TY - JOUR T1 - Intestinal and Hepatic Metabolic Activity of Five Cytochrome P450 Enzymes: Impact on Prediction of First-Pass Metabolism JF - Journal of Pharmacology and Experimental Therapeutics JO - J Pharmacol Exp Ther SP - 1220 LP - 1229 DO - 10.1124/jpet.106.106013 VL - 318 IS - 3 AU - Aleksandra Galetin AU - J. Brian Houston Y1 - 2006/09/01 UR - http://jpet.aspetjournals.org/content/318/3/1220.abstract N2 - The contribution of the gut is not routinely incorporated into in vitro-in vivo predictions of either clearance or drug-drug interactions, and this omission may partially explain the general underprediction trend often observed. In the current study, the metabolic ability of hepatic and intestinal pooled microsomes was compared for eight CYP3A substrates (midazolam, triazolam, diazepam, alprazolam, flunitrazepam, nifedipine, testosterone, and quinidine) and paclitaxel, tolbutamide, S-mephenytoin, and bufuralol as CYP2C8, CYP2C9, CYP2C19, and CYP2D6 probes, respectively. A general agreement in the type of kinetics was observed between the two systems for the substrates investigated. Of the 16 pathways investigated, 75% of Km (S50) values obtained in intestinal microsomes (5.9-769 μM) were within 2-fold of hepatic estimates. Irrespective of the cytochrome P450 (P450) investigated and normalization of Vmax values for the P450 abundance, clearance was 4.5- to 50-fold lower in intestinal microsomes (0.0005-0.51 μl/min/P450) compared with the hepatic estimates (0.002-5.8 μl/min/P450), whereas the rank order was consistent between the systems. Assessment of two enterocyte isolation methods (mucosal scraping or enterocyte elution) was performed at the substrate concentrations corresponding to the determined Vmax conditions for 11 pathways. The activity difference between the methods (3-29-fold) was P450-related in the following rank order: CYP2C19 > CYP3A4 > CYP2C9 ∼ CYP2D6. After correction for the loss of activity between the methods, the intrinsic activities of hepatic and intestinal CYP3A4, CYP2C9, CYP2C19, and CYP2D6 were comparable for the 16 pathways. The implications of these findings on the prediction of intestinal first-pass metabolism are discussed. The American Society for Pharmacology and Experimental Therapeutics ER -