Gallotannins and Tannic Acid: First Chemical Syntheses and In Vitro Inhibitory Activity on Alzheimer's Amyloid ß-Peptide Aggregation.

The screening of natural products in the search for new lead compounds against Alzheimer's disease has unveiled several plant polyphenols that are capable of inhibiting the formation of toxic ß-amyloid fibrils. Gallic acid based gallotannins are among these polyphenols, but their antifibrillogenic activity has thus far been examined using "tannic acid", a commercial mixture of gallotannins and other galloylated glucopyranoses. The first total syntheses of two true gallotannins, a hexagalloylglucopyranose and a decagalloylated compound whose structure is commonly used to depict "tannic acid", are now described. These depsidic gallotannins and simpler galloylated glucose derivatives all inhibit amyloid ß-peptide (Aß) aggregation in vitro, and monogalloylated α-glucogallin and a natural ß-hexagalloylglucose are shown to be the strongest inhibitors.

3D NMR structure of a complex between the amyloid beta peptide (1-40) and the polyphenol ε-viniferin glucoside: implications in Alzheimer's disease.

BACKGROUND: Alzheimer's disease (AD) is a progressive neurodegenerative disorder. There is a consensus that Aß is a pathologic agent and that its toxic effects, which are at present incompletely understood, may occur through several potential mechanisms. Polyphenols are known to have wide-ranging properties with regard to health and for helping to prevent various diseases like neurodegenerative disorders. Thus inhibiting the formation of toxic Aß assemblies is a reasonable hypothesis to prevent and perhaps treat AD METHODS: Solution NMR and molecular modeling were used to obtain more information about the interaction between the Aß1-40 and the polyphenol ε-viniferin glucoside (EVG) and particularly the Aß residues involved in the complex. RESULTS: The study demonstrates the formation of a complex between two EVG molecules and Aß1-40 in peptide characteristic regions that could be in agreement with the inhibition of aggregation. Indeed, in previous studies, we reported that EVG strongly inhibited in vitro the fibril formation of the full length peptides Aß1-40 and Aß1-42, and had a strong protective effect against PC12 cell death induced by these peptides. CONCLUSION: For the full length peptide Aß1-40, the binding sites observed could explain the EVG inhibitory effect on fibrillization and thus prevent amyloidogenic neurotoxicity. GENERAL SIGNIFICANCE: Even though this interaction might be important at the biological level to explain the protective effect of polyphenols in neurodegenerative diseases, caution is required when extrapolating this in vitro model to human physiology.

Viniphenol A, a complex resveratrol hexamer from Vitis vinifera stalks: structural elucidation and protective effects against amyloid-ß-induced toxicity in PC12 cells.

Stilbenes have received much attention during the last two decades following the discovery of resveratrol in wine. Since then, there have been a growing number of papers reporting various biological activities of naturally occurring stilbenes. The aim of this study was to determine new minor stilbenes from Vitis vinifera stalks. Purification of these compounds was achieved by means of centrifugal partition chromatography, a versatile separation technique that does not require a solid stationary phase. Viniphenol A (1), a new resveratrol hexamer, was isolated along with five oligostilbenoids identified in V. vinifera for the first time, ampelopsin C, davidiol A, leachianol F, leachianol G, and E-maackin, a dimer with an unusual dioxane moiety, and 14 known hydroxystilbenes. The structure and stereochemistry of viniphenol A were determined on the basis of spectroscopic data analysis and molecular modeling under NMR constraints. Viniphenol A showed protective effects against amyloid-ß-induced toxicity in PC12 cell cultures.

Unambiguous Determination of the Absolute Configuration of Dimeric Stilbene Glucosides from the Rhizomes of Gnetum africanum.

Dimeric stilbene glucosides 1-3 [two diastereomers of (-)-gnemonoside A (1a and 1b), (-)-gnemonoside C (2), and (-)-gnemonoside D (3)] as well as a mixture of the two enantiomers of gnetin C (4) were isolated from the rhizomes of Gnetum africanum. The two enantiomers of gnetin C, (+)-4 and (-)-4, were obtained from the aglycones of 1a and 1b, respectively. The configurations of these stilbenoids were investigated by NMR and vibrational circular dichroism (VCD) experiments. The absolute configurations of (-)-1a, (-)-2, (-)-3, and (-)-4 were established as 7aS,8aS by VCD spectroscopy in combination with density functional theory calculations. The antiamyloidogenic activity of the isolated stilbenes was also evaluated versus beta-amyloid fibrils. The four glucosides of gnetin C (1a, 1b, 2, and 3) were found to be the most active compounds, with inhibition percentages of 56, 56, 58, and 54 at 10 µM, respectively.

Bioactive stilbenes from Vitis vinifera grapevine shoots extracts.

