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Differences Between Human and Rat Intestinal and Hepatic Bisphenol-A Glucuronidation and the Influence of Alamethicin on In vitro Kinetic Measurements
Citation:
MAZUR, C. S., J. F. KENNEKE, J. HESS-WILSON, AND J. C. LIPSCOMB. Differences Between Human and Rat Intestinal and Hepatic Bisphenol-A Glucuronidation and the Influence of Alamethicin on In vitro Kinetic Measurements. DRUG METABOLISM AND DISPOSITION. American Society for Pharmacology and Experimental Therapeutics, Bethesda, MD, 38(12):2232-2238, (2010).
Impact/Purpose:
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Description:
The extent to which membrane disrupting agents, such as alamethicin, may alter cofactor transport and influence in vitro kinetic measurements of glucurondiation is a major concern regarding the characterization and extrapolation of inter-and intra-species pharmacokinetics of bisphenol-A (BPA). Additional concern is the omission of a BPA intestinal metabolism component in current pharmacokinetic models used to assess oral exposure. In this study, BPA glucuronidation in native hepatic microsomes from female rat and female human liver displayed higher Vmax values compared to males. In the presence of alamethicin, all hepatic Vmax values increased; however, this increase was disproportionately greater in males and gender differences were no longer observed. Female rat exhibited a much higher KM than all other species and genders; the addition of alamethicin had little influence on KM values for any of the test systems. The dissimilar KM measured for female rat suggests differing UGT enzyme(s)are involved in BPA glucuronidation. The presence of different UGTs in female rat was confirmed using Hill coefficients measured from diclofenac-mediated chemical inhibition assays within hepatic microsomes and purified human UGT2B7 and UGT2B15. Mixed gender human intestinal microsomes showed little BPA glucuronidation reactivity in comparison to male rat intestine. Male rat intestinal microsomes in the presence of alamethicin exhibited a Vmax that was nearly 30 fold higher than the mixed human. The species and gender metabolic differences we observed between rat and human liver and intestine provide key information for delineating BPA pharmacokinetics needed for human health risk assessment.
