Species Comparison of In Vivo P-Glycoprotein-Mediated Brain Efflux Using mdr1a-Deficient Rats and Mice

Abstract

ABSTRACT:The experiments described herein compared the extent of in vivo P-glycoprotein (P-gp)-mediated brain efflux between rats and mice for a set of known central nervous system compounds. With use of newly introduced genetically modified mdr1a-deficient rats and their gene-competent counterparts, the brain to plasma distribution was assessed and compared with the distribution pattern in mdr1a-deficient and wild-type mice. Four compounds (aripiprazole, citalopram, risperidone, and venlafaxine) were administered using a continuous subcutaneous osmotic minipump infusion paradigm. Steady-state brain and plasma concentrations of the compounds, including selected metabolites (9-hydroxyrisperidone, O-desmethyl-venlafaxine and N-desmethyl-venlafaxine) were measured in mdr1a-deficient rats and mice and their wild-type counterparts along with their free fractions to determine total and unbound brain to plasma distribution between genotypes within and between species. The results revealed qualitative as well as quantitative similarities between P-gp functionality in vivo at the blood-brain barrier level in rats and mice. All compounds tested were shown to have a significantly higher brain to plasma distribution in both mdr1a-deficient rats and mice compared with that in their wild-type counterparts. Moreover, the relative enhancement in extent of brain penetration between mdr1a-deficient and wild-type rats could be directly correlated to the enhancement ratios obtained in mice. From the unbound brain to unbound plasma distributions, the impact of P-gp on the overall brain penetration capabilities showed minor differences between rats and mice for the compounds tested. In conclusion, a comparable functional role of P-gp between rats and mice with respect to brain efflux mediated by this transporter is suggested.

Minor Compensatory Changes in SAGE Mdr1a (P-gp), Bcrp, and Mrp2 Knockout Rats Do Not Detract from Their Utility in the Study of Transporter-Mediated Pharmacokinetics

“…Independent studies established that SAGE Mdr1a knockout rats exhibited increased brain distribution of seven P-glycoprotein (P-gp) substrates quantitatively consistent with established murine models (Bundgaard et al, 2012), and SAGE Bcrp knockout rats showed expected increases in oral absorption and decreased biliary excretion of relevant probes (Huang et al, 2012). Proprietary Mdr1a knockout rats generated in the Wistar strain also exhibited increased oral absorption and central nervous system distribution of P-gp substrate drugs (Chu et al, 2012).…”

“…Together, these data show that clearance of drugs that are not substrates of the knocked-out transporter can be 30-60% higher in SAGE knockout rats, which correlate with the 22-53% increase in liver and kidney relative weights. However, this trend of modestly decreased exposure of nonsubstrate drugs resulting from increased clearing capacity is irrelevant to the study of efflux transporter-mediated pharmacokinetics, whose goal is to identify increases in exposure (Bundgaard et al, 2012;Chu et al, 2012;Huang et al, 2012;Zamek-Gliszczynski et al, 2012a). Finally, prediction of the drug-interaction potential is based on the increase in exposure in the relevant knockout versus wild-type controls (Zamek-Gliszczynski et al, 2009).…”

“…Transporter gene knockout rats generated with zinc finger nucleases garnered considerable interest for mechanistic pharmacokinetic studies (Bundgaard et al, 2012;Chu et al, 2012;Huang et al, 2012;ZamekGliszczynski et al, 2012aZamekGliszczynski et al, , 2013. Although detailed absorption, distribution, metabolism, and excretion (ADME) experiments can be conducted in knockout mice (Tian et al, 2007;Zamek-Gliszczynski et al, 2011;Higgins et al, 2012), rats are practically advantageous and more relevant as the most often used nonclinical species in drug development.…”

Brain Penetration of WEB 2086 (Apafant) and Dantrolene in Mdr1a (P-Glycoprotein) and Bcrp Knockout Rats

“…Zamek-Gliszczynski et al (2012) reported that the brain distribution of paclitaxel was markedly enhanced in Mdr1a knockout rats. In addition, Bundgaard et al (2012) found that the brain distribution of several central nervous system drugs and active metabolites showed the same changes in brain penetration in rats as in mice when Mdr1a knockout animals were compared with wild-type animals. Liu et al (2014) have recently used a cassette-dosing approach to study BCRP and P-gp substrates and inhibitors in Mdr1a knockout rats.…”

“…Knockout rats have advantages compared with previously established mouse knockout models (Kodaira et al, 2010;Bundgaard et al, 2012) due to the high relevance of rats for toxicological testing during preclinical drug development and their better suitability for pharmacokinetic studies using repeated blood sampling.…”