Quercetin

Last updated
Quercetin
Quercetin.svg
Quercetin-3D-balls.png
Names
Pronunciation /ˈkwɜːrsɪtɪn/
IUPAC name
3,3′,4′,5,7-Pentahydroxyflavone
Systematic IUPAC name
2-(3,4-Dihydroxyphenyl)-3,5,7-trihydroxy-4H-1-benzopyran-4-one
Other names
5,7,3′,4′-flavon-3-ol, Sophoretin, Meletin, Quercetine, Xanthaurine, Quercetol, Quercitin, Quertine, Flavin meletin
Identifiers
3D model (JSmol)
317313
ChEBI
ChEMBL
ChemSpider
DrugBank
ECHA InfoCard 100.003.807 OOjs UI icon edit-ltr-progressive.svg
EC Number
  • 204-187-1
579210
KEGG
PubChem CID
UNII
UN number 2811
  • InChI=1S/C15H10O7/c16-7-4-10(19)12-11(5-7)22-15(14(21)13(12)20)6-1-2-8(17)9(18)3-6/h1-5,16-19,21H Yes check.svgY
    Key: REFJWTPEDVJJIY-UHFFFAOYSA-N Yes check.svgY
  • InChI=1/C15H10O7/c16-7-4-10(19)12-11(5-7)22-15(14(21)13(12)20)6-1-2-8(17)9(18)3-6/h1-5,16-19,21H
    Key: REFJWTPEDVJJIY-UHFFFAOYAW
  • O=C1c3c(O/C(=C1/O)c2ccc(O)c(O)c2)cc(O)cc3O
Properties
C15H10O7
Molar mass 302.236 g/mol
Appearanceyellow crystalline powder [1]
Density 1.799 g/cm3
Melting point 316 °C (601 °F; 589 K)
Practically insoluble in water; soluble in aqueous alkaline solutions [1]
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
X mark.svgN  verify  (what is  Yes check.svgYX mark.svgN ?)
UV visible spectrum of quercetin, with lambda max at 369 nm Spectre UV vis Quercetine.PNG
UV visible spectrum of quercetin, with lambda max at 369 nm

Quercetin is a plant flavonol from the flavonoid group of polyphenols. It is found in many fruits, vegetables, leaves, seeds, and grains; capers, red onions, and kale are common foods containing appreciable amounts of it. [2] [3] It has a bitter flavor and is used as an ingredient in dietary supplements, beverages, and foods.

Contents

Occurrence

Quercetin is a flavonoid widely distributed in nature. [2] The name has been used since 1857, and is derived from quercetum (oak forest), after the oak genus Quercus . [4] [5] It is a naturally occurring polar auxin transport inhibitor. [6]

Quercetin is one of the most abundant dietary flavonoids, [2] [3] with an average daily consumption of 25–50 mg. [7]

FoodsQuercetin,
mg / 100 g
capers, raw234 [3]
capers, canned173 [3]
lovage leaves, raw170 [3]
dock like sorrel 86 [3]
radish leaves70 [3]
carob fiber58 [3]
dill weed, fresh55 [3]
coriander 53 [3]
yellow wax pepper, raw51 [3]
fennel leaves49 [3]
onion, red 32 [3]
radicchio 32 [3]
watercress 30 [3]
kale 23 [3]
chokeberry 19 [3]
bog blueberry 18 [3]
buckwheat seeds15 [3]
cranberry 15 [3]
lingonberry 13 [3]
plums, black 12 [3]

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. [8] One study found that organically grown tomatoes had 79% more quercetin than non-organically grown fruit. [9] Quercetin is present in various kinds of honey from different plant sources. [10]

Biosynthesis

In plants, 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. [11] One molecule of 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 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. [11]

Glycosides

3-O-Glycosides of quercetin 3-O-Glycosides of quercetin-en.svg
3-O-Glycosides of quercetin

Quercetin is the aglycone form of a number of other flavonoid glycosides, such as rutin (also known as quercetin-3-O-rutinoside) and quercitrin, found in citrus fruit, buckwheat, and onions. [2] 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. [12]

Several taxifolin (also known as dihydroquercetin) glycosides also exist. Isoquercetin is the 3-O-glucoside of quercetin.

