Quercetin metabolites

Shirai, M., Moon, J.H., Tsushida, T., and Terao, J., Inhibitory effect of a quercetin metabolite, quercetin 3-0-p-D-glucuronide, on lipid peroxidation in liposomal membranes, J. Agric. Food Chem., 49, 5602, 2001. 

Manach, C. et al.. Quercetin metabolites in plasma of rats fed diets containing rutin or quercetin, J. Nutr., 125, 1911, 1995. 

Justino GC, Santos MR, Canario S, Borges C, Florencio MH, Mira L. 2004. Plasma quercetin metabolites Structure-antioxidant activity relationships. Arch Biochem Biophys 432 109-121. 

Conjugated metabolites delivered to the liver are metabolized by hepatic phase II enzymes. The latter were reported to convert conjugated quercetin metabolites to a wide variety of their conjugates with and without deconjugation [Day et al., 1998 van de Woude et al., 2004]. Conjugated metabolites are released into the circulation after secondary metabolism in the liver. Considerable amounts of conjugated metabolites also simultaneously enter bile and return to the intestinal tract together with bile components. This enterohepatic circulation should be considered if the overall bioavailability of flavonols is discussed. 

In human plasma, quercetin metabolites transiently increased at 1 pM after the intake of a flavonol-rich diet [Hollman et al., 1995], after which concentration gradually decreased to nearly zero in <8 h [Manach et al., 1997]. Continuous ingestion of flavonol-rich foods may maintain a low level of quercetin metabolites in plasma, but this baseline level may be greatly influenced by individual differences [Moon et al., 2000]. 

Whether or not dietary quercetin and other flavonols can accumulate in internal organs is controversial. It is unclear if they accumulate in the human body, but dietary quercetin was found to be distributed in each organ in experimental animals [de Boer et al., 2005]. In rats fed 0.1% quercetin for 11 weeks, the highest accumulation was in the lungs. Low amounts of quercetin metabolites were detected in the brain. This indicates that quercetin metabolites can access the central nervous system by passing the blood-brain barrier, although the mechanism of this passage is incompletely understood. 

Table 8.1 Biological Activities of Conjugated Quercetin Metabolites...

Figure 8.5 Detection of quercetin metabolites in human atherosclerotic aorta using Q3GA-specific monoclonal antibody mAbl4A2. (Data from Kawai et al. [2008].)...

Murota K, Hotta A, Ido H, Kawai Y, Moon J-H, Sekido K, Hayashi H, Inakuma T, Terao J. 2007. Antioxidant capacity of albumin-bound quercetin metabolites after onion consumption in humans. J Med Invest 54 37-374. 

To study the interaction between dsDNA and quercetin metabolites, a multi-layer newly prepared biosensor is immersed for 10 min in a solution of 100 pM quercetin. After incubation, the biosensor is washed in water and transferred to another electrochemical cell that contains only pure supporting electrolyte. A... 

Wang L, Morris ME (2005) Liquid chromatography-tandem mass spectroscopy assay for quercetin and conjugated quercetin metabolites in human plasma and urine. J Chromatogr B 821 194-201... 

Table 13.4 Recent reports on biological activity of quercetin metabolites in relation to antiatherosclerotic effect.

Fig. 13.8 Proposed mechanism for the antiatherosclerotic action of quercetin metabolites.

Yamamoto N, Moon JH, Tsushida T, Nagao A, Terao J. Inhibitory effect of quercetin metabolites and their related derivatives on copper ion-induced hpid peroxidation in human low-density lipoprotein. Arch Biochem Biophys 1999 372 347-354. 

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