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Iron absorption and phenolic compounds: importance of different phenolic structures.

The phenolic compounds (phenolic monomers, polyphenols, tannins) are considered to interfere with iron absorption by complex formation with iron in the gastro-intestinal lumen, making the iron less available for absorption. Very little is known about the extent to which different types of phenolic compounds of different size and chemical structure inhibit iron absorption. The relationship between iron absorption and the amount and type of phenolic compounds was studied by the extrinsic tag method. The aims of the studies were as follows: (i) To study the effect of small phenolic compounds with different hydroxylation patterns (gallic acid, catechin, chlorogenic acid) on iron absorption, (ii) To study the effect of different amounts of a hydrolysable tannin containing ten gallic acid residues (tannic acid) on iron absorption. (iii) To study the degree of inhibition of iron absorption by some foods and beverages (oregano, spinach, coffee and tea) in relation to their respective content of iron-binding phenolic groups, measured by a newly developed method. The inhibition of iron absorption by tannic acid was strongly dose-related. The smallest amount (5 mg) inhibited absorption by 20 per cent, 25 mg by 67 per cent and 100 mg by 88 per cent. Gallic acid inhibited iron absorption to the same extent as tannic acid, per mol galloyl groups, whereas no inhibition was observed when catechin was added to the test meal. Chlorogenic acid inhibited iron absorption to a lesser extent. Oregano and tea inhibited iron absorption in proportion to their respective content of galloyl groups, whereas the inhibitory effect of spinach was less marked. The inhibiting effect of coffee was explained mainly by its content of galloyl groups, but also by some other factor, probably chlorogenic acid. It is concluded that the content of iron-binding galloyl groups might be a major determinant of the inhibitory effect of phenolic compounds on iron absorption from the diet, whereas the phenolic catechol groups seem to be of minor importance. The results further suggest that the group of condensed tannins do not interfere with iron absorption.

Absorption↗

Comparison of the 2,2'-azinobis-3-ethylbenzotiazo-line-6-sulfonic acid (ABTS) and ferric reducing anti-oxidant power (FRAP) methods to asses the total antioxidant capacity in extracts of fruit and vegetables.

A comparison was made on the use of two spectrophotometric methods, the ferric reducing antioxidant power (FRAP) method and the 2,2'-azinobis-3-ethylbenzotiazoline-6-sulfonic acid (ABTS) method, for the measurement of the total antioxidant capacity (TAC) of plant foods. The correlations of TAC measured by the two methods were highly significant in both water-soluble (r2= 0.90) and water-insoluble extracts (r2= 0.98) from 13 strawberry samples. Also a corresponding comparison of TAC in extracts from 14 plant species showed high correlation coefficients, r2= 0.98 for water-soluble extracts and r2= 0.88 for water-insoluble extracts. The ratio of TAC values obtained with the two methods (ABTS/FRAP) varied between 0.7 and 3.3 for different plant extracts indicating that they contained antioxidants with varying reactivity in the two methods. TACs in six pure antioxidant substances were ranked in the following order by both methods: quercetin > ferulic acid > catechin > rutin > caffeic acid > Trolox = chlorogenic acid. The two methods showed similar TAC values for quercetin, rutin, caffeic acid and chlorogenic acid while ferulic acid and catechin gave higher results with the ABTS method than with the FRAP method, and such differences probably explain the varying ratios of ABTS/FRAP obtained in foods. Regarding storage TAC in water-soluble strawberry extracts stored at -20 or -80 degrees C was stable for at least five months while storage at 4 degrees C decreased the TAC value with 40% during five weeks of storage. The study showed that both the ABTS and FRAP methods can be used for convenient monitoring of the antioxidant capacities in fruit and vegetables, and that different antioxidants had varying reactivity in the two methods.

Antioxidants↗

Effects of phenolic compounds on bromobenzene-mediated hepatotoxicity in mice.