Rutin degradation pathway

The enzyme quercitrinase can be found in Aspergillus flavus . [13] This enzyme hydrolyzes the glycoside quercitrin to release quercetin and L-rhamnose. It is an enzyme in the rutin catabolic pathway. [14]

Pharmacology

Pharmacokinetics

The bioavailability of quercetin in humans after oral intake is very low, with one study concluding it must be less than 1%. [15] Intravenous injection of quercetin shows a rapid decay in concentration described by a two-compartment model (initial half-life of 8.8 minutes, terminal half-life of 2.4 hours). [15] Because it undergoes rapid and extensive metabolism, the biological effects presumed from in vitro studies are unlikely to apply in vivo. [2] [16] [17] [18] Quercetin supplements in the aglycone form are less bioavailable than the quercetin glycoside often found in foods, especially red onions. [2] [19] Ingestion with high-fat foods may increase bioavailability compared to ingestion with low-fat foods, [19] and carbohydrate-rich foods may increase absorption of quercetin by stimulating gastrointestinal motility and colonic fermentation. [2] Whereas quercetin has been shown to be a potent anti-inflammatory compound in a variety of in vitro and in vivo bioassay models, oral quercetin in human subjects has not exhibited the desired effects. [20] Because of low solubility and poor bioavailability of quercetin, derivatives have been synthesized to overcome these challenges and enhance its biological activity, leading to compounds with improved properties for possible therapeutic applications. [21]

Metabolism

Quercetin is rapidly metabolized (via glucuronidation) after the ingestion of quercetin foods or supplements. [22] Five metabolites (quercetin glucuronides) have been found in human plasma after quercetin ingestion. [23] [22] Taken together, the quercetin glucuronides have a half-life around 11–12 hours. [22]

In rats, quercetin did not undergo any significant phase I metabolism. [24] In contrast, quercetin did undergo extensive phase II (conjugation) to produce metabolites that are more polar than the parent substance, hence are more rapidly excreted from the body. In vitro, the meta-hydroxyl group of catechol is methylated by catechol-O-methyltransferase. Four of the five hydroxyl groups of quercetin are glucuronidated by UDP-glucuronosyltransferase. The exception is the 5-hydroxyl group of the flavonoid ring, which generally does not undergo glucuronidation. The major metabolites of orally absorbed quercetin are quercetin-3-glucuronide, 3'-methylquercetin-3-glucuronide, and quercetin-3'-sulfate. [24] A methyl metabolite of quercetin has been shown in vitro to be more effective than quercetin at inhibiting lipopolysaccharide-activated macrophages. [18]

Compared to other flavonoids, quercetin is one of the most effective inducers of the phase II detoxification enzymes. [25]

In vitro studies show that quercetin is a strong inhibitor of the cytochrome P450 enzymes CYP3A4 and CYP2C19 and a moderate inhibitor of CYP2D6. [26] [27] Drugs that are metabolized by these pathways may have increased effect. An in vivo study found that quercetin supplementation slows the metabolism of caffeine to a statistically significant extent in a particular genetic subpopulation, but in absolute terms the effect was almost negligible. [28]

Food safety

In 2010, the U. S. Food and Drug Administration acknowledged high-purity quercetin as generally recognized as safe for use as an ingredient in various specified food categories at levels up to 500 mg per serving. [29]

Health claims

Quercetin has been studied in basic research and small clinical trials. [2] [30] [31] [32] While supplements have been promoted for the treatment of cancer and various other diseases, [2] [33] there is no high-quality evidence that quercetin (via supplements or in food) is useful to treat cancer [34] or any other disease. [2] [35]

The US Food and Drug Administration has issued warning letters to several manufacturers advertising on their product labels and websites that quercetin product(s) can be used to treat diseases. [36] [37] The FDA regards such quercetin advertising and products as unapproved – with unauthorized health claims concerning the anti-disease products – as defined by "sections 201(g)(1)(B) and/or 201 (g)(1)(C) of the Act [21 U.S.C. § 321(g)(1)(B) and/or 21 U.S.C. § 321(g)(1)(C)] because they are intended for use in the diagnosis, cure, mitigation, treatment, or prevention of disease", [36] [37] conditions not met by the manufacturers.

