Abstract
The hepatic disposition of estradiol 17β-d-glucuronide (E217G), a substrate of the organic anion-transporting polypeptides Oatp1a1, Oatp1a4, and Oatp1b2, was investigated in Wistar and TR− [multidrug resistance-associated protein (Mrp) 2-mutant] rats to elucidate how absence of Mrp2, the major excretory transporter for both E217G and its 3-sulfate metabolite (E23S17G), affected the net sulfation. With absence of Mrp2, lower microsomal desulfation activity and higher Mrp3 but unchanged immunoreactive protein expression of other transporters (Oatps and Mrp4) and estrogen sulfotransferase were found in TR− rats. In recirculating, perfused liver preparations, the rapid decay of E217G and sluggish appearance of low levels of E23S17G in perfusate for Wistar livers were replaced by a protracted, biexponential decay of E217G and greater accumulation of E23S17G, whose levels reached plateaus upon the almost complete obliteration of biliary excretion of E217G and E23S17G in the TR− liver. Much higher amounts of E217G (28×) and E23S17G (11×) in liver and reduced net sulfation (40 ± 6 from 77 ± 6% dose, P < 0.05) were observed at 2 h for the TR− versus the Wistar rats. With use of a physiologically based pharmacokinetic model, analytical solutions for the areas under the curve for the precursor and metabolite were obtained to reveal how enzyme- and transporter-mediated processes affected the hepatic disposition of the precursor and metabolite in futile cycling. The analytical solutions were useful to explain transporter-enzyme interplay in futile cycling and predicted that a shutdown of Mrp2 function led to decreased net sulfation of E217G by raising the intracellular concentration of the metabolite, E23S17G, which readily refurnished E217G via desulfation.
Footnotes
This work was supported by the Canadian Institutes of Health Research [Grant MOP89850]. H.S. was a recipient of the University of Toronto Open Fellowship.
Article, publication date, and citation information can be found at http://dmd.aspetjournals.org.
doi:10.1124/dmd.109.029959.
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ABBREVIATIONS:
- OATP/Oatp
- organic anion transporting polypeptide
- MRP/Mrp
- multidrug resistance-associated protein
- SULT/Sult
- sulfotransferase
- E217G
- estradiol 17β-d-glucuronide
- E23S17G
- estradiol 3-sulfate-17β-d-glucuronide
- Sult1e1
- estrogen sulfotransferase
- HPLC
- high-performance liquid chromatography
- 4-MUS
- 4-methylumbelliferyl sulfate
- AUC
- area under the concentration-time curve
- PBPK model
- physiologically based pharmacokinetic model
- GAPDH
- glyceraldehyde-3-phosphate dehydrogenase.
- Received August 24, 2009.
- Accepted February 2, 2010.
- Copyright © 2010 by The American Society for Pharmacology and Experimental Therapeutics
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