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PubMed1996

Anti-complementary activity of Crataegus sinaica.

The 80% and 70% acetone extracts from fruits and leaves of Crataegus sinaica Boiss (Rosaceae) and the ethyl acetate-, butanol-, and water-fractions obtained from these initial extracts as well as the isolated compounds, quercetin (1) (1), hyperoside (quercetin 3-O-galactoside) (2) (2), rutin (quercetin 3-O-rutinoside) (3) (2), vitexin (4) (1), rhamnosylvitexin (5) (3), monoacetylrhamnosylvitexin (6) (3), epicatechin (7) (4), procyanidin B-5 (8) (4), proanthocyanidin A-2 (9) (5), procyanidin B-2 (10) (4), and procyanidin C-1 (11) (4), were tested for their influence on the classical (CP) and alternative (AP) pathways of complement-mediated hemolysis. All extracts and fractions showed a strong anti-complementary effect in a dose-dependent way which was more pronounced on the CP than on the AP. The results indicated that the pure proanthocyanidins were active on the CP. Procyanidin C-1 and proanthocyanidin A-2 were the most active on the CP and also showed activity on AP, whereas the flavonoids isolated were generally less active. However, rutin, showed a strong activity, quercetin and rhamnosylvitexin a moderate activity on the CP. This is the first report on the chemical constituents and complement-modulating activity of C. sinaica and on the occurrence of proanthocyanidin A-2 (9) in hawthorn.

Biflavonoids↗

PubMed2004

Inhibitory action of conventional food-grade natural antioxidants and of natural antioxidants of new development on the thermal-induced oxidation of cholesterol.

Cholesterol is a molecule with an unsaturated bond; therefore, like polyunsaturated fatty acids, it is prone to oxidation. Cholesterol oxidation products (COPs) are found in many common foods and have been shown to be atherogenic, cytotoxic, mutagenic and possibly carcinogenic. Therefore, efforts to prevent or to avoid COPs formation during manufacture and/or processing of foods are of high priority. The effect of natural antioxidants on COPs formation has not been extensively studied. We assayed the effect of some widely applied natural antioxidants, such as tocopherol homologs (alpha-T, gamma-T, and delta-T) and rosemary extract, and of some natural products of newly developed as antioxidants, such as the flavonoids quercetin, catechin, morin, and rutin, and also of an alkaloid-derived product, boldine, to inhibit cholesterol oxidation of soybean oil, added of cholesterol, induced in the Rancimat test conditions (150 degrees C and air bubbling). Formation of six different COPs at the induction period and at the 100 microS conductivity value was monitored by gas chromatography. Under the experimental conditions gamma-T, quercetin, and rosemary extract prove effective to inhibit both soybean oil oxidation and COP formation. alpha-T, catechin, and morin are less efficient to prevent COP formation. delta-T, rutin and boldine are devoid of protective action against COP formation. gamma-T, quercetin and rosemary extract may inhibit COP formation from the nucleus and from the lateral chain of the cholesterol molecule.

Antioxidants↗

PubMedDate not supplied

The effects of natural flavonoids on lipoxygenase-mediated oxidation of compounds with a benzene ring structure--a new possible mechanism of flavonoid anti-chemical carcinogenesis and other toxicities.

Numerous studies have strongly suggested that flavonoids exhibit antimutagenic, anticarcinogenic, antiallergic, and anti-inflammatory properties, but the mechanism is still far from clear. In this study, the effect of natural flavonoid compounds, such as green tea polyphenol, epigallocatechin gallate, quercetin, and rutin on lipoxygenase-mediated co-oxidation of guaiacol, benzidine, paraphenylenediamine, and dimethoxybenzidine was investigated. Green tea polyphenol, epigallocatechin gallate, quercetin, and rutin can reduce the co-oxidation reaction speed of tested compounds mediated by soybean lipoxygenase and the production of oxidative products and free radical intermediates. Their median inhibition concentrations on guaiacol oxidation mediated by soybean lipoxygenase were 8.22 mg.L-1, 17.8 micromol.L-1, 41.5 micromol.L-1, and 46.3 micromol.L-1, respectively. These were all significantly lower than glutathione, dithiothreitol, butylated hydroxyanisole and gossypol. The data collected in this study suggest that flavonoids may have an anticarcinogenicity and antitoxicity effect through inhibition of oxidative activation.

