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PubMed2000

Anti-oxidant, pro-oxidant properties of tannic acid and its binding to DNA.

Tannic acid has numerous food and pharmacological applications. It is an additive in medicinal products, and is used as a flavouring agent and as an anti-oxidant in various foods and beverages. We have previously shown that tannic acid in the presence of Cu(II) causes DNA degradation through generation of reactive oxygen species. On the other hand, it exhibits antimutagenic and anticarcinogenic activities, and induces apoptosis in animal cells. It is known that most plant-derived polyphenolic anti-oxidants also act as pro-oxidants under certain conditions. In this paper, we compare the anti-oxidant and pro-oxidant properties of tannic acid and its structural component gallic acid. It is shown that tannic acid is the most efficient generator of the hydroxyl radical in the presence of Cu(II), as compared with gallic acid and its analogues syringic acid and pyrogallol. The anti-oxidant activity of tannic acid was studied by its effect on hydroxyl radical and singlet oxygen mediated cleavage of plasmid DNA. Again, tannic acid provided the maximum protection against cleavage, while gallic acid and its structural analogues were found to be non-inhibitory or partially inhibitory. The results suggest that the structural features of tannic acid that are important for its anti-oxidant action are also those that contribute to the generation of hydroxyl radicals in the presence of Cu(II). Restriction analysis of treated phage DNA and thermal melting profiles of calf thymus DNA indicated that tannic acid strongly binds to DNA. Indirect evidence indicates that modification of DNA bases may also occur.

Animals↗
PubMed2004

Phytochemical inhibition of aflatoxigenicity in Aspergillus flavus by constituents of walnut (Juglans regia).

Tulare walnut, a cultivar highly resistant to aflatoxin formation, was investigated for endogenous phytochemical constituents capable of inhibiting aflatoxigenesis in Aspergillus flavus. The activity, located entirely in the pellicle (seed coat), was extractable to various degrees with polar solvents, although some activity remained unextractable, indicating that the bioactivity resided in a complex of hydrolyzable tannins. These tannins can be hydrolyzed by a fungal tannase present in A. flavus, yielding gallic acid and ellagic acid, testing of which showed that only gallic acid had potent inhibitory activity toward aflatoxin biosynthesis. Comparison of the gallic and ellagic acid content in the pellicle of Tulare and Chico cultivars, over the 2002 and 2003 growing seasons, showed that the gallic acid content increased rapidly with maturation of the nut and was 1.5-2 times higher in Tulare than in Chico. Gallic acid content in the pellicle at maturity of a series of commercial English walnut cultivars, and two black walnut species, was determined as an indicator of potential for inhibition of aflatoxigenesis. Regulation of gallic acid levels in the hydrolyzable tannins of walnuts by conventional breeding or genetic manipulation has the potential to provide new cultivars with high resistance to aflatoxigenesis.

Aflatoxins↗
PubMedDate not supplied

Evaluation of colour parameters and antioxidant activities of fruit wines.

The evaluation of oenological colorimetric indexes, CIELAB parameters, total phenols and antioxidant activities has been studied in different fruit wines made from black mulberry, blackberry, quince, apple, apricot, melon, red raspberry, bilberry, sour cherry and strawberry. The highest value of antioxidant activities and total phenolic contents were determined in bilberry, blackberry and black mulberry wines (61.80%, 1161 mg/l gallic acid equivalents; 60.00%, 1232 mg/l gallic acid equivalents; 58.10%, 1081 mg/l gallic acid equivalents), respectively. The highest values for A420 nm, A520 nm, A620 nm, the proportion of blue, wine colour, wine total colour of pigments, wine polymeric pigment colour and K-K values logarithmic colour intensity) were determined in bilberry fruit wine. Positive correlation was found between antioxidant activities and total phenols (r=0.958, P = 0.001). The results of grouping of different parameters in n-dimensional space with different fruit wines demonstrated the importance of bilberry, blackberry and black mulberry wines as natural antioxidants and colourants.