BACKGROUND: Viticultural residues from commercial viticultural activities represent a potentially important source of bioactive stilbenes such as resveratrol. The main aim of the present study was therefore to isolate, identify and perform biological assays against amyloid-ß peptide aggregation of original stilbenes from Vitis vinifera shoots. RESULTS: A new resveratrol oligomer, (Z)-cis-miyabenol C (3), was isolated from Vitis vinifera grapevine shoots together with two newly reported oligostilbenes from Vitis vinifera shoots, vitisinol C (1) and (E)-cis-miyabenol C (2), and six known compounds: piceatannol, resveratrol, (E)-ε-viniferin (trans-ε-viniferin), ω-viniferin, vitisinol C and (E)-miyabenol C. The structures of these resveratrol derivatives were established on the basis of detailed spectroscopic analysis including nuclear magnetic resonance experiments. All the newly reported compounds were tested for their anti-aggregative activity against amyloid-ß fibril formation. Vitisinol C was found to exert a significant activity against amyloid-ß aggregation. CONCLUSION: Vitis vinifera grapevine shoots are potentially interesting as a source of new bioactive stilbenes, such as vitisinol C.

Anthocyanin phytochemical profiles and anti-oxidant activities of Vitis candicans and Vitis doaniana.

INTRODUCTION: Grapes are one of the most important fruit crops in the world. The quality of red grape berries greatly depends on skin colour, mainly due to the anthocyanin profile. Today, the American Vitis species have the greatest potential for breeding work. They have multiple resistance properties in comparison with Vitis vinifera but little is known about their anthocyanin content. OBJECTIVE: To determine the anti-oxidant properties and anthocyanin profile of two American species, Vitis candicans and Vitis doaniana, by using LC-MS(n) and LC-NMR. METHODS: Grape extracts were prepared by extraction of berry skins with acidified methanol. The complete structure elucidation of the individual anthocyanins was performed with LC-MS(n) , LC-NMR and NMR experiments. Individual anthocyanins in the extracts were quantified by using malvidin glucoside as external standard. The anti-oxidant activities of grape skin extracts were evaluated by using 1,1-diphenyl-2-picrylhydrazyl (DPPH•) radical scavenging and oxygen radical absorbance capacity (ORAC) assays. RESULTS: By using LC-MS(n) and LC-NMR experiments, 30 anthocyanins were identified and quantified in the two Vitis species, including two new cis-p-coumaroyl derivatives. Vitis candicans and V. doaniana showed significant differences in their anthocyanin profile. These two Vitis species possess low-to-medium anti-oxidant activities in comparison with V. vinifera. CONCLUSION: The profiles of 30 anthocyanins were established unambiguously in two American Vitis species.

Protective effect of ε-viniferin on ß-amyloid peptide aggregation investigated by electrospray ionization mass spectrometry.

Abnormal ß-amyloid peptide accumulation and aggregation is considered to be responsible for the formation and cerebral deposition of senile plaques in the brains of patients with Alzheimer's disease (AD). Inhibition of the formation of ß-amyloid (Aß) fibrils would be an attractive therapeutic target for the treatment of AD. Resveratrol and its derivatives exhibit a broad range of pharmacological properties such as protection against cardiovascular diseases and cancers, as well as promoting antiaging effects. We reported previously that ε-viniferin glucoside (VG), a resveratrol-derived dimer, strongly inhibits Aß (25-35) fibril formation in vitro. In this study, we investigated the effects of VG on the aggregation of the full-length peptides (Aß (1-40) and Aß (1-42)) and on the ß-amyloid-induced toxicity in PC12 cells. VG inhibited Aß cytotoxicity and the non-covalent complex between VG and Aß was observed by electrospray ionization mass spectrometry.

New stilbene dimers against amyloid fibril formation.

Twenty stilbene derivatives and moracin M extracted from natural products were tested against amyloid-beta peptide (Abeta) aggregation. Results of stilbene monomer derivatives indicated that interaction with resveratrol and piceid was specific. Concerning oligomers, scirpusin A and epsilon-viniferin glucoside demonstrated a strong inhibition of the aggregation process.

Impact of polyphenols on receptor-ligand interactions by NMR: the case of neurotensin (NT)-neurotensin receptor fragment (NTS1) complex.

Ligand-receptor interactions can be implicated in many pathological events such as chronic neurodegenerative diseases. Thus, the discovery of molecules disrupting this type of interactions could be an interesting therapeutic approach. Polyphenols are well known for their affinity for proteins and several studies have characterized these direct interactions. But studying the direct influence of multi-therapeutic drugs on a ligand-receptor complex relevant to a neurodegenerative disorder is a challenging issue. Solution NMR, molecular modeling and iterative calculations were used to obtain information about the interaction between a phenolic compound, α-glucogallin (α-2) and a ligand/fragment receptor complex neurotensin (NT) and its receptor NTS1. The α-2 was shown to bind to NT and a peptidic fragment of its NTS1 receptor, independently. Although the formation of the corresponding ligand-receptor complex did not seem to be affected, this experimental modeling protocol will enable the evaluation of other anti-amyloidogenic compounds such as blockers of NT-NTS1 binding. These types of studies help in understanding the specificity and influence in binding and can provide information to develop new molecules with a putative pharmacological interest.Communicated by Ramaswamy H. Sarma.

