Antiphoto-oxidative activity of sesamol in methylene blue- and chlorophyll-sensitized photo-oxidation of oil

The effects and mechanism of sesamol on the methylene blue- or chlorophyll-sensitized photo-oxidations of soybean oil have been studied. Sesamol showed strong antiphoto-oxidative activity in both methylene blue-and chlorophyll-sensitized photo-oxidations of soybean oil in a dose-dependent manner. The 1.0 x 10(-3) M sesamol treatments showed 84.7 and 43.4% inhibitions of methylene blue- and chlorophyll-sensitized photo-oxidations of soybean oil in methylene chloride. The antiphoto-oxidative activity of sesamol was comparable to that of delta-tocopherol in both methylene blue- and chlorophyll-sensitized photo-oxidations, at the same molar basis. Sesamol effectively inhibited rubrene oxidation with a chemical source of singlet oxygen in microemulsion, showing its strong singlet oxygen quenching ability. The results suggested that the antiphoto-oxidative activity of sesamol in the photo-oxidation of oil was, at least in part, due to its singlet oxygen scavenging activity. The singlet oxygen quenching rate constant (k(ox-Q) + k(q)) of sesamol was determined to be 1.9 +/- 0.3 x 10(7) M(-1) s(-1). This represents the first report on the antiphoto-oxidative activity of sesamol in the sensitized photo-oxidation of oil, and its bimolecular singlet oxygen quenching ability.     

Effects, quenching mechanisms, and kinetics of water soluble compounds in riboflavin photosensitized oxidation of milk

To protect the nutrient and flavor stability of milk under light, the effects of 0, 0.01, 0.03, and 0.05 M 1,4-diazabicyclo[2,2,2]octane (DABCO) and 2,5-dimethylfuran (DMF) on the riboflavin photosensitized oxidation of milk were studied. The oxidation of milk was studied by measuring the headspace oxygen in sample bottles after 3 h of light exposure at 3000 lux. As the concentration of DABCO and DMF, which are water soluble compounds, increased in the sample from 0, 0.01, and 0.03 to 0.05 M, the depleted headspace oxygen content significantly decreased (P < 0.05). Steady state kinetic studies of singlet oxygen oxidation showed that the antioxidant activity of DABCO and DMF was due to singlet oxygen quenching. The reaction rate constant of singlet oxygen with milk fat was 8.1 x 10(5) M(-1) s(-1). Total singlet oxygen quenching rates of DABCO and DMF were 1.5 x 10(7) and 2.6 x 10(7) M(-1) s(-1), respectively. DABCO and DMF could be used to slow the reaction between singlet oxygen and milk components to protect nutrients, especially riboflavin, and to improve the oxidative stability of milk fat during storage or processing under light.     

Radical scavenging and singlet oxygen quenching activity of marine carotenoid fucoxanthin and its metabolites

Antioxidant activity of carotenoids is suggested to be one of the factors for their disease preventing effects. Marine carotenoids fucoxanthin and its two metabolites, fucoxanthinol and halocynthiaxanthin, have been shown to exhibit several biological effects. The antioxidant activities of these three carotenoids were assessed in vitro with respect to radical scavenging and singlet oxygen quenching abilities. The 1,1-diphenyl-2-picrylhydrazyl radical scavenging activity of fucoxanthin and fucoxanthinol was higher than that of halocynthiaxanthin, with the effective concentration for 50% scavenging (EC 50) being 164.60, 153.78, and 826.39 microM, respectively. 2,2'-Azinobis-3-ethylbenzo thizoline-6-sulphonate radical scavenging activity of fucoxanthinol (EC 50, 2.49 microM) was stronger than that of fucoxanthin (EC 50, 8.94 microM). Hydroxyl radical scavenging activity as measured by the chemiluminescence technique showed that the scavenging activity of fucoxanthin was 7.9 times higher than that by fucoxanthinol, 16.3 times higher than that by halocynthiaxanthin, and 13.5 times higher than that by alpha-tocopherol. A similar trend was observed when the hydroxyl radical scavenging was assessed by the electron spin resonance (ESR) technique. ESR analysis of the superoxide radical scavenging activity also showed the superiority of fucoxanthin over the other two carotenoids tested. Singlet oxygen quenching ability of the three carotenoids was lower than that of beta-carotene, with quenching rate constants ( k Q, x10 (10) M (-1) s (-1)) being 1.19, 1.81, 0.80, and 12.78 for fucoxanthin, fucoxanthinol, halocynthiaxanthin, and beta-carotene, respectively. The higher radical scavenging activity of fucoxanthin and fucoxanthinol compared with halocynthiaxanthin is assumed to be due to presence of the allenic bond.     

