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PubMed2005

Determination of phenolic compounds by a polyphenol oxidase amperometric biosensor and artificial neural network analysis.

The determination of phenolic compounds is significant given its toxicity, even at very low concentration levels. Amperometric determination of phenols is a simple technique available. Direct oxidation of phenols can be used, but another possibility is the use of polyphenol oxidase (tyrosinase) enzyme biosensors that oxidises the phenolic compounds into their corresponding quinones. Reduction of the resulting quinones accomplishes the amplification of the amperometric signal, as long as the result of the reduction process is the corresponding cathecol, this being able to be oxidised again by the polyphenol oxidase immobilized on the surface of the biosensor. In this communication, simultaneous determination of different phenols was carried out combining biosensor measurements with chemometric tools, in what is known as electronic tongue. The departure information used was the overlapped reduction voltammogram generated with the amperometric biosensor based on polyphenol oxidase. Artificial Neural Networks (ANN) were used for extraction and quantification of each compound. Phenol, cathecol and m-cresol formed the three-analyte study case resolved in this work. Good prediction ability was attained, and so, the separate quantification of these three phenols was accomplished.

Algorithms↗

PubMed2003

In vitro assessment of inhibition by natural polyphenols of metabolic activation of procarcinogens by human CYP1A1.

Previously, inhibitors of CYP1A1 were rated as candidate chemopreventive agents against cancer mainly according to their effects on the 7-ethoxyresorufin O-deethylation (EROD) of diagnostic probe substrates. Surprisingly, several polyphenols including resveratrol, formerly identified as potent inhibitors by the EROD assay, exhibited no or weak inhibition of procarcinogen activation. We compared the effects of 11 representative natural polyphenols, which normally occur in food, on different activities of CYP1A1, namely epoxidation of 7,8-dihydrodiol-benzo[a]pyrene, the terminal step in the activation leading to the ultimate carcinogenic diolepoxides, hydroxylation of benzo[a]pyrene, and EROD. For the first time, a reconstituted system was used for the determination of IC(50) values, consisting of purified enzymes (human CYP1A1 and human NADPH-cytochrome P450 reductase) and dilaurylphosphatidylcholine. The results demonstrate that the inhibitory effects of dietary polyphenols on CYP1A1 activity depend on both the structure of the inhibitor and the type of the reaction and substrate used in the assay. Consequently, a potent EROD inhibition alone is insufficient to count a substance among the chemoprotective agents.

Anticarcinogenic Agents↗

PubMed1996

Inhibition of the efflux of glutathione S-conjugates by plant polyphenols.

The formation of dinitrophenylglutathione (DNP-SG) in human colon adenocarcinoma cells was identified and quantified by an HPLC-UV method, following exposure to 1-chloro-2,4-dinitrobenzene (CDNB) at 10 degrees for 40 min. The rate of efflux of DNP-SG at 37 degrees likewise, was measured by monitoring the DNP-SG content in the extracellular medium. Among the polyphenols examined for their action on DNP-SG export, butein was the most potent inhibitor with an IC50 value of 15 microM. The others, in order of decreasing potencies, were quercetin, tannic acid, 2'-hydroxychalcone, 2-hydroxychalcone anIIC50 values in the micromolar range. These polyphenols did not affect the ATP or the glutathione content of the cells. Mg(2+)-ATPase extracted from the plasma membrane of the cells was activated by DNP-SG in a concentration-dependent manner, and the reaction showed saturation kinetics with K(m) and Vmax values of 110 microM and 12.3 nmol/min/mg protein, respectively. However, the six polyphenols mentioned above had negligible effects on the Mg(2+)-ATPase activity, suggesting that this was probably not the target of their inhibitory action. Probenecid, p-trifluoromethoxy-phenylhydrazone (FCCP) and chlorambucil also showed varying degrees of inhibition of the export of DNP-SG.

ATP Binding Cassette Transporter, Subfamily B, Mem↗

PubMed2000

Antioxidative effects of green tea polyphenols on free radical initiated and photosensitized peroxidation of human low density lipoprotein.