Safety

Little research has been conducted into the safety of quercetin supplementation in humans, and the results are insufficient to give confidence that the practice is safe. In particular, a lack of safety information exists on the effect of quercetin supplementation for pregnant women, breastfeeding women, children, and adolescents. The hormonal effects of quercetin found in animal studies raise the suspicion of a parallel effect in humans, particularly in respect of estrogen-dependent tumors. [38]

Quercetin supplementation can interfere with the effects of medications. The precise nature of this interaction is known for some common medicines, but for many, it is not. [38]

See also

Related Research Articles

<span class="mw-page-title-main">Flavonoid</span> Class of plant and fungus secondary metabolites

Flavonoids are a class of polyphenolic secondary metabolites found in plants, and thus commonly consumed in the diets of humans.

<span class="mw-page-title-main">Flavan-3-ol</span> Category of polyphenol compound

Flavan-3-ols are a subgroup of flavonoids. They are derivatives of flavans that possess a 2-phenyl-3,4-dihydro-2H-chromen-3-ol skeleton. Flavan-3-ols are structurally diverse and include a range of compounds, such as catechin, epicatechin gallate, epigallocatechin, epigallocatechin gallate, proanthocyanidins, theaflavins, thearubigins. They play a part in plant defense and are present in the majority of plants.

<span class="mw-page-title-main">Polyphenol</span> Class of chemical compounds

Polyphenols are a large family of naturally occurring phenols. They are abundant in plants and structurally diverse. Polyphenols include flavonoids, tannic acid, and ellagitannin, some of which have been used historically as dyes and for tanning garments.

<span class="mw-page-title-main">Phytochemical</span> Chemical compounds produced by plants

Phytochemicals are chemical compounds produced by plants, generally to help them resist fungi, bacteria and plant virus infections, and also consumption by insects and other animals. The name comes from Greek φυτόν (phyton) 'plant'. Some phytochemicals have been used as poisons and others as traditional medicine.

<span class="mw-page-title-main">Glycoside</span> Molecule in which a sugar is bound to another functional group

In chemistry, a glycoside is a molecule in which a sugar is bound to another functional group via a glycosidic bond. Glycosides play numerous important roles in living organisms. Many plants store chemicals in the form of inactive glycosides. These can be activated by enzyme hydrolysis, which causes the sugar part to be broken off, making the chemical available for use. Many such plant glycosides are used as medications. Several species of Heliconius butterfly are capable of incorporating these plant compounds as a form of chemical defense against predators. In animals and humans, poisons are often bound to sugar molecules as part of their elimination from the body.

<span class="mw-page-title-main">Naringenin</span> Chemical compound

Naringenin is a flavanone from the flavonoid group of polyphenols and is commonly found in a variety of citrus fruits and is the predominant flavonone in grapefruit. Naringenin has demonstrated numerous biological activities, including anti-inflammatory properties, antioxidant activity and skin healing. It is used as a cosmetic ingredient and dietary supplement.

<span class="mw-page-title-main">Rutin</span> Chemical compound

Rutin is the glycoside combining the flavonol quercetin and the disaccharide rutinose. It is a flavonoid glycoside found in a wide variety of plants, including citrus.

<span class="mw-page-title-main">Quercitrin</span> Chemical compound

Quercitrin is a glycoside formed from the flavonoid quercetin and the deoxy sugar rhamnose.

<span class="mw-page-title-main">Kaempferol</span> Chemical compound

Kaempferol (3,4′,5,7-tetrahydroxyflavone) is a natural flavonol, a type of flavonoid, found in a variety of plants and plant-derived foods including kale, beans, tea, spinach, and broccoli. Kaempferol is a yellow crystalline solid with a melting point of 276–278 °C (529–532 °F). It is slightly soluble in water and highly soluble in hot ethanol, ethers, and DMSO. Kaempferol is named for 17th-century German naturalist Engelbert Kaempfer.