Antioxidants↗
PubMed1999

Biodegradation of tannic acid by Citrobacter freundii isolated from a tannery effluent.

A bacterial strain capable of utilizing tannic acid as sole carbon source was isolated from the effluent of a tannery and was identified as Citrobacter freundii. This organism could grow at concentrations as high as 5% (w/v) of tannic acid and produced extracellular tannase to hydrolyze the same. When grown in minimal medium containing 1% tannic acid (w/v) at 30 degrees C, this strain produced 1.87 U/ml of tannase at 6 h. At that time, tannic acid degradation products, namely glucose and gallic acid, were detectable in the culture filtrate; the other intermediate metabolites formed were pyrogallol (extracellular) and pyruvate (intracellular). 2-hydroxymuconic acid is presumed to form as a result of ortho-cleavage of pyrogallol. The proposed biochemical pathway for the degradation of tannic acid by Citrobacter freundii is: Tannic acid-->[Glucose + Gallic acid]-->Pyrogallol -->2-hydroxymuconic acid -->[?]-->Pyruvate.

Biodegradation, Environmental↗
PubMed1992

Inhibition of peptidase and glycosidase activities of Porphyromonas gingivalis, Bacteroides intermedius and Treponema denticola by plant extracts.

Aqueous extracts from 5 plants used widely in Kenya as chewing sticks (mswaki) for the control of oral hygiene were tested for their ability to inhibit extracellular peptidase and glycosidase enzyme activities produced by the periodontopathic bacteria Porphyromonas gingivalis (formerly Bacteroides gingivalis), Bacteroides intermedius and Treponema denticola. The plants studied were Rhus natalensis, Cupressus hisitanica, Sida cordifolia, Olea africana and Euclea divinorum. Protease activities, including glycylprolyl dipeptidase and trypsin-like activities of P. gingivalis, chymotrypsin-like and glycylprolyl dipeptidase activities of B. intermedius and the trypsin-like activity of T. denticola, were particularly affected by extracts from Rhus natalensis and Euclea divinorum. Glycosidase activities were generally less affected with the notable exceptions of the inhibition of beta-mannosidase activity of P. gingivalis by all extracts and the inhibition of neuraminidase activity of T. denticola by Rhus natalensis and Euclea divinorum. Generally, these same proteolytic and glycosidic activities were inhibited by tannic acid and to lesser extents by gallic acid and gallic acid methyl ester. An inhibitory component, present in all extracts, exhibited physical and chemical properties identical to those of tannic acid. The inhibition of these enzyme activities is likely to reduce the virulence of these periodontophathic bacteria and to reduce the rate of dental plaque formation.

Bacteroides↗
PubMed2005

Speciation of dissolved iron(II) and iron(III) in environmental water samples by gallic acid-modified nanometer-sized alumina micro-column separation and ICP-MS determination.

A method has been developed for the speciation of trace dissolved Fe(II) and Fe(III) in water by coupling gallic acid (GA) modified nanometer-sized alumina micro-column separation with inductively coupled plasma mass spectrometry (ICP-MS). The separation of Fe(II) and Fe(III) was achieved based on the obvious difference in reaction kinetics between Fe(II) and Fe(III) with GA. Fe(III) was selectively retained on the micro-column at pH 5.5-6.5, while Fe(II) could not be retained by the micro-column at the whole tested pH range of 1.0-6.5, and passed through the micro-column. The Fe(II) can be determined by ICP-MS directly without preconcentration/separation procedure, while Fe(III) retained on the micro-column was then eluted with 1.0 mL of 1 mol L(-1) HCl and determined by ICP-MS. The parameters affecting the separation of Fe(II) and Fe(III) were investigated systematically and the optimum separation conditions were established. Under the optimized conditions, the detection limits of 0.48 microg L(-1) and 0.24 microg L(-1) with relative standard deviation of 5.6% and 4.3%(C= 5 microg L(-1), n= 7) for Fe(II) and Fe(III) were found, respectively. No obvious effect on the speciation of Fe(II) and Fe(III) was found with the change of the ratio of Fe(II) and Fe(III) from 0 ratio 10 to 10 ratio 0. The proposed method was applied for the determination of trace Fe(II) and Fe(III) in environmental water and the recoveries for spiked samples were found to be in the range of 97-105%.