Antioxidative effects of the main polyphenolic components extracted from green tea leaves, i.e. (-)-epicatechin (EC), (-)-epigallocatechin (EGC), (-)-epicatechin gallate (ECG), (-)-epigallocatechin gallate (EGCG) and gallic acid (GA), against free radical initiated peroxidation of human low density lipoprotein (LDL) were studied. The peroxidation was initiated either thermally by a water-soluble initiator 2,2'-azobis(2-amidinopropane hydrochloride) (AAPH), or photochemically by a triplet sensitizer benzophenone (BP). The reaction kinetics was monitored by the uptake of oxygen and the depletion of alpha-tocopherol (TOH) presented in the native LDL. Kinetic analysis of the antioxidation process demonstrates that these green tea polyphenols are effective antioxidants against both AAPH-initiated and BP-photosensitized LDL peroxidation. The antioxidative action of the green tea polyphenols includes trapping the initiating and/or propagating peroxyl radicals with the activity sequence EC>EGCG>ECG>EGC>GA for the AAPH initiated peroxidation, and reducing the alpha-tocopheroxyl radical to regenerate alpha-tocopherol with the activity sequence of ECG>EC>EGCG>EGC>GA and ECG>EGCG>GA>EC>EGC for the AAPH-initiated and BP-photosensitized peroxidations respectively.

Antioxidants↗

PubMed1999

Prooxidant toxicity of polyphenolic antioxidants to HL-60 cells: description of quantitative structure-activity relationships.

Polyphenolic antioxidants exhibited a dose-dependent toxicity against human promyelocytic leukemia cells (HL-60). Their action was accompanied by malondialdehyde formation, and was partly prevented by desferrioxamine and the antioxidant N,N'-diphenyl-p-phenylene diamine. This points to a prooxidant character of their cytotoxicity. A quantitative structure-activity relationship (QSAR) has been obtained to describe the cytotoxicity of 13 polyphenolic antioxidants belonging to three different groups (flavonoids, derivatives of gallic and caffeic acid): log cL50 (microM) = (2.7829+/-0.2339)+(1.2734+/-0.4715) Ep/2 (V)-(0.3438+/-0.0582) log P (r2 = 0.8129), where cL50 represents the concentration for 50% cell survival, Ep/2 represents the voltammetric midpoint potential, and P represents the octanol/water partition coefficient. Analogous QSARs were obtained using enthalpies of single-electron oxidation of these compounds, obtained by quantum-mechanical calculations. These findings clearly point to two important characteristics determining polyphenol cytotoxicity, namely their ease of oxidation and their lipophilicity.

Antioxidants↗

PubMed2002

Enhancement of inward Ca(2+) currents in bovine chromaffin cells by green tea polyphenol extracts.

Green tea contains four major polyphenol compounds: they are (-)-epigallocatechin-3-gallate (EGCG), (-)-epigallocatechin (EGC), (-)-epicatechin-3-gallate (ECG), and (-)-epicatechin (EC). Although all four polyphenol compounds are known to affect tumor suppression, little is known about whether they alter membrane properties. In this study, we examined the effects of ECG and EGCG on ionic currents and secretion. Membrane capacitance changes were used to monitor secretion in bovine chromaffin cells. ECG had the ability to reversibly enhance the inward Ca(2+) current by 21%, and inhibited the peak sodium current by 34%. EGCG had no effect on Ca(2+) current even though it differs from ECG by just a hydroxyl group. The EC(50) of ECG in enhancing Ca(2+) current was 7.6 microM. The maximum enhancement of Ca(2+) current was observed at 0 mV and the maximum current was shifted approximately 10 mV in the hyperpolarizing direction. When cells were stimulated by trains of depolarizations, the exocytosis elicited was enhanced by ECG treatment and the largest enhancement of secretion was observed in later stimulations. EGCG, although it had no significant effect on Ca(2+) current, enhanced exocytosis and slowed endocytosis. These results suggest that green tea polyphenol compounds modulate stimulus-secretion coupling in bovine chromaffin cells.

Adrenal Medulla↗

PubMed1998

Potent suppressive activity of pheophytin a and b from the non-polyphenolic fraction of green tea (Camellia sinensis) against tumor promotion in mouse skin.

Chlorophyll-related compounds pheophytin a and b have been recently identified as antigenotoxic substances in the non-polyphenolic fraction of green tea (Camellia sinensis), which suppressed umu C gene expression in tester bacteria induced by various genotoxins (Okai and Higashi-Okai, Cancer Lett. 118 (1997) 117-123). In the present study, the authors analyzed in vivo and in vitro effects of pheophytin a and b from the non-polyphenolic fraction of green tea on tumor promotion in mouse skin as follows. (1) When pheophytin a and b from green tea were topically applied prior to each treatment with a tumor promoter, 12-O-tetradecanoylphorbol-13-acetate (TPA) on BALB/c mouse skin initiated by 7,12 dimethylbenz[a]anthracene (DMBA), they caused suppression in a dose-dependent fashion against skin tumorigenesis. (2) Pheophytin a and b exhibited significant suppressions against TPA-induced inflammatory reaction, such as edema formation, in BALB/c mouse ear skin in a dose-dependent manner. (3) Pheophytin a and b from green tea showed inhibitory effects against early induction of ornithine decarboxylase (ODC) in BALB/c mouse skin fibroblasts caused by TPA. These results suggest that pheophytin a and b from the non-polyphenolic fraction have potent suppressive activities against tumor promotion in mouse skin.