Anticarcinogenic Agents↗

PubMed2006

Differential effects of flavonoids on bovine kidney low molecular mass protein tyrosine phosphatase.

Among the structurally related flavonoids tested on the bovine kidney low molecular weight protein tyrosine phosphatase (LMrPTP) activity, quercetin activated by about 2.6-fold the p-nitrophenyl-phosphate (p-NPP)-directed reaction, in contrast to morin that acted as a competitive inhibitor, with Ki values of 87, 73 and 50 microM for p-NPP, FMN, and tyrosine-phosphate, respectively. Other related flavonoids, such as rutin, kaempferol, catechin, narigin, phloretin and taxifolin did not significantly affect the LMrPTP activity. The positions of the hydroxyl groups in the structures of the flavonoids were important for their distinct effects on LMrPTP activity. The hydroxyl groups at C3' and C4' and the presence of a double bond at C2 and C3 were essential for the activating effect of quercetin. The absence of the 3'-OH (kaempferol), absence of the double bond (taxifolin) and the presence of the sugar rutinose at the 3-OH (rutin) suppressed the effect of quercetin. The C2'- and C4'-hydroxyl groups, the presence of the double bond, and a C4-ketone group were important requirements for the inhibitory effects of morin.

Animals↗

PubMed1998

Effects of flavonoids and vitamin C on oxidative DNA damage to human lymphocytes.

This study assessed the antioxidant potencies of several widespread dietary flavonoids across a range of concentrations and compared with vitamin C as a positive control. The antioxidant effects of pretreatment with flavonoids and vitamin C, at standardized concentrations (7.6, 23.2, 93, and 279.4 micromol/L), on oxygen radical-generated DNA damage from hydrogen peroxide (100 micromol/L) in human lymphocytes were examined by using the single-cell gel electrophoresis assay (comet assay). Pretreatment with all flavonoids and vitamin C produced dose-dependent reductions in oxidative DNA damage. At a concentration of 279 micromol/L, they were ranked in decreasing order of potency as follows: luteolin (9% of damage from unopposed hydrogen peroxide), myricetin (10%), quercetin (22%), kaempferol (32%), quercitrin (quercetin-3-L-rhamnoside) (45%), apigenin (59%), quercetin-3-glucoside (62%), rutin (quercetin-3-beta-D-rutinoside) (82%), and vitamin C (78%). The protective effect of vitamin C against DNA damage at this concentration was significantly less than that of all the flavonoids except apigenin, quercetin-3-glucoside, and rutin. The ranking was similar with estimated ED50 (concentration to produce 50% protection) values. The protective effect of quercetin and vitamin C at a concentration of 23.2 micromol/L was found to be additive (quercetin: 71% of maximal DNA damage from unopposed hydrogen peroxide; vitamin C: 83%; both in combination: 62%). These data suggest that the free flavonoids are more protective than the conjugated flavonoids (eg, quercetin compared with its conjugate quercetin-3-glucoside, P < 0.001). Data are also consistent with the hypothesis that antioxidant activity of free flavonoids is related to the number and position of hydroxyl groups.

Adult↗

PubMed2000

Plant phenolics decrease intestinal tumors in an animal model of familial adenomatous polyposis.

