Flavonoids are abundant polyphenols in nature. They are extensively biotransformed in enterocytes and hepatocytes, where conjugated (methyl, sulfate, and glucuronide) metabolites are formed. However, bacterial microflora in the human intestines also metabolize flavonoids, resulting in the production of smaller phenolic fragments (e.g., hydroxybenzoic, hydroxyacetic and hydroxycinnamic acids, and hydroxybenzenes). Despite the fact that several colonic metabolites appear in the circulation at high concentrations, we have only limited information regarding their pharmacodynamic effects and pharmacokinetic interactions. Therefore, in this in vitro study, we investigated the interactions of 24 microbial flavonoid metabolites with human serum albumin and cytochrome P450 (CYP2C9, 2C19, and 3A4) enzymes. Our results demonstrated that some metabolites (e.g., 2,4-dihydroxyacetophenone, pyrogallol, O-desmethylangolensin, and 2-hydroxy-4-methoxybenzoic acid) form stable complexes with albumin. However, the compounds tested did not considerably displace Site I and II marker drugs from albumin. All CYP isoforms examined were significantly inhibited by O-desmethylangolensin; nevertheless, only its effect on CYP2C9 seems to be relevant. Furthermore, resorcinol and phloroglucinol showed strong inhibitory effects on CYP3A4. Our results demonstrate that, besides flavonoid aglycones and their conjugated derivatives, some colonic metabolites are also able to interact with proteins involved in the pharmacokinetics of drugs.

Department of Organic and Bioorganic Chemistry Faculty of Pharmacy in Hradec Králové Charles University Akademika Heyrovského 1203 500 05 Hradec Králové Czech Republic

Department of Pharmacology and Pharmacotherapy Medical School University of Pécs Szigeti út 12 H 7624 Pécs Hungary

Department of Pharmacology and Toxicology Faculty of Pharmacy in Hradec Králové Charles University Heyrovského 1203 500 05 Hradec Králové Czech Republic

Department of Pharmacology Faculty of Pharmacy University of Pécs Szigeti út 12 H 7624 Pécs Hungary

Department of Social and Clinical Pharmacy Faculty of Pharmacy in Hradec Králové Charles University Zborovská 2089 500 05 Hradec Králové Czech Republic

Institute of Organic and Medicinal Chemistry Medical School University of Pécs Szigeti út 12 H 7624 Pécs Hungary

János Szentágothai Research Center University of Pécs Ifjúság útja 20 H 7624 Pécs Hungary

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