title: Intestinal metabolism promotes regional differences in apical uptake of indinavir: coupled effect of P-glycoprotein and cytochrome P450 3A on indinavir membrane permeability in rat.
abstract: The purpose of this study was to investigate transport and metabolism contributions to low indinavir permeability in rat ileum and enhanced drug permeability in the jejunum. Permeability models utilized included single pass in situ rat intestinal perfusion and rat intestinal tissue mounted in Ussing chambers. Intestinal metabolism was measured by fractional appearance of metabolite (F(met)), determined as the percentage of the predominant metabolite M6 over luminal loss of indinavir in the perfusion model. Among the results, indinavir exhibited bidirectional transport across rat ileum. Verapamil and cyclosporin A inhibited net flux by 37 and 38%, respectively. Intestinal metabolism of indinavir was most significant in upper jejunum (F(met) = 65.78 +/- 19.02%), decreasing in midjejunum (F(met) = 31.58 +/- 5.63%). M6 was not detectable in ileum or colon. Western blot analysis of rat intestinal mucosal tissue samples confirmed that the axial expression of CYP3A was consistent with the regional pattern of formation of M6. Intestinal metabolism was saturable and could be inhibited by the CYP3A inhibitor, ketoconazole. A low luminal concentration of indinavir (1 microM) was associated with high F(met) (87.90 +/- 14.30%), whereas a high luminal concentration of indinavir (50 microM) was associated with low F(met) (35.84 +/- 11.59%). In the presence of ketoconazole, both F(met) and permeability of indinavir were reduced in the jejunum. These results suggest that 1) intracellular metabolism of indinavir enhances apical uptake of indinavir in the rat jejunum as a function of the increased concentration gradient generated across the epithelial cell membrane and 2) the efflux transporter P-glycoprotein limits apical uptake of indinavir in the ileum, resulting in low apparent permeability.
authors.affiliation: Division of Pharmaceutical Sciences, College of Pharmacy, University of Michigan, Ann Arbor, Michigan 48109-1065, USA.
authors.forename: Lilian Y
authors.initials: LY
authors.lastname: Li
authors.forename: Gordon L
authors.initials: GL
authors.lastname: Amidon
authors.forename: Jae Seung
authors.initials: JS
authors.lastname: Kim
authors.forename: Tycho
authors.initials: T
authors.lastname: Heimbach
authors.forename: Filippos
authors.initials: F
authors.lastname: Kesisoglou
authors.forename: John T
authors.initials: JT
authors.lastname: Topliss
authors.forename: David
authors.initials: D
authors.lastname: Fleisher
mesh_terms: D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1 / Q000378:metabolism*; D000818:Animals; D001189:Aryl Hydrocarbon Hydroxylases; D002463:Cell Membrane Permeability / Q000187:drug effects; D051544:Cytochrome P-450 CYP3A; D003577:Cytochrome P-450 Enzyme System / Q000378:metabolism*; D017320:HIV Protease Inhibitors / Q000378:metabolism / Q000493:pharmacokinetics*; D019469:Indinavir / Q000378:metabolism / Q000493:pharmacokinetics*; D007413:Intestinal Mucosa / Q000378:metabolism*; D008297:Male; D008968:Molecular Conformation; D010089:Oxidoreductases, N-Demethylating / Q000378:metabolism*; D051381:Rats; D017207:Rats, Sprague-Dawley
chemical_list: D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1; D017320:HIV Protease Inhibitors; D019469:Indinavir; D003577:Cytochrome P-450 Enzyme System; D001189:Aryl Hydrocarbon Hydroxylases; D051544:Cytochrome P-450 CYP3A; D010089:Oxidoreductases, N-Demethylating