Epidemiological studies consistently indicate that consumption of fruits and vegetables lowers cancer risk in humans and suggest that certain dietary constituents may be effective in preventing colon cancer. Plant-derived phenolic compounds manifest many beneficial effects and can potentially inhibit several stages of carcinogenesis in vivo. In this study, we investigated the efficacy of several plant-derived phenolics, including caffeic acid phenethyl ester (CAPE), curcumin, quercetin and rutin, for the prevention of tumors in C57BL/6J-Min/+ (Min/+) mice. These animals bear a germline mutation in the Apc gene and spontaneously develop numerous intestinal adenomas by 15 weeks of age. At a dietary level of 0.15%, CAPE decreased tumor formation in Min/+ mice by 63%. Curcumin induced a similar tumor inhibition. Quercetin and rutin, however, both failed to alter tumor formation at dietary levels of 2%. Examination of intestinal tissue from the treated animals showed that tumor prevention by CAPE and curcumin was associated with increased enterocyte apoptosis and proliferation. CAPE and curcumin also decreased expression of the oncoprotein beta-catenin in the enterocytes of the Min/+ mouse, an observation previously associated with an antitumor effect. These data place the plant phenolics CAPE and curcumin among a growing list of anti-inflammatory agents that suppress Apc-associated intestinal carcinogenesis.

Adenomatous Polyposis Coli↗

PubMed2003

Determination of flavones in Crataegus pinnatifida by capillary zone electrophoresis.

A capillary electrophoretic method for the separation of four flavones in Crataegus pinnatifida is developed. The four flavones in Crataegus pinnatifida are separated on baseline within 15 min using 50mM borax buffer containing 15% acetonitrile and adjusted to pH 8.15 with phosphoric acid. The detection limits of vitexin-2"-rhamnoside, hyperside, rutin, and vitexin are 0.35, 0.30, 0.40 and, 0.29 microg/mL, respectively. The recovery of these flavones is as follows: vitexn-2"-rhamnoside 96.8%, hyperside 99.9%, rutin 97.1%, and vitexin 97.8%. The results are in accordance with those obtained in the high-performance liquid chromatography system. The content of flavones is higher in Crataegus pinnatifida leaves than in its fruits, and hyperside is not detected in either Crataegus pinnatifida fruits or flowers.

Buffers↗

PubMed2006

Flavonoids and vitamin E reduce the release of the angiogenic peptide vascular endothelial growth factor from human tumor cells.

Neoangiogenesis is required for tumor development and progression. Many solid tumors induce vascular proliferation by production of angiogenic factors, prominently vascular endothelial growth factor (VEGF). Because nutrition is a causative factor for tumor prevention and promotion, we determined whether secondary plant constituents, i.e., flavonoids, tocopherols, curcumin, and other substances regulate VEGF in human tumor cells in vitro. VEGF release (concurrent with synthesis) from MDA human breast cancer cells and, for comparison, U-343 and U-118 glioma cells was measured by ELISA. Of 21 compounds tested, 9 showed significant inhibitory activity at 0.1 micromol/L in MDA human breast cancer cells. The rank order of inhibitory potency was naringin > rutin > alpha-tocopheryl succinate (alpha-TOS) > lovastatin > apigenin > genistein > alpha-tocopherol >or= kaempferol > gamma-tocopherol; chrysin and curcumin were inactive except at a concentration of 100 micromol/L. Glioma cells were similarly sensitive, with U343 more than U118, especially for alpha-TOS and tocopherols. Among the tocopherol derivatives, alpha-TOS (0.1 micromol/L) was the most effective in reducing VEGF release. Overall, the glycosylated flavonoids (i.e., naringin, a constituent of citrus fruits, and rutin, a constituent of cranberries) induced the greatest response to treatment at the lowest concentration in MDA human breast cancer cells. Inhibition of VEGF release by flavonoids, tocopherols, and lovastatin in these models of neoplastic cells suggests a novel mechanism for mammary cancer prevention.

Angiogenesis Inhibitors↗

PubMed1990

Synergistic antiproliferative activity of quercetin and cisplatin on ovarian cancer cell growth.

It has been demonstrated that the flavonoid quercetin (3,3',4',5-7-pentahydroxyflavone) (Q) inhibits the growth of several cancer cell lines and that the antiproliferative activity of this substance is mediated by a so-called type II estrogen binding site (type II EBS). We investigated the effects of quercetin and cisplatin (CDDP) alone and in combination on the proliferation of the ovarian cancer cell line OVCA 433. Both drugs exhibited a dose-related growth inhibition in a range of concentrations between 0.01 and 2.5 microM and 0.01 and 2.5 micrograms/ml for Q and CDDP respectively. The combination of the two drugs resulted in a synergistic antiproliferative activity. Two other flavonoids tested, i.e., rutin (3-rhamnosylglucoside of quercetin) and hesperidin [7-b rutinoside of hesperetin (3'-5-3-hydroxy-4-methoxyflavone)] were ineffective both alone and in combination with CDDP. Since both rutin and hesperidin do not bind to type II EBS it can be hypothesized that Q synergizes with CDDP by acting through an interaction with these binding sites.

