Hepatic uptake of estradiol-3-glucuronide and estradiol-3-sulfate-17β-glucuronide by human organic anion transporting polypeptides 1B1, 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 (E₂3G), estradiol-17β-glucuronide, and estradiol-3-sulfate-17β-glucuronide (E₂3S17βG). 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, E₂3G and E₂3S17βG are substrates for MRP2/BCRP. However, whether E₂3G and E₂3S17βG 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 E₂3G and E₂3S17βG. Our results showed that E₂3G and E₂3S17βG are transported by human OATPs. Specifically, E₂3G 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. E₂3S17βG 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, E₂3G and E₂3S17βG are selective substrates for OATP2B1 and OATP1B1, respectively. Furthermore, mutual and differential inhibition between E₂3G/E₂3S17βG 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 E₂3G and E₂3S17βG 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 (E₂3G), and OATP1B1/1B3 are hepatic uptake transporters for estradiol-3-sulfate-17β-glucuronide (E₂3S17βG). At low concentrations, E₂3G and E₂3S17βG 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 E₂3G and E₂3S17βG.

Estradiol glucuronide; Hepatic transporter; Liquid chromatography-tandem mass spectrometry; Organic anion transporting polypeptide; Selective substrate.