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PubMed2001

Unusually large numbers of electrons for the oxidation of polyphenolic antioxidants.

Reaction mechanisms of polyphenolic antioxidants were studied using electrochemical methods (flow column electrolysis and cyclic voltammetry). In flow column electrolysis, the numbers (ns) of electrons involved in the oxidation of catechols (chlorogenic acid and caffeic acid) became larger than two (i.e. the number of -OH moieties) at pH > 7; the n-values finally reached ca. 4 at pH 10. Other polyphenols including catechin, ellagic acid, and curcumin exhibited higher n-values than the numbers of -OH moieties in the whole pH range studied (4 < pH < 10). Such unusually large n-values for polyphenols were found to correlate to their irreversible behavior in cyclic voltammetry. A digital simulation analysis of the voltammograms of chlorogenic acid clearly showed that the electrode reaction at higher pHs can be elucidated in terms of a quasi-reversible electron transfer followed by a chemical reaction and also suggested that the chemical reaction is of second order to the concentration of chlorogenic acid, i.e. a dimerization reaction. In a similar manner, polyphenolic antioxidants generally undergo certain chemical reactions on the occasion of their oxidation. As a result, some oxidizable, phenolic -OH moieties are reproduced in the polymeric products. The unusually large n-values of polyphenols and thus their higher radical scavenging activities may be ascribed to such reproduction of -OH moieties by oxidative polymerization.

Antioxidants↗
PubMed2002

Polyphenols: do they play a role in the prevention of human pathologies?

Polyphenols are the most abundant antioxidants in our diets. The main classes of polyphenols are phenolic acids (mainly caffeic acid) and flavonoids (the most abundant in the diet are flavanols (catechins plus proanthocyanidins), anthocyanins and their oxidation products), which account for one- and two-thirds, respectively. Polyphenols are reducing agents, and together with other dietary reducing agents, such as vitamin C, vitamin E and carotenoids, referred to as antioxidants, protect the body's tissues against oxidative stress and associated pathologies such as cancers, coronary heart disease and inflammation. The biological properties, bioavailability, antioxidant activity, specific interactions with cell receptors and enzymes, are related to the chemical structure of polyphenols. It is, therefore, essential to know the nature of the main polyphenols ingested, their dietary origin, the amounts consumed in different diets, their bioavailability and the factors controlling their bioavailability.

Antioxidants↗
PubMed2002

Absorption and metabolism of polyphenols in the gut and impact on health.

Polyphenols are the most abundant antioxidants in the human diet. They show a considerable structural diversity, which largely influences their bioavailability. Phenolic acids like caffeic acid are easily absorbed through the gut barrier, whereas large molecular weight polyphenols such as proanthocyanidins are very poorly absorbed. Once absorbed, polyphenols are conjugated to glucuronide, sulphate and methyl groups in the gut mucosa and inner tissues. Non-conjugated polyphenols are virtually absent in plasma. Such reactions facilitate their excretion and limit their potential toxicity. The polyphenols reaching the colon are extensively metabolised by the microflora into a wide array of low molecular weight phenolic acids. The biological properties of both conjugated derivatives and microbial metabolites have rarely been examined. Their study will be essential to better assess the health effects of dietary polyphenols. Alternatively, some health effects of polyphenols may not require their absorption through the gut barrier. Their role as iron chelators in the gut lumen is briefly discussed.

Animals↗
PubMed1994

The specific inhibition of crystal growth of monohydrogen potassium L-tartrate by d-catechin.

Crystal growth of monohydrogen potassium L-tartrate in an ethanolic aqueous solution was specifically inhibited by d-catechin, but not by either its epimeric isomer at C3, l-epicatechin or by gallic acid and caffeic acid. 3D-Structure similarity search of d-catechin with two molecules of the tartrate and docking study of d-catechin with the crystal model of the tartrate suggested that d-catechin mimics a structure consisting of the two tartrate molecules in the inhibition. Differences in the conformation of the catechol moieties of d-catechin and l-epicatechin may explain the distinct inhibitory effects of the epimeric isomers.