Antineoplastic Combined Chemotherapy Protocols↗

PubMed1980

Energization of the sugar transport mechanism in the plasmalemma of isolated mesophyll protoplasts.

The mechanism of 3-O-methyl-d-glucose transport through the plasmalemma has been investigated in protoplasts isolated from the mesophyll of Pisum sativum L. var. Dan.Analysis of the fluxes after 50 minutes of uptake showed that the gradual decrease in slope of the net uptake curve with time was not due to any decline in uptake capacity; it represented the approach to flux equilibrium of a small compartment of the protoplast, probably the cytoplasm.The energy of activation for initial flux into this compartment was 20 kilocalories per mole between 17 and 27 C. Very high discrimination was shown with regard to sugar isomers. Light strongly promoted flux (by a factor of 2.5 in the case of methyl glucose). Initial flux showed sharply contrasting inhibitor sensitivity in the light and the dark. Light uptake was sensitive to the proton conductor carbonyl cyanide m-chlorophenylhydrazone (CCCP), but stable for at least the first 10 minutes to the ATPase inhibitors quercetin, rutin, and diethylstilbestrol, as well as to arsenate. Dark uptake, on the other hand, was stable to CCCP but was immediately depressed by quercetin, rutin, diethylstilbestrol, and arsenate.Protoplasts which received a light pretreatment before incubation in the dark took up methyl glucose at the accelerated light rate for the first 7 minutes. Moreover, the light pretreatment sensitized subsequent initial dark uptake to CCCP, and conferred on it the stability to ATPase inhibitors and arsenate characteristic of light uptake. After about 7 minutes the characteristic inhibitor responses of dark uptake were resumed.It is proposed that more than one mode of energy-coupling for sugar transport may operate in these protoplasts.

Journal Article↗

PubMed1998

In vitro antioxidant properties of calcium dobesilate.

Calcium dobesilate, a vascular protective agent, was tested in vitro for its scavenging action against oxygen free radicals. Calcium dobesilate was as potent as rutin to scavenge hydroxyl radicals (IC50 = 1.1 vs 0.7 microM, respectively). It was also able to scavenge superoxide radicals, but with 23 times less potency than rutin (IC50 = 682 vs 30 microM, respectively). Calcium dobesilate significantly reduced platelet activating factor (PAF)-induced chemiluminescence in human PMN cells and lipid peroxidation by oxygen free radicals in human erythrocyte membranes, although these actions required calcium dobesilate concentrations > or = 50 microM. Finally, in cultured bovine aortic endothelial cells, magnesium dobesilate reduced the increase in cytosolic free calcium induced by hydrogen peroxide and inhibited phenazine methosulfate-induced cell potassium loss. In conclusion, calcium dobesilate was effective in scavenging hydroxyl radicals in vitro, at therapeutically relevant concentrations. Conversely, higher concentrations of the compound were required to scavenge superoxide radicals or to protect the cells against the deleterious effects of intracellular reactive oxygen species. Further studies in vivo are required to determine if these antioxidant properties of calcium dobesilate can play a role in its vascular protective mechanisms.

Animals↗

PubMed2003

Polyphenol pattern and antioxidant activity of different tomato lines and cultivars.