Fresh Water↗
PubMed2006

Protease-assisted clarification of black currant juice: synergy with other clarifying agents and effects on the phenol content.

Conventional clarification with gelatin and silica sol removes a considerable amount of antioxidant phenolics from berry juices. This study examined the clarification and haze-diminishing effects of alternative clarification strategies on black currant juice including centrifugation and addition of acidic protease and pectinolytic enzyme preparations and gallic acid. Centrifugation of freshly pressed juice (10,000 g for 15 min) resulted in a approximately 95% reduction of immediate turbidity and had a decreasing effect on haze development in the juice during cold storage without significantly compromising the total phenols levels. The extent of clarification and haze diminishment varied after individual treatments with five different acidic proteases, but one of the protease preparations, Enzeco, derived from Aspergillus niger, consistently tended to perform best. The individual and interactive effects on juice turbidity, total phenols, and total anthocyanin contents of clarification treatments involving the use of two selected acid proteases (Enzeco and Novozyme 89L), a pectinase (Pectinex BE 3-L), and gallic acid were evaluated in a full factorial 2(4) experimental design. Haze development during cold storage decreased when gallic acid or any of the enzyme preparations were employed individually, but negative interaction effects resulted when the pectinase was employed in combination with any of the proteases. After 28 storage days at 2 degrees C, the lowest levels of haze formation were achieved when the Enzeco protease preparation, added at 0.025 g/L, was added with 0.050 g/L of gallic acid and allowed to react in the juice for 90 min at 50 degrees C. The corresponding anthocyanin reduction was approximately 12% (compared to approximately 30% with gelatin silica sol treatment). The data support the hypothesis that phenol-protein interactions are involved in juice turbidity development during cold storage of berry juices and demonstrate that precentrifugation and protease-assisted clarification show promise as an alternative, phenolics-retaining clarification strategy in black currant juice processing.

Anthocyanins↗
PubMed2001

Efficiency of enzymatic and other alternative clarification and fining treatments on turbidity and haze in cherry juice.

Several alternative strategies were examined for improving conventional juice fining procedures for cherry juice clarification and fining in laboratory-scale experiments: Centrifugation of freshly pressed juice from 1000g to 35,000g induced decreased turbidity according to a steep, negative power function. Individual and interactive effects on turbidity and haze formation in precentrifuged and uncentrifuged cherry juice of treatments with pectinase, acid protease, bromelain, gallic acid, and gelatin-silica sol were investigated in a factorial experimental design with 32 different parameter combinations. Gelatin-silica sol consistently had the best effect on juice clarity. Centrifugation of cherry juice (10,000g for 15 min) prior to clarification treatment significantly improved juice clarity and diminished the rate of haze formation during cold storage of juice. Both treatment of precentrifuged cherry juice with Novozym 89L protease and co-addition of pectinase and gallic acid improved cherry juice clarity and diminished haze levels. None of the alternative treatments produced the unwieldy colloids notorious to gelatin-silica sol treatment. The data suggest that several alternative clarification strategies deserve further consideration in large-scale cherry juice processing. Precentrifugation of juice before clarification and fining is immediately recommended.

Beverages↗
PubMed2001

Specific antioxidant activity of caffeoyl derivatives and other natural phenolic compounds: LDL protection against oxidation and decrease in the proinflammatory lysophosphatidylcholine production.

