Abstract
Estradiol is the most potent and biologically active form of estrogen, with glucuronide as its predominant conjugation form. Major estradiol glucuronides include estradiol-3-glucuronide (E(2)3G), estradiol-17β-glucuronide, and estradiol-3-sulfate-17β-glucuronide (E(2)3S17βG). Hepatic disposition of estradiol-17β-glucuronide involves basolateral uptake transporters organic anion transporting polypeptide (OATP) 1B1/1B3 and apical efflux transporters multidrug resistance-associated protein 2 (MRP2)/breast cancer resistance protein (BCRP). In addition, E(2)3G and E(2)3S17βG are substrates for MRP2/BCRP. However, whether E(2)3G and E(2)3S17βG across the basolateral membrane of hepatocytes are transporter-mediated and which transporters play the most significant roles are largely unknown. Therefore, in the present study, we investigated the human hepatic uptake transporters for E(2)3G and E(2)3S17βG. Our results showed that E(2)3G and E(2)3S17βG are transported by human OATPs. Specifically, E(2)3G is a substrate for OATP1B1, 1B3, and 2B1, with K(m) values of 16.0, 23.8, and 6.4 μM, respectively, and OATP2B1 possesses the highest transport efficiency. E(2)3S17βG is a substrate for OATP1B1 and 1B3, with K(m) values of 0.5 and 23.7 μM, respectively, and OATP1B1 has a higher transport efficiency. At low concentrations, E(2)3G and E(2)3S17βG are selective substrates for OATP2B1 and OATP1B1, respectively. Furthermore, mutual and differential inhibition between E(2)3G/E(2)3S17βG and known OATP substrates/inhibitors has been observed. In summary, our results demonstrated that basolateral OATPs and apical MRP2/BCRP could constitute the hepatic vectorial transport of E(2)3G and E(2)3S17βG from the blood to the bile. SIGNIFICANCE STATEMENT: This study demonstrated that organic anion transporting polypeptide (OATP) 1B1/1B3/2B1 are hepatic uptake transporters for estradiol-3-glucuronide (E(2)3G), and OATP1B1/1B3 are hepatic uptake transporters for estradiol-3-sulfate-17β-glucuronide (E(2)3S17βG). At low concentrations, E(2)3G and E(2)3S17βG are selectively transported by OATP2B1 and OATP1B1, respectively. The findings in this study unveil the underlying molecular mechanisms for the hepatic disposition of estradiol glucuronides E(2)3G and E(2)3S17βG.