Quercetin conjugates

The interaction of flavonoids with MDR proteins is of interest not only in the field of cancer prevention and therapy but also in the field of flavonoid bioavailability. Indeed, using specific inhibitors of MDR proteins, it was shown that multiresistant protein 2 (MRP2), but not Pgp, is involved in the efflux of quercetin conjugates from human hepatic cells. Similar observations were made with the cell line Caco-2 (a popular model for human intestinal absorption) where MRP2 was found responsible for the efficient efflux of chrysin after its conjugation into a mixture of glucuronide and sulfate. ... 

One of the main flavonols studied is quercetin. Indirect evidence for the presence of quercetin conjugates in humans was obtained by Manach et al [73], who found the presence of quercetin in plasma after the consumption of a complex meal rich in plant products only after P-glucuronidase and sulfatase treatment. Furthermore, the authors reported... 

A whole range of other quercetin conjugates such as quercetin-3-O-galacto-side, quercetin-3-O-rhamnoside, quercetin-3-O-xyloside, quercetin-3-O-rutino-side, quercetin-3-O-arabinopyranoside, and quercetin-3-O-arabinofuranoside are found in apples (Malus x domestica) (Fig. 1.4) [Marks et al., 2008]. 

Mochizuki M, Kajiya K, Terao J, Kaji K, Kumazawa S, Nakayama T, Shimoi K. 2004. Effect of quercetin conjugation on vascular permeability and expression of adhesion molecules. Biofactors 22 201-204. 

Moon J-H, Nakata R, Oshima S, Inakuma T, Terao J. 2000. Accumulation of quercetin conjugates in blood plasma after the short-term ingestion of onion by women. Am J Physiol 279 R461-R467. 

Donnini S, Finetti F, Lusini L, Morbidelli L, Oieynier V, Barron D, Williamson G, Waltenberger J, Ziche M (2006) Divergent effects of quercetin conjugates on angiogenesis. Br J Nutr 95 1016-1023... 

Also, Proteggente and coworkers [13] have found quercetin conjugates, as identified from the spectral characteristics, to be the main components in lettuce, which also contained small amounts of chlorogenic acid and anthocyanin... 

Janisch, K.M. et al. (2004) Properties of quercetin conjugates modulation of LDL oxidation and binding to human serum albumin. Free Radic Res 38 (8), 877-884... 

The main flavonols in onions are glycosylated derivatives, principally quercetin-4 -0-glucoside and quercetin-3,4 -O-diglucoside with smaller amounts of isorhamnetin-4 -0-glucoside (Figure 7.10) and other quercetin conjugates (Mullen et al. 2004). Yellow onions form one of the main sources of flavonols in the Northern European diet, the edible... 

Figure 8.4 The structures of the four major quercetin conjugates present in plasma following ingestion of a quercetin glucoside-rich meal.

The levels of the individual quercetin glucosides and quercetin aglycone were determined for the ethanol extracts from all the three onion powder samples. Changes in the composition of the quercetin conjugates due to drying... 

Cirillo G, Puoci F, lemma F, Curcio M, Parisi 01, Spizzirri UG, Altimari I, Picci N (2012). Starch-quercetin conjugate by radical grafting nthesis and biological characterization. Pharm DevTechnoI, 17, 466-476. 

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