Specific antioxidant activity (SAA) (i.e., activity related to the molar or gallic acid equivalent amount of antioxidant) of natural polyphenolic mixtures or pure phenolic compounds was studied using their capacity to delay the conjugated diene production brought about by in vitro LDL copper-mediated or AAPH-mediated oxidation. The cinnamic acid series (caffeic, sinapic, ferulic acids) displayed a constant SAA over a large range of concentrations, whereas the benzoic acid series (gallic and protocatechuic acids) showed much higher SAA at low concentrations. The natural phenolic mixtures had a constant SAA. The highest SAA was obtained with caffeoyl esters (caffeoylquinic, rosmarinic, and caffeoyltartaric acids) and catechin for the copper-oxidation and the AAPH-oxidation system, respectively. Phenolic mixtures and acids delayed vitamin E depletion and decreased proinflammatory lysophosphatidylcholine production. As with polyphenols, probucol delayed lysophosphatidylcholine and conjugated dienes production, at higher concentrations, but was not effective at preventing vitamin E depletion. Polyphenols prevent the oxidation of LDL and its constituents (vitamin E, phosphatidylcholine), which is compatible with an antiinflammatory and antiatherosclerotic role in pathophysiological conditions.

Antioxidants↗
PubMed2006

Effect of ascorbic acid on the chemiluminescence of polyphenols.

The chemiluminescence of gallic acid by hydrogen peroxide had completely inhibited by the presence of ascorbate. After ascorbate had disappeared by oxidation, chemiluminescence returned. The concentration of gallic acid was virtually unchanged by presence of ascorbate, but started to decrease after the disappearance of ascorbate. This might be attributable to the rapid reduction of quinone, which was the first product of the chemiluminescence reactions, to gallic acid by ascorbate or the donation of proton to the phenoxy radical from ascorbate to stop the chemiluminescence reaction at the first stage. The effects of ascorbate on the chemiluminescence of other polyphenols depended on their oxidation rate.

Ascorbic Acid↗
PubMed2002

Flavonoids uptake and their effect on cell cycle of human colon adenocarcinoma cells (Caco2).

Green tea, mainly through its constituents epigallocatechin gallate, epigallocatechin, epicatechin gallate and epicatechin, has demonstrated anticarcinogenic activity in several animal models, including those for skin, lung and gastro-intestinal tract cancer, although less is known about colorectal cancer. Quercetin, the major flavonoid present in vegetables and fruit, exerts potential anticarcinogenic effects in animal models and cell cultures, but less is known about quercetin glucosides. The objectives of this study were to investigate (i) the antioxidant activity of the phenolic compounds epicatechin, epigallocatechin gallate, gallic acid and quercetin-3-glucoside; (ii) the cytotoxicity of different concentrations of epicatechin, epigallocatechin gallate, and gallic acid; (iii) the cellular uptake of epicatechin, epigallocatechin gallate, gallic acid and quercetin-3-glucoside and (iv) their effect on the cell cycle. Human colon adenocarcinoma cells were used as experimental model. The results of this study indicate that all dietary flavonoids studied (epicatechin, epigallocatechin gallate, gallic acid and quercetin-3-glucoside) show a significant antioxidant effect in a chemical model system, but only epigallocatechin gallate or gallic acid are able to interfere with the cell cycle in Caco2 cell lines. These data suggest that the antioxidant activity of flavonoids is not related to the inhibition of cellular growth. From a structural point of view, the galloyl moiety appears to be required for both the antioxidant and the antiproliferative effects.

Adenocarcinoma↗
PubMed2000

Tandem mass spectrometry studies of green tea catechins. Identification of three minor components in the polyphenolic extract of green tea.