1. The hepatic protective effects of the phenolic compounds 7,8-dihydroxyflavone, morin, silymarin, caffeic acid and chlorogenic acid on bromobenzene-induced toxicity in mice were studied. 2. Morin, caffeic acid and chlorogenic acid at an oral dose of 200 mg/kg failed to influence hepatotoxicity in vivo, while 7,8-dihydroxyflavone exhibited efficacy and potency higher than those of the reference compound silymarin. 3. 7,8-Dihydroxyflavone, an antioxidant and hepatoprotective agent in vitro, decreased serum glutamate-pyruvate transaminase levels (SGPT) in a dose-related manner, and at 200 mg/kg inhibited bromobenzene-induced glutathione depletion in liver.

Animals↗

[In vitro studies of the antiviral activity of enzymatically oxidized o-diphenolic compounds against herpes simplex virus type 1 and 2 (author's transl)].

Oxidation of the o-diphenolic compounds, catechol, protocatechuic acid, caffeic acid, and chlorogenic acid by o-diphenol oxidase (EC 1.10.3.1) resulted in compounds with antiviral activity against herpes simplex virus types 1 and 2. In the system HSV-1/rabbit kidney primary cells, a 90 per cent plaque reduction was obtained by the oxidation product from 1 mug caffeic acid, 9 mug catechol, 13 mug chlorogenic acid, or 20 mug protocatechuic acid (per ml), respectively. In comparision to the basic compounds or those oxidized in the presence of bovine serum albumin, the inhibitory effect of oxidized o-diphenolic compounds free from albumin was higher. From the basic o-diphenolic compounds, only catechol and caffeic acid showed remarkable antiviral activities in the system investigated. Although there have not experiments on the mechanism of action yet been the compounds are supposed to act during the earliest phases of the HSV-multiplication, because o-diphenolic compounds had been found to be present in the virus-cell system only 90 minutes after infection. In this respect the substances were similar to those of humic acids which also inhibit the adsorption phase of herpes simplex virus. There were no essential differences between herpes simplex virus type 1 and type 2 in respect of their sensitivity to enzymatically oxidized o-diphenolic compounds.

Animals↗

Inhibition of chlorogenic acid-induced cytotoxicity by CoCl2.

Chlorogenic acid (CGA) induced apoptotic cell death in human oral squamous cell carcinoma (HSC-2) and salivary gland tumor (HSG) cell lines. CGA exhibited oxidation potential in the culture medium, as demonstrated by NO monitor. Both cytotoxic activity and oxidation potential were significantly reduced by the addition of CoCl2. ESR spectroscopy showed that CGA produced seven peaks of radicals under alkaline condition, while addition of CoCl2 altered the spectral pattern and diminished the radical intensity of CGA. CoCl2 accelerated the CGA-induced coloration of the culture medium and modified the difference spectrum at around 325 nm, an absorption maximum characteristic of CGA. These data suggest that CoCl2 induced conformational changes in the CGA molecule.

Carcinoma, Squamous Cell↗

LC coupled to ion-trap MS for the rapid screening and detection of polyphenol antioxidants from Helichrysum stoechas.

Liquid Chromatography-Ion Trap Mass Spectrometry with an atmospheric pressure chemical ionization (APCI) interface in the negative and positive-ion modes in parallel to UV-diode-array detection (DAD), was applied for the rapid detection/characterization in crude extracts of the water-soluble antioxidant phenolics from Helichrysum stoechas. APCI-MS provides unequivocal molecular weight data of these compounds and useful information about their structures (diagnostic fragments ions), which were confirmed by the UV-DAD fingerprints. This combined approach allows the identification of ten constituents, including the three naturally occurring isomers of caffeoylquinic acid (CGAs), namely neo-chlorogenic acid, chlorogenic acid and crypto-chlorogenic acid, 2 isomeric dicaffeoyl quinic acids, 2 isomeric naringenin glucosides, quercetin, kaempferol and apigenin glucosides and a tetrahydroxychalcone-glucoside. The water-soluble extract from H. stoechas, standardized in both total polyphenol and kaempferol-3-glucoside content, exhibits strong antioxidant activity in vitro when tested in both artificial membrane systems (phosphatidylcholine liposomes) and in a cell model (rat erythrocytes).

Animals↗

Mutagenic activity of some coffee flavor ingredients.

The mutagenicity of 4 coffee flavor ingredients (chlorogenic acid, caffeic acid, pyrazine, and trigonelline) was evaluated in the Salmonella plate incorporation assay and mouse lymphoma L5178Y TK +/- assay. Two of the compounds, pyrazine and trigonelline, were negative in both assays. The other two compounds, caffeic acid and chlorogenic acid, were positive in the mouse lymphoma assay but negative in the Salmonella assay.