BACKGROUND/AIMS: Besides antioxidant vitamins and minerals, fruits and vegetables contain flavonoids and related phenolics. The biological activities of these polyphenols have become well known in recent years evidencing their beneficial effects on human health. In this context, the characterization of the flavonoids present in tomatoes is of great interest. Thus the polyphenol pattern (including flavonols, flavanones and cinnamate derivatives), lycopene and beta-carotene concentrations and the total antioxidant activity (TAA) of the phenolic fraction from different tomato lines and cultivars have been determined. METHODS: The characterization was obtained by means of spectrophotometry and HPLC analyses. RESULTS: Mean values for single flavonoids were 0.68 +/- 0.16 for naringenin, 0.74 +/- 0.12 for rutin and 0.32 +/- 0.06 for a rutin-pentoside. Mean total polyphenol content was 13.15 +/- 1.15 mg/100 g and mean TAA value was 1.3 +/- 0.10 mmol/g. The obtained TAA values resulted in good accordance with the total polyphenol content (R(2) = 0.7928). The main phenolic acids were chlorogenic (mean +/- SE 0.20 +/- 0.03) and caffeic acid (mean +/- SE 0.03 +/- 0.01). Mean levels of lycopene and beta-carotene were 5.38 +/- 0.90 and 1.18 +/- 0.40 mg/100 g, respectively. CONCLUSIONS: Almost all the lines characterised by low carotenoid content produce high levels of polyphenols, and consequently have the most powerful antioxidant potential.

Antioxidants↗

PubMed1988

Use of minoxidil to demonstrate that prostacyclin is not the mediator of bone resorption stimulated by growth factors in mouse calvariae.

Growth factors, such as human transforming growth factor-alpha (hTGF alpha) and epidermal growth factor, as well as human tumor necrosis factor (hTNF) stimulate the resorption of bone in neonatal mouse calvariae in organ culture via a prostaglandin (PG)-mediated pathway. In response to such factors mouse calvariae produce substantial quantities of prostaglandin E2 (PGE2) and prostacyclin (PGI2). We have selectively inhibited the production of PGI2, but not PGE2, using the drug minoxidil and have measured the effects on stimulated bone resportion and arachidonic acid metabolism. The increased production of 6-keto-PGF1 alpha (6k-PGF1 alpha), the hydrolytic product of PGI2, stimulated by recombinant hTGF alpha and hTNF as well as murine epidermal growth factor was inhibited by minoxidil. There was no inhibition by minoxidil of PGE2 production. Despite essentially complete inhibition of stimulated 6k-PGF1 alpha formation, there was no inhibition of bone resorption. The possibility was investigated that growth factors and TNF enhanced enzymatic conversion of PGI2 to 6k-PGE1, which stimulates bone resorption in mouse calvariae with a potency about one fourth that of PGE2. Enzymatic conversion of PGI2 to 6k-PGE1 is inhibited by rutin. Rutin did not inhibit bone resorption stimulated by hTGF alpha or hTNF. We conclude, on the basis of these new results and previously published data, that the cyclooxygenase product that acts as the mediator of bone resorption enhanced by growth factors and TNF in mouse calvariae is probably PGE2.

6-Ketoprostaglandin F1 alpha↗

PubMed2006

Inhibition of rat vas deferens contractions by flavonoids in-vitro.

Flavonoids are a large heterogeneous group of benzo-gamma-pyrone derivatives, which are abundantly present in our diet. In this study we investigated the effect of ten flavonoids (quercetin, kaempferol, morin, galangin, rutin, apigenin, flavone, naringenin, hesperitin and silybin) on the contractile response elicited by electrical field stimulation in the rat isolated vas deferens. All flavonoids tested inhibited vas deferens contractions. The relative order of potency of the tested flavonoids was naringenin > hesperitin > morin > kaempferol > apigenin > silybin > flavone > rutin > quercetin > galangin. Analysis of the chemical structures showed that the saturation of C-2-C-3 double bond and the presence of hydroxyl groups on the flavonoidic scaffold play an important role in the activity of flavonoids.

Animals↗

PubMed2003

Effect of carotenoid on calcium content and alkaline phosphatase activity in rat femoral tissues in vitro: the unique anabolic effect of beta-cryptoxanthin.

