Estradiol17-(β-D-glucuronide) (E217G) is an estrogen metabolite formed in the liver and subsequently excreted in bile.1It acts as a substrate of the multidrug resistance protein 2 (MRP2; Km= 75 μM), and through MRP2-mediated transport, functions as a cholestatic agent, decreasing bile flow.1,2In addition to binding to the MRP2 transport site, E217G has been shown to bind to an allosteric site that through positive cooperativity activates its own transportviaMRP2 and the transport of other MRP2 substrates, including the non-cholestatic estrogen metabolite, estradiol 3-(β-D-glucuronide) .2,3E217G has also been reported to be transported by MDR1, MRP1, MRP3, MRP4, MRP7, ABCG2 (a breast cancer resistance protein transporter), and the rat organic anion-transporting polypeptides 1-4.2 1.Loe, D.W., Almquist, K.C., Cole, S.P., et al.ATP-dependent 17β-estradiol17-(β-D-glucuronide) transport by multidrug resistance protein (MRP). Inhibition by cholestatic steroidsThe Journal of Biological Chemisty271(16)9683-9689(1996) 2.Gerk, P.M., Li, W., and Vore, M.Estradiol 3-glucuronide is transported by the multidrug resistance-associated protein 2 but does not activate the allosteric site bound by estradiol17-glucuronideDrug Metabolism and Disposition32(10)1139-1145(2004) 3.Gerk, P.M., Li, W., Megaraj, W., et al.Human multidrug resistance protein 2 transports the therapeutic bile salt tauroursodeoxycholateJournal of Pharmacology and Experimental Therapeutics320(2)893-899(2007)
17-Epiestriol is a metabolite of estrone .1It is formed from estroneviaa 16α-hydroxy estrone intermediate by reduction of the C-17 ketone. 17-Epiestriol binds to estrogen receptor α (ERα) and ERβ with relative binding affinities of 29 and 80 compared with 17β-estradiol .2 1.Brinton, L.A., Trabert, B., Anderson, G.L., et al.Serum estrogens and estrogen metabolites and endometrial cancer risk among postmenopausal womenCancer Epidemiol. Biomarkers Prev.25(7)1081-1089(2016) 2.Kuiper, G.G.J.M., Lemmen, J.G., Carlsson, B., et al.Interaction of estrogenic chemicals and phytoestrogens with estrogen receptor βEndocrinology139(10)4252-4263(1998)