amyloid-beta-peptides and epigallocatechin-gallate

In this study, we compared the effects of two well-known natural compounds on the early step of the fibrillation process of amyloid-β (1-40), responsible for the formation of plaques in the brains of patients affected by Alzheimer's disease (AD). The use of extensive replica exchange simulations up to the µs scale allowed us to characterize the inhibition activity of (-)-epigallocatechin-3-gallate (EGCG) and curcumin (CUR) on unfolded amyloid fibrils. A reduced number of β-strands, characteristic of amyloid fibrils, and an increased distance between the amino acids that are responsible for the intra- and interprotein aggregations are observed. The central core region of the amyloid-β (Aβ(1-40)) fibril is found to have a high affinity to EGCG and CUR due to the presence of hydrophobic residues. Lastly, the free binding energy computed using the Poisson Boltzmann Surface Ares suggests that EGCG is more likely to bind to unfolded Aβ(1-40) fibrils and that this molecule can be a good candidate to develop new and more effective congeners to treat AD.

Topics: Alzheimer Disease; Amyloid; Amyloid beta-Peptides; Brain; Catechin; Curcumin; Humans; Hydrophobic and Hydrophilic Interactions; Molecular Dynamics Simulation; Peptide Fragments; Plaque, Amyloid; Protein Aggregates

Protein aggregation is a hallmark of several neurodegenerative diseases, including Alzheimer's and Parkinson's diseases. It has been shown that lysine residues play a key role in the formation of these aggregates. Thus, the ability to disrupt aggregate formation by covalently modifying lysine residues could lead to the discovery of therapeutically relevant antiamyloidogenesis compounds. Herein, we demonstrate that an ortho-iminoquinone (IQ) can be utilized to inhibit amyloid aggregation. Using alpha-synuclein and Aβ

Topics: alpha-Synuclein; Amyloid beta-Peptides; Animals; Catechin; Cell Survival; Cells, Cultured; Chickens; Dopaminergic Neurons; HEK293 Cells; Humans; Lysine; Methionine; Mice; Micrococcus luteus; Microtubule-Associated Proteins; Muramidase; Neuroprotective Agents; Oxidation-Reduction; Peptide Fragments; Protein Aggregation, Pathological; Quinones; Tyrosine 3-Monooxygenase

Alzheimer's disease (AD) is the leading cause of dementia, and as its prevalence increases, so does its detrimental impact on society. The currently available therapies have limited efficacy, leaving AD patients on an irrevocably fatal path of this disease.. The purpose of this study was to test efficacy of a novel combinatorial treatment approach to alleviate AD-like pathology.. We selected four naturally occurring compounds and used them in different combinations to test their effect on AD-like pathology. Employing a well-established cell culture AD model system, we evaluated levels of several diverse biomarkers associated with a number of cellular pathways associated with AD. The readouts included: amyloid-β peptides, anti-inflammatory and anti-apoptotic proteins, oxidative enzymes, and reactive oxygen species.. Using this approach, we demonstrated that the compounds delivered in combination had higher efficacy than individual treatments. Specifically, we observed significant reduction in levels of the amyloid-β peptides, as well as pro-inflammatory proteins and reactive oxygen species. Similarly, delivery of compounds in combination resulted in an increased expression of anti-apoptotic proteins and anti-oxidative enzymes. Collectively, these modifications in AD pathology biomarkers reflect a promising therapeutic and preventive strategy to combat this disease.. The above findings support a novel therapeutic approach to address a currently unmet medical need, which would benefit not only AD patients and their caregivers, but also society as a whole.

Topics: Amyloid beta-Peptides; Amyloid beta-Protein Precursor; Animals; Antipsychotic Agents; Catechin; Cell Line, Tumor; Cytokines; Drug Combinations; Gene Expression Regulation, Neoplastic; Humans; Melatonin; Mice; Mutation; Neuroblastoma; Peptide Fragments; Proto-Oncogene Proteins c-bcl-2; Reactive Oxygen Species; Resveratrol; Stilbenes; Transfection

The accumulation of β-amyloid (Aβ) peptide plaques is a major pathogenic event in Alzheimer's disease (AD). Aβ is a cleaved fragment of APP via BACE1, which is the rate-limiting enzyme in APP processing and Aβ generation. Nuclear receptor peroxisome proliferator-activated receptor gamma (PPARγ) is considered to be a potential target for AD treatment, because of its potent antioxidant and inhibitory effects on Aβ production by negatively regulating BACE1. Epigallocatechin gallate (EGCG), a highly active catechin found in green tea, is known to enhance metabolic activity and cognitive ability in the mice model of AD. To investigate whether the therapeutic effect of EGCG is related to the PPARγ pathway, we analysed the alterations in the intracellular molecular expression of PPARγ after EGCG treatment in the N2a/APP695 cell line. In this study, we observed that EGCG attenuated Aβ generation in N2a/APP695 cells, such as the PPARγ agonist, pioglitazone, by suppressing the transcription and translation of BACE1 and that its effect was attenuated by the PPARγ inhibitor, GW9662. Intriguingly, EGCG significantly reinforced the activity of PPARγ by promoting its mRNA and protein expressions in N2a/APP695 cells. Moreover, EGCG also decreased the expression of pro-apoptotic proteins (Bax, caspase-3), reduced the activity of the anti-inflammatory agent NF-κB and inhibited the oxidative stress by decreasing the levels of ROS and MDA and increasing the expression of MnSOD. Co-administration of GW9662 also significantly decreased the EGCG-mediated neuroprotective effect evidenced by the increase in oxidative stress and inflammatory markers. The therapeutic efficacy of EGCG in AD may be derived from the up-regulation of PPARγ mRNA and protein expressions.