<span class="mw-page-title-main">Myricetin</span> Chemical compound

Myricetin is a member of the flavonoid class of polyphenolic compounds, with antioxidant properties. Common dietary sources include vegetables, fruits, nuts, berries, tea, and red wine.

<span class="mw-page-title-main">Antioxidant effect of polyphenols and natural phenols</span>

A polyphenol antioxidant is a hypothetized type of antioxidant, in which each instance would contain a polyphenolic substructure; such instances which have been studied in vitro. Numbering over 4,000 distinct chemical structures, such polyphenols may have antioxidant activity {{{1}}} in vitro (although they are unlikely to be antioxidants in vivo). Hypothetically, they may affect cell-to-cell signaling, receptor sensitivity, inflammatory enzyme activity or gene regulation, although high-quality clinical research has not confirmed any of these possible effects in humans as of 2020.

<span class="mw-page-title-main">Flavones</span> Class of flavonoid chemical compounds

Flavones are a class of flavonoids based on the backbone of 2-phenylchromen-4-one (2-phenyl-1-benzopyran-4-one).

<span class="mw-page-title-main">Epigallocatechin gallate</span> Catechin (polyphenol) in tea

Epigallocatechin gallate (EGCG), also known as epigallocatechin-3-gallate, is the ester of epigallocatechin and gallic acid, and is a type of catechin.

In enzymology, a quercetin-3,3'-bissulfate 7-sulfotransferase is an enzyme that catalyzes the chemical reaction

<span class="mw-page-title-main">Phenolic content in wine</span> Wine chemistry

The phenolic content in wine refers to the phenolic compounds—natural phenol and polyphenols—in wine, which include a large group of several hundred chemical compounds that affect the taste, color and mouthfeel of wine. These compounds include phenolic acids, stilbenoids, flavonols, dihydroflavonols, anthocyanins, flavanol monomers (catechins) and flavanol polymers (proanthocyanidins). This large group of natural phenols can be broadly separated into two categories, flavonoids and non-flavonoids. Flavonoids include the anthocyanins and tannins which contribute to the color and mouthfeel of the wine. The non-flavonoids include the stilbenoids such as resveratrol and phenolic acids such as benzoic, caffeic and cinnamic acids.

<span class="mw-page-title-main">Fisetin</span> Chemical compound

Fisetin (7,3′,4′-flavon-3-ol) is a plant flavonol from the flavonoid group of polyphenols. It can be found in many plants, where it serves as a yellow/ochre colouring agent. It is also found in many fruits and vegetables, such as strawberries, apples, persimmons, onions and cucumbers. Its chemical formula was first described by Austrian chemist Josef Herzig in 1891.

<span class="mw-page-title-main">Isorhamnetin</span> Chemical compound

Isorhamnetin is an O-methylated flavon-ol from the class of flavonoids. A common food source of this 3'-methoxylated derivative of quercetin and its glucoside conjugates are pungent yellow or red onions, in which it is a minor pigment, quercetin-3,4'-diglucoside and quercetin-4'-glucoside and the aglycone quercetin being the major pigments. Pears, olive oil, wine and tomato sauce are rich in isorhamnetin. Almond skin is a rich source of isorhamnetin-3-O-rutinoside and isorhamnetin-3-O-glucoside, in some cultivars they comprise 75% of the polyphenol content, the total of which can exceed 10 mg/100 gram almond. Others sources include the spice, herbal medicinal and psychoactive Mexican tarragon (Tagetes lucida), which is described as accumulating isorhamnetin and its 7-O-glucoside derivate. Nopal is also a good source of isorhamnetin, which can be extracted by supercritical fluid extraction assisted by enzymes.

<span class="mw-page-title-main">Miquelianin</span> Chemical compound

Miquelianin is a flavonol glucuronide, a type of phenolic compound present in wine, in species of St John's wort, like Hypericum hirsutum, in Nelumbo nucifera or in green beans.

Quercetin 3-<i>O</i>-sulfate Chemical compound

Quercetin 3-sulfate is a plasma human metabolite of quercetin. It is the sulfate conjugate of quercetin.

References

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