Web site: "Information
About Herbs, Botanicals and Other Products"
URL: http://www.mskcc.org/aboutherbs
© 2003 Memorial Sloar-Kettering Cancer Center
(Monograph)
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Full Text |
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Barrie Cassileth
and K. Simon Yeung
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Quercetin
(3,3’,4’,5,7-pentapentahydroxyflavone)
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| Clinical Summary |
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Quercetin
is a flavonol that constitutes the major bioflavonoid sources in the human
diet. The glycoside form is readily available in dietary plants such as
teas, onions, apple and buckwheat. Quercetin is thought to have
antioxidant, anti-inflammatory and anti-allergy properties. In vitro data
suggest quercetin may have anti-cancer effects, but more clinical study is
needed to explore this potential. No significant adverse events have been
reported for this product.
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| Scientific Name |
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3,3’,4’,5,7-pentapentahydroxyflavone
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| Also Known As |
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Polyphenolic
flavonoid
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| Food Sources |
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Teas,
onions, apples, buckwheat
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| Purported Uses |
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• Allergies
• Cancer
prevention
• Cancer
treatment
• Cardiovascular
disease
• Inflammation
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Mechanism Of Action
[1], [2], [6], [7], [8], [9], [10] |
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Quercetin
constitutes the major bioflavonoid in the human diet. Its antioxidant
activity is due to the reactivity of its phenolic group, which reacts with
free radicals to form the more stable phenoxy radicals. Quercetin is
thought to have anti-inflammatory and anti-allergy properties. The
proposed mechanism of action is inhibition of lipoxygenase and
cyclooxygenase resulting in reduced production of inflammatory mediators
(e.g., leukotrienes and histamine). Quercetin appears to inhibit
cyclooxygenase to a greater degree than lipoxygenase. It also has been
shown to have membrane-stabilizing capabilities and to inhibit aldose
reductase and low-density lipoprotein oxidation. Significant antiviral
activity has been shown in vitro and in vivo. Proposed anti-cancer
mechanisms of action include down-regulation of mutant p53 proteins; G1
phase arrest; tyrosine kinase inhibition; estrogen receptor binding;
inhibition of heat shock proteins; and RAS protein expression inhibition.
Presently, considerable in vitro data support the concept of quercetin as
an anti-cancer compound. However, clinical studies that support these uses
are few and the results are mixed.
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Pharmacokinetics
[1], [2], [3] |
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Absorption
Following oral administration, quercetin glycosides are absorbed from the
gut. These glycosides may then undergo hydrolysis in the enterocyte via
b-glucosidases before draining into the portal vein. Absorption rate from
dietary sources is influenced by the position and chemical nature of the
glycoside in combination with the various compounds in the food matrix.
Distribution
Quercetin is found predominantly in plasma in the form of its conjugates
(e.g., quercetin glucuronides and/or sulfates) and small amounts of
unconjugated quercetin aglycone. Maximum plasma concentrations are
achieved within the first two hours of administration. This suggests that
the absorption site is in the upper gut compartment, and may rule out
intestinal bacteria degradation.
Excretion
Previous pharmacokinetic studies using intravenous administration suggest
that quercetin is quickly eliminated in humans, with an approximate
elimination half-life of less than two hours. Several studies report that
quercetin is present in urine as conjugates of glucuronic acid and sulfate
groups.
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| Adverse Reactions
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No
adverse effects have been reported with single oral doses up to 4 grams.
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Drug Interactions
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Papain
and Bromelain: May assist the absorption of Quercetin in the
intestine.
Quinolone antibiotic: Quercetin may compete for DNA
gyrase binding sites on bacteria.
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| Literature Summary And Critique |
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Shoskes
D, et al. Quercetin
in men with category III chronic prostatitis: a preliminary prospective,
double-blind, placebo-controlled trial. Urology 1999;54:960-3.
Thirty men with chronic pelvic pain syndrome received either placebo or
500 mg of quercetin orally twice a day for 1 month. 67% of the patients
taking quercetin as compared to 20% of patients from the placebo
group had an at least 25% improvement of symptoms. A follow-up unblinded,
open-label study suggested that bromelain and papain can enhance the
absorption of quercetin.
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Beatty
E, et al. Effect
of dietary quercetin on oxidative DNA damage in healthy human subjects. Br
J Nutr
2000;84:919-25.
Thirty-six
subjects participated in this randomized crossover study. They were given
either a low-flavonol or a high-flavonol diet for 14 days. The study was
designed to detect a change of 20% in DNA damage products (p<0.05).
Although the plasma quercetin levels were higher in the high-flavonol
group, no significant difference in oxidative damage in leucocytes
was found between groups.
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| References |
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[1] Lamson
DW, Brignall MS. Antioxidant and cancer III: quercetin. Altern Med Rev
2000;5:196-208.
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[2] Graefe
EU, et al. Pharmacokinetics
and bioavailability of the flavonol quercetin in humans. Int J Clin
Pharmacol Therapy 1999;37:219-33.
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[3] Erlund
I, et al. Pharmacokinetics of quercetin aglycone and rutin in healthy volunteers. Eur
J Clin Pharmacol
2000;56:545-53.
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[4] Sampson
S, et al. Flavonol
and flavone intakes in US health professionals. J Am Diet Assoc
2002;102:1414-20.
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[5]
Herr,
SM. Herb-Drug Interaction Handbook. Chuch Street books. 2nd
ed. Nassau NY 2002.
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[6]
Shoskes
D, et al. Quercetin
in men with category III chronic prostatitis: a preliminary prospective,
double-blind, placebo-controlled trial. Urology 1999;54:960-3.
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[7]
Janssen
K, et al. Effects of the flavonoids quercetin and apigenin on hemostasis
in healthy volunteers: results from an in vitro and dietary supplement
study. Am J Clin
Nutr
1998;67:255-62.
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[8]
Chopra
M, et al. Nonalcoholic red wine extract and quercetin inhibit LDL
oxidation without affecting plasma antioxidant vitamin and carotenoid
concentrations. Clin
Chem
2000;46:1162-70.
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[9]
Beatty
ER, et al. Effect
of dietary quercetin on oxidative DNA damage in healthy human subjects. Br
J Nutr
2000;84:919-25.
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[10]
Ferry
DR, et al. Phase
I clinical trial of the flavonoid quercetin: pharmacokinetics and evidence
for in vivo tyrosine kinase inhibition. Clin Cancer Res
1996;2:659-68
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| Written |
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11/18/2002 |
| Updated |
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11/25/2002
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Disclaimer: http://www.mskcc.org/mskcc/print/11790.cfm |
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Source:
http://www.mskcc.org/mskcc/print/11571.cfm?RecordID=550 |
