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 (Fmet), 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 (Fmet = 65.78 ± 19.02%), decreasing in midjejunum (Fmet = 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 μM) was associated with highFmet (87.90 ± 14.30%), whereas a high luminal concentration of indinavir (50 μM) was associated with lowFmet (35.84 ± 11.59%). In the presence of ketoconazole, both Fmet 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.
Footnotes
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This study was supported in part by an Upjohn and Vahlteich Research Award from the University of Michigan College of Pharmacy and a Rackham Predoctoral Fellowship from the University of Michigan Department of Graduate Studies.
- Abbreviations:
- HIV
- human immunodeficiency virus
- P-gp
- P-glycoprotein
- LC/MS
- liquid chromatography/mass spectrometry
- ECL
- enhanced chemiluminescence
- MES
- 4-morpholineethanesulfonic acid
- DEX
- dexamethasone
- Received August 21, 2001.
- Accepted January 7, 2002.
- The American Society for Pharmacology and Experimental Therapeutics
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