Quenching mechanisms and kinetics of Trolox and ascorbic acid on the riboflavin-photosensitized oxidation of tryptophan and tyrosine

The effects of 0, 0.3, 0.6, and 0.9 mM Trolox and ascorbic acid on the singlet oxygen oxidation of tryptophan and tyrosine containing 25 ppm of riboflavin were determined by measuring tryptophan and tyrosine concentration by high-performance liquid chromatography analysis. The samples were stored in the a 1000 lx light storage box for 4 h at 30 degrees C. As the concentration of Trolox and ascorbic acid increased, the degradation of tryptophan and tyrosine decreased significantly at p < 0.05. Trolox reduced tryptophan and tyrosine degradation by quenching both singlet oxygen and excited triplet riboflavin, whereas ascorbic acid quenched singlet oxygen only. The total singlet oxygen quenchings of Trolox in the presence of tryptophan and tyrosine were 1.55 x 10(7) and 1.32 x 10(7) M(-1) s(-1), respectively. The total singlet oxygen quenchings of ascorbic acid in the presence of tryptophan and tyrosine were 1.16 x 10(7) and 1.10 x 10(7) M(-1) s(-1), respectively. Trolox was more effective than ascorbic acid in preventing the degradation of tryptophan and tyrosine.     

Photoinduced oxidation of the insecticide phenothrin on soil surfaces

Photodegradation profiles of the pyrethroid insecticide phenothrin on a moistened U.S. soil thin layer was investigated by using its predominant component, the 1R-trans-isomer (I), under continuous exposure to light at >290 nm from a xenon arc lamp. Its degradation was moderately accelerated by irradiation with half-lives of 5.7-5.9 days (dark control 21-24 days), mainly via successive oxidation of the 2-methylprop-1-enyl group and ester cleavage followed by mineralization to carbon dioxide. Spectroscopic and cochromatographic analyses showed that the major degradates were the alcohol and ketone derivatives of I formed via photoinduced oxidation of the 2-methylprop-1-enyl group by singlet oxygen. The photoinduced generation of singlet oxygen in/on the soil surface was confirmed by using chemical trapping reactions together with ESR spectroscopy.     

Development of Singlet Oxygen Absorption Capacity (SOAC) Assay Method. 3. Measurements of the SOAC Values for Phenolic Antioxidants

Measurements of the singlet oxygen ((1)O(2)) quenching rates (k(Q) (S)) and the relative singlet oxygen absortpion capacity (SOAC) values were performed for 16 phenolic antioxidants (tocopherol derivatives, ubiquinol-10, caffeic acids, and catechins) and vitamin C in ethanol/chloroform/D(2)O (50:50:1, v/v/v) solution at 35 °C. It has been clarified that the SOAC method is useful to evaluate the (1)O(2)-quenching activity of lipophilic and hydrophilic antioxidants having 5 orders of magnitude different rate constants from 1.38 × 10(10) M(-1) s(-1) for lycopene to 2.71 × 10(5) for ferulic acid. The logarithms of the k(Q) (S) and the SOAC values for phenolic antioxidants were found to correlate well with their peak oxidation potentials (E(p)); the antioxidants that have smaller E(p) values show higher reactivities. In previous works, measurements of the k(Q) (S) values for many phenolic antioxidants were performed in ethanol. Consequently, measurements of the k(Q) (S) and relative SOAC values were performed for eight carotenoids in ethanol to investigate the effect of solvent on the (1)O(2)-quenching rate. The k(Q) (S) values for phenolic antioxidants and carotenoids in ethanol were found to correlate linearly with the k(Q) (S) values in ethanol/chloroform/D(2)O solution with a gradient of 1.79, except for two catechins. As the relative rate constants (k(Q)(AO) (S)/k(Q)(α-Toc) (S)) of antioxidants (AO) are equal to the relative SOAC values, the SOAC values do not depend on the kinds of solvent used, if α-tocopherol is used as a standard compound. In fact, the SOAC values obtained for carotenoids in mixed solvent agreed well with the corresponding ones in ethanol.     