Catechin↗
PubMed2000

Purification and characterization of a polyphenol oxidase from the seeds of field bean (Dolichos lablab).

The polyphenol oxidase from field bean (Dolichos lablab) seeds has been purified to apparent homogeneity by a combination of ammonium sulfate precipitation, DEAE-Sephacel chromatography, phenyl agarose chromatography, and Sephadex G-200 gel filtration. The purified enzyme has a molecular weight of 120 +/- 3 kDa and is a tetramer of 30 +/- 1.5 kDa. Native polyacrylamide gel electrophoresis of the purified enzyme revealed the presence of a single isoform with an observed pH optimum of 4.0. 4-Methyl catechol is the best substrate, followed by catechol, and L-3,4-dihydroxyphenylalanine, all of which exhibited a phenomenon of inhibition by excess substrate. No activity was detected toward chlorogenic acid, catechin, caffeic acid, gallic acid, and monophenols. Tropolone, both a substrate analogue and metal chelator, proved to be the most effective competitive inhibitor with an apparent K(i) of 5.8 x 10(-)(7) M. Ascorbic acid, metabisulfite, and cysteine were also competitive inhibitors.

Amino Acid Sequence↗
PubMed2001

Antioxidant capacities and phenolics levels of French wines from different varieties and vintages.

Phenolics from grapes and wines can play a role against oxidation and development of atherosclerosis. Levels of phenolics, major catechins [(+)-catechin, (-)-epicatechin, procyanidin dimers B1, B2, B3, and B4], phenolic acids (gallic acid and caffeic acid), caftaric acid, malvidin-3-glucoside, peonidin-3-glucoside, and cyanidin-3-glucoside were quantified by HPLC with UV detection for 54 French varietal commercial wines taken from southern France to study the antioxidant capacity and the daily dietary intake of these compounds for the French population. The highest antioxidant capacity was obtained with red wines and ranged from 12.8 mmol/L (Grenache) to 25.2 mmol/L (Pinot Noir). For white wines, Chardonnay enriched in phenolics by special wine-making was found to have an antioxidant capacity of 13.8 mmol/L, comparable to red wine values. For red wines classified by vintages (1996-1999) antioxidant capacities were approximately 20 mmol/L and then decreased to 13.4 mmol/L for vintages 1995-1991. Sweet white wines have 1.7 times more antioxidant capacity (3.2 mmol/L) than dry white wines (1.91 mmol/L). On the basis of a still significant French wine consumption of 180 mL/day/person, the current daily intake of catechins (monomers and dimers B1, B2, B3, and B4) averaged 5 (dry white wine), 4.36 (sweet white wines), 7.70 (rosé wines), 31.98 (red wines), and 66.94 (dry white wine enriched in phenolic) mg/day/resident for the French population. Red wine, and particularly Pinot Noir, Egiodola, Syrah, Cabernet Sauvignon, and Merlot varieties, or Chardonnay enriched in phenolics during wine-making for white varieties contribute to a very significant catechin dietary intake.

Anthocyanins↗
PubMed2003

Effects of phenolic acids on human phenolsulfotransferases in relation to their antioxidant activity.