Alkaloids↗

Urinary excretion of hydroxycinnamates and flavonoids after oral and intravenous administration.

The urinary recoveries of the hydroxycinnamates, ferulic acid (3-methoxy, 4-hydroxy cinnamic acid), and chlorogenic acid (the quinic acid ester of 3,4-dihydroxycinnamic acid), and three structurally related flavonoids were studied in the rat. For the latter, the aglycone quercetin was compared with its 3-glucoside (isoquercitrin) and 3-rhamnoglucoside (rutin). Doses of 50 mg/kg were administered via the oral and intravenous routes and urine collected over the subsequent 24-h period. Reverse phase HPLC with photo-diode array detection was used to analyze the unchanged compound and their metabolites excreted in the urine. Ferulic acid and isoquercitrin were orally absorbed (5.4 and 0.48% of administered dose, respectively) and are therefore bioavailable. In contrast, neither unchanged chlorogenic acid, rutin, quercetin, nor the conjugated metabolites in the form of glucuronide or sulphate were detected in the urine after oral dosing. All the flavonoids studied produced low total urinary recoveries after intravenous administration, 9.2% for quercetin-3-rhamnoglucoside, 6.7% for the 3-glucoside, and 2.4% for the aglycone, indicating that extensive metabolism to low molecular weight compounds or excretion via other routes may be occurring. Overall it can be stated that renal excretion is not a major pathway of elimination for intact flavonoids and hydroxycinnamates in the rat.

Administration, Oral↗

Microbial metabolism of caffeic acid and its esters chlorogenic and caftaric acids by human faecal microbiota in vitro.

Caffeic acid and its esters, chlorogenic and caftaric acids, are major dietary polyphenols present in various foods and beverages. Although caffeic acid is easily absorbed in the small intestine, its esterification with quinic acid, as in chlorogenic acid, decreases its gut absorption and increases the quantities reaching the colon and its microbiota. The microbial conversion of caftaric acid, the tartaric acid ester of caffeic acid, has not been studied earlier. In this work we compared the direct action of a human faecal microbiota on the metabolism of caffeic, chlorogenic and caftaric acids in an in vitro fermentation model. All substrates disappeared quickly and none of the free acids (caffeic, quinic or tartaric acids) were detected after 2 hours of incubation. Two major microbial metabolites were identified by HPLC-ESI-MS-MS as 3-hydroxyphenylpropionic (3-HPP) and benzoic acids (BA). Maximal levels of 3-HPP were reached after 2 h of fermentation and accounted for 9-24% of the dose of caffeic acid and its esters. BA was formed steadily throughout the incubation, accounting for 4-5% of the initial dose of the substrates after 24 h of incubation. The similarities in the metabolic patterns observed for caffeic, chlorogenic and caftaric acids suggest that esterification does not influence the metabolism of caffeic acid by the gut microbiota.

Bacteria↗

Potential nitrite scavengers as inhibitors of the formation of N-nitrosamines in solution and tobacco matrix systems.

