Quercetin biological effects

The biological effects of quercetin are believed to result from its antioxidant properties. Recently, it was clearly demonstrated that quercetin could function both as an antioxidant and a prooxidant, depending on concentration and free radical sources and their location in the cell. Also, quercetin was observed to be cytotoxic in a dose-dependent manner. Although the exact mechanism of cytotoxicity has not yet been fully elucidated, it may involve formation of 02 or its metabolite o-quinone (Fig. 7). Such species are known to be toxic and to bind irreversibly to various cell constituents by covalent binding with sulfhydryl groups or other essential groups. 

As detailed, a variety of biological effects of flavonoids may be related to their binding to ATP-binding sites of various proteins, including transport ATPases and protein kinases. In fact, quite a few commercially available protein kinase inhibitors have been developed on the basis of the stmcture of quercetin. These compounds include the widely used PI-3-K inhibitor LY294002 (IC50 1-5 pM the IC50 of quercetin is approximately 4—8 pM), the MEK inhibitor... 

Moskaug JO, Carlsen H, Myhrstad M, Blomhoff R (2004) Molecular imaging of the biological effects of quercetin and quercetin-rich foods. Mech Ageing Dev 125 315-324... 

Many flavonoids are subjected to enzymatic oxidation. Quercetin, one of the most famous flavonoids, has received much attention due to its interesting biological effects. The oxidation of quercetin by PPO was examined [51]. hi reaction monitoring by UV-vis spectroscopy, the peak at 291 nm increased, and the peak at 372 nm decreased. The oxidation was inhibited by the specific inhibitor for PPO (4-hexylresorcinol). 

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... 

Day, A.J. et al.. Conjugation position of quercetin glucuronides and effect on biological activity. Free Radical Biol Med, 29, 1234, 2000. 

Lopez-Lopez G, Moreno L, Cogolludo A, Galisteo M, Ibarra M, Duarte J, Tamargo J. 2004. NO scavenging and NO protecting effects of quercetin and their biological significance in vascular smooth muscle. Mol Pharmacol 65 851-859. 

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