3T3 Cells↗

PubMed2000

Protective effects of the green tea polyphenol (-)-epigallocatechin gallate against hippocampal neuronal damage after transient global ischemia in gerbils.

Recent studies have shown that green tea polyphenols reduce free radical-induced lipid peroxidation. Oxygen free radical injury plays an important role in neuronal damage induced by brain ischemia and reperfusion. The purpose of this study was to examine whether (-)-epigallocatechin gallate (EGCG) would reduce neuronal damage after transient global ischemia in the gerbils because EGCG has a potent antioxidant property as a green tea polyphenol. To produce transient global ischemia, both common carotid arteries were occluded for 3 min with microaneurysmal clips. The gerbils were treated with EGCG (10, 25, or 50 mg/kg, i.p.) immediately after ischemia. Neuronal cell damage in the hippocampal CA1 region was evaluated quantitatively 5 days after ischemia by a blinded investigator. EGCG at the dose of 10 mg/kg failed to reduce hippocampal neuronal damage. However, EGCG when administered at the dose of 25 or 50 mg/kg significantly reduced hippocampal neuronal damage in a dose-dependent manner (P<0.001, respectively). The present results show that the green tea polyphenol, EGCG, has a neuroprotective effect against neuronal damage following global ischemia in the gerbils.

Animals↗

PubMed2000

Polyphenolics enhance red blood cell resistance to oxidative stress: in vitro and in vivo.

In this study we investigated the potential antioxidant properties of blueberry polyphenolics in vitro and vivo, using red blood cell (RBC) resistance to reactive oxygen species (ROS) as the model. In vitro incubation with anthocyanins or hydroxycinnamic acids (HCA) (0.5 and 0.05 mg/ml) was found to enhance significantly RBC resistance to H2O2 (100 microM) induced ROS production. This protection was also observed in vivo following oral supplementation to rats at 100 mg/ml. However, only anthocyanins were found to afford protection at a significant level, this at 6 and 24 h post supplementation. This protection was not consistent with the measured plasma levels of anthocyanins. Indeed, plasma polyphenolic concentrations were highest after 1 h, declining considerably after 6 h and not detected after 24 h. The difference in absorption between anthocyanins and HCA is likely to have contributed to the observed difference in their abilities to afford protection to RBC. This protection represents a positive role following dietary consumption of polyphenolics from blueberries, against ROS formation within RBC in vivo.

Animals↗

PubMed2001

Ultrasensitive assay for three polyphenols (catechin, quercetin and resveratrol) and their conjugates in biological fluids utilizing gas chromatography with mass selective detection.

The concentrations of three polyphenols ((+)-catechin, quercetin and trans-resveratrol) in blood serum, plasma and urine, as well as whole blood, have been measured after their oral and intragastric administration, respectively, to humans and rats. The method developed for this purpose utilized ethyl acetate extraction of 100 microl samples and their derivatization with bis(trimethylsilyl)trifluoroacetamide (BSTFA) followed by gas-chromatographic analysis on a DB-5 column followed by mass selective detection employing two target ions and one qualifier ion for each compound. Total run time was 17 min with excellent resolution and linearity. The limits of detection (LOD) and quantitation (LOQ) were an order of magnitude less than for any previously published method, being 0.01 microg/l and 0.1 microg/l, respectively, for all compounds. Recovery at 1 microg/l and 10 microg/l was >80% in all instances but one, and was >90% in 50%. Imprecision was acceptable at 0.25 and 1.0 microg/l, concentrations below the LOQ of previous methods. Aglycones released from conjugates after hydrolysis were easily measurable. Optimal conditions for hydrolysis were established. After oral administration of the three polyphenols to humans, their conjugates vastly exceeded the concentrations of the aglycones in both plasma and urine. Concentrations peaked within 0.5-1.0 h in plasma and within 8 h in urine. During the first 24 h, 5.1% of the (+)-catechin and 24.6% of the trans-resveratrol given were recovered in the urine (free plus conjugated). This method can be proposed as the method of choice to assay these polyphenols and their conjugates in biological fluids.

Calibration↗

PubMed2000

Green tea polyphenols (flavan 3-ols) prevent oxidative modification of low density lipoproteins: an ex vivo study in humans.