Sulfate conjugation by phenolsulfotransferase (PST) enzyme is an important process in the detoxification of xenobiotics and endogenous compounds. There are two forms of PST that are specific for the sulfation of small phenols (PST-P) and monoamines (PST-M). Phenoilc acids have been reported to have important biological and pharmacological properties and may have benefits to human health. In the present study, human platelets were used as a model to investigate the influence of 13 phenolic acids on human PST activity and to evaluate the relationship to their antioxidant activity. The results showed that chlorogenic acid, syringic acid, protocatechuic acid, vanillic acid, sinapic acid, and caffeic acid significantly (p < 0.05) inhibited the activities of both forms of PST by 21-30% at a concentration of 6.7 microM. The activity of PST-P was enhanced (p < 0.05) by p-hydroxybenzoic acid, gallic acid, gentisic acid, o-coumaric acid, p-coumaric acid, and m-coumaric acid at a concentration of 6.7 microM, whereas the activity of PST-M was enhanced by gentisic acid, gallic acid, p-hydroxybenzoic acid, and ferulic acid. The phenolic acids exhibited antioxidant activity as determined by the oxygen radical absorbance capacity (ORAC) assay and Trolox equivalent antioxidant capacity (TEAC) assay, especially gallic acid, p-hydroxybenzoic acid, gentisic acid, and coumaric acid, which had strong activity. The overall effect of phenolic acids tested on the activity of PST-P and PST-M was well correlated to their antioxidant activity of ORAC value (r = 0.71, p < 0.01; and r = 0.66, p < 0.01). These observations suggest that antioxidant phenolic acids might alter sulfate conjugation.

Adult↗
PubMed2005

Antioxidant properties of roasted coffee residues.

The antioxidant activity of roasted coffee residues was evaluated. Extraction with four solvents (water, methanol, ethanol, and n-hexane) showed that water extracts of roasted coffee residues (WERCR) produced higher yields and gave better protection for lipid peroxidation. WERCR showed a remarkable protective effect on oxidative damage of protein. In addition, WERCR showed scavenging of free radicals as well as the reducing ability and to bind ferrous ions, indicating that WERCR acts as both primary and secondary antioxidants. The HPLC analyses showed that phenolic acids (chlorogenic acid and caffeic acid) and nonphenolic compounds [caffeine, trigonelline, nicotinic acid, and 5-(hydroxymethyl)furfuraldehyde] remained in roasted coffee residues. These compounds showed a protective effect on a liposome model system. The concentrations of flavonoids and polyphenolic compounds in roasted coffee residues were 8,400 and 20,400 ppm, respectively. In addition, the Maillard reaction products (MRPs) remaining in roasted coffee residues were believed to show antioxidant activity. These data indicate that roasted coffee residues have excellent potential for use as a natural antioxidant source because the antioxidant compounds remained in roasted coffee residues.

Antioxidants↗
PubMed2005

Interactions between volatile and nonvolatile coffee components. 1. Screening of nonvolatile components.

This study is the first of two publications that investigate the phenomena of coffee nonvolatiles interacting with coffee volatile compounds. The purpose was to identify which coffee nonvolatile(s) are responsible for the interactions observed between nonvolatile coffee brew constituents and thiols, sulfides, pyrroles, and diketones. The overall interaction of these compounds with coffee brews prepared with green coffee beans roasted at three different roasting levels (light, medium, and dark), purified nonvolatiles, and medium roasted coffee brew fractions (1% solids after 1 or 24 h) was measured using a headspace solid-phase microextraction technique. The dark roasted coffee brew was slightly more reactive toward the selected compounds than the light roasted coffee brew. Selected pure coffee constituents, such as caffeine, trigonelline, arabinogalactans, chlorogenic acid, and caffeic acid, showed few interactions with the coffee volatiles. Upon fractionation of medium roasted coffee brew by solid-phase extraction, dialysis, size exclusion chromatography, or anion exchange chromatography, characterization of each fraction, evaluation of the interactions with the aromas, and correlation between the chemical composition of the fractions and the magnitude of the interactions, the following general conclusions were drawn. (1) Low molecular weight and positively charged melanoidins present significant interactions. (2) Strong correlations were shown between the melanoidin and protein/peptide content, on one hand, and the extent of interactions, on the other hand (R = 0.83-0.98, depending on the volatile compound). (3) Chlorogenic acids and carbohydrates play a secondary role, because only weak correlations with the interactions were found in complex matrixes.

Carbohydrates↗
PubMed2005

Determination of phenolic compounds in Perilla frutescens L. by capillary electrophoresis with electrochemical detection.

