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-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 inhibitorN-{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 (Pblood = 5 ± 3 × 10−6 cm/s) was increased 3-fold with GG918, whereas midazolam permeability (Pblood = 1.1 ± 0.3 × 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 −Pblood/Plumen and the extraction ratio (ER) determined from the direct measurement of known metabolites as ER = sum metabolitesall/(sum metabolitesall + 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.
Footnotes
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This study was supported by National Institutes of Health CA72006 (to L.Z.B.) and Affymax Research Institute (to C.L.C.), as well as by an unrestricted gift from Amgen, Inc. (Thousand Oaks, CA). L.Z.B. has a financial interest in and serves as Chairman of the Board of AvMax, Inc. (South San Francisco, CA), a biotechnology company whose main interest is in increasing drug bioavailability by inhibiting intestinal CYP3A and P-glycoprotein. This work was presented in part at the XIVth World Congress of Pharmacology (International Union of Pharmacology), July 2002 (San Francisco, CA).
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DOI: 10.1124/jpet.102.044719
- Abbreviations:
- P-gp
- P-glycoprotein
- K02
- K11002, morpholine-urea-Phe-homoPhe-vinylsulfone phenyl
- K77
- K11777,N-methyl piperazine-Phe-homoPhe-vinylsulfone phenyl
- GG918
- GF120918,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
- IS
- internal standard
- HPLC
- high-performance liquid chromatography
- ER
- extraction ratio
- Received September 23, 2002.
- Accepted December 30, 2002.
- The American Society for Pharmacology and Experimental Therapeutics
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