The ability of 20 compounds, all but one tobacco constituents, to inhibit the formation of tobacco-specific N-nitrosamines (TSNA) was investigated in buffer and detergent solution and in tobacco midrib and lamina systems. In solution at pH 5.5, ascorbic acid and the phenolic acids caffeic and ferulic acid were the most potent inhibitors of the reaction between nornicotine and nitrite, with nearly complete inhibition at molar ratios test compound/nitrite > 1:1. Also, cysteine > dihydrocaffeic acid > protocatechuic acid approximately catechin acted as strong inhibitors with >90% inhibition at a ratio of 3:1. Lower inhibitions were observed with chlorogenic acid > p-coumaric acid > sclareol > serine. Rutin showed an inhibition of 34% at a ratio of 0.1:1. Sclareol, alanine, proline, and serine did not significantly affect the N-nitrosonornicotine (NNN) formation. alpha-Tocopherol and glutathione enhanced NNN formation at pH 5.5 but were inhibitors at pH 3. Cinnamic acid, vanillic acid, eugenol, and esculin enhanced NNN formation. Increased NNN formation was also observed for dihydrocaffeic acid, chlorogenic acid, protocatechuic acid, and catechin at a less-than-equimolar ratio of test compound to nitrite. The tobacco matrix experiments were performed with air-cured, ground tobacco midrib and lamina. Caffeic acid, ferulic acid, dihydrocaffeic acid and catechin were potent inhibitors of the formation of TSNA in the midrib as well as in the lamina. Also protocatechuic acid, glutathione, ascorbic acid, p-coumaric acid, chlorogenic acid and cysteine were inhibitors, while alpha-tocopherol and rutin inhibited the reaction in the midrib but not in the lamina. Cinnamic acid, vanillic acid, eugenol, alanine, proline and serine showed small effects only. The molar ratio of secondary alkaloid(s)/nitrite in the test systems were 0.1:1 (solution), approximately 0.25:1 (midrib), and approximately 1:1 (lamina) and is most likely the major contributor to the observed order of inhibition potency (solution > midrib > lamina) of the test compounds. The vicinal phenolic hydroxyl groups of polyphenols and the simultaneous presence of a phenol group and an olefinic bond in hydroxycinnamic acids were the most characteristic structural elements of the potent inhibitors.

Free Radical Scavengers↗

Inhibition of 4-nitroquinoline-1-oxide-induced rat tongue carcinogenesis by the naturally occurring plant phenolics caffeic, ellagic, chlorogenic and ferulic acids.

The modifying effects of dietary administration of the plant phenolic antioxidants caffeic acid (CA), ellagic acid (EA), chlorogenic acid (CGA) and ferulic acid (FA) during the initiation phase on 4-nitroquinoline-1-oxide (4-NQO)-induced tongue carcinogenesis and on the number and area of silver-stained nucleolar organizer region proteins (AgNORs), a new cell proliferation marker, of the tongue squamous epithelium were investigated in male F344 rats. Rats were fed the diet containing 500 p.p.m. CA, 400 p.p.m. EA, 250 p.p.m. CGA or 500 p.p.m. FA for 7 weeks. One week after the commencement of the diets, 4-NQO (20 p.p.m.) was administered in the drinking water for 5 weeks. Feeding of four phenolic compounds significantly reduced the incidences of tongue neoplasms (squamous cell papilloma and carcinoma) and preneoplastic lesions (hyperplasia and dysplasia) by 32 weeks, and rats fed CA or EA had no tongue neoplasms. The number and area of AgNORs per nucleus were decreased significantly by dietary treatment with these four phenolics. Thus, CA, EA, CGA and FA inhibited the tongue carcinogenesis induced by 4-NQO when they were administered concurrently with the carcinogen. These results might suggest possible application of these natural substances for cancer chemoprevention in tongue in addition to other tissues (skin, lung, liver and esophagus).

4-Nitroquinoline-1-oxide↗

Overexpression of L-Phenylalanine Ammonia-Lyase in Transgenic Tobacco Plants Reveals Control Points for Flux into Phenylpropanoid Biosynthesis.

Transgenic tobacco (Nicotiana tabacum L.) plants overexpressing the enzyme L-phenylalanine ammonia-lyase (PAL; EC 4.3.1.5) were grown from seeds of a primary transformant containing the bean PAL2 gene, which had shown homology-dependent silencing of the endogenous tobacco PAL genes. Analysis of endogenous and transgene-encoded PAL transcripts and protein in the primary transformant (T0) and first-generation (T1) overexpressor plants indicated that the transgene-encoded PAL is the cause of the greater than wild-type levels of PAL activity (up to 5- and 2-fold greater in leaf and stem tissue, respectively) in the T1 plants. Leaves of PAL-overexpressing plants contained increased levels of the hydroxycinnamic acid ester chlorogenic acid but not of the flavonoid rutin, indicating that PAL is the key control point for flux into chlorogenic acid. In addition, levels of the glucoside of 4-coumaric acid increased in the overexpressing plants, suggesting that the 4-coumarate:coenzyme A ligase or coumarate hydroxylase reactions might have become limiting. These results help to define the regulatory architecture of the phenylpropanoid pathway and indicate the possibility of engineering-selective changes in this complex metabolic pathway by overexpression of a single early pathway gene.

