Investigation of the interactions between flavonoids and human organic anion transporting polypeptide 1B1 using fluorescent substrate and 3D-QSAR analysis.

Organic anion transporting polypeptide 1B1 (OATP1B1) is a key hepatic uptake transporter whose inhibition could lead to adverse drug-drug and drug-food interactions. Flavonoids are widely distributed in food and beverages and thus our bodies are frequently exposed to them. Therefore, investigation of the interactions between OATP1B1 and flavonoids could be of great significance. In the present study, 25 common flavonoids were investigated for their interactions with OATP1B1 using the fluorescent substrate 2',7'-dichlorofluorescein (DCF) and three-dimensional quantitative structure-activity relationship (3D-QSAR) analysis. Kinetic study showed that OATP1B1-mediated DCF uptake exhibited a monophasic saturation kinetics with a Km value of 9.7 ± 2.4 µM. Inhibition assay for flavonoids on OATP1B1-mediated DCF uptake was performed and their IC50 values were determined upon which reliable and predictive CoMFA (q2 = 0.604, r2 = 0.841) and CoMSIA (q2 = 0.534, r2 = 0.807) models were developed. Our experimental and computational results showed that flavonoid aglycones interacted with OATP1B1 much stronger than their glycosides such as 3-O- and 7-O-glycosides as bulky hydrophilic and hydrogen-bond forming substituents at C-3 and C-7 positions on rings A and C were unfavorable for their binding. On the other hand, the presence of hydrogen-bond forming groups on ring B was beneficial as long as the number of hydroxyl groups was not >2. Our results also indicated that flavones usually interacted with OATP1B1 much stronger than their 3-hydroxyflavone counterparts (flavonols). The obtained information and 3D-QSAR models could be useful for elucidating and predicting the interactions between flavonoids and human OATP1B1.

Gly45 and Phe555 in Transmembrane Domains 1 and 10 Are Critical for the Activation of Organic Anion Transporting Polypeptide 1B3 by Epigallocatechin Gallate.

Organic anion transporting polypeptides (OATPs) 1B1 and 1B3 are two highly homologous transporters expressed in the human liver. However, epigallocatechin gallate (EGCG), which is the most predominant catechin in green tea, has opposite effects on the function of OATP1B1 and OATP1B3. In the present study, the critical structural domains and amino acid residues for the activation of OATP1B3 by EGCG have been determined by characterizing the function of a series of OATP1B3-derived chimeric transporters, site-directed mutagenesis, and kinetic studies. Our results showed that G45 and F555 in transmembrane domains 1 and 10 are the most important amino acid residues for OATP1B3 activation. Kinetic studies showed that the activation of OATP1B3 by EGCG at a low substrate concentration was due to its increased substrate binding affinity. However, EGCG caused increased Km and decreased Vmax for 1B3-G45A and 1B3-F555H. The flexibility at position 45 and aromaticity at position 555 might be important for OATP1B3 activation. While 1B3-G45A and 1B3-F555H could not be activated by EGCG, their transport activity for EGCG was comparable to that of wild-type OATP1B3. In conclusion, the present study elucidated the molecular mechanism for OATP1B3 activation by EGCG.