Flavonoids antioxidative activity

Thompson M, Williams CR, Elliot GE. 1976. Stability of flavonoid complexes of copper(II) and flavonoid antioxidant activity. Anal Chim Acta 85 375-381. 

Although phospholipid bilayers are better mimics of biomembranes than are micelles, there are few reliable quantitative data on flavonoid antioxidant activities in lipid bilayers. Terao and coworkers compared the antioxidant efficiency of quercetin and catechins (epicatechin and epicatechin gallate) with that of a-Toc in egg yolk PC liposomes using initiation by the water-soluble initiator, ABAP, and analysis of hydroperoxide formation and antioxidant consumption by HPLC. Based on the length of the induction periods and the profile of suppressed hydroperoxide formation, they concluded that quercetin and the catechins were more efficient antioxidants than a-Toc in these bilayers. Apparently the unique behavior of a-Toc in bUayers is responsible for these results (vide supra). In hexane and alcohols solution during suppressed peroxidation of methyl linoleate, the relative antioxidant activities reversed so that the flavonoids were 5-20 times less active... 

Reliable quantitative studies of flavonoid antioxidant activities in model membranes are lacking. 

The results presented in table 2 show that when 3-hydroxyl is absent or substituted, its contribution to electron dislocation is substantially reduced and so is consequently the flavonoid antioxidant activity, although this reduction is smaller when this hydroxyl group is substituted (rutin) than when it is absent (diosmin). These results confirm the importance of the 3-hydroxyl group for a better capacity to revert radicals [29, 138, 159, 163], However, the presence of a double bond between C2 and C3 when 3-hydroxyl group is absent (diosmin) does not significantly increase the antioxidant capacity of flavonoids in respect to those that do not present this double bond (hesperidin) in spite of the fact that the double bond should increase the conjugation of the structure according to the aforementioned [139],... 

The total antioxidant activity of teas and tea polyphenols in aqueous phase oxidation reactions has been deterrnined using an assay based on oxidation of 2,2 -azinobis-(3-ethylbenzothiazoline-sulfonate) (ABTS) by peroxyl radicals (114—117). Black and green tea extracts (2500 ppm) were found to be 8—12 times more effective antioxidants than a 1-mAf solution of the water-soluble form of vitamin E, Trolox. The most potent antioxidants of the tea flavonoids were found to be epicatechin gallate and epigallocatechin gallate. A 1-mAf solution of these flavanols were found respectively to be 4.9 and 4.8 times more potent than a 1-mAf solution of Trolox in scavenging an ABT radical cation. 

The antioxidant activities of carotenoids and other phytochemicals in the human body can be measured, or at least estimated, by a variety of techniques, in vitro, in vivo or ex vivo (Krinsky, 2001). Many studies describe the use of ex vivo methods to measure the oxidisability of low-density lipoprotein (LDL) particles after dietary intervention with carotene-rich foods. However, the difficulty with this approach is that complex plant foods usually also contain other carotenoids, ascorbate, flavonoids, and other compounds that have antioxidant activity, and it is difficult to attribute the results to any particular class of compounds. One study, in which subjects were given additional fruits and vegetables, demonstrated an increase in the resistance of LDL to oxidation (Hininger et al., 1997), but two other showed no effect (Chopra et al, 1996 van het Hof et al., 1999). These differing outcomes may have been due to systematic differences in the experimental protocols or in the populations studied (Krinsky, 2001), but the results do indicate the complexity of the problem, and the hazards of generalising too readily about the putative benefits of dietary antioxidants. 

CAO G, SOFIC E and prior r l (1997) Antioxidant and prooxidant behavior of flavonoids structure-activity relationships . Free Rad Biol Med, 22 (5), 749-60. 

The electron transfer mechanism for antioxidant activity corresponding to eq. 16.5 makes the standard reduction potentials of interest for evaluation of antioxidative activity. The standard reduction potential of the phenoxyl radical of several flavonoids has been determined and forms the basis for correlation of rate of electron transfer for various oxidants from the flavonoid (Jovanovic etal., 1997 Jorgensen and Skibsted, 1998). The standard reduction potentials have also been used to establish antioxidant hierarchies. 

RICE-EVANS c A, MILLER N J and PAGANGA G (1996) Structure-antioxidant activity relationships of flavonoids and phenolic acids, Free Rad Biol Med, 20, 933-56. 

Heim, K.E. et al., Flavonoid antioxidants chemistry, metabolism and structure-activity relationships, J. Nutr. Biochem., 13, 572, 2002. 