Kinetic study of the quenching reaction of singlet oxygen by Pyrroloquinolinequinol (PQQH(2), a reduced form of Pyrroloquinolinequinone) in micellar solution

A kinetic study of the quenching reaction of singlet oxygen ((1)O(2)) with pyrroloquinolinequinol (PQQH(2), a reduced form of pyrroloquinolinequinone (PQQ)), PQQNa(2) (disodium salt of PQQ), and seven kinds of natural antioxidants (vitamin C (Vit C), uric acid (UA), epicatechin (EC), epigallocatechin (EGC), α-tocopherol (α-Toc), ubiquinol-10 (UQ(10)H(2)), and β-carotene (β-Car)) has been performed. The second-order rate constants k(Q) (k(Q) = k(q) + k(r), physical quenching and chemical reaction) for the reaction of (1)O(2) with PQQH(2), PQQNa(2), and seven kinds of antioxidants were measured in 5.0 wt % Triton X-100 micellar solution (pH 7.4), using UV-visible spectrophotometry. The k(Q) values decreased in the order of β-Car > PQQH(2) > α-Toc > UA > UQ(10)H(2) > Vit C ～ EGC > EC ? PQQNa(2). PQQH(2) is a water-soluble antioxidant. The singlet oxygen-quenching activity of PQQH(2) was found to be 6.3, 2.2, 6.1, and 22 times as large as the corresponding those of water-soluble antioxidants (Vit C, UA, EGC, and EC). Further, the activity of PQQH(2) was found to be 2.2 and 3.1 times as large as the corresponding activity of lipid-soluble antioxidants (α-Toc and UQ(10)H(2)). On the other hand, the activity of PQQH(2) is 6.4 times as small as that of β-Car. It was observed that the chemical reaction (k(r)) is almost negligible in the quenching reaction of (1)O(2) by PQQH(2). The result suggests that PQQH(2) may contribute to the protection of oxidative damage in biological systems, by quenching (1)O(2).     

Photodegradation of the acaricide abamectin: a kinetic study

The acaricide abamectin is a mixture of two colorless homologues in a molar ratio of at least 4:1 with the same structure of macrocyclic lactone. The kinetics of its degradation under direct (254 nm) and dye-sensitized (>400 nm) photoirradiation in methanol solution has been studied by UV-vis spectrophotometry, potentiometric detection of dissolved oxygen, stationary fluorescence, laser flash photolysis, and time-resolved detection of singlet molecular oxygen (O2((1)Delta(g))) phosphorescence. The results indicate that the degradation is very efficient under direct irradiation with UV light (254 nm), with a quantum yield of 0.23. On the contrary, under visible-light irradiation, using the natural pigment riboflavin or the synthetic dye rose bengal as sensitizers, the degradation is very inefficient and proceeds through a O2((1)Delta(g))-mediated mechanism, with a bimolecular rate constant for the overall O2((1)Delta(g)) quenching (the sum of physical and chemical quenching) of 5.5 x 10(5) M(-1) s(-1). This value is similar to those reported for the rate constants of the reactions of O2((1)Delta(g)) with isolated double bonds or conjugated dienes and points to similar processes in the case of abamectin.     