Oxidation of low density lipoprotein (LDL) plays crucial roles in atherogenesis. We previously reported that green tea polyphenols (flavan 3-ols), especially epigallocatechingallate (EGCg) and epicatechingallate, exerted potent inhibitory effects on LDL oxidation in vitro. To examine whether intake of green tea polyphenols renders LDL resistant to ex vivo oxidation in humans, 22 male volunteers aged between 22 and 32 years were recruited and assigned the same dietary regimen for 2 weeks. After a 1-week baseline period, they were equally divided into two groups: control and tea. The tea group ingested 300 mg of green tea polyphenol extract twice daily for 1 week. Plasma EGCg concentration at the end of the experiment was 56 nmol/L on average (56% in free form) in the tea group; no EGCg was detected before the experiment. Plasma concentrations of lipids, ascorbate, alpha-tocopherol, and lipid peroxides did not change before and after the experiment in either group, but beta-carotene was higher in the tea group (P< 0.01 by paired Student'st-test). LDL (0.1 mg/mL) was incubated with 5 microM Cu(2+) and the oxidation was measured by absorbance at 234 nm. The lag time was significantly prolonged by 13.7 min in the tea group (P < 0.05 by paired Student'st-test, before versus after), whereas such a change was not observed in the control group. These results suggest that daily consumption of seven to eight cups (approximately 100 mL each cup) of green tea may increase resistance of LDL to in vivo oxidation, leading to reduction in the risk of cardiovascular diseases.

Journal Article↗

PubMed1999

Comparative content of total polyphenols and dietary fiber in tropical fruits and persimmon.

Recent studies have shown that dietary fiber and polyphenols of vegetables and fruits improve lipid metabolism and prevent the oxidation of low density lipoprotein cholesterol (LDL-C), which hinder the development of atherosclerosis. The goal of this study was to measure the total polyphenol and dietary fiber contents of some tropical fruits (i.e., pineapple, wax apple, rambutan, lichi, guava, and mango) and compare the results to the content of these substances in the better characterized persimmon. It was found that lichi, guava, and ripe mango (cv. Keaw) have 3.35, 4.95, and 6.25 mg of total polyphenols in 100 g fresh fruit, respectively. This is significantly higher than in persimmon, pineapple, wax apple, mature green mango, and rambutan [P < 0.0005 for pineapple (Smooth Cayene variant), wax apple, persimmon, rambutan, mature green mango (cv. Keaw); the value of P < 0.001 is found only for pineapple (Phuket, Queen variant)]. The same relationship was observed for the contents of gallic acid and of dietary fiber. It can be supposed that among the studied fruit, lichi, guava, and ripe mango may be preferable for dietary prevention of atherosclerosis.

Journal Article↗

PubMed2000

Antioxidant effect of red wine polyphenols on red blood cells.

The protective effect of red wine polyphenols against hydrogen peroxide (H(2)O(2))-induced oxidation was investigated in normal human erythrocytes (RBCs). RBCs, preincubated with micromolar amounts of wine extract and challenged with H(2)O(2), were analyzed for reactive oxygen species (ROS), hemolysis, methemoglobin production, and lipid peroxidation. All these oxidative modifications were prevented by incubating the RBCs with oak barrel aged red wine extract (SD95) containing 3.5 mM gallic acid equivalent (GAE) of phenolic compounds. The protective effect was less apparent when RBCs were incubated with wines containing lower levels of polyphenols. Furthermore, resveratrol and quercetin, well known red wine antioxidants, showed lower antioxidant properties compared with SD95, indicating that interaction between constituents may bring about effects that are not necessarily properties of the singular components. Our findings demonstrate that the nonalcoholic components of red wine, mainly polyphenols, have potent antioxidant properties, supporting the hypothesis of a beneficial effect of red wine in oxidative stress in human system.

Journal Article↗

PubMed2000

Electrochemical behavior of polyphenol oxidase immobilized in self-assembled structures layer by layer with cationic polyallylamine.

We report here a novel bioelectrode based on self-assembled multilayers of polyphenol oxidase intercalated with cationic polyallylamine built up on a thiol-modified gold surface. We use an immobilization strategy previously described by Hodak J. et al. (Langmuir 1997, 13, 2708-2716) Quartz crystal microbalance with electroacustic impedance experiments were carried out to follow quantitatively the multilayer film formation. The response of the self-assembly polyphenol oxidase-polyallylamine electrodes toward different metabolically related catecholamines was studied, to evaluate enzyme kinetics. For the analyzed compounds, only dopamine and its metabolite Dopac gave catalytic currents at applied potential close to 0 V. These responses were proportional to the number of polyphenol oxidase-immobilized layers and were also controlled by the enzymatic reaction. The combination of microgravimetric and electrochemical techniques allowed us to determine the kinetic enzymatic constants, showing that the decomposition rate for the enzyme-substrate complex is slower than the enzymatic reoxidation step.