Solid microcapsules using maltodextrins or starch as matrices were incorporated into cosmetic, pharmaceutical, dietetic, and food compositions using the interfacial crosslinking of flavonoids. Such microcapsules prevented discoloration while maintaining both the anti-free radical and antioxidant activities of the flavonoids." ... 

Naturally occurring compounds such as phytochemicals, which possess anticar-cinogenic and other beneficial properties, are referred to as chemopreventers. One of the predominant mechanisms of their protective action is due to their antioxidant activity and the capacity to scavenge free radicals. Among the most investigated chemopreventers are some vitamins, plant polyphenols, and pigments such as carotenoids, chlorophylls, flavonoids, and betalains. Resolution of the potential protective roles of... 

Lee Y, Howard LR and Villalon B. 1995. Flavonoids and antioxidant activity of fresh pepper (Capsicum annuum) cultivars. J Food Sci 60 473—476. 

Flavonoids protect LDL from oxidation, delaying the onset of lipid peroxidation, however, the prevention of atherosclerosis by flavonoids occurs not only by the inhibition of LDL oxidation, but also by the increase of cellular resistance to harmful effects of the oxidized LDL (de Luis and Aller, 2008). The antioxidant activity of anthocyanidins, as well as their protective role against LDL oxidation, has been well demonstrated in different in vitro systems (Aviram and Fuhrman, 2002 Satue-Gracia and others 1997 Teissedre and others 1996). 

Flavonoids are present in other beverages besides wine and tea. For example, pomegranate and cranberry juice contain high concentrations of polyphenols and a strong antioxidant activity against LDL oxidation. Their antioxidant capacity depends not only on the amount but also on the type of flavonoids present (Aviram and Fuhrman 2003). 

The foregoing method has been adapted by Davalos and others (2004) using a conventional fluorescence microplate reader and applied to pure compounds (benzoic and cinnamic acids and aldehydes, flavonoids, and butylated hydroxyanisole) and to wines, as well as to commercial dietary antioxidant supplements. Eberhardt and others (2005) have also proposed a similar method for the determination of the antioxidant activity in broccoli. 

Aaby K, Hvattum E and Skrede G. 2004. Analysis of flavonoids and other phenolic compounds using high-performance liquid chromatography with coulometric array detection relationship to antioxidant activity. J Agric Food Chem 52(15) 4595 1603. 

Bahomn T, Luximon-Ramma A, Crozier A and Aruoma OI. 2004. Total phenol, flavonoid, proantho-cyanidin and vitamin C levels and antioxidant activities of Mauritian vegetables. J Sci Food Agric 84(12) 1553-1561. 

Choi CW, Kim SC, Hwang SS, Choi BK, Ahn HJ, Lee MY, Park SH and Kim SK. 2002. Antioxidant activity and free radical scavenging capacity between Korean medicinal plants and flavonoids by assay-guided comparison. Plant Sci 163(6) 1161-1168. 

Yu J, Wang L, Walzem RL, Miller EG, Pike LM and Patil BS. 2005. Antioxidant activity of citrus limonoids, flavonoids, and coumarins. J Agric Food Chem 53(6) 2009—2014. 

Zhao M, Yang B, Wang J, Li B and Jiang Y. 2006. Identification of the major flavonoids from pericarp tissues of lychee fruit in relation to their antioxidant activities. Food Chem 98(3) 539—544. 

Antioxidant activity of flavonoids has already been shown about 40 years ago [90,91]. (Early data on antioxidant flavonoid activity are cited in Ref. [92].) Flavonoids are polyphenols, and therefore, their antioxidant activity depends on the reactivity of hydroxyl substituents in hydrogen atom abstraction reactions. As in the case of vitamins E and C, the most studied (and most important) reactions are the reactions with peroxyl radicals [14], hydroxyl radicals [15], and superoxide [16]. 

As mentioned above, in contrast to classic antioxidant vitamins E and C, flavonoids are able to inhibit free radical formation as free radical scavengers and the chelators of transition metals. As far as chelators are concerned their inhibitory activity is a consequence of the formation of transition metal complexes incapable of catalyzing the formation of hydroxyl radicals by the Fenton reaction. In addition, as shown below, some of these complexes, for example, iron- and copper-rutin complexes, may acquire additional antioxidant 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],... 

A comparison with its different derivatives shows that 4 -OH is not a sole reactive group responsible for the antioxidant activity of resveratrol, while the trans-conformation is absolutely necessary for the inhibition of cell proliferation [187], However, similar to flavonoids resveratrol may exhibit prooxidant properties, for example to promote DNA fragmentation, although its prooxidant activity seems to be unimportant under physiological conditions [188],... 

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