A method based on capillary electrophoresis with electrochemical detection has been developed to analyze flavonoids and phenolic acids in Perilla frutescens L. for the first time. Catechin, ferulic acid, apigenin, luteolin, rosmarinic acid, and caffeic acid are major important active ingredients in the plant. Operated in a wall-jet configuration, a 300 microm diameter carbon-disk electrode was used as the working electrode, which exhibits a good response at 0.90 V (versus saturated calomel electrode) for the analytes. Under the optimum conditions, the analytes were baseline separated within 20 min in a 100 mmol/L borax buffer (pH 8.7). Notably, excellent linearity was obtained over 3 orders of magnitude with detection limits (S/N = 3) ranging from 2 x 10(-7) to 1 x 10(-6) g/mL for all analytes. This proposed method has been successfully applied to monitor the flavonoids and phenolic acids contents in the leaves and seeds of P. frutescens L. at different growth stages with relatively simple extraction procedures, and the assay results were satisfactory.

Electrophoresis, Capillary↗
PubMed2006

Significance of phenol-protein interactions in modifying the antioxidant capacity of peas.

The aim of this study is to evaluate the contribution of phenol-protein interaction (PPI) and its binding activity in strengthening the antioxidant capacity of peas after immersion with five phenolics under different heating conditions. The results showed that hydroxycinnamic acids (ferulic acid, coumaric acid, or caffeic acid) are better than hydroxybenzoic acid (gallic acid) in increasing superoxide dismutase (SOD) heat stability. In addition, the higher the temperature, the more evident was the enhancement. DPPH scavenging capacity and reducing power showed the same tendency. Further kinetic analysis proved that SOD with the best heat stability showed the largest activation energy during heating. Moreover, the contribution of phenol-protein binding to the antioxidant capacity was further estimated through complex purification and calculation of binding capacity. Coumaric acid was the most efficient phenolic compound in increasing antioxidant capacity and showed the highest binding capacity with pea protein. These results indicated that phenolic compounds might enhance the antioxidant capacity of peas during heating through phenol-protein interaction.

Anions↗
PubMed2006

Synthesis and structure determination of covalent conjugates formed from the sulfury-roasty-smelling 2-furfurylthiol and di- or trihydroxybenzenes and their identification in coffee brew.

Recent investigations demonstrated that the reaction of odor-active thiols such as 2-furfurylthiol with thermally generated chlorogenic acid degradation products is responsible for the rapid aroma staling of coffee beverages. To get a clear understanding of the molecular mechanisms underlying this aroma staling, the existence of putative phenol/thiol conjugates needs to be verified in coffee. The aim of the present study was therefore to synthesize such conjugates for use as reference substances for LC-MS screening of coffee. To achieve this, catechol, 3-methyl-, 4-methyl-, and 4-ethylcatechol, pyrogallol, hydroxyhydroquinone, 5-O-caffeoylquinic acid, and caffeic acid, respectively, were reacted with 2-furfurylthiol in the presence of iron(III) chloride and air oxygen. After purification, the structures of 25 phenol/thiol conjugates were identified by means of LC-MS/MS and 1D/2D NMR experiments. Using these compounds as reference materials, four conjugates, namely, 3-((2-furylmethyl)sulfanyl)catechol, 3-((2-furylmethyl)sulfanyl)-5-ethylcatechol, 4-((2-furylmethyl)sulfanyl)hydroxyhydroquinone, and 3,4-bis((2-furylmethyl)sulfanyl) hydroxyhydroquinone, were identified for the first time in coffee brew by means of HPLC-MS/MS(MRM). These findings clearly demonstrate catechol, 4-ethylcatechol, and hydroxyhydroquinone as the primary thiol trapping agents involved in the aroma staling of coffee beverages.