Liquid chromatography/electrospray ionization mass and tandem mass spectrometry (MS/MS) techniques were used to identify two minor components and one new compound in the polyphenolic extract of green tea (Camellia sinensis). Identification and structure assignments were based on previously reported sub-structural features in the MS/MS product, precursor and neutral loss scans of reference samples. The structures of two minor components, related to the known green tea components epicatechin gallate (ECG, 5) and epigallocatechin gallate (EGCG, 6), are formed by methylation at the 3"-O-position of the gallic acid moiety. The new compound contained a gallic acid ester group, but had only one phenolic group in either the A- or B-ring, relative to the structure of 5. High-resolution mass measurements supported the empirical formula assigned to the new compounds. An important fragmentation for defining the position of methylation of the ester function involves ionization of the phenolic group at the 4"-position of the gallic acid, followed by elimination of the ester function as a neutral with concomitant formation of the m/z 169 ion. If the 4"-position is blocked by methylation, the formation of m/z 169 incorporating the gallic acid group would be blocked. Thus, the presence of an ion representing the ester group indicates a free 4"-phenol and the absence of this ion would signify the 4"-position as a site of methylation. The operation of this mechanism should be general and useful in assigning the site of methylation of any polyphenolic ester group in natural products. A similar conclusion can be drawn concerning alkylation or esterification of the 4'-position of the catechins, i. e. blocking the 4'-phenol would prevent formation of the m/z 125 ion common to all of the catechin compounds thus far examined. Therefore, mass spectral data are of considerable importance in deducing the sites of alkylation or esterification in the structures of the components of green tea.

Catechin↗
PubMed2005

Anti-tumour potential of a gallic acid-containing phenolic fraction from Oenothera biennis.

A phenolic fraction purified form defatted seeds of Oenothera biennis promoted selective apoptosis of human and mouse bone marrow-derived cell lines following first-order kinetics through a caspase-dependent pathway. In non-leukemia tumour cell lines, such as human colon carcinoma CaCo(2) cells and mouse fibrosarcoma WEHI164 cells, this fraction inhibited (3)H-thymidine incorporation but not cell death or cell cycle arrest. Human peripheral blood mononuclear cells showed low sensitivity to treatment. Single bolus injection of the phenolic fraction could delay the growth of established myeloma tumours in syngeneic animals. HPLC and mass spectrometry analysis revealed that the fraction contains gallic acid. However, the biological activity of the fraction differs from the activity of this phenol and hence it should be attributed to other co-purified molecules which remain still unidentified.

Animals↗
PubMed2002

Isolation, identification, and characterization of compounds from acer rubrum capable of oxidizing equine erythrocytes.

OBJECTIVE: To identify compounds in Acer rubrum that cause hemolysis or oxidation of equine erythrocytes and determine whether these toxins are found in other Acer spp. SAMPLE POPULATION: Equine erythrocytes. PROCEDURE: Washed erythrocytes were incubated with extracts and fractions of Acer spp that were separated by thin layer chromatography. Methemoglobin and hemolysis were measured spectrophotometrically. Compounds within Acer spp fractions associated with cell oxidation or hemolysis were identified by gas chromatography-mass spectrometry. RESULTS: Erythrocytes incubated separately with either A. rubrum, A. saccharum, or A. saccharinum extracts had increased methemoglobin formation, compared with extract-free control samples. Two Acer spp fractions had toxic effects on erythrocytes in vitro. A major component of the Acer fraction that caused a significant amount of methemoglobin formation was identified as gallic acid. An amount of gallic acid equivalent to that found in A. rubrum extract significantly increased methemoglobin, compared with extract-free control erythrocytes, but caused less methemoglobin formation than A. rubrum extracts did. A potential co-oxidant, 2,3-dihydro-3,5-dihydroxy-6-methoxy-4H-pyran-4-one, was found in the A. rubrum extract and may have been responsible for increasing methemoglobin formation. A second A. rubrum fraction caused methemoglobin formation and significant hemolysis. A. saccharum and A. saccharinum extracts caused hemolysis but less than the A. rubrum extracts did. CONCLUSION AND CLINICAL RELEVANCE: Oxidants in A. rubrum are also found in A. saccharum and A. saccharinum, and the ingestion of A. saccharum and A. saccharinum poses a potential threat to horses.

