Abstract
It was recently proposed that the improved oral bioavailability of genistein aglycone and conjugates in Bcrp1(−/−) mice is mainly due to increased intestinal absorption of aglycone and subsequent elevated exposure to conjugation enzymes. Here we tested this proposed mechanism and found that intestinal absorption of genistein aglycone did not increase in Bcrp1(−/−) mice compared with wild-type mice using an in situ mouse intestinal perfusion model and that inhibition of breast cancer resistance protein (BCRP) in Caco-2 cells also did not significantly increase permeability or intracellular concentration of aglycone. Separately, we showed that 5- to 10-fold increases in exposures of conjugates and somewhat lower fold increases (<2-fold) in exposures of aglycone were apparent after both oral and intraperitoneal administration in Bcrp1(−/−) mice. In contrast, the intestinal and biliary excretion of genistein conjugates significantly decreased in Bcrp1(−/−) mice without corresponding changes in aglycone excretion. Likewise, inhibition of BCRP functions in Caco-2 cells altered polarized excretion of genistein conjugates by increasing their basolateral excretion. We further found that genistein glucuronides could be hydrolyzed back to genistein, whereas sulfates were stable in blood. Because genistein glucuronidation rates were 110% (liver) and 50% (colon) higher and genistein sulfation rates were 40% (liver) and 42% (colon) lower in Bcrp1(−/−) mice, the changes in genistein exposures are not mainly due to changes in enzyme activities. In conclusion, improved bioavailability of genistein and increased plasma area under the curve of its conjugates in Bcrp1(−/−) mice is due to altered distribution of genistein conjugates to the systemic circulation.
Footnotes
The work was supported by the National Institutes of Health Institute of General Medical Sciences [Grants GM070737] (to M.H.).
Article, publication date, and citation information can be found at http://dmd.aspetjournals.org.
↵ The online version of this article (available at http://dmd.aspetjournals.org) contains supplemental material.
ABBREVIATIONS:
- UGT
- UDP-glucuronosyltransferase
- SULT
- sulfotransferase
- BCRP/Bcrp
- breast cancer resistance protein
- WT
- wild type
- Ko143
- 3-(6-isobutyl-9-methoxy-1,4-dioxo-1,2,3,4,6,7,12,12α-octahydropyrazino[1′,2′:1,6]pyrido[3,4-b]indol-3-yl)-propionic acid tert-butyl ester
- AUC
- area under the plasma concentration curve
- HBSS
- Hanks' balanced salt solution
- UPLC
- ultraperformance liquid chromatography
- MS/MS
- tandem mass spectrometry
- G-7-G
- genistein-7-O-glucuronide
- G-4′-G
- genistein-4′-O-glucuronide
- UDPGA
- uridine-5′-diphosphate-β, d-glucuronic acid
- G-4′-S
- genistein-4′-O-sulfate
- G-7-S
- genistein-7-O-sulfate
- N.A.
- not available
- MRP
- multidrug resistance-associated protein.
- Received November 21, 2011.
- Accepted June 26, 2012.
- Copyright © 2012 by The American Society for Pharmacology and Experimental Therapeutics
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