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Abstract
Quercetin is an anti-oxidative flavonoid widely distributed in the plant kingdom.
Phenolic hydroxyl groups at the B-ring and the 3-position are responsible for its
free radical-scavenging activity. Quercetin is commonly present as a glycoside and
is converted to glucuronide/sulfate conjugates during intestinal absorption and only
conjugated metabolites are therefore found in circulating blood. Although metabolic
conversion attenuates its biological effects, active aglycone may be generated from
the glucuronide conjugates by enhanced beta-glucuronidase activity during inflammation.
With respect to its relationship with molecular targets relevant to cancer prevention,
quercetin aglycone has been shown to interact with some receptors, particularly an
aryl hydrocarbon receptor, which is involved in the development of cancers induced
by certain chemicals. Quercetin aglycone has also been shown to modulate several signal
transduction pathways involving MEK/ERK and Nrf2/keap1, which are associated with
the processes of inflammation and carcinogenesis. Rodent studies have demonstrated
that dietary administration of this flavonol prevents chemically induced carcinogenesis,
especially in the colon, whilst epidemiological studies have indicated that an intake
of quercetin may be associated with the prevention of lung cancer. Dietary quercetin
is, therefore, a promising agent for cancer prevention and further research is warranted.