Flavonoids antioxidant effect

Erlejman AG, Verstraeten SV, Fraga CG, Oteiza PI. 2004. The interaction of flavonoids with membranes Potential determinant of flavonoid antioxidant effects. Free Radic Res 38 1311-1320. 

Among the plant phenols, the flavonoids and the anthocyanidins, belonging to the 1,3-diphenylpropans, have been studied in most detail, mainly because of their potential health benefits. With more than 4,000 different flavonoids known, systematic studies of the effects of variation in molecular structure on physico-chemical properties of importance for antioxidative effects have also been possible (Jovanovic et al, 1994 Seeram and Nair, 2002). Flavonoids were originally found not to behave as efficiently as the classic phenolic antioxidants like a-tocopherol and synthetic phenolic antioxidants in donating... 

There has been some evidence of a higher antioxidant effect when both flavonoids and a-tocopherol are present in systems like LDL, low-density lipoproteins (Jia et al., 1998 Zhu et al, 1999). LDL will incorporate a-tocopherol, while flavonoids will be present on the outside in the aqueous surroundings. A similar distribution is to be expected for oil-in-water emulsion type foods. In the aqueous environment, the rate of the inhibition reaction for the flavonoid is low due to hydrogen bonding and the flavonoid will not behave as a chain-breaking antioxidant. Likewise, in beer, none of the polyphenols present in barley showed any protective effect on radical processes involved in beer staling, which is an oxidative process (Andersen et al, 2000). The polyphenols have, however, been found to act synergistically... 

Flavonoids are chain-breaking antioxidants in lipid-like solvents like chlorobenzene, although the k(inh) is smaller than for a-tocopherol and the lag-phase accordingly less evident. For peroxidating lipids in chlorobenzene the clear lag-phase for a-tocopherol became longer when quercetin or catechin were present. The effect appears to be additive and a regeneration of a-tocopherol by quercetin or catechin in this lipid-like solvent should rather be termed a co-antioxidative effect (Pedrielli and Skibsted, 2002). 

Knowledge of the identity of phenolic compounds in food facilitates the analysis and discussion of potential antioxidant effects. Thus studies of phenolic compounds as antioxidants in food should usually by accompanied by the identification and quantification of the phenols. Reversed-phase HPLC combined with UV-VIS or electrochemical detection is the most common method for quantification of individual flavonoids and phenolic acids in foods (Merken and Beecher, 2000 Mattila and Kumpulainen, 2002), whereas HPLC combined with mass spectrometry has been used for identification of phenolic compounds (Justesen et al, 1998). Normal-phase HPLC combined with mass spectrometry has been used to identify monomeric and dimeric proanthocyanidins (Lazarus et al, 1999). Flavonoids are usually quantified as aglycones by HPLC, and samples containing flavonoid glycosides are therefore hydrolysed before analysis (Nuutila et al, 2002). 

PEDRIELLI p, PEDULLi G F and SKIBSTED L H (2001a) Antioxidant mechanism of flavonoids. Solvent effect on rate constant for chain-braining reaction of quercetin and epicatechin in autoxidation of methyl linoleate, JAgric Food Chem, 49, 3034-40. 

YOUNG J F, DRAGSTED L O, HARALDSDOTTIR J, DANESHVAR B, KALL M A, LOFT S, NILSSON L, NIELSEN S E, MAYER B, SKIBSTED L H, HUYNH-BA T, HERMETTER A and SANDSTROM B (2002) Green tea extract only affects markers of oxidative status postprandially lasting antioxidant effect of flavonoid-free diet, Brit J Nutr, 87, 343-55. 