Journal Article↗

Phenolic compounds from the leaf extract of artichoke (Cynara scolymus L.) and their antimicrobial activities.

A preliminary antimicrobial disk assay of chloroform, ethyl acetate, and n-butanol extracts of artichoke (Cynara scolymus L.) leaf extracts showed that the n-butanol fraction exhibited the most significant antimicrobial activities against seven bacteria species, four yeasts, and four molds. Eight phenolic compounds were isolated from the n-butanol soluble fraction of artichoke leaf extracts. On the basis of high-performance liquid chromatography/electrospray ionization mass spectrometry, tandem mass spectrometry, and nuclear magnetic resonance techniques, the structures of the isolated compounds were determined as the four caffeoylquinic acid derivatives, chlorogenic acid (1), cynarin (2), 3,5-di-O-caffeoylquinic acid (3), and 4,5-di-O-caffeoylquinic acid (4), and the four flavonoids, luteolin-7-rutinoside (5), cynaroside (6), apigenin-7-rutinoside (7), and apigenin-7-O-beta-D-glucopyranoside (8), respectively. The isolated compounds were examined for their antimicrobial activities on the above microorganisms, indicating that all eight phenolic compounds showed activity against most of the tested organisms. Among them, chlorogenic acid, cynarin, luteolin-7-rutinoside, and cynaroside exhibited a relatively higher activity than other compounds; in addition, they were more effective against fungi than bacteria. The minimum inhibitory concentrations of these compounds were between 50 and 200 microg/mL.

Anti-Bacterial Agents↗

Localized changes in peroxidase activity accompany hydrogen peroxide generation during the development of a nonhost hypersensitive reaction in lettuce

Peroxidase activity was characterized in lettuce (Lactuca sativa L.) leaf tissue. Changes in the activity and distribution of the enzyme were examined during the development of a nonhost hypersensitive reaction (HR) induced by Pseudomonas syringae (P. s.) pv phaseolicola and in response to an hrp mutant of the bacterium. Assays of activity in tissue extracts revealed pH optima of 4.5, 6.0, 5.5 to 6.0, and 6.0 to 6.5 for the substrates tetramethylbenzidine, guaiacol, caffeic acid, and chlorogenic acid, respectively. Inoculation with water or with wild-type or hrp mutant strains of P. s. pv phaseolicola caused an initial decline in total peroxidase activity; subsequent increases depended on the hydrogen donor used in the assay. Guaiacol peroxidase recovered more rapidly in tissues undergoing the HR, whereas changes in tetramethylbenzidine peroxidase were generally similar in the two interactions. In contrast, increases in chlorogenic acid peroxidase were significantly higher in tissues inoculated with the hrp mutant. During the HR, increased levels of Mn2+/2, 4-dichlorophenol-stimulated NADH and NADPH oxidase activities, characteristic of certain peroxidases, were found in intercellular fluids and closely matched the accumulation of H2O2 in the apoplast. Histochemical analysis of peroxidase distribution by electron microscopy revealed a striking, highly localized increase in activity within the endomembrane system and cell wall at the sites of bacterial attachment. However, no clear differences in peroxidase location were observed in tissue challenged by the wild-type strain or the hrp mutant. Our results highlight the significance of the subcellular control of oxidative reactions leading to the generation of reactive oxygen species, cell wall alterations, and the HR.

Journal Article↗

Polyphenol profiles of apple juices.

