Abstract
The purpose of this study is to determine the importance of coupling of efflux transporters and metabolic enzymes in the intestinal disposition of six isoflavones (genistein, daidzein, formononetin, glycitein, biochanin A, and prunetin), and to determine how isoflavone structural differences affect the intestinal disposition. A rat intestinal perfusion model was used, together with rat intestinal and liver microsomes. In the intestinal perfusion model, significant absorption and excretion differences were found between isoflavones and their respective glucuronides (p <0.05), with prunetin being the most rapidly absorbed and formononetin glucuronides being the most excreted in the small intestine. In contrast, glucuronides were excreted very little in the colon. In an attempt to account for the differences, we measured the glucuronidation rates of six isoflavones in microsomes prepared from rat intestine and liver. Using multiple regression analysis, intrinsic clearance (CLint) and other enzyme kinetic parameters (Vmax and Km) were determined using appropriate kinetic models based on Akaike's information criterion. The kinetic parameters were dependent on the isoflavone used and the types of microsomes. To determine how metabolite excretion rates are controlled, we plotted excretion rates versus calculated microsomal rates (at 10 μM), CLint values, Km values, or Vmax values, and the results indicated that excretion rates were not controlled by any of the kinetic parameters. In conclusion, coupling of intestinal metabolic enzymes and efflux transporters affects the intestinal disposition of isoflavones, and structural differences of isoflavones, such as having methoxyl groups, significantly influenced their intestinal disposition.
Footnotes
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This work is supported by a grant from the National Institutes of Health (CA87779) to M.H. X.J. was funded by a training grant from Jiangsu Province, The People's Republic of China. Some work was started at Washington State University, where this laboratory was based.
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Article, publication date, and citation information can be found at http://dmd.aspetjournals.org.
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doi:10.1124/dmd.106.009910.
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ABBREVIATIONS: MRP, multidrug resistance-associated protein; HPLC, high-performance liquid chromatography; UGT, UDP-glucuronosyltransferase; AIC, Akaike's information criterion; GLM, general linear model; ANOVA, analysis of variance; CLint, intrinsic clearance; BCRP, breast cancer resistance protein.
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↵1 Current affiliation: Department of Pharmaceutical Sciences, College of Pharmacy, The University of Michigan, Ann Arbor, MI.
- Received February 27, 2006.
- Accepted July 26, 2006.
- The American Society for Pharmacology and Experimental Therapeutics
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