Quercetin antioxidative activity

The application of flavonoids for the treatment of various diseases associated with free radical overproduction is considered in Chapter 29. However, it seems useful to discuss here some studies describing the activity of flavonoids under certain pathophysiological conditions. Oral pretreatment with rutin of rats, in which gastric lesions were induced by the administration of 100% ethanol, resulted in the reduction of the area of gastric lesions [157]. Rutin was found to be an effective inhibitor of TBAR products in the gastric mucosa induced by 50%i ethanol [158]. Rutin and quercetin were active in the reduction of azoxymethanol-induced colonic neoplasma and focal area of dysplasia in the mice [159], Chemopreventive effects of quercetin and rutin were also shown in normal and azoxymethane-treated mouse colon [160]. Flavonoids exhibited radioprotective effect on 7-ray irradiated mice [161], which was correlated with their antioxidative activity. Dietary flavones and flavonols protected against the toxicity of the environmental contaminant dioxin [162], Rutin inhibited ovariectomy-induced osteopenia in rats [163],... 

Zhang, Y., Yang, Y., Tang, K., Hu, X., Zou, G. (2008). Physicochemical characterization and antioxidant activity of quercetin-loaded chitosan nanoparticles. Journal of Applied Polymer Science, 107, 891-897. 

The olives themselves contain many phenolic compounds with antioxidant properties. Bouaziz et al. (2005) investigated the olive cultivar Chemlali from Tunisia. Oleuropein (7.14), a bitter glycoside esterified with a phenolic acid, was the major compound present. Phenolic monomers and twelve flavonoids were also identified. The antioxidant activity of the extract was evaluated. Acid hydrolysis of the extract enhanced its antioxidant activity. / -Hydroxyphenyl-cthanol (7.12) and quercetin (1.43) showed antioxidant activities similar to that of 2,6-di-fert-butyl-4-methyl phenol (7.15), a reference compound with known antioxidant properties. It was suggested that a hydroxyl group at the ortho-position on the flavonoid B ring could contribute to the antioxidant activity of the flavonoids. 

Whatever the mechanism of action for the inhibition of 5-lipoxygenase by flavonoids, it appears to be distinct from the antioxidant properties of these compounds. The results comparing antioxidant activity with leukotriene inhibitory activity clearly demonstrate this distinction. The profound effects of metabolic transformation on the anti-inflammation activity of dietary flavonoids such as quercetin must also be considered in relation to in vitro studies, and further highlights the need to use actual metabolic forms of flavonoids rather than the free aglycone or glycosides occurring in the diet. 

Justino GC, Santos MR, Canario S, Borges C, Florencio MH, Mira L. 2004. Plasma quercetin metabolites Structure-antioxidant activity relationships. Arch Biochem Biophys 432 109-121. 

Flavonones and flavanonol are other heterocyclic pigments found in wine. Taxifolin 41 (2,3-dihydroquercetin) has only 50% of the antioxidative activity of quercetin, but it is both less mutagen and toxic (09MI451,07MI1074) ... 

The antioxidant activity of flavonoids in liposomes has also been extensively studied. Gordon and Roedig-Penman [93] used liposomes formed from egg PC to compare the antioxidant potencies of myricetin (31) and quercetin... 

Interestingly, products of chlorination of quercetin with hypochlorous acid were found to have higher antioxidant activity (estimated by inhibition of ABTS oxidation) than the parent compound, with monochloroquercetin and dichloroquercetin, showing activity 1.76 times and 1.84 times, respectively, of that of quercetin (B13). 

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