Abstract
Estradiol-17β-glucuronide (E217G) is an estrogen metabolite that has cholestatic properties. In humans, circulating E217G is transported into hepatocytes by organic anion transporting polypeptides (OATPs) and is excreted into bile by multidrug-resistance associated protein 2 (MRP2). E217G is also a substrate of the basolateral efflux transporters MRP3 and MRP4, which translocate E217G from hepatocytes to blood. However, the contribution of basolateral efflux to hepatocyte disposition of E217G has not been evaluated previously. To address this question, E217G disposition was studied in sandwich-cultured human hepatocytes and mechanistic modeling was applied to calculate clearance values (mean ± S.D.) for uptake, intrinsic biliary excretion (CLint,bile) and intrinsic basolateral efflux (CLint,BL). The biliary excretion index of E217G was 45% ± 6%. The CLint,BL of E217G [0.18 ± 0.03 (ml/min)/g liver) was 1.6-fold higher than CLint,bile [0.11 ± 0.06 (ml/min)/g liver]. Simulations were performed to study the effects of increased CLint,BL and a concomitant decrease in CLint,bile on hepatic E217G exposure. Results demonstrated that increased CLint,BL can effectively reduce hepatocellular and biliary exposure to this potent cholestatic agent. Simulations also revealed that basolateral efflux can compensate for impaired biliary excretion and, vice versa, to avoid accumulation of E217G in hepatocytes. However, when both clearance processes are impaired by 90%, hepatocyte E217G exposure increases up to 10-fold. These data highlight the contribution of basolateral efflux transport, in addition to MRP2-mediated biliary excretion, to E217G disposition in human hepatocytes. This elimination route could be important, especially in cases where basolateral efflux is induced, such as cholestasis. SIGNIFICANCE STATEMENT: The disposition of the cholestatic estrogen metabolite estradiol-17β-glucuronide (E217G) was characterized in sandwich-cultured human hepatocytes. The intrinsic basolateral efflux clearance was estimated to be 1.6-fold higher than the intrinsic biliary excretion clearance, emphasizing the contribution of basolateral elimination in addition to biliary excretion. Simulations highlight how hepatocytes can effectively cope with increased E217G through the regulation of both basolateral and biliary transporters.