This method is also used to measure ex vivo low-density lipoprotein (LDL) oxidation. LDL is isolated fresh from blood samples, oxidation is initiated by Cu(II) or AAPH, and peroxidation of the lipid components is followed at 234 nm for conjugated dienes (Prior and others 2005). In this specific case the procedure can be used to assess the interaction of certain antioxidant compounds, such as vitamin E, carotenoids, and retinyl stearate, exerting a protective effect on LDL (Esterbauer and others 1989). Hence, Viana and others (1996) studied the in vitro antioxidative effects of an extract rich in flavonoids. Similarly, Pearson and others (1999) assessed the ability of compounds in apple juices and extracts from fresh apple to protect LDL. Wang and Goodman (1999) examined the antioxidant properties of 26 common dietary phenolic agents in an ex vivo LDL oxidation model. Salleh and others (2002) screened 12 edible plant extracts rich in polyphenols for their potential to inhibit oxidation of LDL in vitro. Gongalves and others (2004) observed that phenolic extracts from cherry inhibited LDL oxidation in vitro in a dose-dependent manner. Yildirin and others (2007) demonstrated that grapes inhibited oxidation of human LDL at a level comparable to wine. Coinu and others (2007) studied the antioxidant properties of extracts obtained from artichoke leaves and outer bracts measured on human oxidized LDL. Milde and others (2007) showed that many phenolics, as well as carotenoids, enhance resistance to LDL oxidation. 

Takamatsu S, Galal AM, Ross SA, Ferreira D, ElSohly MA, Ibrahim ARS and El-Feraly FS. 2003. Antioxidant effect of flavonoids on DCF production in HL-60 cells. Phytother Res 17(8) 963—966. 

Huge literature on biological functions of flavonoids and their antioxidant and free radical scavenging activities successfully competes with work on antioxidant effects of vitamins E and C. Flavonoids have been reported to exert multiple biological effects and exhibit antiinflammatory, antiallergic, antiviral, and anticancer activities [85 89], However, considering flavonoids as the inhibitors of free radical-mediated processes, two types of their reactions should be discussed flavonoids as free radical scavengers (antioxidants) and flavonoids as metal chelators. 

It must be noted that the inhibitory effects of flavonoids and other antioxidants in nonhomogenous biological systems can depend not only on their reactivities in reactions with free radicals (the chain-breaking activities) but also on the interaction with biomembranes. Thus, Saija et al. [137] compared the antioxidant effects and the interaction with biomembranes of four flavonoids quercetin, hesperetin, naringen, and rutin in iron-induced... 

At present, considerable interest is drawn to the use of natural mixtures of antioxidants isolated from various vegetable materials. Some authors claim that such mixtures manifest stronger antioxidant effects than individual components due to synergistic interactions. It is of course quite possible, but it should be noted that synergistic interactions are not a single mechanism of the interaction between components for example, the simultaneous presence of the antioxidant and prooxidant flavonoids might diminish summary antioxidant effect of the mixture. Furthermore, natural mixtures contain, as a rule, some unknown compounds, which affect the summary effect by unknown manner. 

It has been established that the free radical scavenger activity of flavonoids is responsible for the antioxidant effect [95,96], The beneficial antitumour effect of quercetin has also been demonstrated [97,98],... 

Kamalakkannan N, Prince PS. (2006) Antihyperglycaemic and antioxidant effect of rutin, a polyphenolic flavonoid, in streptozotocin-induced diabetic wistar rats. Basic Clin Pharmacol Toxicol 98 97-103. 

Resveratrol is another type of polyphenol, a stilbene derivative, that has assumed greater relevance in recent years as a constituent of grapes and wine, as well as other food products, with antioxidant, anti-inflammatory, anti-platelet, and cancer preventative properties. Coupled with the cardiovascular benefits of moderate amounts of alcohol, and the beneficial antioxidant effects of flavonoids, red wine has now emerged as an unlikely but most acceptable medicinal agent. 

Mainly during the last decade structural information regarding flavonoids associated with other molecules has been reported. High-resolution H magic angle spinning (MAS) NMR spectroscopy has been used to investigate the structural basis for the antioxidative effects of... 

O Byrne, D.J., Devaraj, S., Grundy, S.M., and Jialal, I., Comparison of the antioxidant effects of Concord grape juice flavonoids alpha-tocopherol on markers of oxidative stress in healthy adults. Am. J. Clin. Nutr., 76, 1367, 2002. 

Zi, X.L. et al., A flavonoid antioxidant, silymarin, inhibits activation of erbBl signaling and induces cyclin-dependent kinase inhibitors, G1 arrest and anticarcinogenic effects in human prostate carcinoma DU145 cells, Cancer Res., 58, 1920, 1998. 

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