trans-resveratrol content in commercial peanuts and peanut products

A modified high-performance liquid chromatographic (HPLC) method for determination of trans-resveratrol (resveratrol) in peanuts and peanut products has been developed. Resveratrol was extracted with acetonitrile-water (90/10, v/v) by blending with diatomaceous earth at high speed followed by purification of an aliquot of the extract on a minicolumn packed with Al(2)O(3)-ODS (C(18)) mixture. The column was eluted with acetonitrile-water (90/10, v/v), eluate was evaporated under nitrogen, and residue was dissolved in HPLC mobile phase. Resveratrol in an aliquot of purified extract was quantitated by HPLC on silica gel with n-hexane-2-propanol-water-acetonitrile-acetic acid (1050/270/17/5/1, v/v) as a mobile phase. The recovery of resveratrol added to diatomaceous earth at 0.05 microg/g was 98.95 +/- 17.79%; the recovery of the standard added to fresh peanuts (with 0.070 microg/g natural level of resveratrol) at 0.50, 5.00, and 10.00 microg/g was 117.23 +/- 8.87, 100.10 +/- 2.49, and 100.45 +/- 1.51%, respectively. The quantitation limit of resveratrol in fresh peanuts was about 0. 01 microg/g. Roasted peanuts had the lowest content of resveratrol of 0.055 +/- 0.023 microg/g (n = 21), while in peanut butter its concentration was significantly higher, 0.324 +/- 0.129 microg/g (n = 46), and boiled peanuts had the highest level of 5.138 +/- 2.849 microg/g (n = 12). Resveratrol content in commercial peanut products was similar to the resveratrol content of the raw peanut fractions routinely used for making them.     

An LC-MS method for analyzing total resveratrol in grape juice, cranberry juice, and in wine.

Resveratrol is an antioxidant found in grapes, grape products, and some other botanical sources with antiinflammatory and anticancer properties. In grapes and wine, it occurs both as free resveratrol and piceid, the 3beta-glucoside of resveratrol. Here we report a liquid chromatography-mass spectrometry method to analyze total resveratrol (including free resveratrol and resveratrol from piceid) in fruit products and wine. Samples were extracted using methanol, enzymatically hydrolyzed, and analyzed using reversed phase HPLC with positive ion atmospheric pressure chemical ionization (APCI) mass spectrometric detection. Following APCI, the abundance of protonated molecules was recorded using selected ion monitoring (SIM) of m/z 229. An external standard curve was used for quantitation, which showed a linear range of 0.52-2260 pmol of trans-resveratrol injected on-column with a correlation coefficient 0.9999. The coefficient of variance of the response factor over the same concentration range was determined to be 5.8%, and the intra-assay coefficient of variance was determined to be 4.2% (n = 7). The limit of quantitation, defined as signal-to-noise 10:1, was determined to be 0.31 pmol injected on-column. The extraction efficiency of the method was determined to be 92%. The stability of resveratrol under different conditions was also examined. For example, resveratrol was stable for up to 5 days at 4 degrees C in the dark but was not stable at room temperature without protection from light. Resveratrol was detected in grape, cranberry, and wine samples. Concentrations ranged from 1.56 to 1042 nmol/g in Concord grape products, and from 8.63 to 24.84 micromol/L in Italian red wine. The concentrations of resveratrol were silmilar in cranberry and grape juice at 1.07 and 1.56 nmol/g, respectively.     

Resveratrol oligomers isolated from Carex species inhibit growth of human colon tumorigenic cells mediated by cell cycle arrest

