Dietary flavonoids antioxidant activity

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. 

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. 

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],... 

Because of human consumption of plant and plant products, there has been much interest on the impact of flavonoids on human health and this has been recently reviewed [149, 150 and ref therein]. Additionally, Passamonti et al. [151] have recently reviewed the issue of bioavailability of dietary flavonoids. Citrus flavonoids have been shown to have many beneficial effects on human health including anti-inflammatory activity, anticancer activity, antioxidant activity, and protection against coronary heart disease [reviewed in 152-154]. This has led to... 

Dangles, O. and Dufour, C., Antioxidant activity of dietary flavonoids, in Proceedings of the Xlth Biennial Meeting of the Society for Free Radical Research, Pasquier, C., Ed., 2002, 533. 

Other potential health benefits of dietary flavonoids are too numerous to mention here. Suffice it to say that our understanding of the importance of flavonoids in the human diet is continuing to advance rapidly. One suspects that much of the physiological activity associated with flavonoids can be attributed to (i) their proven effectiveness as antioxidants and free radical scavengers, (ii) to their metal complexing capabilities (a capability that drove early advances in absorption spectroscopy and NMR studies), and (iii) to their ability to bind with a high degree of specificity to proteins. 

Tea is another important dietary source for flavonoids, In fact, about half of the flavonoid intake in western populations is derived from black tea. Tea was the major source of flavonoids in the Dutch [6,13] and Welsh studies [17]. Only a small number of studies investigated the association between tea consumption and cardiovascular disease risk. No association between tea consumption and cardiovascular disease risk were reported in Scottish men and women [28] and in U.S. men in the Health Professionals follow-up study [29]. However, in a Norwegian population an inverse association was reported between tea intake, serum cholesterol, and mortality from coronary heart disease [30]. Several studies reported that tea consumption did not affect plasma antioxidant activity [31] and hemostatic factors [32]. However, a recent prospective study (the Rotterdam study) of 3,454 men and women 55 years and older followed for 2 to 3 years, showed a significant, inverse association of tea intake with severe (> 5 cm the length of the calcified area) aortic atherosclerosis. Odds ratios decreased approximately 70 % for drinking more than 500 mL/day (4 cups per day). The associations were stronger in women than in men. However, the risk reductions for moderate and mild atherosclerosis were only weak or absent [33]. 

Recent evidence on the bioavailability and metabolism of these compounds in vivo suggests that dietary flavonoids are less likely to act as antioxidants. Most flavonoids may not have significant antioxidant activity in vivo for two reasons (1) bioavailability of dietary flavonoids is very poor (their concentration in vivo... 

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. 

Laughton MJ, Evans PJ, Moroney MA, et al, Inhibition of mammalian 5-lipoxygenase by flavonoids and phenolic dietary additives, Relationship to antioxidant activity and iron ion-reducing ability. Biochem Pharmacol 1991 42 1 673-1 681. 

Anthocyanins are a proanthocyanidin-type of flavonoid distributed in various fruits. These anthocyanins are the most important visible plant pigments in the natural kingdom. Anthocyanins have been clinically used in many folklore medicines worldwide for the treatment of age-related diseases and other disease. This review presents the functionality of anthocyanins in relation to their chemistry, synthetic pathway, antioxidant activity, antitumor activity (including apoptosis-inducing activity), pharmacodynamics (absorption, metabolism, distribution, and excretion) and toxicity, and discusses their possible use as food and dietary supplements and usage in potential nutraceuticals. 

It is difficult to tell how much dietary flavonoids contribute to our free radical defense system they have a high pro-oxidant activity and are poorly absorbed. Nonetheless, we generally consume large amounts of flavonoids (approximately 800 mg/day), and there is evidence that they can contribute to the maintenance of vitamin E as an antioxidant. 

In this chapter, the phenolic composition and content of regularly consumed fruits and vegetables are extensively discussed through the analysis of the current relevant literature, in order to provide a comprehensive summary of the current compositional and quantitative data on some flavonoid-rich foods. Furthermore, the formal relation of the in vitro antioxidant potential of these fruits and vegetables to the quality of the phenolic and, to a lesser extent, vitamin C content is emphasized. The potential for antioxidant activity of flavonoid-rich fruits and vegetables in vivo is also discussed. The data described here allow identification of the potentially most effective fruits and vegetables in terms of phenolic content and antioxidant activity. However, much research is still needed the elucidation of the metabolism and bioavailability of flavonoids in vivo, as well as of the amounts and the forms in which they are taken up into cells and tissues, is cmcial in order to establish the mechanisms and the forms in which dietary phenolics may act in vivo [58]. Finally, it... 

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