Chromatography, High Pressure Liquid↗
PubMed2001

Microbial transformations of p-coumaric acid by Bacillus megaterium and Curvularia lunata.

p-Coumaric acid (1) is an abundant phenolic natural product that exhibits both chemoprotectant and antioxidant properties. Microbial transformation screening studies showed that 1 was converted to 4-vinylphenol (4), 4-hydroxybenzoic acid (2), caffeic acid (5), protocatechuic acid (6), and other unidentified metabolites over 144 h. 4-Vinylphenol (4) and its dimer, (2R,2S)-4-(2,3-dihydro-5-hyroxy-2-benzofuranyl) phenol (11), were produced by Bacillus megaterium, and 5-[(E)-2-carboxyethenyl]-2,3-dihydro-2-(4-hydroxyphenyl)-3-benzofurancarboxylic acid (15) and 4-hydroxybenzoic acid (2) were produced by Curvularia lunata. On the basis of deuterium-labeling experiments, B. megaterium catalyzes the nonoxidative enzymatic tautomerization of 1 to a vinylogous beta-keto acid intermediate that decarboxylates to 4. The presence of peroxidase and laccase activities in C. lunata extracts suggests that these enzymes may be involved in one-electron, p-coumaric acid dimerization in this organism.

Bacillus megaterium↗
PubMed1999

Immunomodulatory principles of Dichrocephala bicolor.

From the ethanolic extract of Dichrocephala bicolor eight compounds-4,5-dicaffeoyl quinic acid (1); 3,4-dicaffeoyl quinic acid (2); 3,5-dicaffeoyl quinic acid (3); ethyl 4,5-dicaffeoyl quinate (4); methyl 3,5-dicaffeoyl quinate (5); 5-caffeoyl quinic acid (6); caffeic acid (7); and quercetin-3-O-rutinoside (8)-were isolated and identified. All of them were selected for immunopharmacological activity testing. Human mononuclear cells (HMNC) were used as target cells. Cell proliferation was determined by 3H-thymidine uptake. Compounds 2 and 6 potently enhanced HMNC proliferation and interferon-gamma production. Enhancement mechanisms may involve the increase of cytokines production.

Adjuvants, Immunologic↗
PubMed2006

Delphinidin and cyanidin inhibit PDGF(AB)-induced VEGF release in vascular smooth muscle cells by preventing activation of p38 MAPK and JNK.

BACKGROUND AND PURPOSE: Red wine polyphenols (RWPs) inhibit the expression of vascular endothelial growth factor (VEGF), a major pro-angiogenic and pro-atherosclerotic factor, in vascular smooth muscle cells (VSMCs). The aim of this study was to identify which red wine polyphenols were inhibitory and to determine the mechanism underlying the inhibitory effects. EXPERIMENTAL APPROACH: Release of VEGF stimulated by platelet derived growth factor(AB) (PDGF(AB)), from human aortic VSMCs was measured by immunoassay and phosphorylation of kinases by Western blot analysis. The direct antioxidant properties of polyphenols were determined by electron paramagnetic resonance and the cellular formation of reactive oxygen species (ROS) by dichlorofluorescein. KEY RESULTS: The inhibitory effect of RWPs on PDGF(AB)-induced release of VEGF was mimicked by delphinidin but not by quercetin, catechins, resveratrol, gallic acid or caffeic acid. In the anthocyanin class, not only delphinidin but also cyanidin prevented VEGF release whereas malvidin and peonidin were without effect. RWPs, delphinidin and cyanidin directly scavenged ROS and prevented the PDGF(AB)-induced formation of ROS in VSMCs. Malvidin and peonidin did not scavenge ROS but prevented the cellular formation of ROS. Although the p38 MAPK, ERK1/2 and JNK pathways have been involved in the PDGF(AB)-induced expression of VEGF, in our experiments, only phosphorylation of p38 MAPK and JNK was inhibited by RWPs, delphinidin and cyanidin. CONCLUSIONS AND IMPLICATIONS: Anthocyanins presenting a hydroxyl residue at position 3' are able to inhibit PDGF(AB)-induced VEGF expression by preventing activation of p38 MAPK and JNK in VSMCs.

Anthocyanins↗
PubMed1969

o-Quinones formed in plant extracts. Their reactions with amino acids and peptides.

