Influence of the flavonoids apigenin, kaempferol, and quercetin on the function of organic anion transporting polypeptides 1A2 and 2B1
Graphical abstract
Introduction
Flavonoids represent the most abundant polyphenols in vegetables, fruits, and plants. They are also ingredients of tea, wine, juices, numerous multivitamin preparations and herbal products (e.g. Ginkgo biloba formulations). In vitro and in vivo studies indicate pharmacological effects of flavonoids on prevention of cardiovascular diseases as well as anticancerogenic and antioxidative effects [1], [2], [3], [4].
It has recently been shown that several of these compounds inhibit drug metabolizing enzymes and drug transporters such as cytochrome P450 3A4 and the drug efflux transporter P-glycoprotein (ABCB1) [5], highlighting their potential for food–drug interactions. For example, the flavonoids apigenin, kaempferol, and quercetin which are constituents of Ginkgo biloba formulations, onions, strawberries, and apples [2] were characterized by inhibition and/or induction of CYP3A4, ABCB1, and ABCC2 [6], [7]. OATP1A2 and OATP2B1 are members of the human OATP family and are localized in the apical membrane of human enterocytes [8], [9]. OATP1A2 mediates the intracellular uptake of drugs such as fexofenadine [10] as well as of endogenous compounds such as taurocholate [11]. OATP2B1 mediates the cellular uptake of drugs such as fluvastatin [12], atorvastatin [13] and of endogenous compounds such as estrone-3-sulfate [14].
The influence of flavonoids on intestinal drug metabolism and transport is of special interest because flavonoids such as apigenin, kaempferol, and quercetin can reach high concentrations in the gut lumen. The inhibition of an OATP-mediated drug uptake in the intestine may decrease the plasma concentration of a substrate of OATPs, due to a reduced absorption.
In vitro studies in HeLa cells and additional in vivo studies showed that the flavonoid naringin, a constituent of grapefruit juice, inhibits the uptake of fexofenadine mediated by OATP1A2 [9], [15], [16]. This inhibition leads to a reduced area under the plasma concentration time curve (AUC) of the OATP1A2 substrate fexofenadine when grapefruit juice is coadministered with orally taken fexofenadine. Grapefruit juice or orange juice at a concentration of 5% significantly inhibited the OATP2B1-mediated uptake of estrone-3-sulfate by 82% and 53% in HEK293 cells stably expressing OATP2B1 [17].
Furthermore it was shown in an in vitro study that several herbal extracts, such as Ginkgo biloba extracts, potently inhibited the OATP2B1-mediated uptake of estrone-3-sulfate in HEK293 cells. These results suggest that coadministration of some dietary supplements may decrease the absorption of orally administered OATP2B1 substrates [18].
However, there are no data showing the influence of the flavonoids apigenin, kaempferol, and quercetin, which are chemically related to the grapefruit juice flavonoid naringin, on the function of human intestinal OATPs such as OATP1A2 and OATP2B1.
Therefore, we investigated the potential influence of the flavonoids apigenin, kaempferol, and quercetin on the transport function of OATP1A2 and OATP2B1 in order to gain more insights regarding further possible mechanisms of food–drug or drug–drug interactions. Changes in function of the OATP1A2- and OATP2B1-mediated drug uptake by apigenin, kaempferol, and quercetin may influence the absorption and systemic exposure of OATP substrates. Considering the frequent intake of herbal preparations of Ginkgo biloba, vegetables, and fruits containing these flavonoids, the hypothesized interaction with the intestinal uptake transporters OATP1A2 and OATP2B1 might be an important determinant of intraindividual variability of drug disposition.
Section snippets
Chemicals
[3H]Sulphobromophthalein (14 Ci/mmol) was obtained from Hartmann Analytic (Braunschweig, Germany). Unlabeled sulphobromophthalein was purchased from Applichem GmbH (Darmstadt, Germany). Sodium butyrate was purchased from Merck KGaA (Darmstadt, Germany). Apigenin (purity ≥95.0%, HPLC), kaempferol (purity ≥96%, HPLC), quercetin (purity ≥98%, HPLC), and fexofenadine hydrochloride were purchased from Sigma–Aldrich Chemie GmbH (Munich, Germany). [3H]Atorvastatin (10 Ci/mmol) and unlabeled atorvastatin
Characterization of a HEK293 cell line stably expressing OATP1A2
In the present study, we established a HEK293 cell line stably expressing the human uptake transporter OATP1A2. The selected cell clones of the HEK293-OATP1A2 and HEK293-VC cells were investigated regarding their expression, localization, and function of OATP1A2 using real-time PCR, immunoblot and immunofluorescence analysis. The HEK293-OATP1A2 cells were characterized by a significantly higher expression of SLCO1A2 mRNA and OATP1A2 protein compared to the control cells (Fig. 1a and b). The
Discussion
The major findings of the present study were that the flavonoids apigenin, kaempferol and quercetin affect the transport function of OATP1A2- and OATP2B1-mediated uptake of BSP and of the drugs fexofenadine and atorvastatin.
Because most of the drugs used in pharmacotherapy are orally administered, the bioavailability of these compounds can already be influenced by intestinal drug transport and metabolism. Drug uptake transporters such as OATP1A2 expressed in the apical membrane of enterocytes
Acknowledgements
This work was funded by a grant of the Deutsche Forschungsgemeinschaft [DFG GL 588/2-1] and the German Federal Ministry of Education and Research [grant, InnoProfile 03IP612].
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These authors contributed equally to the study.