In vivo modulation of intestinal CYP3A metabolism by P-glycoprotein: studies using the rat single-pass intestinal perfusion model

J Pharmacol Exp Ther. 2003 Apr;305(1):306-14. doi: 10.1124/jpet.102.044719.


P-Glycoprotein (P-gp) has been hypothesized to modulate intestinal drug metabolism by increasing the exposure of drug to intracellular CYP3A through repeated cycles of drug absorption and efflux. The rat single-pass intestinal perfusion model was used to study this interplay in vivo. N-Methyl piperazine-Phe-homoPhe-vinylsulfone phenyl (K77), a peptidomimetic cysteine protease inhibitor (CYP3A/P-gp substrate), and midazolam (CYP3A substrate) were each perfused through a segment of rat ileum alone and with the P-gp inhibitor N-(4-[2-(1,2,3,4-tetrahydro-6,7-dimethoxy-2-isoquinolinyl)-ethyl]-phenyl)-9,10-dihydro-5-methoxy-9-oxo-4-acridine carboxamine (GG918). Samples were obtained continuously from the outlet perfusate and the mesenteric vein at 5-min intervals for 40 to 60 min. The parent drug and two main metabolites of K77 (N-desmethyl and N-oxide) and midazolam (1-OH and 4-OH) were quantitated by liquid chromatography/mass spectrometry. K77 appearance in the mesenteric blood (P(blood) = 5 +/- 3 x 10(-6) cm/s) was increased 3-fold with GG918, whereas midazolam permeability (P(blood) = 1.1 +/- 0.3 x 10(-4) cm/s) was unchanged by GG918. K77 metabolites were preferentially excreted into the lumen, 4-OH midazolam was found equally in lumen and blood, and 1-OH was mainly excreted into blood. The extent of metabolism was estimated by calculating the fraction metabolized = 1 - P(blood)/P(lumen) and the extraction ratio (ER) determined from the direct measurement of known metabolites as ER = sum metabolites(all)/(sum metabolites(all) + drug in blood). When P-gp was inhibited, the fraction metabolized for K77 was decreased (95 to 85%) and the ER tended toward a decrease, whereas no differences in either parameter were observed for midazolam (not a P-gp substrate). These data support a role for P-gp in modulating the extent of intestinal metabolism in vivo by controlling drug access to the enzyme.

Publication types

  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • ATP Binding Cassette Transporter, Subfamily B, Member 1 / metabolism*
  • Animals
  • Aryl Hydrocarbon Hydroxylases / metabolism*
  • Cytochrome P-450 CYP3A
  • Dipeptides / metabolism
  • Drug Stability
  • Intestinal Absorption / physiology
  • Intestinal Mucosa / metabolism*
  • Intestines / enzymology
  • Male
  • Midazolam / metabolism
  • Models, Biological
  • Oligopeptides / metabolism
  • Oxidoreductases, N-Demethylating / metabolism*
  • Perfusion
  • Rats
  • Rats, Sprague-Dawley
  • Sulfones / metabolism


  • ATP Binding Cassette Transporter, Subfamily B, Member 1
  • Dipeptides
  • N-methyl piperazine-Phe-homoPhe-vinylsulfone phenyl
  • Oligopeptides
  • Sulfones
  • morpholin- urea-phenylalanyl-homophenylalanyl-vinylsulfone-phenyl
  • Aryl Hydrocarbon Hydroxylases
  • Cytochrome P-450 CYP3A
  • Oxidoreductases, N-Demethylating
  • Midazolam