1. The reactions of amino acids and peptides with the o-quinones produced by the enzymic oxidation of chlorogenic acid and caffeic acid have been studied manometrically and spectrophotometrically. 2. Amino acids, except lysine and cysteine, react primarily through their alpha-amino groups to give red or brown products. These reactions, which compete with the polymerization of the quinones, are followed by secondary reactions that may absorb oxygen and give products with other colours. 3. The in-amino group of lysine reacts with the o-quinones in a similar way. The thiol group of cysteine reacts with the quinones, without absorbing oxygen, giving colourless products. 4. Peptides containing cysteine react with the o-quinones through their thiol group. 5. Other peptides, such as glycyl-leucine and leucylglycine, react primarily through their alpha-amino group and the overall reaction resembles that of the N-terminal amino acid except that it is quicker. 6. With some peptides, the secondary reactions differ from those that occur between the o-quinones and the N-terminal amino acids. The colours produced from carnosine resemble those produced from histidine rather than those from beta-alanine, and the reactions of prolylalanine with o-quinones are more complex than those of proline.

Amino Acids↗
PubMed2005

Phenolic esters from the rhizomes of Cimicifuga racemosa do not cause proliferation effects in MCF-7 cells.

Five phenylpropanoid esters, caffeoylglycolic acid, 2-caffeoylpiscidic acid (cimicifugic acid D), 3,4-dihydroxyphenacyl caffeate (petasiphenone), 3,4-dihydroxyphenyl-2-oxopropyl isoferulate (cimiciphenol) and 3,4-dihydroxyphenacyl isoferulate (cimiciphenone) were isolated from a commercially available extract of the rhizomes of Cimicifuga racemosa (L.) Nutt. (syn. Actaea racemosa L.) for the first time; the known cimicifugic acids A, B, E, F, fukinolic acid, fukiic acid and caffeic acid were also obtained. Cimiciphenone and caffeoylglycolic acid are new natural products. The structures were elucidated by means of spectroscopic data (ESI-MS, 1H-, 13C-NMR, COSY, HMQC, HMBC and NOE experiments). Ferulic acid and isoferulic acid were detected by HPLC analysis in comparison to standards. The estrogenic activity of the isolated compounds was tested in an estrogen-dependent MCF-7 mamma carcinoma cell line; 17beta-estradiol (10(-11) M) and the phytoestrogen coumestrol (10(-7) - 10(-5) M) were used as references. The results suggest that, in contrast to an earlier report, the phenolic esters do not exert a proliferative (estrogenic) effect in this test system.

Antineoplastic Agents, Phytogenic↗
PubMed2001

CYP98A3 from Arabidopsis thaliana is a 3'-hydroxylase of phenolic esters, a missing link in the phenylpropanoid pathway.

The 4- and 5-hydroxylations of phenolic compounds in plants are catalyzed by cytochrome P450 enzymes. The 3-hydroxylation step leading to the formation of caffeic acid from p-coumaric acid remained elusive, however, alternatively described as a phenol oxidase, a dioxygenase, or a P450 enzyme, with no decisive evidence for the involvement of any in the reaction in planta. In this study, we show that the gene encoding CYP98A3, which was the best possible P450 candidate for a 3-hydroxylase in the Arabidopsis genome, is highly expressed in inflorescence stems and wounded tissues. Recombinant CYP98A3 expressed in yeast did not metabolize free p-coumaric acid or its glucose or CoA esters, p-coumaraldehyde, or p-coumaryl alcohol, but very actively converted the 5-O-shikimate and 5-O-d-quinate esters of trans-p-coumaric acid into the corresponding caffeic acid conjugates. The shikimate ester was converted four times faster than the quinate derivative. Antibodies directed against recombinant CYP98A3 specifically revealed differentiating vascular tissues in stem and root. Taken together, these data show that CYP98A3 catalyzes the synthesis of chlorogenic acid and very likely also the 3-hydroxylation of lignin monomers. This hydroxylation occurs on depsides, the function of which was so far not understood, revealing an additional and unexpected level of networking in lignin biosynthesis.

Arabidopsis↗