Research has shown that members of the Carex genus produce biologically active stilbenoids including resveratrol oligomers. This is of great interest to the nutraceutical industry given that resveratrol, a constituent of grape and red wine, has attracted immense research attention due to its potential human health benefits. In the current study, five resveratrol oligomers (isolated from Carex folliculata and Carex gynandra ), along with resveratrol, were evaluated for antiproliferative effects against human colon cancer (HCT-116, HT-29, Caco-2) and normal human colon (CCD-18Co) cells. The resveratrol oligomers included one dimer, two trimers, and two tetramers: pallidol (1); α-viniferin (2) and trans-miyabenol C (3); and kobophenols A (4) and B (5), respectively. Although not cytotoxic, the resveratrol oligomers (1-5), as well as resveratrol, inhibited growth of the human colon cancer cells. Among the six stilbenoids, α-viniferin (2) was most active against the colon cancer cells with IC(50) values of 6-32 μM (>2-fold compared to normal colon cells). Moreover, α-viniferin (at 20 μM) did not induce apoptosis but arrested cell cycle (in the S-phase) for the colon cancer but not the normal colon cells. This study adds to the growing body of knowledge supporting the anticancer effects of resveratrol and its oligomers. Furthermore, Carex species should be investigated for their nutraceutical potential given that they produce biologically active stilbenoids such as α-viniferin.     

Photosensitizing properties of protein hydrolysate-based fertilizers

The use of protein hydrolysate-based fertilizers (PHF) as adjuvant for pesticides or herbicides has been proposed; however, the behaviors of mixtures of PHFs and pesticides under solar light are not known, and various photochemical reactions may occur. The photosensitizing properties of PHFs were investigated in water solutions (0.8 g of total organic carbon L(-1)) within the wavelength range of 300-450 nm, using furfuryl alcohol (FA) as a probe to test the involvement of singlet oxygen and Irgarol 1051 as an example of organic pollutant. Two commercial PHFs and one standard PHF were studied, all of the products being of animal origin. PHFs photosensitize the transformation of FA (10(-4) M), and the kinetics of FA disappearance follows an apparent first-order rate law. Through the use of sodium azide (1 x 10(-3) M) as singlet oxygen scavenger and deuterium oxide (D2O) for increasing the singlet oxygen lifetime it was shown that singlet oxygen contributes largely to the phototransformation of FA. The replacement of water by D2O increases the apparent first-order rate constant 6 times, whereas the addition of sodium azide reduces it by approximately 90%. These results are confirmed using Irgarol 1051 (10(-5) M). The photosensitizing properties of PHFs might be due to pigments naturally present in tissues from which they are extracted or to compounds generated during the production processes.     

Resveratrol inhibits the activity of equine neutrophil myeloperoxidase by a direct interaction with the enzyme

Resveratrol is a polyphenolic antioxidant present in beverage and food known for its multiple protective effects. We report the inhibitory effects of resveratrol on equine myeloperoxidase (MPO), a hemic peroxidase present in the granules of the neutrophils involved in the inflammatory response. Resveratrol inhibited the production of reactive oxygen species (ROS) by stimulated equine neutrophils by acting as a direct scavenger of the ROS released by the cells but did not modify the degranulation of the stimulated neutrophils as the amounts of released MPO were unchanged. Resveratrol strongly inhibited the chlorination, oxidation, and nitration activities of MPO in a dose-dependent manner. By an original technique of specific immunological extraction followed by enzymatic detection (SIEFED), we demonstrated that resveratrol inhibited the peroxidasic activity of the MPO measured by a direct interaction such as the fixation of resveratrol on the enzyme. The observation of a decrease of the accumulation of compound II suggested that resveratrol acts as an electron donor for MPO reduction.     

Model studies on the photosensitized isomerization of bixin

The photosensitized isomerization reaction of the natural cis carotenoid bixin (methyl hydrogen 9'-cis-6, 6'-diapocarotene-6, 6'-dioate) with rose bengal or methylene blue as the sensitizer in acetonitrile/methanol (1:1) solution was studied using UV-vis spectroscopy, high-performance liquid chromatography (HPLC), and time-resolved spectroscopic techniques, such as laser-flash photolysis and singlet oxygen phosphorescence detection. In both N(2)- and air-saturated solutions, the main product formed was all-trans-bixin. The observed isomerization rate constants, k(obs), decreased in the presence of air or with increase in the bixin concentration, suggesting the participation of the excited triplet state of bixin, (3)Bix, as precursor of the cis--> trans process. On the other hand, bixin solutions in the absence of sensitizer and/or light did not degrade, indicating that the ground state of bixin is stable to thermal isomerization at room temperature. Time-resolved spectroscopic experiments confirmed the formation of the excited triplet state of bixin and its deactivation by ground state bixin and molecular oxygen quenching processes. The primary isomerization products only degraded in the presence of air and under prolonged illumination conditions, probably due to the formation of oxidation products by reaction with singlet molecular oxygen. An energy-transfer mechanism was used to explain the observed results for the bixin transformations, and the consequences for food color are discussed.     

