF-α), interleukin-1β (IL-1β), and interleukin-6 (IL-6) through downregulating the nuclear factor-κB (NF-κB) signaling pathway using ELISA, RT-PCR, and Western blotting methods. Furthermore, catechin and procyanidin A2 could inhibit Aβ-induced apoptosis in BV-2 cells by upregulating Bcl-2 and downregulating Bax protein expression. Therefore, the current study illustrated the active substances in lychee seed, and first reported that catechin and procyanidin A2 could suppress neuroinflammation in Aβ-induced BV-2 cells, which provides detailed insights into the molecular mechanism of catechin and procyanidin A2 in the neuroprotective effect, and their further validations of anti-neuroinflammation in vivo is also essential in future research.