Animals↗
PubMed1995

Peroxyl radical scavenging activities of hamamelitannin in chemical and biological systems.

The antioxidative activities of hamamelitannin (2',5-di-O-galloyl-hamamelose), gallic acid and dl-alpha-tocopherol against lipid peroxyl radicals were evaluated in chemical and biological systems. The peroxyl radical scavenging activity was evaluated by electron spin resonance (ESR) method in which both spin-trapping and direct reaction methods were used. In the spin-trapping method, as evaluated by 50% inhibition concentration (IC50) of peroxyl radicals generated in a t-butylhydroperoxide-methemoglobin system, hamamelitannin (IC50 = 95.3 +/- 2.7 microM) showed the highest activity, followed by gallic acid (IC50 = 152.8 +/- 14.6 microM) and dl-alpha-tocopherol (IC50 = 221.5 +/- 4.6 microM) as a positive control. When estimating by the direct method, IC50 values of hamamelitannin, gallic acid and dl-alpha-tocopherol were 93.5 +/- 2.1 microM, 141.6 +/- 2.0 microM and 1590.0 +/- 330.0 microM, respectively. On peroxidation of lipid bilayers induced by 2,2'-azobis-(2-amidinopropane) dihydrochloride (AAPH) in terms of inhibition period (tinh), hamamelitannin showed the longest tinh time (1107.0 +/- 38.18 sec), followed by those of dl-alpha-tocopherol (877.5 +/- 31.8 sec) and gallic acid (771.0 +/- 4.2 sec). The kinetic chain length, defined as the propagation numbers of a lipid peroxyl radical, and calculated from the ratio (Rp/Ri) of the rate of lipid peroxidation to that of inhibition by dl-alpha-tocopherol, hamamelitannin and gallic acid were 27.23, 7.86 and 7.09, respectively. The effects of hamamelitannin, gallic acid and dl-alpha-tocopherol were evaluated on murine fibroblasts exposed to t-butylhydroperoxide (BHP) in terms of the cell survivals. In the protection, hamamelitannin induced the highest survival of 27.6 +/- 0.6% at 50 microM, while both gallic acid and dl-alpha-tocopherol were less active at the same concentrations. On the basis of the results, hamamelitannin was concluded to have a high protective activity on cell damage induced by peroxides.

Animals↗
PubMed1995

Protective activity of hamamelitannin on cell damage of murine skin fibroblasts induced by UVB irradiation.

The protective activities of hamamelitannin (2',5-di-O-galloyl-hamamelose) in Hamamelis virginiana L. and its related compound, gallic acid, on damaged murine skin fibroblasts induced by UVB irradiation were investigated. In order to exclude the UV absorbing effect of the compounds, the protection study was performed such that the fibroblasts were pretreated with hamamelitannin or gallic acid for 24 h before UVB irradiation. At 200 microM concentration, hamamelitannin gave the higher survival of 72.6 +/- 0.4% in comparison with that of gallic acid (35.5 +/- 1.0%), while UVB absorbers such as 2-ethylhexyl p-methoxycinnamate and hexylbenzoate did not show such protection. The scavenging activities of hamamelitannin and gallic acid against active oxygens such as superoxide anion radicals, hydroxyl radicals and singlet oxygens were evaluated using electron spin resonance (ESR-spin trapping method). Hamamelitannin and gallic acid showed potent scavenging activities against all active oxygens tested. Furthermore, the association of hamamelitannin to fibroblasts was examined by comparing it with that of gallic acid, and the following results were obtained: (1) hamamelitannin reduces the reaction rate of liposome entrapped-nitroblue tetrazolium (NBT) with external superoxide anions, and (2) several glycosides associate with fibroblasts. From these results, it was concluded that hamamelitannin protects murine fibroblasts against external active oxygens by associating with the cell surface through its sugar moiety.