Topics: Amyloid beta-Peptides; Anilides; Animals; Catechin; Cell Line, Tumor; Cell Survival; Dose-Response Relationship, Drug; Mice; Oxidative Stress; Peptide Fragments; PPAR gamma

Despite the significance of Alzheimer's disease, the link between metal-associated amyloid-β (metal-Aβ) and disease etiology remains unclear. To elucidate this relationship, chemical tools capable of specifically targeting and modulating metal-Aβ species are necessary, along with a fundamental understanding of their mechanism at the molecular level. Herein, we investigated and compared the interactions and reactivities of the green tea extract, (-)-epigallocatechin-3-gallate [(2R,3R)-5,7-dihydroxy-2-(3,4,5-trihydroxyphenyl)-3,4-dihydro-2H-1-benzopyran-3-yl 3,4,5-trihydroxybenzoate; EGCG], with metal [Cu(II) and Zn(II)]-Aβ and metal-free Aβ species. We found that EGCG interacted with metal-Aβ species and formed small, unstructured Aβ aggregates more noticeably than in metal-free conditions in vitro. In addition, upon incubation with EGCG, the toxicity presented by metal-free Aβ and metal-Aβ was mitigated in living cells. To understand this reactivity at the molecular level, structural insights were obtained by ion mobility-mass spectrometry (IM-MS), 2D NMR spectroscopy, and computational methods. These studies indicated that (i) EGCG was bound to Aβ monomers and dimers, generating more compact peptide conformations than those from EGCG-untreated Aβ species; and (ii) ternary EGCG-metal-Aβ complexes were produced. Thus, we demonstrate the distinct antiamyloidogenic reactivity of EGCG toward metal-Aβ species with a structure-based mechanism.

Topics: Alzheimer Disease; Amyloid beta-Peptides; Camellia sinensis; Catechin; Copper; Humans; Metals; Models, Molecular; Neuroprotective Agents; Nuclear Magnetic Resonance, Biomolecular; Peptide Fragments; Plant Extracts; Protein Binding; Protein Conformation; Protein Multimerization; Tandem Mass Spectrometry; Zinc

A number of human protein misfolding disorders, including Alzheimer's disease (AD), are closely related to the accumulation of β-sheet-rich amyloid fibrils or aggregates. Neuronal toxicity in AD has been linked to the interactions of amyloid-β (Aβ) with metals, especially Zn(2+), Cu(2+), and Fe(3+), which leads to the production of reactive oxygen species. Nucleation-dependent Aβ aggregation, or "seeding", is thought to propagate fibril formation. In this surface plasmon resonance imaging (SPRi) study, we have shown that the fibril seeds formed with the incubation of Aβ in the presence of metals are better at promoting monomer elongation compared to Aβ alone or in the presence of a well-described polyphenol, (-)-epigallocatechin-3-gallate (EGCG). This is a novel attempt to simultaneously monitor the effects of multiple modulators on fibril elongation using a single chip. EGCG was shown in transmission electron microscopy (TEM) and thioflavin T (ThT) studies to promote the formation of off-pathway, highly stable unstructured oligomers, supporting the SPRi results. These findings suggest that SPRi provides a promising platform as a screening tool for small molecules that can affect the aggregation pathways in neurodegenerative diseases.

Topics: Alzheimer Disease; Amyloid beta-Peptides; Benzothiazoles; Catechin; Copper; Ferric Compounds; Humans; Ions; Kinetics; Metals; Microscopy, Electron, Transmission; Peptide Fragments; Surface Plasmon Resonance; Thiazoles; Zinc

Green tea extract and its main polyphenol constituent (-)-epigallocatechin-3-gallate (EGCG) possess potent neuroprotective activity in cell culture and mice model of Parkinson's disease. The central hypothesis guiding this study is that EGCG may play an important role in amyloid precursor protein (APP) secretion and protection against toxicity induced by beta-amyloid (Abeta). The present study shows that EGCG enhances (approximately 6-fold) the release of the non-amyloidogenic soluble form of the amyloid precursor protein (sAPPalpha) into the conditioned media of human SH-SY5Y neuroblastoma and rat pheochromocytoma PC12 cells. sAPPalpha release was blocked by the hydroxamic acid-based metalloprotease inhibitor Ro31-9790, which indicated mediation via alpha-secretase activity. Inhibition of protein kinase C (PKC) with the inhibitor GF109203X, or by down-regulation of PKC, blocked the EGCG-induced sAPPalpha secretion, suggesting the involvement of PKC. Indeed, EGCG induced the phosphorylation of PKC, thus identifying a novel PKC-dependent mechanism of EGCG action by activation of the non-amyloidogenic pathway. EGCG is not only able to protect, but it can rescue PC12 cells against the beta-amyloid (Abeta) toxicity in a dose-dependent manner. In addition, administration of EGCG (2 mg/kg) to mice for 7 or 14 days significantly decreased membrane-bound holoprotein APP levels, with a concomitant increase in sAPPalpha levels in the hippocampus. Consistently, EGCG markedly increased PKCalpha and PKC in the membrane and the cytosolic fractions of mice hippocampus. Thus, EGCG has protective effects against Abeta-induced neurotoxicity and regulates secretory processing of non-amyloidogenic APP via PKC pathway.

Topics: Amyloid beta-Peptides; Amyloid beta-Protein Precursor; Animals; Catechin; Cell Survival; Enzyme Activation; Enzyme Inhibitors; Hippocampus; Humans; Hydroxamic Acids; Indoles; Isoenzymes; Maleimides; Metalloendopeptidases; Mice; Neuroprotective Agents; PC12 Cells; Peptide Fragments; Protein Kinase C; Rats; Tumor Cells, Cultured