scispace - formally typeset
Search or ask a question
Author

J. de Vries

Bio: J. de Vries is an academic researcher from Open University. The author has contributed to research in topics: Ozonide & Glutathione. The author has an hindex of 5, co-authored 8 publications receiving 809 citations.

Papers
More filters
Journal ArticleDOI
TL;DR: It is suggested that quercetin glucoside is actively absorbed from the small intestine, whereas quercettin rutinoside is absorbed fromThe colon after deglycosylation, suggesting that Absorption of other food components might also be enhanced by attachment of a glucose group.
Abstract: Flavonoids are antioxidants present in plant foods. They occur mainly as glycosides, i.e. linked with various sugars. It is uncertain to what extent dietary flavonoid glycosides are absorbed from the gut. We investigated how the nature of the sugar group affected absorption of one major flavonoid, quercetin. Quercetin linked with glucose, i.e. quercetin glucoside and quercetin linked with rutinose, i.e. quercetin rutinoside, both occur widely in foods. When we fed these compounds to nine volunteers, the peak concentration of quercetin (Cmax) in plasma was 20 times higher and was reached (Tmax) more than ten times faster after intake of the glucoside (Cmax = 3.5 ± 0.6 μM (mean ± SE); Tmax < 0.5 h) than after the rutinoside (Cmax = 0.18 ± 0.04 μM; Tmax = 6.0 ± 1.2 h). The bioavailability of the rutinoside was only 20% of that of the glucoside. We suggest that quercetin glucoside is actively absorbed from the small intestine, whereas quercetin rutinoside is absorbed from the colon after deglycosylation. Abso...

507 citations

Journal ArticleDOI
TL;DR: The cytotoxicity of etoposide is caused by the induction of DNA damage, and the occurrence of the DNA lesions can be explained by the capacity of the drug to interfere with the scission-reunion reaction of mammalian topoisomerase II by stabilizing a cleavable complex.
Abstract: Metabolism studies of the antitumor drug etoposide show the formation of metabolites in the lactone ring, which are probably not important for the drug's mechanism of action, and oxidative transformations in the dimethoxyphenol ring (E ring), which lead to products that can cause DNA damage and may play a role in the drug's mechanism of action. The cytotoxicity of etoposide is caused by the induction of DNA damage. The occurrence of the DNA lesions can be explained by the capacity of the drug to interfere with the scission-reunion reaction of mammalian topoisomerase II by stabilizing a cleavable complex.

293 citations

Journal ArticleDOI
TL;DR: St studies on inactivation of phi X174 DNA by the system ortho-quinone of VP-16-213/NADPH cytochrome P-450 reductase suggest that the semi-quin one radical may play a role in the process of in activation of DNA.
Abstract: The catechol metabolite of the antitumor agent VP-16-213 and the ortho-quinone of VP-16-213--a secondary metabolite formed from the catechol--easily undergo auto-oxidation into a free radical at pH greater than or equal to 7.4. By elevation of the pH from 7.4 to 10, an increase in the production of the free radical was observed, which was accompanied by the formation of products with higher hydrophylicity than the catechol and ortho-quinone, as found by HPLC-analysis. The hyperfine structure of the free radical indicates that it is the semi-quinone radical of VP-16-213. At pH 12.5 a secondary radical is formed from the catechol and the ortho-quinone of VP-16-213 besides the semi-quinone radical. One-electron oxidation of the catechol with horseradish peroxidase/hydrogen peroxide resulted in the formation of the same radical as observed under alkaline conditions and subsequent oxidation to the ortho-quinone. If the ortho-quinone was incubated with NADPH cytochrome P-450 reductase, a free radical was detected by spin-trapping with POBN, but not without spin-trapping. Studies on inactivation of phi X174 DNA by the system ortho-quinone of VP-16-213/NADPH cytochrome P-450 reductase suggest that the semi-quinone radical may play a role in the process of inactivation of DNA.

27 citations

Journal ArticleDOI
TL;DR: In this article, the in vitro toxicities of methyl linoleate-9,10-ozonide (MLO) and Cumene hydroperoxide (CumOOH), a model peroxidative agent, are compared.

