Peroxidase-Catalyzed Formation of Quercetin Quinone Methide–Glutathione Adducts

Awad, Hanem M.; Boersma, Marelle G.; Vervoort, Jacques; Rietjens, Ivonne M. C. M.

doi:10.1006/abbi.2000.1832

Cited by 162 publications

(138 citation statements)

References 36 publications

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“…As recently reported, o-quinone trapping method by glutathione appeared to be an accurate method for quantification of o-quinone metabolites (Awad et al, 2000;Boersma et al, 2000;Awad et al, 2001;Awad et al, 2002a,b). In these studies, the method proved useful for analysing the nature and biochemical behavior of quercetin o-quinone, and characterization of its p-quinone methide isomers (Awad et al, 2000;Boersma et al, 2000;Awad et al, 2001;Awad et al, 2002a,b). According to these authors, for quercetin o-quinone and p-quinone methide III, glutathione adducts can be formed only at C2´, C5´, and C6´, whereas for pquinone methides I and II, adduct formation at C2´, C5´, C6´, C6, and C8 is possible Awad et al, 2001).…”

Section: Reactions At the Reactive Side Chains Of Proteins: Amino- Smentioning

confidence: 72%

“…This is a further indication, that the bonds formed between the molecules must be of covalent nature. A summary of the nature of several of the reaction products reported in the literature to be formed upon the chemical or enzymatic oxidation of flavonoids is given in Awad et al (2000). The general picture emerging from these studies is that the oxidation of fla- vonoids is complex, resulting in a wide variety of, in many cases, unidentified reaction products.…”

Section: Characterization Of the Protein-phenol-derivatives With Elecmentioning

confidence: 99%

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Reactions of Plant Phenolics with Food Proteins and Enzymes under Special Consideration of Covalent Bonds

Kröll

Rawel

Rohn

2003

FSTR

336

273

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Secondary plant metabolites are important native food components, which are becoming more and more interesting due to their physiological effects on human beings. One of the largest groups of these compounds is represented by plant phenols. This review summarizes the structure, classification and distribution of the phenolic compounds in plant foods, their chemistry and signification with regard to food processing and -storage as well as their physiological effects. This work focuses mainly on such reactions of the phenolic substances with proteins and enzymes that lead to covalent bonds. The derivatives formed have been characterized in terms of changes in their physicochemical and structural properties. The effect on the proteolytic in vitro digestion has been also illustrated. Further aspects reported include the influence on enzyme activity and -kinetic parameters. The different aspects of the nutritional-physiological consequences of such reactions in food and body, especially considering their significance to food science and technology are discussed.

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Section: Reactions At the Reactive Side Chains Of Proteins: Amino- Smentioning

confidence: 72%

Section: Characterization Of the Protein-phenol-derivatives With Elecmentioning

confidence: 99%

Reactions of Plant Phenolics with Food Proteins and Enzymes under Special Consideration of Covalent Bonds

Kröll

Rawel

Rohn

2003

FSTR

336

273

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“…These reactions were described previously and have been taken into account to explain the antioxidant and pro-oxidant activities of quercetin in pharmacological researches. 24,25 According to Figure 10, the oxidation of quercetin I involving the participation of one-electron and one-proton leads to the formation of the ortho-semiquinone II, which can be further oxidized in a one-electron and one-proton forming the para-quinone methide IV. The intermediate IV can subsequently turn into one of its analogous III, V or VI through tautomerization.…”

Section: Temperature (~ 2 O C) After a Given Period Of Time (96 H)mentioning

confidence: 99%

Electrochemical oxidation of quercetin in hydro-alcoholic solution

Timbola¹,

Souza²,

Giacomelli³

et al. 2006

J. Braz. Chem. Soc.

137

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O comportamento eletroquímico da quercetina em meio hidro-alcoólico foi estudado na faixa de pH 2,2-9,2 aplicando-se as técnicas voltametria cíclica, eletrólise com potencial controlado e espectroscopia UV-Vis. Voltamogramas cíclicos para a quercetina mostraram três picos de oxidação e um pico de redução dependente das condições experimentais. Um processo de oxidação envolvendo dois prótons e dois elétrons no primeiro pico conduziu à formação da orto-quinona correspondente, a qual é uma espécie eletroquimicamente ativa e instável, como evidenciado pela dependência do perfil dos voltamogramas cíclicos com a velocidade de variação de potencial, em concordância com um mecanismo do tipo eletroquímico-químico (EC). Eletrólises com potencial controlado geraram três produtos caracterizados por espectroscopia UV-Vis. Um esquema reacional envolvendo as etapas eletroquímica e química foi proposto para a eletro-oxidação da quercetina em solução hidro-alcoólica, com base em dados obtidos da literatura e em evidências experimentais.The electrochemistry of quercetin hydro-alcoholic solutions of pH 2.2 to 9.2 was studied by cyclic voltammetry, controlled-potential electrolysis and UV-Vis spectroscopy. Cyclic voltammograms for quercetin showed three oxidation peaks and one reduction peak depending on the experimental conditions. The two-electron two-proton oxidation process at the first peak led to the formation of the corresponding ortho-quinone, which is an electrochemically active and unstable species, as evidenced by the dependence of the cyclic voltammogram profile on the applied scan rate, in agreement with the EC mechanism. Controlled-potential electrolysis yielded three products as characterized by UV-Vis spectroscopy. A reaction scheme comprising electrochemical and chemical steps was proposed for the electro-oxidation of the quercetin in hydro-alcoholic solutions on basis of experimental evidences obtained in this work and elsewhere.