Enzymatic Synthesis of Piceid Glucosides Using Maltosyltransferase from Caldicellulosiruptor bescii DSM 6725

Piceid is widely used in food, cosmetics, and pharmaceuticals because of its therapeutic benefits. However, the use of piceid as a drug is limited because of its low solubility. To increase solubility, we synthesized piceid glucosides using maltosyltransferase from Caldicellulosiruptor bescii . The MTase gene was cloned and expressed in Escherichia coli . The enzyme had a unique transfer specificity to the transfer of maltosyl units. Four piceid transglycosylation products were present and identified by thin-layer chromatography and recycling preparative high-performance liquid chromatography. The major product was purified by C(18) and gel filtration chromatography, and its molecular structure was determined using nuclear magnetic resonance spectroscopy to be α-d-maltosyl-(1→4)-piceid. The solubility of maltosyl piceid was 8.54 × 10(3) and 1.86 × 10(3) times those of natural resveratrol and piceid, respectively, suggesting that the transglycosylation greatly increased the water solubility. This suggests that dietary intake of this compound can enhance the bioavailability of resveratrol in the human body.     

Inhibiting effects of resveratrol and its glucoside piceid against Venturia inaequalis, the causal agent of apple scab

Resveratrol is a phytoalexin produced in different unrelated plant species such as grapevine and peanut. The effect of resveratrol and its glucoside trans-resveratrol-3-O-beta-D-glycopyranosid (piceid) against Venturia inaequalis, the causal agent of apple scab, was evaluated using a newly established test based on enzymatically isolated cuticular membranes (CMs) from apple (Malus domestica Borkh.) leaves. The test substances resveratrol and piceid were either sorbed to CMs before inoculation with spores or were applied simultaneously with the Venturia inaequalis spores to the CMs, and their effect on germination, appressoria formation, and penetration was examined. Resveratrol had no influence on spore germination but a significant inhibiting effect on penetration when applied simultaneously as well as before. A percentage inhibition of 89.7 +/- 11.5 and 61.8 +/- 35.1 was observed for simultaneous and preapplication, respectively. The resveratrol glucoside piceid had a significant inhibitory effect on germination and completely inhibited penetration of the fungus at concentrations between 200 and 400 microg mL(-1) when applied simultaneously with the spores to the CMs. On piceid-enriched CM (preapplication), spores germinated but penetration was inhibited nearly completely (96.1 +/- 5.1%). Thus, in vitro experiments showed that resveratrol and its glucoside in fact could contribute to improving the pathogen resistance of apple leaves.     

Oxidation of resveratrol catalyzed by soybean lipoxygenase

In this work the oxidative degradation of resveratrol catalyzed by lipoxygenase-1 (LOX-1) has been studied. The process has been characterized by spectroscopic and polarographic measurements. The oxidation of resveratrol was dependent on the concentration of resveratrol and the enzyme. When resveratrol was incubated in the presence of lipoxygenase at pH 9.0, the reaction displayed a k(M) value of 18.6 x 10(-)(6) M and a catalytic efficiency (k(cat)/k(M)) of 4.3 x 10(4) s(-)(1) M(-)(1). These values are close to those shown by the enzyme when linoleic acid is used as the substrate. The effect of lipoxygenase inhibitors on the lipoxygenase-catalyzed resveratrol oxidation was also evaluated. The rate of resveratrol oxidation was markedly decreased by the presence of NDGA in the incubation mixture. From HPLC measurements, it can be deduced that resveratrol is oxidatively decomposed to a complex mixture of products similar to those obtained when the molecule is oxidized by hydrogen peroxide.     

