title: 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-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.
authors.affiliation: Department of Biopharmaceutical Sciences, University of California, San Francisco, California 94143-0446, USA. benet@itsa.ucsf.edu
authors.forename: Carolyn L
authors.initials: CL
authors.lastname: Cummins
authors.forename: Laurent
authors.initials: L
authors.lastname: Salphati
authors.forename: Michael J
authors.initials: MJ
authors.lastname: Reid
authors.forename: Leslie Z
authors.initials: LZ
authors.lastname: Benet
mesh_terms: D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1 / Q000378:metabolism*; D000818:Animals; D001189:Aryl Hydrocarbon Hydroxylases / Q000378:metabolism*; D051544:Cytochrome P-450 CYP3A; D004151:Dipeptides / Q000378:metabolism; D004355:Drug Stability; D007408:Intestinal Absorption / Q000502:physiology; D007413:Intestinal Mucosa / Q000378:metabolism*; D007422:Intestines / Q000201:enzymology; D008297:Male; D008874:Midazolam / Q000378:metabolism; D008954:Models, Biological; D009842:Oligopeptides / Q000378:metabolism; D010089:Oxidoreductases, N-Demethylating / Q000378:metabolism*; D010477:Perfusion; D051381:Rats; D017207:Rats, Sprague-Dawley; D013450:Sulfones / Q000378:metabolism
chemical_list: D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1; D004151:Dipeptides; C473246:N-methyl piperazine-Phe-homoPhe-vinylsulfone phenyl; D009842:Oligopeptides; D013450:Sulfones; C115125:morpholin- urea-phenylalanyl-homophenylalanyl-vinylsulfone-phenyl; D001189:Aryl Hydrocarbon Hydroxylases; D051544:Cytochrome P-450 CYP3A; D010089:Oxidoreductases, N-Demethylating; D008874:Midazolam