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“…In the light of the indications of its potential nephrotoxicity demonstrated in that trial, we tested the potential of quercetin to undergo biotransformation via conjugation with glutathione (GSH) to a proximate nephrotoxicant, analogous to the nephrotoxicity associated with hydroquinone (Peters et al, 1997), bromohydroquinone (Monks et al, 1985), 17b-estradiol (Butterworth et al, 1997) or haloalkenes (Iverson et al, 1996). Previous reports have indicated that GSH conjugates are formed in vitro (Awad et al, 2000(Awad et al, , 2001Boersma et al, 2000;Galati et al, 2001). Furthermore, mindful of the fact that COX activity is a potential mechanistic target of quercetin, we compared its effect on cellular prostaglandin E-2 (PGE-2) production with that of representative quercetin metabolites.…”

mentioning

confidence: 99%

Characterisation of metabolites of the putative cancer chemopreventive agent quercetin and their effect on cyclo-oxygenase activity

et al. 2004

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Quercetin (3,5,7,3 0 ,4 0 -pentahydroxyflavone) is a flavone with putative ability to prevent cancer and cardiovascular diseases. Its metabolism was evaluated in rats and human. Rats received quercetin via the intravenous (i.v.) route and metabolites were isolated from the plasma, urine and bile. Analysis was by high-performance liquid chromatography and confirmation of species identity was achieved by mass spectrometry. Quercetin and isorhamnetin, the 3 0 -O-methyl analogue, were found in both the plasma and urine. In addition, several polar peaks were characterised as sulphated and glucuronidated conjugates of quercetin and isorhamnetin. Extension of the metabolism studies to a cancer patient who had received quercetin as an i.v. bolus showed that (Quercetin removed) isorhamnetin and quercetin 3 0 -O-sulphate were major plasma metabolites. As a catechol, quercetin can potentially be converted to a quinone and subsequently conjugated with glutathione (GSH). Oxidation of quercetin with mushroom tyrosinase in the presence of GSH furnished GSH conjugates of quercetin, two mono-and one bis-substituted conjugates. However, these species were not found in biomatrices in rats treated with quercetin. As cyclo-oxygenase-2 (COX-2) expression is mechanistically linked to carcinogenesis, we examined whether quercetin and its metabolites can inhibit COX-2 in a human colorectal cancer cell line (HCA-7). Isorhamnetin and its 4 0 -isomer tamarixetin were potent inhibitors, reflected in a 90% decrease in prostaglandin E-2 (PGE-2) levels, a marker of COX-2 activity. Quercetin was less effective, with a 50% decline. Quercetin 3-and 7-O-sulphate had no effect on PGE-2. The results indicate that quercetin may exert its pharmacological effects, at least in part, via its metabolites. Naturally occurring flavonoids in the diet are associated with several beneficial health effects and understanding the mechanisms underlying these effects has become the focus of much research. Quercetin (3,5,7,3 0 ,4 0 -pentahydroxyflavone, for structure see Figure 1) is a prime example of such a flavonoid. Its glycosylated form occurs in kale, French beans, broccoli, apples and especially in onions, with an abundance as high as a quarter to half a gram per kg (Hertog et al, 1992). On ingestion with the diet, quercetin glycosides are rapidly hydrolysed to generate quercetin.Epidemiological evidence links diets rich in quercetin with decreased incidence of cardiovascular and neoplastic diseases

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Peroxidase-Catalyzed Formation of Quercetin Quinone Methide–Glutathione Adducts

Cited by 162 publications

References 36 publications

Reactions of Plant Phenolics with Food Proteins and Enzymes under Special Consideration of Covalent Bonds

Reactions of Plant Phenolics with Food Proteins and Enzymes under Special Consideration of Covalent Bonds

Electrochemical oxidation of quercetin in hydro-alcoholic solution

Characterisation of metabolites of the putative cancer chemopreventive agent quercetin and their effect on cyclo-oxygenase activity

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