The flavonoid isoquercitrin (quercetin-3-O-β-d-glucopyranoside) is commonly found in medicinal herbs, fruits, vegetables and plant-derived foods and beverages. This article reviews the occurrence, preparation, bioavailability, pharmacokinetics, toxicology and biological activity of isoquercitrin and "enzymatically modified (α-glucosylated) isoquercitrin" (EMIQ). Pure isoquercitrin can now be obtained on a large scale by enzymatic rutin hydrolysis with α-l-rhamnosidase. Isoquercitrin has higher bioavailability than quercetin and displays a number of chemoprotective effects both in vitro and in vivo, against oxidative stress, cancer, cardiovascular disorders, diabetes and allergic reactions. Although small amounts of intact isoquercitrin can be found in plasma and tissues after oral application, it is extensively metabolized in the intestine and the liver. Biotransformation of isoquercitrin includes deglycosylation, followed by formation of conjugated and methylated derivatives of quercetin or degradation to phenolic acids and carbon dioxide. The acceptable daily intake of (95%) isoquercitrin and of EMIQ was estimated to be 5.4 and 4.9mg/kg/day, respectively. Adverse effects of higher doses in rats included mostly (benign) chromaturia; nevertheless some drug interactions may occur due to the modulation of the activity and/or expression of drug metabolizing/transporting systems. With respect to the safety, affordability and beneficial pharmacological activities, highly pure isoquercitrin is a prospective substance for food supplementation.

Department of Medical Chemistry and Biochemistry Faculty of Medicine and Dentistry Palacký University Hněvotínská 3 CZ 775 15 Olomouc Czech Republic

Department of Medical Chemistry and Biochemistry Faculty of Medicine and Dentistry Palacký University Hněvotínská 3 CZ 775 15 Olomouc Czech Republic; Centre of Drug Dietary Supplements Interactions and Nutrigenetics Faculty of Medicine and Dentistry Palacký University Hněvotínská 3 CZ 775 15 Olomouc Czech Republic

Department of Medical Chemistry and Biochemistry Faculty of Medicine and Dentistry Palacký University Hněvotínská 3 CZ 775 15 Olomouc Czech Republic; Laboratory of Biotransformation Institute of Microbiology Academy of Sciences of the Czech Republic Vídeňská 1083 Prague 4 CZ 142 20 Czech Republic; Centre of Drug Dietary Supplements Interactions and Nutrigenetics Faculty of Medicine and Dentistry Palacký University Hněvotínská 3 CZ 775 15 Olomouc Czech Republic

Laboratory of Biotransformation Institute of Microbiology Academy of Sciences of the Czech Republic Vídeňská 1083 Prague 4 CZ 142 20 Czech Republic

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