The effects of various carotenoids and rutin on calcium content and alkaline phosphatase activity in the femoral-diaphyseal and femoral-metaphyseal tissues of young rats in vitro were investigated. Bone tissues were cultured for 48 h in serum-free Dulbecco's modified Eagle's medium containing either vehicle or a compound (10(-8)-10(-6) M). The presence of beta-cryptoxanthin (10(-7) or 10(-6) M) caused a significant increase in calcium content and alkaline phosphatase activity in the femoral-diaphyseal and femoral-metaphyseal tissues. Also, the lowest concentration (10(-8) M) of beta-cryptoxanthin used caused a significant increase in diaphyseal and metaphyseal calcium content. Lutein (10(-8)-10(-6) M) had no effect on diaphyseal and metaphyseal calcium contents and diaphyseal alkaline phosphatase activity, while 10(-7) and 10(-6) M lutein significantly decreased metaphyseal alkaline phosphatase activity. Lycopene (10(-8)-10(-6) M) or rutin (10(-8)-10(-6) M) did not have a significant effect on bone calcium content and alkaline phosphatase activity. The present study suggests that the carotenoid beta-cryptoxanthin has a unique anabolic effect on bone calcification in vitro.

Alkaline Phosphatase↗

PubMed2003

Clinical pharmacokinetics of antioxidants and their impact on systemic oxidative stress.

Dietary antioxidants play a major role in maintaining the homeostasis of the oxidative balance. They are believed to protect humans from disease and aging. Vitamin C (ascorbic acid), vitamin E (tocopherol), beta-carotene and other micronutrients such as carotenoids, polyphenols and selenium have been evaluated as antioxidant constituents in the human diet. This article addresses data provided from clinical trials, highlighting the clinical pharmacokinetics of vitamin C, vitamin E, beta-carotene, lycopene, lutein, quercetin, rutin, catechins and selenium. The bioavailability of vitamin C is dose-dependent. Saturation of transport occurs with dosages of 200-400 mg/day. Vitamin C is not protein-bound and is eliminated with an elimination half-life (t((1/2))) of 10 hours. In Western populations plasma vitamin C concentrations range from 54-91 micro mol/L. Serum alpha- and gamma-tocopherol range from 21 micro mol/L (North America) to 27 micro mol/L (Europe) and from 3.1 micro mol/L to 1.5 micro mol/L, respectively. alpha-Tocopherol is the most abundant tocopherol in human tissue. The bioavailability of all-rac-alpha-tocopherol is estimated to be 50% of R,R,R-alpha-tocopherol. The hepatic alpha-tocopherol transfer protein (alpha-TTP) together with the tocopherol-associated proteins (TAP) are responsbile for the endogenous accumulation of natural alpha-tocopherol. Elimination of alpha-tocopherol takes several days with a t((1/2)) of 81 and 73 hours for R,R,R-alpha-tocopherol and all-rac-alpha-tocopherol, respectively. The t((1/2)) of tocotrienols is short, ranging from 3.8-4.4 hours for gamma- and alpha-tocotrienol, respectively. gamma-Tocopherol is degraded to 2, 7, 8-trimethyl-2-(beta-carboxyl)-6-hyrdoxychroman by the liver prior to renal elimination. Blood serum carotenoids in Western populations range from 0.28-0.52 micro mol/L for beta-carotene, from 0.2-0.28 for lutein, and from 0.29-0.60 for lycopene. All-trans-carotenoids have a better bioavailability than the 9-cis-forms. Elimination of carotenoids takes several days with a t((1/2)) of 5-7 and 2-3 days for beta-carotene and lycopene, respectively. The bioconversion of beta-carotene to retinal is dose-dependent, and ranges between 27% and 2% for a 6 and 126mg dose, respectively. Several oxidised metabolites of carotenoids are known. Flavonols such as quercetin glycosides and rutin are predominantly absorbed as aglycones, bound to plasma proteins and subsequently conjugated to glucuronide, sulfate, and methyl moieties. The t((1/2)) ranges from 12-19 hours. The bioavailabillity of catechins is low and they are eliminated with a t((1/2)) of 2-4 hours. Catechins are degraded to several gamma-valerolactone derivatives and phase II conjugates have also been identified. Only limited clinical pharmacokinetic data for other polyphenols such as resveratrol have been reported to date.