The polyphenol piceid destabilizes preformed amyloid fibrils and oligomers in vitro: hypothesis on possible molecular mechanisms.

Alzheimer's disease (AD) is characterized by deposits of amyloid in various tissues. The neuronal cytotoxicity of Abeta peptides is attributed not only to various mechanisms but also to amyloid fibrils and soluble oligomeric intermediates. Consequently, finding molecules to prevent or reverse the oligomerization and fibrillization of Abeta could be of therapeutic value in the treatment of AD. We show that piceid, a polyphenol of the stilbene family, destabilized fibrils and oligomers to give back monomers that are not neurotoxic molecules. The mechanism of this destabilization could be a dynamic interaction between the polyphenol and the Abeta that could open the hydrophobic zipper and shift the reversible equilibrium "random coil<-->beta-sheet" to the disordered structure.

Benzofuran-based hybrid compounds for the inhibition of cholinesterase activity, beta amyloid aggregation, and abeta neurotoxicity.

The complex etiology of Alzheimer's disease (AD) prompts scientists to develop multitarget strategies to combat causes and symptoms. We therefore designed, synthesized, and tested new hybrid molecules linking a benzofuran ring to a N-methyl- N-benzylamine through a heptyloxy chain, affording a series of potential multifunctional drugs for AD. The cholinesterase inhibitory activity was extended to the inhibition of Abeta fibril formation for 1, 3, and 5. Compound 3 showed an additional neuroprotective effect.

New polyphenols active on beta-amyloid aggregation.

New polyphenol classes have been tested against amyloid-beta peptide aggregation. We have identified four novel polyphenols which could be efficient fibril inhibitors in Alzheimer's disease: malvidin and its glucoside and curculigosides B and D. We suggest that molecules with the particular C(6)-linkers-C(6) structure could be potent inhibitors. From the results reported for the flavan-3-ol family, their anti-amyloidogenic effects against whole peptides (1-40 and 1-42) could involve several binding sites.

Anthocyanone A: a quinone methide derivative resulting from malvidin 3-O-glucoside degradation.

A new compound resulting from the oxidative degradation of maldivin 3-O-glucoside under acid conditions was detected in a wine model solution stored under 90 and 25 degrees C. It was isolated by semipreparative HPLC, and its structure was elucidated by UV-vis spectra, mass spectrometry (LC/MS), and NMR spectroscopy (1-D and 2-D). The compound was identified as 8-beta-d-glucopyranosyl-2,4-dihydroxy-6-oxo-cyclohexa-2,4-dienyl acetic acid (anthocyanone A), which results from nucleophilic attack of hydrogen peroxide to maldivin 3-O-glucoside through a Baeyer-Villiger oxidation followed by other oxidations steps.

PVPP-polyphenol complexes: a molecular approach.

In dry white wines, two different forms of instability occur: (i) substantial yellow or yellow-green deposits are observed principally due to flavonol quercetin; and (ii) protein instability leads to protein casse. Polyvinyl polypyrrolidone (PVPP) is used to adsorb phenols from beverages, and bentonite is used to eliminate heat instable protein. However, in both cases, their effects are still largely unknown. This study uses a multitechnique approach to gain a better molecular understanding of the association of polyphenol aglycones with PVPP compared to that of glucosides with PVPP. The work demonstrates, that with aglycones, three forces drive complex formation: hydrophobic interaction, H bonds, and van der Waals bonds. With glucosides, the sugar moiety removes or reduces these driving forces. Thus, if the interaction between proteins and polyphenols is responsible for haze and precipitates, as is classically assumed, PVPP could prevent quercetin sedimentation.

Hopeaphenol: the first resveratrol tetramer in wines from North Africa.