Animals↗
PubMed2005

Changes in hepatic drug metabolizing enzymes and lipid peroxidation by methanol extract and major compound of Orostachys japonicus.

The effects of methanol extract and gallic acid (3,4,5-trihydroxybenzoic acid) of Orostachys japonicus A. Berger on hepatic drug metabolizing enzymes and lipid peroxidation were investigated in rats treated with bromobenzene. The methanol extract of Orostachys japonicus reduced the activities of phase I enzymes, aminopyrine N-demethylase and aniline hydroxylase, that had been increased by i.p. injection of bromobenzene. Gallic acid isolated from Orostachys japonicus also reduced the aniline hydroxylase activity, while it did not affect the aminopyrine N-demethylase activity. The methanol extract and gallic acid restored the activity of epoxide hydrolase which had been decreased by bromobenzene. Hepatic glutathione content was lowered, along with increase in hepatic lipid peroxide, by bromobenzene administration. The hepatic lipid peroxidation induced by bromobenzene was prevented with the methanol extract and gallic acid of Orostachys japonicus. However, the decrease in glutathione was not altered by gallic acid. The present results suggest that the methanol extract and gallic acid of Orostachys japonicus may protect liver from bromobenzene toxicity through, at least in part, inhibiting the cytochrome P450-dependent monooxygenase activities and enhancing the activity of epoxide hydrolase. Antioxidant effect also may contribute to the protection of Orostachys japonicus against the bromobenzene-induced hepatotoxicity.

Aminopyrine N-Demethylase↗
PubMed2001

Wine phenolic antioxidants inhibit AP-1 transcriptional activity.

Some of the beneficial effects of moderate wine consumption may be related to the antioxidant properties of polyphenolic compounds containing tannins, flavonoids, and phenolic acids. Cellular actions have recently been reported and may involve the modulation of transcriptional factors such as AP-1 (activator protein-1), which controls the expression of various genes implicated in inflammation processes, cell differentiation, and proliferation. The aim of this study was to evaluate the modulation of AP-1 activity by the phenolic acids (gallic, caffeic, protocatechic, paracoumaric, sinapic, and ferulic acids) that are present in wine and to compare their modulating pathways to those of lipophilic or hydrophilic "chain-breaking" antioxidants (such as DL-alpha-tocopherol or trolox) vitamin C, nitric oxide, and reduced glutathione. AP-1 response was studied on a cell line (MTLN) derived from MCF-7 cells transfected with luciferase gene under TRE sequence control. After stimulation by phorbol 12-myristate 13-acetate (PMA; 100 nM, 6 h, 10(-7) M), luciferase activity was determined by a luminescence method in the presence of luciferine/coenzyme A solution using a luminometer (LKB 1251, Finland). Antioxidants to be tested were incubated with cells in the presence or absence of PMA. Stimulation with PMA resulted in an AP-1-mediated increase in luciferase gene expression corresponding to an 8-fold increase in luciferase activity. After stimulation by PMA, a dose-dependent inhibition of AP-1 was observed with the six phenolic acids in the 20 nM-20 microM concentration range: gallic acid > caffeic > protocatechic, paracoumaric, sinapic acids > ferulic acid. Inhibition was more pronounced with phenolic acids than with DL-alpha-tocopherol (IC(50) = 5 +/- 4.5 microM for gallic acid vs 85 +/- 11 microM for vitamin E). None of the hydrophilic antioxidants inhibited PMA-induced AP-1 activation. None of the antioxidants tested in the absence of PMA stimulation induced any activation or inhibition of AP-1. Our results suggest that phenolic acids may act directly on cell signaling via inhibition of AP-1 transcriptional activity. In addition to preventing LDL oxidation in the arterial wall, our observations indicate that phenolic acids have a cell-mediated capacity to prevent some of the processes involved in atherosclerosis in a plasma concentration range compatible with nutritional intakes.

Antioxidants↗