Hepatic uptake of estradiol-3-glucuronide and estradiol-3-sulfate-17β-glucuronide by human OATP1B1, 1B3, and 2B1

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 (E 2 17βG), and estradiol-3-sulfate-17β-glucuronide (E 2 3S17βG). Hepatic disposition of E 2 17βG 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 being 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 being 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 OATP1B1/1B3/2B1 are hepatic uptake transporters for E 2 3G, and OATP1B1/1B3 are hepatic uptake transporters for 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.