|CAS number||, 6151-25-3 (Quercetin dihydrate)|
|Jmol-3D images||Image 1|
|Molar mass||302.236 g/mol|
|Appearance||yellow crystalline powder|
|Melting point||316 °C|
|Solubility in water||Practically insoluble in water; soluble in aqueous alkaline solutions|
|Except where noted otherwise, data are given for materials in their standard state (at 25 °C (77 °F), 100 kPa)|
|(what is: / ?)|
Quercetin //, a flavonol, is a flavonoid, in other words, a plant pigment with a molecular structure like or derived from flavone. It is found in fruits, vegetables, leaves and grains. It can be used as an ingredient in supplements, beverages, or foods.
- 1 Occurrence
- 2 Metabolism
- 3 Effects of consumption by humans and other animals
- 4 Preliminary research
- 5 Drug interactions
- 6 See also
- 7 References
- 8 External links
Quercetin is a flavonoid widely distributed in nature. The name has been used since 1857, and is derived from quercetum (oak forest), after Quercus. It is a naturally occurring polar auxin transport inhibitor.
|Foods containing quercetin||Quercetin (mg/100g of edible portion)|
|dock like sorrel||86|
|Hungarian wax pepper||51|
|sea buckthorn berry||8|
|prickly pear cactus fruits||5|
|apples, Red Delicious||4|
|tea, black or green Camellia sinensis||2|
In red onions, higher concentrations of quercetin occur in the outermost rings and in the part closest to the root, the latter being the part of the plant with the highest concentration. One study found that organically grown tomatoes had 79% more quercetin than chemically grown fruit. Quercetin is present in various kinds of honey from different plant sources.
Phenylalanine is converted to 4-coumaroyl-CoA in a series of steps known as the general phenylpropanoid pathway using phenylalanine ammonia-lyase, cinnamate-4-hydroxylase, and 4-coumaroyl-CoA-ligase. 4-Coumaroyl-CoA is added to three molecules of malonyl-CoA to form tetrahydroxychalcone using 7,2’-dihydroxy-4’-methoxyisoflavanol synthase. Tetrahydroxychalcone is then converted into naringenin using chalcone isomerase. Naringenin is then converted into eriodictyol using flavanoid 3’-hydroxylase. Eriodictyol is then converted into dihydroquercetin with flavanone 3-hydroxylase, which is then converted into quercetin using flavonol synthase.
Quercetin release in the rutin degradation pathway
Quercetin 3-O-sulfate is a human plasma quercetin metabolite.
Quercetin is the aglycone form of a number of other flavonoid glycosides, such as rutin and quercitrin, found in citrus fruit, buckwheat and onions. Quercetin forms the glycosides quercitrin and rutin together with rhamnose and rutinose, respectively. Likewise guaijaverin is the 3-O-arabinoside, hyperoside is the 3-O-galactoside, isoquercitin is the 3-O-glucoside and spiraeoside is the 4'-O-glucoside. CTN-986 is a quercetin derivative found in cottonseeds and cottonseed oil. Miquelianin is the quercetin 3-o-β-d-glucuronopyranoside.
Fate in vivo
Effects of consumption by humans and other animals
Quercetin itself (aglycone quercetin), as opposed to quercetin glycosides, is not a normal dietary component. In a bioavailability study in rats, radiolabelled quercetin-4'-glucoside was converted to phenolic acids as it passed through the gastrointestinal tract, producing compounds not monitored in previous animal studies of aglycone quercetin. All but 4% was recovered within 72 hours (69% in urine), indicating low retention and high excretion, a characteristic of ingested polyphenols. Quercetin may also induce insulin secretion by activation of L-type calcium channels in the pancreatic β-cells.
Quercetin has not been confirmed scientifically as a specific therapeutic for any condition nor approved by any regulatory agency. The European Food Safety Authority evaluated possible health claims associated with consumption of quercetin, finding that no cause-and-effect relationship has been established for any physiological effect.
Quercetin has demonstrated significant anti-inflammatory activity in mouse models of asthma because of direct inhibition of several initial processes of inflammation.
Laboratory studies have investigated quercetin's potential for use in anti-cancer applications. The American Cancer Society says while quercetin "has been promoted as being effective against a wide variety of diseases, including cancer," and "some early lab results appear promising, as of yet there is no reliable clinical evidence that quercetin can prevent or treat cancer in humans." In the amounts consumed in a healthy diet, quercetin "is unlikely to cause any major problems or benefits."
Serum IgE levels are highly elevated in eczema patients, and virtually all eczema patients are positive for allergy testing. Excessive histamine release can be minimized by the use of antioxidants. Quercetin has been shown to be effective in reducing IgE levels in rodent models.
Quercetin has been reported to be of use in alleviating symptoms of pollinosis. An enzymatically modified derivative was found to alleviate ocular but not nasal symptoms of pollinosis.
A study with rats showed that quercetin effectively reduced immediate-release niacin (vitamin B3) flush, in part by means of reducing prostaglandin D2 production. A pilot clinical study of four humans gave preliminary data supporting this.
Quercetin has been shown to increase energy expenditure in rats, but only for short periods (fewer than 8 weeks). Effects of quercetin on exercise tolerance in mice have been associated with increased mitochondrial biogenesis. In mice, an oral quercetin dose of 12.5 to 25 mg/kg increased gene expression of mitochondrial biomarkers and improved exercise endurance. Quercetin was also demonstrated to act as agonist of PPARgamma, nuclear receptor that is current pharmacological target for the treatment of metabolic disorders such as diabetes type 2.
Supplements of quercetin with vitamin C and niacin does not cause any significant difference in body mass or composition and has no significant effect on inflammatory markers, diagnostic blood chemistries, blood pressure, and blood lipid profiles.
Possibly an active component of heather (Calluna vulgaris), quercetin was suspected from a bioassay test on crude extracts to selectively inhibit monoamine oxidase, possibly indicating pharmacological properties.
Quercetin is contraindicated with some antibiotics; it may interact with fluoroquinolones (an antibiotic), as quercetin competitively binds to bacterial DNA gyrase. Whether this inhibits or enhances the effect of fluoroquinolones is not certain.
AHFS Drug Information (2010) identifies quercetin as an inhibitor of CYP2C8, and specifically names it as a drug with potential to have harmful interactions with taxol/paclitaxel. As paclitaxel is metabolized primarily by CYP2C8, its bioavailability may be increased unpredictably, potentially leading to harmful side-effects.
Quercetin is described as an inhibitor of CYP2C9. Quercetin is an inhibitor and inducer of CYP3A4 (in other words, it reduces the enzyme's activity in the short term, but the body responds by producing more of it). CYP2C9 and CYP3A4 are members of the cytochrome P450 mixed-function oxidase system, and as such are enzymes involved in the metabolism of xenobiotics in the body. In either case, quercetin may alter serum levels and, therefore, effects of drugs metabolized by these enzymes.
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