RT Journal Article
SR Electronic
T1 Minor Compensatory Changes in SAGE Mdr1a (P-gp), Bcrp, and Mrp2 Knockout Rats do not Detract from their General Utility in the Study of Transporter-mediated Pharmacokinetics
JF Drug Metabolism and Disposition
JO Drug Metab Dispos
FD American Society for Pharmacology and Experimental Therapeutics
SP dmd.113.051409
DO 10.1124/dmd.113.051409
A1 Maciej J Zamek-Gliszczynski
A1 Keith M Goldstein
A1 April Paulman
A1 Thomas K Baker
A1 Timothy P Ryan
YR 2013
UL http://dmd.aspetjournals.org/content/early/2013/04/08/dmd.113.051409.abstract
AB Mdr1a-, Bcrp-, and Mrp2-knockout rats are a more practical species for ADME studies than murine models and previously demonstrated expected alterations in pharmacokinetics of various probe substrates. At present, gene expression and pathology changes were systematically studied in small intestine, liver, kidney, and brain tissue from male SAGE Mdr1a-, Bcrp-, and Mrp2-knockout rats versus wild-type Sprague Dawley controls. Gene expression data supported the relevant knockout genotype. As expected, Mrp2-knockout rats were hyperbilirubinemic and exhibited upregulation of hepatic Mrp3. Overall, few alterations were observed within 112 ADME-relevant genes. The two potentially most consequential changes were upregulation of intestinal carboxylesterase in Mdr1a-knockouts and catechol-O-methyltransferase in all tissues of Bcrp-knockout rats. Previously reported upregulation of hepatic Mdr1b P-glycoprotein in proprietary Wistar Mdr1a-knockout rats was not observed in the SAGE counterpart investigated herein. Relative liver and kidney weights were 22-53% higher in all three knockouts, with microscopic increases in hepatocyte size in Mdr1a- and Mrp2-knockout rats, and glomerular size in Bcrp- and Mrp2-knockouts. Increased relative weight of clearing organs is quantitatively consistent with reported increases in clearance of drugs that are not substrates of the knocked-out transporter. Overall, SAGE knockout rats demonstrated modest compensatory changes, which do not preclude their general application to study transporter-mediated pharmacokinetics. However, until future studies elucidate the magnitude of functional change, caution is warranted in rare instances of extensive metabolism by catechol-O-methyltransferase in Bcrp-knockouts and intestinal carboxylesterase in Mdr1a-knockout rats, specifically for molecules with free catechol groups and esters subject to gut wall hydrolysis.