In Vivo Modulation of Intestinal CYP3A Metabolism by P-Glycoprotein: Studies Using the Rat Single-Pass Intestinal Perfusion Model

Abstract

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-PhehomoPhe-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 ϭ 5 Ϯ 3 ϫ 10 Ϫ6 cm/s) was increased 3-fold with GG918, whereas midazolam permeability (P blood ϭ 1.1 Ϯ 0.3 ϫ 10 Ϫ4 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 ϭ 1 Ϫ P blood /P lumen and the extraction ratio (ER) determined from the direct measurement of known metabolites as ER ϭ sum metabolites all /(sum metabolites all ϩ 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.

Intestinal absorption of novel-dipeptide prodrugs of saquinavir in rats

“…In this model, a known concentration of drug is perfused through a section of the jejunum with intact blood supply. Disappearance of drug from the perfusate is attributed to intestinal absorption (Cummins et al, 2003;Berggren et al, 2004). Anatomical and physiological parameters of the gastrointestinal tract dramatically affect the rate and extent of absorption of ingested compounds.…”

Pharmacogenomics Dictate Pharmacokinetics: Polymorphisms in Drug-Metabolizing Enzymes and Drug-Transporters

“…P-gp, MRP1, and MRP2 were upregulated, especially after stimulation of cells with either the protein kinase-A (PKA) inducer sodium butyrate or the protein kinase-C (PKC) inducer phorbol ester 12-O-tetradecanoylphorbol-13-acetate (PMA) . In an in vivo intestinal perfusion model, these investigators had also shown modulation of intestinal CYP3A metabolism by P-gp (Cummins, CL, 2003). This has led to the hypothesis that both drug-transporter and drug-metabolizing enzymes act as a coordinated barrier against xenobiotic agents.…”

“…Appropriate pharmacological testing in disease models are carried out to determine 50% effective dose (ED 50 ). For some anti-tumor and anti-viral agents, even IC 90 (90% inhibitory concentration) is incorporated in these initial studies in order to demonstrate the potency (Cummins CL, et al, 2003). Following acute administration, analytical methods are developed for determination of absorption, distribution, metabolism and excretion (ADME) of the drug.…”

Utilizing in vitro transporter data in IVIVE-PBPK: an overview

“…The bioavailability of an orally administered drug is primarily dependent on the transporters expressed on the apical/basolateral side of enterocytes that influence both the fraction of drug absorbed [52,53] and the fraction escaping gut metabolism. It is difficult to reproduce the complexity of the human gut within a laboratory setting; therefore, efforts are being made to incorporate drug absorption into PBPK models by taking into account several physiological elements of the gastro-intestinal tract, e.g., pH, active transporters, and metabolizing enzymes [54].…”