Grapes and wines are now known to constitute a rich source of phenolics such as stilbenes and flavonoids. These compounds have been shown to have cancer chemopreventive activity and potential beneficial effects on cardiovascular diseases thanks to their antioxidant and antiplatelet properties. However, because little is known about African wines and their phenolic compositions, we investigated wine samples from North Africa. A three-step method was used for the fractionation of the Merlot variety wine: column chromatography followed by centrifugal partition chromatography and reversed-phase semipreparative high-performance liquid chromatography (HPLC). Six polyphenolic compounds of the Merlot variety (from Algeria) were isolated and identified by NMR spectroscopy, five of which are known (trans-resveratrol, trans-piceid, trans-epsilon-viniferin, pallidol, and astilbin) and one that is reported for the first time in wine, (+)-hopeaphenol, a stilbene tetramer. Furthermore, these molecules were quantified in 10 commercial wines from North Africa by means of an analytical HPLC system coupled with diode array detection. Differences in concentrations were found ranging in mg/L from 4.6 to 45 (trans-piceid), 0.66 to 3.45 (trans-resveratrol), 0.2 to 1.2 (trans-epsilon-viniferin), 0.2 to 9.2 (pallidol), 0.3 to 3.8 (hopeaphenol), and 10.8 to 24.22 (astilbin). Such a high level of pallidol and astilbin has never been recorded in wine. North African wines may contribute to a significant proportion of dietary intake of stilbene and astilbin, which may have health benefits.

Two new benzylbenzoate glucosides from Curculigo orchioides.

An extract from in vitro cultures of Curculigo orchioides grown as bulbils in shake flasks, afforded two new glucosides of substituted benzylbenzoate - curculigoside C (3) and curculigoside D (4) - together with two known compounds - curculigoside A (1) and curculigoside B (2). Their structures were elucidated on the basis of spectral evidence, in particular by using 2D NMR methods. Their vasoactive properties were assessed in isolated rat aortic rings.

First observation of solution structures of bradykinin-penta-O-galloyl-D-glucopyranose complexes as determined by NMR and simulated annealing.

Polyphenols (tannins) are known for their high propensity to precipitate proteins. They bind most strongly to proteins with a high proline content. Understanding the mechanism of this association is of prime interest because this interaction might induce protein conformational changes that may modify their biological activity. To investigate the interaction, an NMR study was carried out on the binding of a representative polyphenol, penta-O-galloyl-D-glucopyranose, to a nonapeptide hormone, bradykinin (BDK), where proline accounts for 30% of residues. Series of 1D and 2D-NMR experiments were performed. For the first time, a three-dimensional structure of complexes was determined using 2D-NMR experiments and molecular modeling. These structure calculations are a potent tool to understand how the association arises. They clearly show that the interaction is a complex phenomenon where several parameters are involved. The PGG/BDK complexes are formed by multiple weak interactions between peptide side chains and galloyl rings. Proline and arginine are good anchoring points and the glycine gives a certain flexibility in the peptide backbone that allows the polyphenol to approach and interact. Therefore, it is not only the hydrophobic stackings between galloyl rings and proline and hydrogen bonding involving arginine and aromatic rings which are important. The residue sequence and the side chain steric bulk also intervene.

Carbon-14 biolabelling of wine polyphenols in Vitis vinifera cell suspension cultures.

14C-L-phenylalanine is incorporated into a range of polyphenolic compounds when fed to grape cell cultures. Optimisation of several parameters such as the quantity of precursor applied and the duration of metabolism led to incorporation yields of 15% and to specific activities of 875 mu Ci g(-1) in stilbenes. Purification of the products by several chromatographic steps is reported. Both trans- and cis-resveratrols were easily obtained by enzymatic hydrolysis of their corresponding glucosides, with specific activity of 1200-1400 mu Ci g(-1). The specific radioactivity obtained for all the compounds is suitable for in vivo feeding trials to trace their metabolic fate when consumed by animals and for in vitro activity mechanism studies. Indeed, these polyphenols seem to be implicated in the health benefits associated with regular and moderate wine consumption but little is known about their pharmacokinetics and cellular uptake.

Galloylated catechins and stilbene diglucosides in Vitis vinifera cell suspension cultures.

Suspension cultures of Vitis vinifera were found to produce catechins and stilbenes. When cells were grown in a medium inducing polyphenol synthesis, (-)-epicatechin-3-O-gallate, dimeric procyanidin B-2 3'-O-gallate and two resveratrol diglucosides were isolated, together with a new natural compound that was identified as cis-resveratrol-3,4'-O-beta-diglucoside by spectroscopical methods.

Intermolecular interactions between the neurotensin and the third extracellular loop of human neurotensin 1 receptor.

Neurotensin (NT) is a tridecapeptide hormone in the periphery and neurotransmitter in the brain that principally activates three receptor subtypes, named NTS1, NTS2, and NTS3. Since little is known about its structure in the presence of its principal receptor NTS1, we determined it using the key domain of the receptor, i.e. the third extracellular loop. We conclude the following: (i) for the receptor fragment, NT binding modifies its central part, underlying the great flexibility and adaptability of this region; (ii) for bound NT, the extended conformation of its C-terminus is confirmed for the first time in experimental conditions and in the presence of a part of the receptor; and (iii) despite some substitutions, the human receptor residues that are involved in the interaction with NT could be similar to those of the rat receptor which play an important role in NT binding.