Detection of free radical transfer in lipoxygenase I-B-catalyzed linoleic acid-soybean protein interaction by electron spin resonance spectroscopy (ESR)

Effects of lipoxygenase I-B (LOX)-catalyzed oxidation of linoleic acid on soybean proteins was evaluated by electron spin resonance (ESR) and fluorescence spectroscopy in different model systems in the presence or absence of antioxidants. A strong central singlet signal was detected by ESR spectroscopy and identified as the carbon radical (g value range 2.0041-2.0054). A downfield shoulder attributed to the sulfur radical (g value 2.019-2.028) was also observed. The changes in soybean proteins were accompanied by an increase in fluorescence, indicating the formation of cross-links. Natural antioxidants such as ascorbic acid and alpha-tocopherol as well as synthetic antioxidants butyl hydroxytoluene (BHT) inhibited the development of both the free radical signal and the fluorescence when added to soybean proteins prior to incubation with linoleic acid and lipoxygenase I-B; the central singlet signal attributed to the carbon radical was reduced by 35-65%. This paper clearly indicates direct free radical transfer from oxidizing linoleic acid catalyzed by LOX to soybean proteins.     

Resveratrol is a potent inhibitor of the dioxygenase activity of lipoxygenase

Resveratrol is a naturally occurring phytoalexin, present in grapes and other food products, with important antioxidant properties. Although still under debate, it is generally assumed that resveratrol has protective effects against heart diseases and probably tumor development. Lipoxygenase is a dioxygenase with peroxidase activity involved in the synthesis of mediators in inflammatory, atherosclerotic, and carcinogenic processes. Lipoxygenase activity is also involved in the generation of flavors and aromas in foods from animal or vegetal sources. The results presented here show that resveratrol was a potent inhibitor of the dioxygenase activity of lipoxygenase, with an IC(50) = 13 microM. Simultaneously, resveratrol was oxidized by the peroxidase activity of lipoxygenase with a V(max) = 0.28 microM min(-1) and a k(M) = 16.6 microM. Furthermore, oxidized resveratrol was as efficient a lipoxygenase inhibitor as in its reduced form. From the data obtained it can be concluded that both resveratrol and its oxidized form can act as inhibitors of the dioxygenase activity of lipoxygenase. In contrast, the hydroperoxidase activity of lipoxygenase was not inhibited by resveratrol. These results suggest that resveratrol may be used as an antioxidant food additive and as a pharmacological agent to prevent the generation of eicosanoids involved in pathological processes.     

Antioxidant functions of selected allium thiosulfinates and S-alk(en)yl-L-cysteine sulfoxides

Pure thiosulfinates, R-S(O)S-R (2), where R = Me (2a), Pr (2b), or All (2c), at levels up to 4 mM were not capable of scavenging hydrogen peroxide or superoxide anion. Relative to standard antioxidants (ascorbic acid, n-propyl gallate, butylated hydroxytoluene, Trolox, and reduced glutathione), these thiosulfinates were 1-3 orders of magnitude less efficient at reducing 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical, 0.5-2 orders of magnitude less efficient at quenching singlet oxygen, and about equally effective at scavenging hydroxyl radical. Generally, AllS(O)SAll (2c) was the most effective and PrS(O)SPr (2b) was the least effective thiosulfinate in these assays, except that MeS(O)SMe (2a) exhibited no quenching effect toward singlet oxygen. These thiosulfinates were also incapable at levels up to 0.1 mM (where they were toxic) of in vitro induction of quinone reductase (QR) in murine hepatoma (hepa 1c1c7) cells. However, S-1-propenyl-L-cysteine sulfoxide (isoalliin, 1a) and cycloalliin (3) induced QR in this system at 2 mM and 1 mM, respectively, although doubling of QR required levels of 10-15 mM.