Catechol Oxidase↗

PubMed2000

Green tea polyphenols inhibit the sodium-dependent glucose transporter of intestinal epithelial cells by a competitive mechanism.

Intestinal glucose uptake is mainly performed by the sodium-dependent glucose transporter, SGLT1. The transport activity of SGLT1 was markedly inhibited by green tea polyphenols, this inhibitory activity being most pronounced in polyphenols having galloyl residues such as epicatechin gallate (ECg) and epigallocatechin gallate (EGCg). Experiments using brush-border membrane vesicles obtained from the rabbit small intestine demonstrated that ECg inhibited SGLT1 in a competitive manner, although ECg itself was not transported via SGLT1. The present results suggest that tea polyphenols such as ECg interact with SGLT1 as antagonist-like molecules, possibly playing a role in controlling the dietary glucose uptake in the intestinal tract.

Animals↗

PubMed2005

A kinetic study of p-cresol oxidation by quince fruit polyphenol oxidase.

The monophenolase activity of quince pulp polyphenol oxidase was characterized by extracting samples using a combination of a two-phase partition step in Triton X-114, followed by a PEG 8000/phosphate partition step, and a final ammonium sulfate fractionation between 30 and 75%. The purification method avoids the loss of cresolase activity described in another quince pulp polyphenol oxidase. The activity was characterized by a lag period, whose duration depended on the substrate concentration, the pH, and the presence of catalytic amounts of o-diphenol. By increasing the concentration of o-diphenols, it was possible to evaluate the enzyme activation constant, K(act), which showed a value of 4.5 microM for 4-methylcatechol. A general kinetic mechanism for this enzyme is used to explain the loss of activity that normally occurs during quince pulp polyphenol oxidase purification.

Catechol Oxidase↗

PubMed2006

Absorption, metabolism, and antioxidant effects of pomegranate (Punica granatum l.) polyphenols after ingestion of a standardized extract in healthy human volunteers.

The intake of polyphenols has been demonstrated to have health-promoting and disease-preventive effects. The pomegranate (Punica granatum L.), which is rich in several polyphenols, has been used for centuries in ancient cultures for its medicinal purposes. The potential health benefits of pomegranate polyphenols have been demonstrated in numerous in vitro studies and in vivo experiments. This study investigated the absorption and antioxidant effects of a standardized extract from pomegranate in healthy human volunteers after the acute consumption of 800 mg of extract. Results indicate that ellagic acid (EA) from the extract is bioavailable, with an observed C(max) of 33 ng/mL at t(max) of 1 h. The plasma metabolites urolithin A, urolithin B, hydroxyl-urolithin A, urolithin A-glucuronide, and dimethyl ellagic acid-glucuronide were identified by HPLC-MS. The antioxidant capacity measured with the oxygen radical absorbance capacity (ORAC) assay was increased with a maximum effect of 32% after 0.5 h, whereas the generation of reactive oxygen species (ROS) was not affected. The inflammation marker interleukin-6 (IL-6) was not significantly affected after 4 h after the consumption of the extract. Overall, this study demonstrated the absorbability of EA from a pomegranate extract high in ellagitannin content and its ex vivo antioxidant effects.

Adult↗

PubMed1999

Analysis of polyphenols using capillary zone electrophoresis and HPLC: detection of soy, lupin, and pea protein in meat products.

The analysis of polyphenols, which are characteristic of certain legumes, enables a rapid and sensitive detection of legume proteins in meat products. Separation of specific isoflavones can be achieved by capillary zone electrophoresis (CZE) or high-performance liquid chromatography (HPLC), both coupled with a photodiode array detector (DAD). The use of CZE in the identification process is an appropriate means of rapid screening; the HPLC is less dependent on matrix effects and clearly more sensitive. Additives of soy protein isolates up to 0.1% could be detected in meat products, even in sausages heated to a high temperature or with hydrolyzed soy proteins. A solid-phase extraction procedure with polyamide cartridges has been developed to concentrate polyphenols. A similar detection of lupin protein is possible in principle. In the case of pea protein, a reliable detection was not possible depending on the coincidental appearance of polyphenols as indicating substances.

Chromatography, High Pressure Liquid↗