Antioxidants↗

PubMed2006

Hypericum perforatum: a 'modern' herbal antidepressant: pharmacokinetics of active ingredients.

Hypericum perforatum (St John's Wort [SJW]) counts among the most favourite herbal drugs, and is the only herbal alternative to classic synthetic antidepressants in the therapy of mild to moderate depression. Several clinical studies have been conducted to verify the effectiveness of ethanolic or methanolic extracts of SJW. Alcoholic SJW extracts are a mixture of substances with widely varying physical and chemical properties and activities. Hyperforin, a phloroglucinol derivative, is the main source of pharmacological effects caused by the consumption of alcoholic extracts of SJW in the therapy of depression. However, several studies indicate that flavone derivatives, e.g. rutin, and also the naphthodianthrones hypericin and pseudohypericin, take part in the antidepressant efficacy. In contrast to the amount of documentation concerning clinical efficacy, oral bioavailability and pharmacokinetic data about the active components are rather scarce. The hyperforin plasma concentration in humans was investigated in a small number of studies. The results of these studies indicate a relevant plasma concentration, comparable with that used in in vitro tests. Furthermore, hyperforin is the only ingredient of H. perforatum that could be determined in the brain of rodents after oral administration of alcoholic extracts. The plasma concentrations of the hypericins were, compared with hyperforin, only one-tenth and, until now, the hypericins could not be found in the brain after oral administration of alcoholic H. perforatum extracts or pure hypericin. Until now, the pharmacokinetic profile of the flavonoids in humans after oral administration of an alcoholic H. perforatum extract has been investigated in only one study. More data are available for rutin and the aglycone quercetin after administration of pure substances or other flavonoid sources.

Animals↗

PubMed1998

Flavonoid deactivation of ferrylmyoglobin in relation to ease of oxidation as determined by cyclic voltammetry.

Fourteen flavonoid aglycones, and the flavonoid glycoside rutin, with redox potentials ranging from 0.20 (myricetin) to 0.83 V (chrysin) vs. NHE, as determined by cyclic voltammetry at 23 degrees C in aqueous 50 mM phosphate, ionic strength 0.16 (NaCl) with pH = 7.4 and compared with redox potentials determined for four cinnamic acid derivatives, were all found to reduce ferrylmyoglobin, MbFe(IV)=O, to metmyoglobin, MbFe(III). Reaction stoichiometry depends strongly on the number of hydroxyl groups in the flavonoid B-ring. All compounds with 3',4'-dihydroxy substitution reduce 2 equivalents of MbFe(IV)=O, whereas naringenin, hesperitin and kaempferol, with one hydroxyl group in the B-ring, reduce with a one-to-one stoichiometry. As studied spectrophotometrically under pseudo-first-order conditions with flavonoids in excess, rutin and apigenin react with MbFe(IV)=O with very similar and moderately high activation enthalpies of deltaH298++ = 69 +/- 1 kJ mol(-1) and deltaH298++ = 65 +/- 3 kJ mol(-1), respectively, and with positive activation entropies of deltaS298++ = 23 +/- 4 J mol(-1) K(-1) and deltaS298++ = 13 +/- 9 J mol(-1) K(-1), respectively, in agreement with outer-sphere electron transfer as rate determining. For the fifteen plant polyphenols only qualitative relations exist between redox potential and rate constants rather than a linear free energy relationship (r2 = 0.503), and especially the flavone apigenin was found more efficient as reducing agent. For the flavanones, a linear relation (r2 = 0.971) indicate that, in the absence of a 2,3 double bond, removal of the 4-carbonyl group or addition of a 3-hydroxy group only has minor effect on reactivity. The flavonols are the most efficient reducing agents, effectively reducing MbFe(IV)=O to MbFe(III) and establishing a steady state distribution between the flavonol and MbFe(III) and oxymyoglobin, MbFe(II)O2. Oxidised flavonols reduces MbFe(III) to MbFe(II)O2 very efficiently and much faster than the parent flavonol.

Animals↗