Dietary quercetin supplements: Assessment of online product informations and quantitation of quercetin in the products by high‐performance liquid chromatography

Abstract

Administration of the increasingly popular dietary supplements containing quercetin may interfere with drug therapy. We intended to evaluate the online availability and quercetin content of the high‐dose mono‐component quercetin products and to review the potential use of quercetin products and their interactions with drugs. We monitored the online access to quercetin‐containing dietary supplements, collected the relevant information from the websites, procured selected products from the vendors, and subjected them to substance analysis. The quercetin content was quantified by an HPLC‐UV method. Twenty‐five websites offered mono‐component quercetin products, and nine products were procured. The quercetin content of eight products differed only ±10% from the nominal dose, whereas one product contained almost 30% more quercetin. Misleading indications such as antitumor and cardiovascular effects were often found on the sellers' websites. Quercetin‐containing dietary supplements are available online with misleading indications. The recommended daily doses are often high (occasionally over 1,000 mg), which may induce clinically relevant interactions with medications. Because high‐quercetin content of dietary supplements was confirmed, health care professionals should be aware of the unregulated internet market of dietary supplements and should consider the interactions of these substances with drugs.

Effects of Chrysin and Its Major Conjugated Metabolites Chrysin-7-Sulfate and Chrysin-7-Glucuronide on Cytochrome P450 Enzymes and on OATP, P-gp, BCRP, and MRP2 Transporters

“…Therefore, it is reasonable to hypothesize the low micromolar plasma concentrations of chrysin conjugates. In agreement with this hypothesis, the repeated administration of 1 g quercetin daily resulted in approximately 2 mM or even higher peak plasma concentration of quercetin conjugates (Conquer et al, 1998;Vida et al, 2019). Considering the above-listed data and our observations, the interactions of chrysin and/or it metabolites with CYP2C9, OATPs, and BCRP may have high pharmacological importance.…”

“…Since high dose flavonoid-containing dietary supplements are widely advertised and marketed on the Internet for various purported uses (Vida et al, 2019), there is a high probability that some people apply these supplements together with their prescribed medicines. Because the pharmacokinetic interactions of dietary supplements are poorly characterized, in this study, the interactions of chrysin and its main conjugates with CYP enzymes, OATP uptake transporters, and ABC exporters were examined.…”

“…Flavonoids are rapidly biotransformed in the body; typically their metabolites reach high concentrations in the systemic circulation (and likely in some tissues) (Manach et al, 2005). As previous studies demonstrated, flavonoids can interfere with the pharmacokinetics of simultaneously administered drugs due to interaction with biotransformation enzymes and drug transporters (Miron et al, 2017;Vida et al, 2019). Chrysin (5,7-dihydroxyflavone; Fig.…”

Testing the Pharmacokinetic Interactions of 24 Colonic Flavonoid Metabolites with Human Serum Albumin and Cytochrome P450 Enzymes

“…Therefore, flavonoid-containing dietary supplements are widely marketed through the Internet. Some of these dietary supplements contain extremely high doses of flavonoids (ranging from several hundreds to thousands of milligrams) [4,5]. Furthermore, flavonoids can interact with proteins involved in drug pharmacokinetics, such as serum albumin, biotransformation enzymes, and drug transporters [6][7][8].…”

“…After the high consumption of some fruits (e.g., cranberry), tea, and/or products produced from them, the plasma concentrations of certain microbial flavonoid metabolites can exceed 10 µM [26,27]. These observations suggest that some metabolites may also achieve relevant concentrations in tissues, which is likely enhanced by the extremely high intake of flavonoids through dietary supplements [4].…”