Flavonol supplements

The raison d etre for the proliferation of flavone and flavonol glycosides in nature continues to intrigue plant scientists. The ability of UV-B radiation to damage DNA, RNA, and proteins as well as to impair processes like photosynthesis is well known. Most flavonoids are very efficient antioxidants and chemoprotectants, and are therefore used in a plethora of food supplements and nutraceuticals [30]. Some flavonoids, however, have a Janus face - they could be excellent antioxidants but also have negative features. 

Fig. 53.7 Biosynthesis of natural and unnatural flavonoids and stillxaies in E. coli. Supplementation of unnatural synthesized carboxylic acids and natural carboxylic acids in E. coli recombinants produced unnatural and natural respective chalcones, flavanones, flavones, flavonols, and stilbenes. The red circle shown in the figure is one of the structure/groups shown in the inset...

Phenolic substances in red wine were shown to inhibit LDL oxidation in vitro [95]. In previous studies, red wine-derived phenolic acids [115,116], resveratrol [117], flavonols (quercetin, myricetin) [68,118,119], catechins [66,120], and the grape extract itself [121,122] have been shown to possess antioxidant properties. The finding that ethanol and wine stripped of phenols did not affect LDL oxidation further confirmed that the active antioxidant components in red wine are phenolic compounds [123]. Red wine fractionation revealed major antioxidative potency to monomeric catechins, procyanidins, monomeric anthocyanidins, and phenolic acids [123]. The flavonol quercetin and the flavonol catechin were both tested for antioxidative and antiatherogenic effects in the atherosclerotic E° mice [111]. E° mice at the age of 4 weeks were supplemented for up to 6 weeks in their drinking water with placebo (1.1% alcohol) or with catechin or quercetin (50 pg/day/mouse). The atherosclerotic lesion area was smaller by 39% or by 46%, respectively, in the treated mice than in E° mice that were treated with placebo (Fig. 4A-E). 

Fig. 4 Structures of phytochemical components in dietary supplements undergoing evaluation of benefits in chronic diseases (+)-catechin (a flavanol), quercetin (a flavonol), resveratrol (a stilbenoid), lycopene (a carotenoid), genistein (an isoflavone) and puerarin and daidzin (8-C- and 7-O-glucosides of the isoflavone daidzein). They are each drawn so that the A ring is in the same orientation...

---