RT Journal Article
SR Electronic
T1 EFFECT OF PROTOTYPICAL INDUCING AGENTS ON P-GLYCOPROTEIN AND CYP3A EXPRESSION IN MOUSE TISSUES
JF Drug Metabolism and Disposition
JO Drug Metab Dispos
FD American Society for Pharmacology and Experimental Therapeutics
SP 1008
OP 1014
VO 32
IS 9
A1 Christopher J. Matheny
A1 Rabia Y. Ali
A1 Xiaodong Yang
A1 Gary M. Pollack
YR 2004
UL http://dmd.aspetjournals.org/content/32/9/1008.abstract
AB P-glycoprotein (P-gp) and CYP3A have considerable overlap in inducers in vitro. Characterizing P-gp induction in vivo and potential coregulation with CYP3A are important goals for predicting drug interactions. This study examined P-gp expression in mouse tissues and potential coinduction with CYP3A following oral treatment with 1 of 7 prototypical inducing agents for 5 days. P-gp expression in brain or liver was not induced by any treatment as determined by Western blot, whereas dexamethasone, pregnenolone-16α-carbonitrile (PCN), St. John's wort (SJW), and rifampin induced hepatic CYP3A expression. In intestine, rifampin and SJW induced P-gp expression 3.7- and 1.6-fold and CYP3A 3.5- and 2.4-fold, respectively, whereas dexamethasone and PCN induced CYP3A only. These observations suggest that P-gp in mouse small intestine is inducible by some, but not all, CYP3A inducers, whereas P-gp expression in liver or brain is not readily induced. Intriguingly, rifampin and SJW, both activators of the human pregnane X receptor (PXR), induced CYP3A in both liver and intestine but induced P-gp only in intestine, whereas PCN, an activator of murine PXR, did not induce P-gp in any tissue. Rifampin disposition was evaluated, and hepatic exposure to rifampin was comparable to intestine; in contrast, brain concentrations were low. Overall, these observations demonstrate that P-gp induction in vivo is tissue-specific; furthermore, there is a disconnect between P-gp induction and CYP3A induction that is tissue- and inducer-dependent, suggesting that PXR activation alone is insufficient for P-gp induction in vivo. Tissue-specific factors and inducer pharmacokinetic/pharmacodynamic properties may underlie these observations. The American Society for Pharmacology and Experimental Therapeutics