7 citations

Journal ArticleDOI
TL;DR: Data show that the main target organ for ozonides is the lung, and that the effects caused by MLO in vivo are in many respects similar to the effects found after acute ozone exposure, which supports the working hypothesis that ozonide may play a role in ozone-induced lung toxicity.

6 citations


Cited by
More filters
Journal ArticleDOI
TL;DR: The nature and contents of the various polyphenols present in food sources and the influence of agricultural practices and industrial processes are reviewed, and bioavailability appears to differ greatly between the variousPolyphenols, and the most abundantpolyphenols in the authors' diet are not necessarily those that have the best bioavailability profile.

6,842 citations

Journal ArticleDOI
TL;DR: The diversity and multiple mechanisms of flavonoid action, together with the numerous methods of initiation, detection and measurement of oxidative processes in vitro and in vivo offer plausible explanations for existing discrepancies in structure-activity relationships.
Abstract: Flavonoids are a class of secondary plant phenolics with significant antioxidant and chelating properties. In the human diet, they are most concentrated in fruits, vegetables, wines, teas and cocoa. Their cardioprotective effects stem from the ability to inhibit lipid peroxidation, chelate redox-active metals, and attenuate other processes involving reactive oxygen species. Flavonoids occur in foods primarily as glycosides and polymers that are degraded to variable extents in the digestive tract. Although metabolism of these compounds remains elusive, enteric absorption occurs sufficiently to reduce plasma indices of oxidant status. The propensity of a flavonoid to inhibit free-radical mediated events is governed by its chemical structure. Since these compounds are based on the flavan nucleus, the number, positions, and types of substitutions influence radical scavenging and chelating activity. The diversity and multiple mechanisms of flavonoid action, together with the numerous methods of initiation, detection and measurement of oxidative processes in vitro and in vivo offer plausible explanations for existing discrepancies in structure-activity relationships. Despite some inconsistent lines of evidence, several structure-activity relationships are well established in vitro. Multiple hydroxyl groups confer upon the molecule substantial antioxidant, chelating and prooxidant activity. Methoxy groups introduce unfavorable steric effects and increase lipophilicity and membrane partitioning. A double bond and carbonyl function in the heterocycle or polymerization of the nuclear structure increases activity by affording a more stable flavonoid radical through conjugation and electron delocalization. Further investigation of the metabolism of these phytochemicals is justified to extend structure-activity relationships (SAR) to preventive and therapeutic nutritional strategies.

3,567 citations

Journal ArticleDOI
TL;DR: Gallic acid and isoflavones are the most well-absorbed polyphenols, followed by catechins, flavanones, and quercetin glucosides, but with different kinetics, and the least well- absorption polyphenol are the proanthocyanidins, the galloylated tea catech ins, andThe anthocyanins.

3,534 citations

Journal ArticleDOI
TL;DR: Some of the recent advances in flavonoid research are reviewed and the role of anthocyanins and flavones in providing stable blue flower colours in the angiosperms is outlined.

3,465 citations

Journal ArticleDOI
TL;DR: Both chemical and biochemical factors that affect the absorption and metabolism of polyphenols are reviewed, with particular emphasis on flavonoid glycosides.
Abstract: The main dietary sources of polyphenols are reviewed, and the daily intake is calculated for a given diet containing some common fruits, vegetables and beverages. Phenolic acids account for about one third of the total intake and flavonoids account for the remaining two thirds. The most abundant flavonoids in the diet are flavanols (catechins plus proanthocyanidins), anthocyanins and their oxidation products. The main polyphenol dietary sources are fruit and beverages (fruit juice, wine, tea, coffee, chocolate and beer) and, to a lesser extent vegetables, dry legumes and cereals. The total intake is approximately 1 g/d. Large uncertainties remain due to the lack of comprehensive data on the content of some of the main polyphenol classes in food. Bioavailability studies in humans are discussed. The maximum concentration in plasma rarely exceeds 1 microM after the consumption of 10-100 mg of a single phenolic compound. However, the total plasma phenol concentration is probably higher due to the presence of metabolites formed in the body's tissues or by the colonic microflora. These metabolites are still largely unknown and not accounted for. Both chemical and biochemical factors that affect the absorption and metabolism of polyphenols are reviewed, with particular emphasis on flavonoid glycosides. A better understanding of these factors is essential to explain the large variations in bioavailability observed among polyphenols and among individuals.

3,394 citations