Focusing on 17 constituents, the polyphenol profiles of juices freshly made from various dessert (n = 4) and cider apple cultivars (n = 7) as well as commercially available apple juices (n = 24) were investigated using high-performance liquid chromatography-photodiode array detection (HPLC-DAD) and (HPLC)-electrospray ionization-tandem mass spectrometry (ESI(neg)-MS/MS) analyses. Significant differences in the total polyphenol content as well as the profiles of the apple cultivars under study were observed. For dessert apples the total polyphenol content ranged from 154 to 178 mg/L, whereas for 'old' German cider apple cultivars 261-970 mg/L were determined. Boskoop showed the highest (970 mg/L) and Granny Smith the lowest (154 mg/L) polyphenol content of the freshly prepared samples under study. Hydroxycinnamic acids, with chlorogenic acid as dominating constituent, ranged from 57 to 68 mg/L as well as from 134-593 mg/L in juices made from dessert apples and that from cider apples, respectively. Dessert apple juices showed lower contents of dihydrochalcones (10-35 mg/L) and flavan-3-ols (50-95 mg/L) compared to that of cider apples (34-171 mg/L and 70-393 mg/L, respectively). Quercetin and its derivatives were found from 0.4-4 mg/L and 0.4-27 mg/L in juices made from dessert apples and that of cider apples, respectively. Compared with freshly made juices, lower contents of polyphenols were determined in the commercial samples under study. Amounts ranging from 110-459 mg/L, dominated by chlorogenic acid with concentrations from 53-217 mg/L, were determined. Information about cultivar-typical apple polyphenol content and profile is important for bioactivity studies and, consequently, essential for the development of consumer-relevant products with particular nutritional functionalities.

Beverages↗

Mechanism of inhibition of N-methyl-N'-nitro-N-nitrosoguanidine-induced mutagenesis by phenolic compounds.

At non-toxic concentrations, 2 naturally occurring phenolic compounds, caffeic acid and chlorogenic acid, suppressed the mutagenic activity of the carcinogen N-methyl-N'-nitro-N-nitrosoguanidine (MNNG) in Salmonella typhimurium strain TA1535. The inhibitory effect was observed only when the phenolic compound and the mutagen were administered concurrently. The interaction between phenolic compounds and MNNG was also studied in a cell-free system using a colorimetric method. The results are consistent with the assumption that phenolic compounds scavenge reactive electrophilic MNNG degradation products, thereby preventing their action on critical cellular targets.

Caffeic Acids↗

Colonic metabolism of dietary polyphenols: influence of structure on microbial fermentation products.

The metabolism of chlorogenic acid, naringin, and rutin, representative members of three common families of dietary polyphenols, the hydroxycinnamates, the flavanones, and the flavonols, respectively, was studied in an in vitro mixed culture model of the human colonic microflora. Time- and concentration-dependent degradation of all three compounds was observed, which was associated with the following metabolic events after cleavage of the ester or glycosidic bond: reduction of the aliphatic double bond of the resulting hydroxycinnamate caffeic acid residue; dehydroxylation and ring fission of the heterocyclic C-ring of the resulting deglycosylated flavanone, naringenin, and of the deglycosylated flavonol, quercetin (which differed depending on the substitution). The metabolic events, their sequences, and major phenolic end products, as identified by GC-MS or LC-MS/MS, were elucidated from the structural characteristics of the investigated compounds. The major phenolic end products identified were 3-(3-hydroxyphenyl)-propionic acid for chlorogenic acid, 3-(4-hydroxyphenyl)-propionic acid and 3-phenylpropionic acid for naringin, and 3-hydroxyphenylacetic acid and 3-(3-hydroxyphenyl)-propionic acid for rutin. The degree of degradation of the compounds studied was significantly influenced by the substrate concentration as well as individual variations in the composition of the fecal flora. The results support extensive metabolism of dietary polyphenols in the colon, depending on substrate concentration and residence time, with resultant formation of simple phenolics, which can be considered biomarkers of colonic metabolism if subsequently absorbed. It is also apparent that a relatively small number of phenolic degradation products are formed in the colon from the diverse group of natural polyphenols.

Chromatography, High Pressure Liquid↗

Inhibition of peroxynitrite dependent tyrosine nitration by hydroxycinnamates: nitration or electron donation?

Peroxynitrite is a cytotoxic species generated by the reaction between superoxide and nitric oxide. In this study the ability of hydroxycinnamate antioxidants to decrease peroxynitrite-mediated nitration of tyrosine was investigated. The results obtained show that all compounds were able to inhibit nitration of tyrosine. The potency of inhibitory activity was in the order; caffeic acid > or = chlorogenic acid > or = ferulic acid > p-coumaric acid > ocoumaric acid > m-coumaric acid. Trolox, which was included in the study for comparative purposes, had an activity between that of ferulic acid and p-coumaric acid. The data obtained suggest that hydroxycinnamates can act by one of two possible mechanisms: preferential nitration for monophenolates and electron donation by catecholates.

Antioxidants↗